2N3055 failure (power supply)
Ben Jackson
power transistor. It's conducting from C->B in a gang with 4 other
transistors driven by a TIP31. The net result was that the failure
caused the supply to jump to 22V+, far higher than its typical max
voltage, and with no current limiting. Are there any obvious mods
I should consider while I'm fixing it?
___
|
TIP31 | ___
LM723 ___ |/ |
[Vout>-|___|-o-----| |
22R | |> o---o---o---o---o
| | | | | | |
| ___ | | | | | |
'-|___|-o |/ |/ |/ |/ |/ 2N3055
2k2 '-----|---|---|---|---|
|> |> |> |> |>
| | | | |
.-. .-. .-. .-. .-.
| | | | | | | | | |
0.1R | | | | | | | | | |
5W '-' '-' '-' '-' '-'
| | | | |
o---o---o---o---o---->>>
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
--
Ben Jackson AD7GD
<b...@ben.com>
http://www.ben.com/
Phil Allison
"Ben Jackson"
>I tracked down the fault in a failed power supply to a failed 2N3055
> power transistor. It's conducting from C->B in a gang with 4 other
> transistors driven by a TIP31. The net result was that the failure
> caused the supply to jump to 22V+, far higher than its typical max
> voltage, and with no current limiting. Are there any obvious mods
> I should consider while I'm fixing it?
** Yes - change all those 0.1 ohm resistors to 0.33 ohms.
Also, use all *new* 2N3055s from the same batch to effect the repair -
or, if funds allow, use all new MJ15003s.
Otherwise device current sharing will likely be haywire.
BTW
Love the old Natsemi LM723 reg IC - versatile as all hell.
....... Phil
John Popelish
Not having any resistance between the common base node and
the output bothers me. This gives the gang of 3055s a slow
turn off and a voltage overshoot when a .load is step reduced.
Something between 10 and 100 ohms might improve this.
Brian
"Ben Jackson" <b...@ben.com> wrote in message
news:slrnep4ef...@saturn.home.ben.com...
The 0.1R resistors are there to promote current sharing between the five
2N3055 transistors. If the circuits that the power supply is connected to,
are not real sensitive to over-voltage then you might replace the 0.1R
resistors with fusable resistors. If you do that, then you might want to put
a resistor and LED circuit across each fusable resistor (to let you know
when one is blown). If you need more protection than that, then you might
want to put a voltage sensing circuit on the output and a fuse in the
collector circuit. Have the voltage sense circuit trigger a SCR, that blows
that fuse in the collector circuit.
Brian Ellis
DaveM
In addition to the other suggestions, I recommend that you consult the 723
datasheet and investigate the foldback current limiting suggestions given there.
It's well worth the trouble if there's a possibility of a short on the output.
Could save your power supply and an expensive repair job on connected equipment.
Cheers!!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)
Some days you're the dog, some days the hydrant.
Jamie
put in a SCR crowbar circuit to clamp and pop the fuse when it over
voltages?
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
Phil Allison
"Brian"
> Have the voltage sense circuit trigger a SCR, that blows that fuse in the
> collector circuit.
** For the benefit of the OP - the simplest crowbar circuit would consist
of a 1 watt zener diode, a 56 ohm resistor and a 10 to 15 amp rated SCR (
TO220 pack).
The zener conduction voltage is chosen and tested to be the same as the
supply's nominal output voltage (ie 13.8 volts ?).
Connect the zener from the supply output to the G (gate) terminal of the
SCR, the 56 ohm goes from G to K (cathode ) while the A (anode ) terminal
connects also to the output positive rail. The K terminal also goes to the
output common or minus terminal.
The ( 20 amp ? ) fuse may be in the unregulated DC supply or low voltage AC
feed to the rectifier.
....... Phil
cbarn...@aol.com
Ben Jackson wrote:
I cant read this circuit very well, it appears to be an emmiter
follower. If thats the case then you have 2 basic problems. Firstly
your output is not inside the regulation loop so your regulation will
be poor. Secondly you have no short circuit protection, or indeed any
current control. Both these problems are easily solved by looking at
the application notes for the 723.
Phil Allison
<cbarn...@aol.com
>
> I cant read this circuit very well, it appears to be an emmiter
> follower. If thats the case then you have 2 basic problems. Firstly
> your output is not inside the regulation loop so your regulation will
> be poor. Secondly you have no short circuit protection, or indeed any
> current control.
** Nonsense.
The OP supplied a partial schem and STATED that it was a current limited
supply.
> Both these problems are easily solved by looking at
> the application notes for the 723.
** The OP very likely has a schem like figure 4 here:
http://www.national.com/ds/LM/LM723.pdf
Rsc is probably one of the 0.1 ohm ballast resistors shown in his schem,
resulting in a 6.5 amp limit per 3055 device.
....... Phil
Ben Jackson
On 2006-12-27, John Popelish <jpop...@rica.net> wrote:
> Ben Jackson wrote:
>> I tracked down the fault in a failed power supply to a failed 2N3055
>
> Not having any resistance between the common base node and
> the output bothers me. This gives the gang of 3055s a slow
> turn off and a voltage overshoot when a .load is step reduced.
>
> Something between 10 and 100 ohms might improve this.
The partial schematic I drew only covered the off-pcb parts of the circuit
that I had traced. There is a 330R from the common base to the output
on the PCB. I had not tracked it down until your post mentioned it.
Phil Allison wrote:
> ** Yes - change all those 0.1 ohm resistors to 0.33 ohms.
Good idea, but I'm not sure this supply (BK Precision 1688) has room
for the 10W resistors I'd need. It was definitely not built for
maintenance. The final assembly consisted of pushing the PCB onto
the lugs of all the front panel stuff (outputs, meters) and soldering
it in place!
> Also, use all *new* 2N3055s from the same batch to effect the repair -
> or, if funds allow, use all new MJ15003s.
Yes, I'm hoping that a new batch of 2N3055s will fix any current sharing
problems. Digikey was out of MJ15003 and a few others I tried.
DaveM wrote:
> In addition to the other suggestions, I recommend that you consult
> the 723 datasheet and investigate the foldback current limiting
> suggestions given there.
The supply does include current limiting, but the nature of the failure
really took the 723 out of the equation. That's one of the reasons I
was looking for mod suggestions, which brings me to:
Jaime wrote and Phil Allison expanded:
>> Have the voltage sense circuit trigger a SCR, that blows that fuse in the
>> collector circuit.
>
>** For the benefit of the OP - the simplest crowbar circuit would consist
>of a 1 watt zener diode, a 56 ohm resistor and a 10 to 15 amp rated SCR (
>TO220 pack).
>
>The zener conduction voltage is chosen and tested to be the same as the
>supply's nominal output voltage (ie 13.8 volts ?).
That seems like the best plan. The max in-spec voltage is 14.5V (I think
this was meant for automotive applications).
Thanks all.
Brian
"Phil Allison" <phila...@tpg.com.au> wrote in message
news:4vgu6qF...@mid.individual.net...
>
> <cbarn...@aol.com
>
>>
>> I cant read this circuit very well, it appears to be an emmiter
>> follower. If thats the case then you have 2 basic problems. Firstly
>> your output is not inside the regulation loop so your regulation will
>> be poor. Secondly you have no short circuit protection, or indeed any
>> current control.
>
That's the way I read it too.
>
> ** Nonsense.
>
> The OP supplied a partial schem and STATED that it was a current limited
> supply.
>
The Op stated: "The net result was that the failure caused the supply to
jump to 22V+, far higher than its typical max voltage, and with NO CURRENT
LIMITING.
>
>> Both these problems are easily solved by looking at
>> the application notes for the 723.
>
>
> ** The OP very likely has a schem like figure 4 here:
>
> http://www.national.com/ds/LM/LM723.pdf
>
> Rsc is probably one of the 0.1 ohm ballast resistors shown in his schem,
> resulting in a 6.5 amp limit per 3055 device.
>
>
>
>
> ....... Phil
>
>
Unless you are seeing something that I'm not seeing, I don't see how you can
think that. In the partial schematic that the OP showed, the 0.1 ohm
resistors are being used to make sure the power transistors in parallel, are
sharing the current (close to equally).
Brian Ellis
Phil Allison
"Ben Jackson"
> Phil Allison wrote:
>
>> ** Yes - change all those 0.1 ohm resistors to 0.33 ohms.
>
> Good idea, but I'm not sure this supply (BK Precision 1688) has room
> for the 10W resistors I'd need.
** How many amps will this supply deliver ?
The reason for the suggested change, BTW, is that 0.1 ohm ballast resistors
only work well with carefully Vbe matched devices.
If your new ones are all suitably Vbe matched, then use 0.1ohms.
...... Phil
Brian
"Brian" <bell...@comcast.net> wrote in message
news:M6OdnZYDc_GK0g7Y...@comcast.com...
When the output power transistor shorts out, there is no current (or
voltage) control.
Brian Ellis
Phil Allison
"Brian"
> "Phil Allison"
>> ** Nonsense.
>>
>> The OP supplied a partial schem and STATED that it was a current
>> limited supply.
>>
>
> The Op stated: "The net result was that the failure caused the supply to
> jump to 22V+, far higher than its typical max voltage, and with NO CURRENT
> LIMITING.
** Indicating that the current limiting inherent in the supply was rendered
ineffective by the faulty 3055.
The OP has now confirmed this IS in fact correct.
>> ** The OP very likely has a schem like figure 4 here:
>>
>> http://www.national.com/ds/LM/LM723.pdf
>>
>> Rsc is probably one of the 0.1 ohm ballast resistors shown in his schem,
>> resulting in a 6.5 amp limit per 3055 device.
>>
>
>
> Unless you are seeing something that I'm not seeing, I don't see how you
> can think that. In the partial schematic that the OP showed, the 0.1 ohm
> resistors are being used to make sure the power transistors in parallel,
> are sharing the current (close to equally).
** Look at the schem again and see what is blindingly obvious.
Any one of the 0.1 ohm ballast resistors can be used as Rsc.
Then the max output current = 5 times the current limit set by that
resistor.
........ Phil
Phil Allison
"Brian"
>
> When the output power transistor shorts out, there is no current (or
> voltage) control.
** Never in dispute.
Your earlier false assertions were.
....... Phil
cbarn...@aol.com
Phil Allison wrote:
> <cbarn...@aol.com
>
> >
> > I cant read this circuit very well, it appears to be an emmiter
> > follower. If thats the case then you have 2 basic problems. Firstly
> > your output is not inside the regulation loop so your regulation will
> > be poor. Secondly you have no short circuit protection, or indeed any
> > current control.
>
>
> ** Nonsense.
>
> The OP supplied a partial schem and STATED that it was a current limited
> supply.
Well i guess Phil, one of us cant read.
>
>
> > Both these problems are easily solved by looking at
> > the application notes for the 723.
>
>
> ** The OP very likely has a schem like figure 4 here:
>
> http://www.national.com/ds/LM/LM723.pdf
Maybe but since he didnt state it its just speculation on your part.
>
> Rsc is probably one of the 0.1 ohm ballast resistors shown in his schem,
> resulting in a 6.5 amp limit per 3055 device.
That would be too bad if it was since the 2n3055 wont survive a short
at that current for long.
>
>
>
>
> ....... Phil
Brian
>
> "Brian"
>> "Phil Allison"
>>> ** Nonsense.
>>>
>>> The OP supplied a partial schem and STATED that it was a current
>>> limited supply.
>>>
>>
>> The Op stated: "The net result was that the failure caused the supply to
>> jump to 22V+, far higher than its typical max voltage, and with NO
>> CURRENT LIMITING.
>
>
> ** Indicating that the current limiting inherent in the supply was
> rendered ineffective by the faulty 3055.
>
> The OP has now confirmed this IS in fact correct.
>
You act like he finally came to that conclusion. He stated that from the
very beginning.
>
>
>>> ** The OP very likely has a schem like figure 4 here:
>>>
>>> http://www.national.com/ds/LM/LM723.pdf
>>>
>>> Rsc is probably one of the 0.1 ohm ballast resistors shown in his schem,
>>> resulting in a 6.5 amp limit per 3055 device.
>>>
Even if that "should" be the case, so what, it has nothing to do with his
problem
>>
>>
>> Unless you are seeing something that I'm not seeing, I don't see how you
>> can think that. In the partial schematic that the OP showed, the 0.1 ohm
>> resistors are being used to make sure the power transistors in parallel,
>> are sharing the current (close to equally).
>
>
> ** Look at the schem again and see what is blindingly obvious.
>
Of course it is.
> Any one of the 0.1 ohm ballast resistors can be used as Rsc.
>
The operative word here is "can". But is it? It doesn't matter, it has
nothing to do with his problem.
Ben Jackson
> "Ben Jackson"
>> Phil Allison wrote:
>>
>>> ** Yes - change all those 0.1 ohm resistors to 0.33 ohms.
>>
>> Good idea, but I'm not sure this supply (BK Precision 1688) has room
>> for the 10W resistors I'd need.
>
> ** How many amps will this supply deliver ?
It's a 20A supply, so 4A per 2N3055, the .1R should dissipate about 1.6W
max and the .33 would be a little over 5W so I'd need the bigger package.
I would also have to trace the rest of the circuit and see what else
might be affected by the change (there's an LM339 looking at at least
temperature and maybe other things that will shut down the 723).
> The reason for the suggested change, BTW, is that 0.1 ohm ballast resistors
> only work well with carefully Vbe matched devices.
>
> If your new ones are all suitably Vbe matched, then use 0.1ohms.
I ordered 10 so maybe I'll measure them and choose the best 5.
Phil Allison
"Brian"
>> ** Indicating that the current limiting inherent in the supply was
>> rendered ineffective by the faulty 3055.
>>
>> The OP has now confirmed this IS in fact correct.
>>
>
> You act like he finally came to that conclusion.
** You have a serious reading comprehension disability.
What the OP has confirmed is the supply IS indeed current limited.
>>>> ** The OP very likely has a schem like figure 4 here:
>>>>
>>>> http://www.national.com/ds/LM/LM723.pdf
>>>>
>>>> Rsc is probably one of the 0.1 ohm ballast resistors shown in his
>>>> schem, resulting in a 6.5 amp limit per 3055 device.
>>>>
>
> Even if that "should" be the case, so what, it has nothing to do with his
> problem.
** You have a serious reading comprehension disability.
Plus an utterly ASD fucked brain.
Go top yourself anytime - ASSHOLE.
........ Phil
Phil Allison
<cbarn...@aol.com>
>> ** Nonsense.
>>
>> The OP supplied a partial schem and STATED that it was a current
>> limited
>> supply.
>
> Well i guess Phil, one of us cant read.
** If you were not such a complete ASSHOLE might feel sorry for you.
>> > Both these problems are easily solved by looking at
>> > the application notes for the 723.
>>
>>
>> ** The OP very likely has a schem like figure 4 here:
>>
>> http://www.national.com/ds/LM/LM723.pdf
>
> Maybe but since he didnt state it its just speculation on your part.
** An educated speculation that has been now confirmed as correct.
Enjoying your sour grapes ????
>> Rsc is probably one of the 0.1 ohm ballast resistors shown in his schem,
>> resulting in a 6.5 amp limit per 3055 device.
>
> That would be too bad if it was since the 2n3055 wont survive a short
> at that current for long.
** Its within the DC safe area curve for a 2N3055.
A temp cut out switch on the heatsink would prevent failure.
PSU design is obviously way over your pointy head - ASSHOLE.
........ Phil
Rich Grise
Once you do get it up and running, it'd be interesting to see the
voltages you measure across your emitter resistors at some given
current (or maybe even a graph ;-) ).
Cheers!
Rich
Brian
Getting a little testy are we? Of all the things that have been suggested so
far, the only thing that has any merit is the over-voltage protection.
Everything else has been hogwash. After all the time and expense, the OP
would have very little (in the way of reliability) to show for it. This
would be very easy for the OP to prove to himself. If he were to change the
one power transistor that went bad, put the power supply under full load and
measure the voltages across each of the ballast resistors (as you call it),
so he could see what each of the power transistor current draw is. Then go
ahead and change the rest of the power transistors and do the same test
again. Look at the data sheet for the 2N3055, and see how close he is to the
specks. I bet he will have plenty of safety factor. If that is so, then what
has he gained? I bet, not much.
Brian Ellis
Paul E. Schoen
This circuit might work well with logic level power MOSFETs, something like
STP20NF06, which is only $0.60, compared to about $1.30 for 2N3055, if you
can use the TO-220 package instead of TO-3. MOSFETs work very well for
current sharing, as their resistance increases by a factor of about 2 from
0 to 100C. The 0.1 ohm resistors will help by giving negative feedback to
the gate voltage. However, you will need a drive voltage about 3 or 4 volts
above the desired output voltage.
If you use bipolars, it is very important to keep all the parallel
transistors at the same temperature. It may even be helpful to arrange the
emitter resistors so they will heat up a different area of the heat sink to
minimize thermal runaway. Thermistors can also help by reducing base
current drive to the hottest devices.
Vbe should be about 0.5 to 0.7 for any similar transistor, so the 0.1 ohm
resistor should provide current equalization of +/- 1 amp from the nominal
4 amps per device. Each device should be running at about 40 watts if the
22 volt raw supply is maintained, but it is probably more like 16 volts
under full load, for a more reasonable 16 watts each.
Good luck,
Paul
Phil Allison
"Paul E. Schoen = Utter CRIMINAL FUCKWIT "
KILLFILE the Autistic SCUM BAG NOW !!!
KILLING the incorrigible PRICK him would be even better !!
> MOSFETs work very well for current sharing,
** BOLLOCKS !!!!!!
No way in a LINEAR regulator - you DUMB ASS !!
> If you use bipolars, it is very important to keep all the parallel
> transistors at the same temperature.
** Being Vbe matched & on the same heatsink does that - cunt brain !!
> It may even be helpful to arrange the emitter resistors so they will heat
> up a different area of the heat sink to minimize thermal runaway.
** This ANENCEPHALIC Schoen Fuckwit must be a CRACK addict !!.
ASD alone simply does not explain this level of congenital INSANITY !!
> Thermistors can also help by reducing base current drive to the hottest
> devices.
** Totally INSANE !!
> Vbe should be about 0.5 to 0.7 for any similar transistor,
** Crapology.
Schoen has no fucking idea what Vbe tracking even is.
FOAD you PITA ASS !!
....... Phil
cbarn...@aol.com
Phil Allison wrote:
> <cbarn...@aol.com>
>
>
> >> ** Nonsense.
> >>
> >> The OP supplied a partial schem and STATED that it was a current
> >> limited
> >> supply.
> >
> > Well i guess Phil, one of us cant read.
>
>
> ** If you were not such a complete ASSHOLE might feel sorry for you.
>
>
>
> >> > Both these problems are easily solved by looking at
> >> > the application notes for the 723.
> >>
> >>
> >> ** The OP very likely has a schem like figure 4 here:
> >>
> >> http://www.national.com/ds/LM/LM723.pdf
> >
> > Maybe but since he didnt state it its just speculation on your part.
>
>
> ** An educated speculation that has been now confirmed as correct.
>
> Enjoying your sour grapes ????
Guessing is clearly your greatest asset. I bow in admiration.
>
>
>
> >> Rsc is probably one of the 0.1 ohm ballast resistors shown in his schem,
> >> resulting in a 6.5 amp limit per 3055 device.
> >
> > That would be too bad if it was since the 2n3055 wont survive a short
> > at that current for long.
>
>
> ** Its within the DC safe area curve for a 2N3055.
No it isn't!! Seems you cant read a data sheet either.
>
> A temp cut out switch on the heatsink would prevent failure.
What you gonna set it at? 10degC?
>
> PSU design is obviously way over your pointy head - ASSHOLE.
Yours too it would seem. You seem to be obsessed with assholes, are you
a little gay?
>
>
>
>
> ........ Phil
Phil Allison
cbarn...@aol.com>
>
>> ** Its within the DC safe area curve for a 2N3055.
>
> No it isn't!!
** BOLLOCKS - YOU CRIMINAL FUCKWIT
PSU design is obviously way over your pointy head - you trolling ASD
fucked ASSHOLE.
A nice bowel carcinoma waits for you - cunt head.
........ Phil
Phil Allison
<cbarn...@aol.com>
** The above pile of slime is another congenital, ASD FUCKED POMMY CUNT .
The UK is just crawling with the vile pukes.
Aussie just hate them to death.
Yanks completely despise them.
Other poms just quietly loathe them.
YOU can use you Killfile to eliminate them anytime.
...... Phil
John Larkin
Actually, no. RdsON isn't relevant here, because they're not
saturated, and if they're on the same heatsink most local
thermoregulation would cancel out anyhow. Even "identical" fets have
to be hand-matched (and expect to throw some away) to get safe levels
of linear-mode sharing. Huge source resistors help the sharing at high
currents but it's hard to find a value that works over a decent load
range.
But it's easy to use paralleled mosfets: just use an opamp per fet as
closed-loop gate drivers, with feedback from small source resistors.
That will linearize and equalize them to microvolts precision.
Switching (saturated) mosfets can share a load reasonably well. [1]
John
[1] I use "saturated" in the bipolar sense, lots of gate drive and low
drain voltage, the ohmic region. Some people consider fet "saturation"
to be the opposite region, the high-voltage constant-current place.
John Perry
> cbarn...@aol.com>
>
>>> ** Its within the DC safe area curve for a 2N3055.
>> No it isn't!!
>
>
...several stupid, profane lines deleted...
Geez, Phil, you were doing so well for a few days. Sorry to see you
going stupid again.
John Perry
Paul E. Schoen
"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in message
news:hhu9p2986hc00gvsa...@4ax.com...
I tried a simulation (LTSpice) using three very different MOSFETs, and
current sharing at high levels was reasonably good. At low levels, one or
more were essentially turned off, but that's not a problem. I have no way
to simulate device variations or temperature effects, however. I used a 20
volt raw source and 15 volts on the gates. The MOSFETs are IRF7811,
IRF7468, and IRF9410. Here's the results:
Rload Vload I(R1) I(R2) I(R3)
10k 13.19 51pA 1.3mA 49pA
1k 13.17 60pA 13.2mA 58pA
100 13.11 -360pA 131mA -346pA
10 12.90 253mA 870mA 167mA
1 12.25 4.31A 4.50A 3.44A
0.5 11.71 8.38A 8.10A 6.95A
0.1 8.91 31.8A 29.4A 27.9A
Paul
John Larkin
<pst...@smart.net> wrote:
I assume you hooked them hard in parallel, with no source resistors.
My experience in building NMR power amps is that it's ugly to parallel
"identical" power fets even with the largest feasible source
resistors. In my situation, a class AB push-pull amp, quiescent
current ran about 10% of peak output current, and with a little bad
luck, one of the fets (out of 4 on each side) would wind up furnishing
most of Iq and getting a lot hotter than the others. We wound up
matching parts, a real nuisance. After that experience on our first
amp, we went to closed-loop control of each fet, which has a number of
side benefits.
If you don't care which fet does most of the work at low loads, and if
you can afford to drop a volt (or preferebly 2) in each source
resistor at full load, it can be made to work. But at 1 volt drop,
there could well be some intermediate load that's embarassing.
I just wouldn't trust those Spice numbers. The last couple of lines
have three different parts whose transfer curves spread less than 20%.
I don't think that's realistic.
John
Phil Allison
"John Perry"
** This ASD fucked criminal cretin is another of the VILE SCUM BAGS.
....... Phil
cbarn...@aol.com
John Perry wrote:
Over in oz they have to pay for their medication, he'll be ok when some
cash comes in.
Phil Allison
Paul E. Schoen
"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in message
I used the same 0.1 ohm source resistors as in the OP's schematic. The last
two lines are at and considerably above the rating of the supply. At 8 amps
each, the source resistors drop 0.8 volts, and there is a large difference
in transconductance over that range. At 90 amps out, the source resistors
are doing most of the work, dropping 3 volts each. Some intermediate
values:
1.5 12.46 2.85A 3.23A 2.22A
2 12.57 2.10A 2.57A 1.61A
3 12.69 1.34A 1.90A 0.99A
4 12.76 0.95A 1.55A 0.69A
6 12.83 0.56A 1.18A 0.39A
The current sharing gets crappy at low currents, but at that point it
doesn't matter very much. What I don't know is how the transconductance
varies with temperature. I don't do much with linear power anymore, now
that PWM is so easy to implement, but linear circuits are still useful. Any
real data, experimental or theoretical, that supports or refutes these
results, would be appreciated.
Just for fun I made a similar circuit with bipolar transistors: ZTX1048A,
2N3055, and FZT849. Results:
Rload Vload I(R1) I(R2) I(R3)
10 13.33 51mA 1.25A 31mA
6 13.23 289mA 1.69A 222mA
4 13.14 647mA 2.08A 560mA
3 13.05 1.02A 2.41A 925mA
2 12.89 1.77A 3.01A 1.67A
1.5 12.74 2.51A 3.55A 2.42A
1 12.42 3.98A 4.54A 3.90A
0.5 11.52 8.07A 6.95A 8.02A
That's pretty good current sharing for such a wide range of transistor
types. I would expect no more than 1 ampere difference between any two
devices at the nominal 4 amperes each for five, with 0.1 ohm resistors.
It is quite possible that an amplifier running at audio frequency may
require much better device matching. There are probably considerable
variations in gain for transistors used for that purpose.
Paul
Phil Allison
"Paul E. Schoen = CRIMINAL FUCKWIT "
> The MOSFETs are IRF7811, IRF7468, and IRF9410. Here's the results:
>
> Rload Vload I(R1) I(R2) I(R3)
>
> 10k 13.19 51pA 1.3mA 49pA
> 1k 13.17 60pA 13.2mA 58pA
> 100 13.11 -360pA 131mA -346pA
> 10 12.90 253mA 870mA 167mA
> 1 12.25 4.31A 4.50A 3.44A
> 0.5 11.71 8.38A 8.10A 6.95A
> 0.1 8.91 31.8A 29.4A 27.9A
** How completely hysterical !!!!!!!
All 3 mosfets are in SO-8 pack & have power ratings of 2.5 watts max !!
Shows what happens when you put a dumb simulator in the hands of an utter
imbecile.
....... Phil
Phil Allison
"Paul E. Schoen = CRIMINAL FUCKWIT "
> Just for fun I made a similar circuit with bipolar transistors:
> ZTX1048A, 2N3055, and FZT849. Results:
>
> Rload Vload I(R1) I(R2) I(R3)
>
> 10 13.33 51mA 1.25A 31mA
> 6 13.23 289mA 1.69A 222mA
> 4 13.14 647mA 2.08A 560mA
> 3 13.05 1.02A 2.41A 925mA
> 2 12.89 1.77A 3.01A 1.67A
> 1.5 12.74 2.51A 3.55A 2.42A
> 1 12.42 3.98A 4.54A 3.90A
> 0.5 11.52 8.07A 6.95A 8.02A
** Whaaaaaaaaaattttttt ?????
This is even STUPIDER !!
A 115 watt TO3, a 1 watt TO92 and 3 watt SOT223 ??
Shows what happens when you put a dumb simulator in the hands of a fucking
imbecile.
ROTFLMAO !!
....... Phil
Paul E. Schoen
I ran another simulation with honking big devices. STB120NF10 (D2PAK),
IRFP2907 (TO-247), and IRF1405 (TO-220).
Rload Vload I(R1) I(R2) I(R3)
0.2 9.11 15.6A 14.3A 15.7A
0.5 10.17 7.16A 5.52A 7.66A
1.0 10.61 3.88A 2.17A 4.56A
1.5 10.78 2.71A 1.03A 3.45A
2.0 10.87 2.09A 0.48A 2.86A
5.0 11.10 0.72A 587pA 1.51A
Even with such major device differences, the current sharing is not too bad
at high levels where it is critical.
Paul
Phil Allison
"Paul E. Schoen Fucking MORON from HELL "
> Since *someone* pointed out that the previous MOSFETs were small packages,
> I ran another simulation with honking big devices. STB120NF10 (D2PAK),
> IRFP2907 (TO-247), and IRF1405 (TO-220).
>
> Rload Vload I(R1) I(R2) I(R3)
> 0.2 9.11 15.6A 14.3A 15.7A
> 0.5 10.17 7.16A 5.52A 7.66A
> 1.0 10.61 3.88A 2.17A 4.56A
> 1.5 10.78 2.71A 1.03A 3.45A
> 2.0 10.87 2.09A 0.48A 2.86A
> 5.0 11.10 0.72A 587pA 1.51A
>
>
> Even with such major device differences,
** BOLLOCKS !!!
Your totally ASININE simulator is **** NOT **** modelling the production
differences that are **specified ** to EXIST with real MOSFET devices.
Read the flaming spec sheet you BLOODY IMBECILE !!!!!!
The *gate threshold* voltage is speced to range from * 2 to 4 volts
* - for all 3 device types.
With transconductance values from 70 to 130 amps per volt - that means
that parallel connected, unmatched devices
operating in linear mode have NO CHANCE of sharing load current.
A 1 volt gate threshold voltage differential equates to circa 100 amp drain
current error !!!!
http://www.st.com/stonline/products/literature/ds/9522.pdf
See specs on page 4 and figure 4 on page 6.
Draw two extra curves, spaced one volt each side of the curve shown - that
is the region where all real devices fall.
Paul Schoen = a COMPLETE FUCKING ASS !!!!
Fuck Off Imbecile !!!!!!
....... Phil
Paul E. Schoen
"Paul E. Schoen" <pst...@smart.net> wrote in message
news:459611a0$0$13286$ecde...@news.coretel.net...
For more technical analysis of MOSFETs in parallel, read this from IR:
http://www.irf.com/technical-info/appnotes/para.pdf
From what I gather after a quick scan, worst case current imbalances of
about 40% may be expected for devices without additional circuitry such as
source resistors.
Paul
John Larkin
If you're still assuming 0.1 ohms in each source, the high-current
point results in about 1.5 volts drop in each source resistor, or
about 22 watts dissipated per resistor. Sure, that works if you don't
mind all that heat. But the low-current sharing is correspondingly
terrible.
It's interesting that the TO-247 part (which will have the fattest
leads and source wirebonds by far) comes out worst at all currents. I
certainly wouldn't do a production design based on Spice simulations
like this.
John
Jamie
Donations any one? :)
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
Paul E. Schoen
"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in message
>
> If you're still assuming 0.1 ohms in each source, the high-current
> point results in about 1.5 volts drop in each source resistor, or
> about 22 watts dissipated per resistor. Sure, that works if you don't
> mind all that heat. But the low-current sharing is correspondingly
> terrible.
>
> It's interesting that the TO-247 part (which will have the fattest
> leads and source wirebonds by far) comes out worst at all currents. I
> certainly wouldn't do a production design based on Spice simulations
> like this.
>
I added the calculated Vgs for these devices with the 0.1 ohm source
resistors:
STB120NF10 IRFP2907 IRF1405
D2PAK TO-247 TO-220
Rload Vload I(R1)/Vg1 I(R2)/Vg2 I(R3)/Vg3
0.1 7.82 26.5A/4.53 25.6A/4.62 26.2/4.56
0.2 9.11 15.6A/4.33 14.3A/4.46 15.7A/4.23
0.5 10.17 7.16A/4.11 5.52A/4.28 7.66A/4.06
1.0 10.61 3.88A/4.00 2.17A/4.17 4.56A/3.93
1.5 10.78 2.71A/3.95 1.03A/4.12 3.45A/3.88
2.0 10.87 2.09A/3.92 0.48A/4.08 2.86A/3.84
5.0 11.10 0.72A/3.83 587pA/3.90 1.51A/3.75
These voltages are generally below the typical cutoff voltages on the
device data sheets, so the results might not be accurate at the low current
levels.
These are high current devices, so I used lower values to get more current:
With 0.01 ohm source resistors:
0.03 8.63 96.2A/5.41 104.3A/5.33 87.1A/5.50
0.05 9.32 57.6A/5.10 65.4A/5.03 57.6A/5.10
0.1 9.98 35.1A/4.67 32.0A/4.70 32.7A/4.69
0.2 10.41 19.2A/4.40 13.9A/4.45 19.0A/4.40
With 1 uohm source resistors (essentially zero):
0.03 9.52 103.8A/5.48 127.5A/5.48 85.9A/5.48
0.05 9.91 67.5A/5.09 73.7A/5.09 56.9A/5.09
0.1 10.30 37.4A/4.70 32.4A/4.70 33.2A/4.70
0.2 10.58 20.5A/4.42 12.4A/4.42 20.0A/4.42
So, even without negative feedback current sensing, there is adequate
sharing at levels where it counts, and the largest device does finally take
its proper share of the load. Also, the positive temperature coefficient of
device resistance even above saturation will provide even better sharing as
devices heat up.
The main problem with parallel devices appears to be for higher frequency
and switching parameters, and not steady state DC conditions. There could
be problems with a non-resistive dynamic load where currents change
quickly. That could also be simulated, but I don't think it is necessary
unless there is an actual application where this would be required.
Paul
John Larkin
Sorry, I just don't believe these numbers. Spice doesn't include
real-life device-device variations. Transfer curves can be all over
the place, even for parts out of the same tube.
I have used multiple mosfets in parallel in switching apps. That works
fine.
John
Paul E. Schoen
"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in message
I guess someone will need to do actual experimentation to see what happens
in real life. I have not found very much information on device variations,
particularly for gain (transconductance) and gate threshold, which are
probably critical for this application. It would probably be a valuable
exercise to do this. I was very surprised at the current sharing without
source resistors. I would think that the "knee" of the Vgs to I curve is a
useful point. I would think it would vary no more that about 0.2 volts from
the nominal 4.5 volts, especially among similar devices. The source
resistors should take care of that much variation without too much power,
and for linear applications one might as well dissipate some of the power
in resistors rather than the MOSFET. Switching applications are a much
different animal, where efficiency is paramount, and transients are
critical.
An interesting discussion. There is some good information at:
http://www.answers.com/topic/mosfet
Paul
Phil Allison
> For more technical analysis of MOSFETs in parallel, read this from IR:
>
> http://www.irf.com/technical-info/appnotes/para.pdf
>
> From what I gather after a quick scan, worst case current imbalances of
> about 40% may be expected for devices without additional circuitry such as
> source resistors.
>
** Totally IRRELEVANT article.
The author only considers switching operation - not LINEAR operation.
Fuck Off - YOU BLOODY IMBECILE !!
........ Phil
Michael A. Terrell
>
> cbarn...@aol.com wrote:
>
> > John Perry wrote:
> >
> >
> >>Phil Allison wrote:
> >>
> >>>cbarn...@aol.com>
> >>>
> >>>>>** Its within the DC safe area curve for a 2N3055.
> >>>>
> >>>>No it isn't!!
> >>>
> >>>
> >>...several stupid, profane lines deleted...
> >>
> >>Geez, Phil, you were doing so well for a few days. Sorry to see you
> >>going stupid again.
> >>
> >>John Perry
> >
> >
> > Over in oz they have to pay for their medication, he'll be ok when some
> > cash comes in.
> >
> Donations any one? :)
I'll donate some laxatives so the shit goes out the other end.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
Tony Williams
> So, even without negative feedback current sensing, there is
> adequate sharing at levels where it counts, and the largest
> device does finally take its proper share of the load. Also, the
> positive temperature coefficient of device resistance even above
> saturation will provide even better sharing as devices heat up.
I had a serious rant here a few years ago about the
way in which manufacturers of VMOS devices perpetuated
the myth that "MOSFETs allow easy paralleling".
In fact nothing could be further from the truth.
For the VMOS, at fixed Vgs, dId/dT is positive. This
means that if any one MOSFET in a bank runs slightly
warmer it will take more current, getting hotter, so
taking more current..... and so on. Thermal runaway.
Look at Fig.3 of the IRF1405. At Vgs= 4.5V, Id is
4.2A at Tj=25C, rising to 28A at 175C. That's roughly
+0.15A/C. For the IRF1405 dI/dT does not approach
zero (and go negative) until Id is about 180A.
Hitachi realised this problem 20-odd years ago and
they produced power MOSFETs where dI/dT went negative
at only about 100mA. ISTR they were called lateral
or long channel MOSFETs, an entirely different process
to the VMOS and it's derivatives. The negative dI/dT
did allow easy paralleling and those Hitachi MOSFETs
were widely used in successful high power audio amps.
--
Tony Williams.
cbarn...@aol.com
Michael A. Terrell wrote:
I think there is so much it would still have to come out both ends.
Phil Allison
cbarn...@aol.com
Phil Allison wrote:
Repeating yourself again, no imagination. Well no brain so thats to be
expected.
Mike Monett
[...]
> I had a serious rant here a few years ago about the way in which
> manufacturers of VMOS devices perpetuated the myth that "MOSFETs
> allow easy paralleling".
> In fact nothing could be further from the truth.
> For the VMOS, at fixed Vgs, dId/dT is positive. This means that if
> any one MOSFET in a bank runs slightly warmer it will take more
> current, getting hotter, so taking more current. And so on.
> Thermal runaway.
> Look at Fig.3 of the IRF1405. At Vgs= 4.5V, Id is 4.2A at Tj=25C,
> rising to 28A at 175C. That's roughly +0.15A/C. For the IRF1405
> dI/dT does not approach zero (and go negative) until Id is about
> 180A.
> Hitachi realised this problem 20-odd years ago and they produced
> power MOSFETs where dI/dT went negative at only about 100mA. ISTR
> they were called lateral or long channel MOSFETs, an entirely
> different process to the VMOS and it's derivatives. The negative
> dI/dT did allow easy paralleling and those Hitachi MOSFETs were
> widely used in successful high power audio amps.
Good info. Thanks, Tony.
What about the current example using source resistors? These provide
negative feedback, so Vgs is no longer fixed. How do we calculate
the minimum value needed to prevent runaway?
Also, source resistors dissipate some heat, which reduces the amount
dissipated in the MOSFET. So in linear applications such as the
current topic, the source resistor can be useful.
Regards,
Mike Monett
Antiviral, Antibacterial Silver Solution:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automation/sampler/intro.htm
John Larkin
A positive drain-current tc doesn't guarantee runaway. If the "loop
gain" is less than 1, it won't run away. The math depends on the Id/t
slope, heat sinking, mutual heat sinking, stuff like that. Actually,
true thermal runaway in paralleled mosfets is rare, almost impossible.
>
> Also, source resistors dissipate some heat, which reduces the amount
> dissipated in the MOSFET. So in linear applications such as the
> current topic, the source resistor can be useful.
In that it reduces power supply headroom and efficiency at peak
output, all it can do is make heat and hurt. In a lot of situations,
there is no value of source resistor that gives decent idle-current
sharing but doesn't introduce huge peak-output losses. The old
nonlinear resistor trick (ie, parallel the emitter resistor with a
diode) often won't work for fets.
John
Mike Monett
John Larkin <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
> On Sun, 31 Dec 2006 12:02:44 -0500, Mike Monett <N...@email.adr>
> wrote:
>> Good info. Thanks, Tony.
>> What about the current example using source resistors? These
>> provide negative feedback, so Vgs is no longer fixed. How do we
>> calculate the minimum value needed to prevent runaway?
> A positive drain-current tc doesn't guarantee runaway. If the
> "loop gain" is less than 1, it won't run away. The math depends on
> the Id/t slope, heat sinking, mutual heat sinking, stuff like
> that.
That's what I hoped Tony might explain.
> Actually, true thermal runaway in paralleled mosfets is rare,
> almost impossible.
Tony was talking about a single MOSFET with fixed Vgs. His
explanation made good sense.
For paralled MOSFETS, aren't you referring to the fully-saturated
condition where the Rds has a positive temperature coefficient? I
don't think that is the case in this thread.
>> Also, source resistors dissipate some heat, which reduces the
>> amount dissipated in the MOSFET. So in linear applications such
>> as the current topic, the source resistor can be useful.
> In that it reduces power supply headroom and efficiency at peak
> output, all it can do is make heat and hurt.
How much headroom is lost? What is the minimum value required? If
it's only 0.1V to 1V, it may be a very good tradeoff due to the
simplicity. If it's greater, there may be some other tradeoffs to
consider.
I'm looking for the equations and design procedures to evaluate
these tradeoffs.
> In a lot of situations, there is no value of source resistor that
> gives decent idle-current sharing but doesn't introduce huge
> peak-output losses.
Isn't that a good thing? The power dissipated at idle should be
quite low. Why not have one device carry most of the load? That
should improve linearity and slew rate. Let the other devices come
on line as the load current increases. If they turn on smoothly, it
should add little distortion.
> The old nonlinear resistor trick (ie, parallel the emitter
> resistor with a diode) often won't work for fets.
Again, where are the equations? What makes it work in some cases and
fail in others?
> John
This could turn into a very useful thread if we could pin down some
numbers:)
Don Bowey
Allison" <phila...@tpg.com.au> wrote:
Phil,
I'm not up-to-date on insults. What does pommy mean?
Tnx
Don
Paul E. Schoen
"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in message
but at a drain current of only 250 uA. I think this is a worst case
scenario. So the change in threshold voltage is 3.3 to 2.7 from 25C to
100C. A 0.1 ohm source resistor will drop 0.4 volts at 4 amps (per the OT
application), so it should ensure reasonable current sharing. Device
temperature difference should not exceed 25C on a good heatsink, so
threshold should only change about 0.2 volts, or 2 amps with the existing
resistors.
Actually a lower current rated MOSFET would probably work better. The
IRF2903Z (75A,30V) shows threshold change from 4.0 to 3.6 volts from 25 to
100C, with drain current of 1 amp, and 3.4 to 2.7 at 1 mA.
The FQB30N06 (30A,60V) shows a current increase from 5A to 9A at fixed gate
voltage of about 4.8V from 25 to 175C, and no change at currents of 25A
with 6.2V Vgs, and negative change above that. Current varies with gate
voltage from 4.5A at 5.0Vgs to 11A at 5.5Vgs.
>>
>> Also, source resistors dissipate some heat, which reduces the amount
>> dissipated in the MOSFET. So in linear applications such as the
>> current topic, the source resistor can be useful.
>
> In that it reduces power supply headroom and efficiency at peak
> output, all it can do is make heat and hurt. In a lot of situations,
> there is no value of source resistor that gives decent idle-current
> sharing but doesn't introduce huge peak-output losses. The old
> nonlinear resistor trick (ie, parallel the emitter resistor with a
> diode) often won't work for fets.
>
Given the 22 VDC input voltage (probably about 16 V at full load), and 20
amp 14 volt maximum output, efficiency is not really a factor. The
resistors provide current limiting of about 40 amps if any one of the
devices should short out, if the load is a battery. Also the resistors can
run hotter, and are less expensive than the semiconductor devices. You lose
only about 0.4 V of headroom. And current sharing at idle levels does not
really matter.
Looking at the specs for the bipolar 2N3055, the Vbe changes sharply as a
function of collector current at moderate levels. It is 0.7V at 0.5A, 0.8V
at 2A, 1.0V at 5A, and 1.5V at 10A. This shows that the 0.1 ohm resistors
are more than adequate to ensure safe current sharing at the rated output
of 20A. Much below that it is not so critical. There does appear to be a
need for current limiting or fusing to protect against severe overloads and
short circuits, however.
Another severe limitation with the 2N3055 is the sharp drop of hfe at high
currents. It takes about 1 ampere to drive the output to 10 amps, and 100
mA to drive it to the rated 4 amps per device. Thus you need a solid 2-15
volt 500 mA base drive circuit to get decent output regulation. For the
MOSFETs, you can use a simple voltage divider or pot.
Paul
martin griffith
from a wiki
One theory is that, as the majority of early immigrants to Australia
were British, it is rhyming slang for "immigrant" from a contraction
of the word "pomegranate", or possibly more directly related to the
appearance of the fruit, as it bears a more than passing resemblance
to the typical pale complexioned Briton's skin after his or her first
few days living under the hot Australian sun.
martin
John Larkin
<phila...@tpg.com.au> wrote:
>
>"Paul E. Schoen = CRIMINAL FUCKWIT "
>
>
>> The MOSFETs are IRF7811, IRF7468, and IRF9410. Here's the results:
>>
>> Rload Vload I(R1) I(R2) I(R3)
>>
>> 10k 13.19 51pA 1.3mA 49pA
>> 1k 13.17 60pA 13.2mA 58pA
>> 100 13.11 -360pA 131mA -346pA
>> 10 12.90 253mA 870mA 167mA
>> 1 12.25 4.31A 4.50A 3.44A
>> 0.5 11.71 8.38A 8.10A 6.95A
>> 0.1 8.91 31.8A 29.4A 27.9A
>
>
>
>
> ** How completely hysterical !!!!!!!
>
> All 3 mosfets are in SO-8 pack & have power ratings of 2.5 watts max !!
>
>
Isn't that what "sharing" is really about, being willing to die for
your fellow FET?
John
Paul E. Schoen
"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in message
Luckily I ran the simulations for only 10 mSec. Otherwise I might have
burned up my computer. I did find burned spots on my CRT where the MOSFETs
were!
Happy Gnu year,
Paul
Phil Allison
"Paul E. Schoen Fucking MORON from HELL "
Your totally ASININE simulator is **** NOT **** modelling the production
differences that are **specified ** to EXIST with real MOSFET devices.
Read the flaming spec sheet you BLOODY IMBECILE !!!!!!
The *gate threshold* voltage is speced to range from * 2 to 4 volts
* - for all 3 device types.
With transconductance values from 70 to 130 amps per volt - that means
that parallel connected, unmatched devices
operating in linear mode have NO CHANCE of sharing load current.
A 1 volt gate threshold voltage differential equates to circa 100 amp drain
current error !!!!
http://www.st.com/stonline/products/literature/ds/9522.pdf
See specs on page 4 and figure 4 on page 6.
Draw two extra curves, spaced one volt each side of the curve shown - that
is the region where all real devices fall.
Paul Schoen = a COMPLETE FUCKING ASS !!!!
Fuck Off - Bloody Imbecile !!!!!!
....... Phil
Phil Allison
** The above pile of sub human slime is another congenital, ASD FUCKED
POMMY CUNT .
The UK is just crawling with such vile pukes.
Aussies just hate them to death.
Don Bowey
"martin griffith" <mart_in_medina@ya___.es> wrote:
> On Sun, 31 Dec 2006 11:52:18 -0800, in sci.electronics.design Don
> Bowey <dbo...@comcast.net> wrote:
>
(snip)
>>
>> I'm not up-to-date on insults. What does pommy mean?
>>
>> Tnx
>>
>> Don
> from a wiki
> One theory is that, as the majority of early immigrants to Australia
> were British, it is rhyming slang for "immigrant" from a contraction
> of the word "pomegranate", or possibly more directly related to the
> appearance of the fruit, as it bears a more than passing resemblance
> to the typical pale complexioned Briton's skin after his or her first
> few days living under the hot Australian sun.
>
>
> martin
Thanks.
I should have taken my own, usual, advice for such questions, and Googled
it.
Don
jasen
>> martin
>
> Thanks.
>
> I should have taken my own, usual, advice for such questions, and Googled
> it.
google can even explain the meaning of "ASD"
Bye.
Jasen
Paul E. Schoen
"Paul E. Schoen" <pst...@smart.net> wrote in message
news:4596fe4e$0$13299$ecde...@news.coretel.net...
>
> I guess someone will need to do actual experimentation to see what
> happens in real life. I have not found very much information on device
> variations, particularly for gain (transconductance) and gate threshold,
> which are probably critical for this application. It would probably be a
> valuable exercise to do this. I was very surprised at the current sharing
> without source resistors. I would think that the "knee" of the Vgs to I
> curve is a useful point. I would think it would vary no more that about
> 0.2 volts from the nominal 4.5 volts, especially among similar devices.
> The source resistors should take care of that much variation without too
> much power, and for linear applications one might as well dissipate some
> of the power in resistors rather than the MOSFET. Switching applications
> are a much different animal, where efficiency is paramount, and
> transients are critical.
>
> An interesting discussion. There is some good information at:
> http://www.answers.com/topic/mosfet
>
> Paul
>
So I did an experiment. I connected four MOSFETs, HUF75645P, 100V, 75A,
310W, 0.014 ohm. Sources to GND. Gates tied together, through 100 ohms to a
pot across 10 VDC supply. Each drain to a 100 ohm resistor and a red LED to
+10 VDC.
Vgs: 2.50 2.60 2.73 2.86 3.00 3.20 3.50
Vd(1) 8.80 8.75 8.60 8.48 7.95 3.43 0.016
Vd(2) 8.80 8.76 8.62 8.51 8.15 4.56 0.018
Vd(3) 8.76 8.72 8.58 8.45 7.93 2.95 0.015
Vd(4) 8.79 8.76 8.63 8.53 8.21 5.40 0.020
LEDs were all about equal brightness and were barely lit at 2.73V and
fairly bright at 3.00V to 3.20V.
The spec sheet shows threshold from 2.0 to 4.0 V, but this is probably more
the spread over temperature, which is 0.6 to 1.1 normalized, or 2.1 to 3.85
from -40 to +160C. My experiment shows threshold at about 2.8 to 3.2 V at
20C.
I even tried heating one device with a soldering iron. At 2.76 Vgs, the Vd
changed from 8.60V to 7.90V. This does show a positive temperature
coefficient of current to temperature at near threshold, which would be
detrimental to current sharing, but it appears that the reverse is true at
higher currents. The LED for the hot device was a bit brighter, but not too
much.
I'm pretty well satisfied that MOSFETs can be paralleled successfully
without extreme measures. Moderate source resistors dropping 0.2 volts or
so at maximum current should be enough to provide adequate current sharing
without loss of headroom or efficiency for most applications. It would be a
good idea to try this same type experiment at higher levels, but I think
these (or similar) MOSFETs would work fine for the OP's power supply. I
bought 50 of them on eBay for $20, although shipping from Sweden added
about $6.
Happy 2007!
Paul
cbarn...@aol.com
martin griffith wrote:
> >
> >I'm not up-to-date on insults. What does pommy mean?
> >
> >Tnx
> >
> >Don
> from a wiki
> One theory is that, as the majority of early immigrants to Australia
> were British, it is rhyming slang for "immigrant" from a contraction
> of the word "pomegranate", or possibly more directly related to the
> appearance of the fruit, as it bears a more than passing resemblance
> to the typical pale complexioned Briton's skin after his or her first
> few days living under the hot Australian sun.
>
>
> martin
It comes from the days when the brits used to send all the
undesireables there instead of prison. POM was short for "Prisoner Of
her Majesty". With hind sight this was not such a good policy, just
look at Phill, and the Aussies are still very sensitive about it. If
you ever visit Australia and the immigration official ask you if you
have a crimminal record, DO NOT ask if it's still compulsorary.
Tony Williams
Mike Monett <N...@email.adr> wrote:
> What about the current example using source resistors? These
> provide negative feedback, so Vgs is no longer fixed. How do
> we calculate the minimum value needed to prevent runaway?
I think it is a question of doing sums to calculate
the dP(fet)/dT and making sure that that value is
less than the reciprocal of the Theta(junction-case)
of the heatsinking allocated to that individual FET.
I've just scribbled out a few sums, based on the
assumption that the main Id tempco comes from the
negative tempco of Vgs(Threshold), (values given in
various publications ranging from 1mV/C to 2.8mV/C).
The sums looked plausible but some example calcs
resulted in negative values for the external Rs, so
it is back to the dwg board on that. :(
> Also, source resistors dissipate some heat, which reduces the
> amount dissipated in the MOSFET. So in linear applications
> such as the current topic, the source resistor can be useful.
AFAIK the worst case for potential thermal runaway is
a MOSFET with high transcoductance (gfs), running with
high voltage and low current, with inadequate heatsink.
This is the typical circumstance of (audio) power amps,
with paralleled big Hexfets, in class AB, running idling.
See <http://sound.westhost.com/articles/hexfet.htm>
which is an article proposing the use of Hexfets in
paralleled complementary format....... but then read to
the end, at the Update, to see the remarks after one
was built.
--
Tony Williams.
Phil Allison
** The above pile of sub human slime is another congenital, ASD FUCKED
POMMY CUNT .
The UK is just CraWling with the vile pukes.
Aussies just HATE them to death.
Septic Tanks completely despise them.
Other poms just quietly loathe them.
YOU can use you Killfile to eliminate this CUNT anytime.
...... Phil
Phil Allison
"Paul E. Schoen Fucking MORON from HELL "
> The spec sheet shows threshold from 2.0 to 4.0 V, but this is probably
> more the spread over temperature,
** Go read page 4 - asshole !!!!!!!!!!!!!
You stinking, monstrously autistic, kiddie fiddling pile of dog vomit!!!
http://www.st.com/stonline/products/literature/ds/11035.pdf
see " Tcase = 25C " ?????????
Wanked yourself totally blind - cunt brain ??
........ Phil
Winfield Hill
> "Paul E. Schoen" <pst...@smart.net> wrote in message
> news:4596fe4e$0$13299$ecde...@news.coretel.net...
>>
>> I guess someone will need to do actual experimentation to see what
>> happens in real life. I have not found very much information on device
>> variations, particularly for gain (transconductance) and gate threshold,
>> which are probably critical for this application. It would probably be a
>> valuable exercise to do this. I was very surprised at the current sharing
>> without source resistors. I would think that the "knee" of the Vgs to I
>> curve is a useful point. I would think it would vary no more that about
>> 0.2 volts from the nominal 4.5 volts, especially among similar devices.
>> The source resistors should take care of that much variation without too
>> much power, and for linear applications one might as well dissipate some
>> of the power in resistors rather than the MOSFET. Switching applications
>> are a much different animal, where efficiency is paramount, and
>> transients are critical.
>
Phil responds to that by calling you a "stinking, monstrously
autistic, kiddie fiddling pile of dog vomit!!! " I simply think
you're badly misinformed, despite our attempts to rectify that.
But, you do get serious points for trying a bench experiment.
Sadly, your experiment was nearly meaningless, because the power
dissipation was so low it didn't increase the junction temperature
sufficiently to get interesting. There's a smidgin of interesting
data when you compare the next-to-last two columns. The
Vgs = 3.00V column at about (10-1.2)/100 = 8mA shows
modestly-matched currents, but the next column with higher 34
to 58mA currents shows a 70% mismatch. However, these tiny
currents are silly: these are 75A 310W mosfets, for Pete's sake!
Device #3 drawing 58mA had only 0.17W of power dissipation,
and Intersil's datasheet tells us this will raise the FET's junction
temperature only 0.17*62 = 10C, which is not enough to learn
anything. I suggest you replace the LED+100 with 0.1-ohm
3-W current-sensing resistors, etc., to maintain the MOSFETs
at the same Vds. You can run them at currents of say 0.2 to
2A each, for 2 to 20W dissipation, without heatsinks, natch,
and measure the relative voltage drops across the 0.1 sense
resistors. Then perhaps you'll learn something interesting.
Paul E. Schoen
"Winfield Hill" <hi...@rowland.org> wrote in message
news:1167666022.8...@48g2000cwx.googlegroups.com...
> Sadly, your experiment was nearly meaningless, because the power
> dissipation was so low it didn't increase the junction temperature
> sufficiently to get interesting. There's a smidgin of interesting
> data when you compare the next-to-last two columns. The
> Vgs = 3.00V column at about (10-1.2)/100 = 8mA shows
> modestly-matched currents, but the next column with higher 34
> to 58mA currents shows a 70% mismatch. However, these tiny
> currents are silly: these are 75A 310W mosfets, for Pete's sake!
>
Vd(1) 8.80 8.75 8.60 8.48 7.95 3.43 0.016
Vd(2) 8.80 8.76 8.62 8.51 8.15 4.56 0.018
Vd(3) 8.76 8.72 8.58 8.45 7.93 2.95 0.015
Vd(4) 8.79 8.76 8.63 8.53 8.21 5.40 0.020
The threshold voltage is usually specified at very low current, such as 250
uA. I expected the greatest mismatch to occur here, at what I would call
the "knee" of the curve. The point is that a few tenths of a volt Vgs take
the device from just barely conducting to a full ON condition. Certainly I
would not recommend running in parallel without adequate source resistors,
which would equalize the currents due to negative feedback.
> Device #3 drawing 58mA had only 0.17W of power dissipation,
> and Intersil's datasheet tells us this will raise the FET's junction
> temperature only 0.17*62 = 10C, which is not enough to learn
> anything. I suggest you replace the LED+100 with 0.1-ohm
> 3-W current-sensing resistors, etc., to maintain the MOSFETs
> at the same Vds. You can run them at currents of say 0.2 to
> 2A each, for 2 to 20W dissipation, without heatsinks, natch,
> and measure the relative voltage drops across the 0.1 sense
> resistors. Then perhaps you'll learn something interesting.
>
OK. I changed the circuit to source follower. Devices 1, 2, and 3 are
connected through 12 ohm 10 watt resistors to GND, device 4 has a 100 ohm
to GND. All drains connected to a 10 VDC supply. Gates in parallel through
100 ohms to a pot across the supply. Results:
Vg: 5.00 6.00 7.00 7.50 8.00 9.00 10.0
7.50(cold)
Vs(1) 2.25 3.13 4.11 4.65 5.13 6.12 7.11 4.53
Vs(2) 2.31 3.23 4.09 4.73 5.20 6.16 7.18 4.60
Vs(3) 2.18 3.12 4.09 4.60 5.09 6.07 7.06 4.27
Vs(4) 2.26 3.20 4.17 4.67 5.03 6.16 7.16 4.66
This seems to be a reasonable test within the lower normal limits of the
power supply being discussed. Current in each device varies from 0.18 A to
0.60 A. As a reference, device 4 is running at about 1/8 the current of the
others. It does have some thermal connection to the others, as I have them
mounted in free air next to each other (and probably touching). I started
measuring at 7.50 (labeled cold), and those values were drifting as the
devices heated up, so they are not very accurate, but do show the increased
current as temperature rises. Also, device 2 is probably the hottest since
it is sandwiched between 1 and 3, so with good heat sinking the current
sharing may be even better.
An exhaustive test would involve hours of work taking measurements or
setting up a data acquisition system to plot curves at many points. Also
more devices would be needed to achieve true statistical confidence. But I
would be comfortable using these devices for the OP's application, and I'd
expect current sharing to be within 20% or better. With the 0.1 ohm
resistors, it would be easy to try.
Right now there is a tube of 50 pieces on eBay item 170062103958, for $0.01
plus $8.00 shipping from Sweden, if you'd like to give it a Schottky.
Paul
JoeBloe
skenn_ie
Hey guys, if you insist on insulting eachother, please lose the
expletives. They only show that you don't know enough english to make
meaningful comments !.
As far as 3055's are concerned...I'd bin them..they may be cheap, but
they are also horrible devices..use a TIP, or better still, a HexFET
Phil Allison
"skenn_ie" <sken...@eircom.net> wrote in message
news:1167685687.1...@s34g2000cwa.googlegroups.com...
** Beware - Skinhead Google Groper Troll. !!
> Hey guys, if you insist on insulting eachother, please lose the
> expletives. They only show that you don't know enough english to make
> meaningful comments !.
** Bollocks it does.
> As far as 3055's are concerned...I'd bin them..they may be cheap, but
> they are also horrible devices..use a TIP, or better still, a HexFET
** Only show asses like you do not know enough electronics to make any
valid comment.
Bug OFF - IDIOT
....... Phil
jasen
> It comes from the days when the brits used to send all the
> undesireables there instead of prison. POM was short for "Prisoner Of
> her Majesty".
That's definately wrong... aparently this word was first
recorded last century. be very suspicious of any acronyms claiming to
predate SCUBA and RADAR
> If you ever visit Australia and the immigration official ask you if you
> have a crimminal record, DO NOT ask if it's still compulsorary.
:)
--
Bye.
Jasen
Don Bowey
<ja...@free.net.nz> wrote:
Are you claiming it took the Australians until 1900 to write and keep a
history?
Don
Homer J Simpson
"Don Bowey" <dbo...@comcast.net> wrote in message
news:C1BF11C8.532FC%dbo...@comcast.net...
> Are you claiming it took the Australians until 1900 to write and keep a
> history?
They were British for a long time.
skenn_ie
ngland
skenn_ie
business, and have done so for 30 years !
I won't even grace you with a comment about YOUR intelligence, or even
if you are part of the human race !
John Larkin
>Being an idiot, it seems strange that I can earn my living from this
>business, and have done so for 30 years !
>I won't even grace you with a comment about YOUR intelligence, or even
>if you are part of the human race !
We pitiful mortals are all idiots in the light of Phil's blazing
intelligence and literary skills.
John
JoeBloe
us:
Yes, and regardless of what the SCUBA RADAR dip says, acronyms have
been around for a LONG time. We just did not give them the moniker
"acronym" until the middle of the last century.
mark krawczuk
allit cost me is $00.00 dollars, better than usa , dont know what merry
old england is like ?
<>> going stupid again.
>>
>> John Perry
>
> Over in oz they have to pay for their medication, he'll be ok when some
> cash comes in.
>
MassiveProng
<krawc...@dodo.com.au> Gave us:
>hey , at least we dont have to pay medical bills here.........broke my arm
>allit cost me is $00.00 dollars, better than usa , dont know what merry
>old england is like ?
>
>
Is it better, you top posting Usenet retard?
I make more money here so that I can afford paid for medical care.
We call that standard of living up here.
amdx
"MassiveProng" <Massiv...@thebarattheendoftheuniverse.org> wrote in
message news:jd20t2tfc9ia58vfh...@4ax.com...
> On Mon, 12 Feb 2007 16:19:29 +1030, "mark krawczuk"
> <krawc...@dodo.com.au> Gave us:
>
>>hey , at least we dont have to pay medical bills here.........broke my
>>arm
>>allit cost me is $00.00 dollars, better than usa , dont know what merry
>>old england is like ?
>>
>>
>
I think you mean, I didn't have to pay for my medical bills by writing a
check
to the doctor or hospital.
But what you didn't say is this; I pay some taxes every day to a wasteful
bureaucracy
so they can write the check to pay my medical bills .
I just read what I wrote, and golly gee I think you did pay for your
medical bills.
And if your lucky enough to be healthy and take care of yourself, you don't
pay
any of those taxes to help pay your medical bills, you pay the taxes to pay
for other
peoples medical bills.
If this isn't a quote it should be;
"It's not free if the government pays for it."
Mike
Michael A. Terrell
>
> hey , at least we dont have to pay medical bills here.........broke my arm
> allit cost me is $00.00 dollars, better than usa , dont know what merry
> old england is like ?
We break arms for free in the USA, as well. Treatment would cost me
the same in a VA hospital.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
Homer J Simpson
"amdx" <am...@knology.net> wrote in message
news:35cb4$45d055dd$45011502$34...@KNOLOGY.NET...
> But what you didn't say is this; I pay some taxes every day to a wasteful
> bureaucracy
> so they can write the check to pay my medical bills .
It is much cheaper in Canada where each province has a medical plan and you
get a health credit card to pay for care.
amdx
"Homer J Simpson" <nob...@nowhere.com> wrote in message
news:9d3Ah.56258$Fd.35430@edtnps90...
for health care. Now where does the government get the money to pay the
bill?
The Taxpayers.
So it is not free. And it's not cheap, unless you are a heavy user of the
system.
Mike
Homer J Simpson
>> It is much cheaper in Canada where each province has a medical plan and
>> you get a health credit card to pay for care.
>>
> I'm sorry, I probably didn't explain it well. The Canadian government
> pays
> for health care. Now where does the government get the money to pay the
> bill?
> The Taxpayers.
> So it is not free. And it's not cheap, unless you are a heavy user of the
> system.
In Canada the overhead is a tiny part of the cost. In the US it is a major
part, so it costs more in the US per head of population and you still wind
up with worse or no health care and a shorter life span. However many
executives get very rich.
Who pays for the indigent, Medicare, Medicaid, services for the armed
services and the deluxe care systems for government employees and
politicians?
amdx
and we will just be a Canada but with better weather.
Mike
Homer J Simpson
>> In Canada the overhead is a tiny part of the cost. In the US it is a
>> major part, so it costs more in the US per head of population and you
>> still wind up with worse or no health care and a shorter life span.
>> However many executives get very rich.
>>
>> Who pays for the indigent, Medicare, Medicaid, services for the armed
>> services and the deluxe care systems for government employees and
>> politicians?
>>
>>
> Yep, we're on our way down that socialist road, won't be long and
> and we will just be a Canada but with better weather.
Even the auto companies can no longer handle the old 'system'.
Richard The Dreaded Libertarian
> "Homer J Simpson" <nob...@nowhere.com> wrote in message
>>>> you get a health credit card to pay for care.
>>>>
>>> I'm sorry, I probably didn't explain it well. The Canadian government
>>> pays
>>> for health care. Now where does the government get the money to pay the
>>> bill?
>>> The Taxpayers.
>>> So it is not free. And it's not cheap, unless you are a heavy user of the
>>> system.
>>
>> In Canada the overhead is a tiny part of the cost. In the US it is a major
>> part, so it costs more in the US per head of population and you still wind
>> up with worse or no health care and a shorter life span. However many
>> executives get very rich.
>>
>> Who pays for the indigent, Medicare, Medicaid, services for the armed
>> services and the deluxe care systems for government employees and
>> politicians?
>>
> Yep, we're on our way down that socialist road, won't be long and
> and we will just be a Canada but with better weather.
The only reason the Canadians can continue to pretend that their
socialist system works is because those who DO have money come to the
US and use the Free Market. (that's "free" as in "free to choose", not
as in "free beers".)
Without that, we're both going to go the way of the Soviet Union, Mao's
China , and Great Britain's nightmare of a medical system, and so on.
The only thing that saved China was (1) they had the population to
absorb the collapse, and (2) they decided to go to the Free Market system,
in case you haven't noticed.
Thanks,
Rich
Homer J Simpson
"Richard The Dreaded Libertarian" <nu...@example.net> wrote in message
news:pan.2007.02.13....@example.net...
> The only reason the Canadians can continue to pretend that their
> socialist system works is because those who DO have money come to the
> US and use the Free Market. (that's "free" as in "free to choose", not
> as in "free beers".)
The only reason the Americans can continue to pretend that their
exploitative system works is because those who DO have money can come to
Canada and use the Free Market. (that's "free" as in "free to choose", not
as in "free beers".)
They simply pay cash and find the prices of both services and drugs are
substantially lower due to the elimination of the medical mafia and their
extractive procedures.
Eeyore
Richard The Dreaded Libertarian wrote:
> .... Great Britain's nightmare of a medical system, and so on.
What's a nightmare about it ?
Graham
Richard The Dreaded Libertarian
I've heard that you have to wait in line for like two years to get
major care.
Or maybe they just pop over to France or something.
Thanks,
Rich
Homer J Simpson
> On Tue, 13 Feb 2007 03:23:12 +0000, Eeyore wrote:
>> Richard The Dreaded Libertarian wrote:
>>
>>> .... Great Britain's nightmare of a medical system, and so on.
>>
>> What's a nightmare about it ?
>
> I've heard that you have to wait in line for like two years to get
> major care.
I waited 5 minutes.
I've heard you can wait up to 12 hours or more in a US 'emergency' room.
john jardine
"Richard The Dreaded Libertarian" <nu...@example.net> wrote in message
news:pan.2007.02.13...@example.net...
If you Google on "hospital waiting lists". The gov' supplies the current
data.
"Waiting times" are a very traditional, typically British, national hobby
horse.
If it's a no-news day then reporters are sent out to scour the kingdom for
an old dear who's been waiting 'too long' for a hip replacement. (always an
old dear). Makes a good filler item and the gov' of the day invariably has
to respond by apologising and setting up an enquiry.
On the other hand, a guy I know casually called at his vets with a chest
pain and 2 days later had had a triple bypass. The serious stuff always
receives prompt attention.
Having said this, I do believe the French healthcare is even better :).
john
--
Posted via a free Usenet account from http://www.teranews.com
Homer J Simpson
"john jardine" <jo...@jjdesigns.fsnet.co.uk> wrote in message
news:45d224c1$0$16317$8826...@free.teranews.com...
> If you Google on "hospital waiting lists". The gov' supplies the current
> data.
> "Waiting times" are a very traditional, typically British, national hobby
> horse.
> If it's a no-news day then reporters are sent out to scour the kingdom for
> an old dear who's been waiting 'too long' for a hip replacement. (always
> an
> old dear). Makes a good filler item and the gov' of the day invariably has
> to respond by apologising and setting up an enquiry.
> On the other hand, a guy I know casually called at his vets with a chest
> pain and 2 days later had had a triple bypass. The serious stuff always
> receives prompt attention.
>
> Having said this, I do believe the French healthcare is even better :).
I've heard the German system is spectacularly fast and efficient.
Robert Baer
everyhospital around, starting with -->false advertising claims<--,
-->breach of implied contract<-- and i cannot think what else.
Paul Burke
>
> I've heard that you have to wait in line for like two years to get
> major care.
>
> Or maybe they just pop over to France or something.
There's a lot of public dissatisfaction with it, but broadly it works
pretty well. Far too well for our government, who want to privatise it
so their mates can make money out of it, and have consequently imposed a
lunatic finance scheme such that hospitals are closing and being
replaced with privately built (but publicly financed) ones that have
less beds and cost a fortune, and that hospitals run out of budget half
way through the financial year. The health service is fine, but it's
private business that hands out directorships to retired politicians.
Paul Burke
amdx
medical bills, costs would not have soared.
The downside of that is we would not have as many of the high tech
testing machines readily accessible.
Oh well, terror, immigration, healthcare, insurance, taxes, government
growth,
sometimes I just need a break, I stop watching cable news and listening to
talk radio and listen to 60s and 70s music. ahhh
hmm hmm hmm
Mike :-)
amdx
wealthy American system.