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zener diode pulse current rating
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panfilero
Apr 20, 2012, 4:36:49 PM4/20/12
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I need a 30V zener to drop the a high voltage of 100V down to 60V so I
can use it with a switch mode power supply chip. So while this
circuit is in use the zener will be exposed to current pulses from the
switching, these current pulses are in the neighborhood of 1A. I've
gone to digikey and pulled up some zeners but I don't see this rating,
where can I find the rating that tells me whether or not it's ok to
pulse 1A through my zener?
here's the one I'm looking at
http://www.nxp.com/documents/data_sheet/NZX_SER.pdf
much thanks!
can use it with a switch mode power supply chip. So while this
circuit is in use the zener will be exposed to current pulses from the
switching, these current pulses are in the neighborhood of 1A. I've
gone to digikey and pulled up some zeners but I don't see this rating,
where can I find the rating that tells me whether or not it's ok to
pulse 1A through my zener?
here's the one I'm looking at
http://www.nxp.com/documents/data_sheet/NZX_SER.pdf
much thanks!
panfilero
Apr 20, 2012, 6:44:34 PM4/20/12
to
power rating of 500mW, then max current is I = .5/30 = 17mA.... weak!
but this doesn't tell me about current pulses...spikes...
Bill Martin
Apr 20, 2012, 6:46:28 PM4/20/12
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leaves about 10V of "smoke" to dispose of...:-)
bill
panfilero
Apr 20, 2012, 6:58:22 PM4/20/12
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mike
Apr 20, 2012, 7:18:29 PM4/20/12
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the zener rating, you can fix that with a cap...but then you have to
worry about the turn-on transient current thru the zener to charge the cap.
Look at the thermal time constant graphs and put in your unspecified
pulse durations.
Put an emitter follower after the zener.
Jamie
Apr 20, 2012, 10:00:38 PM4/20/12
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zener circuit?
Cathode equal
+
|
|
+---+-----+------------------------+
| | |
+ | |
z | |
zener diode A | |
+ + |
| |/ |
+-----+-| NPN +
| |> |
|+ + - Reverse
.-. | ^ protect
| | + +
10k | | V Protection diode |
'-' - |
+----+----+------------------------+
|
|
|
+
Anode Equal
You may not need the reverse protect diode, but to simulate a real
zener as a stand alone in a circuit where reverse flow may occur, this
is needed.
Your zener voltage would be what you want - ~ 1.8 volts. (2 diode
drops and saturation voltage of the NPN)
The other protect diode in the emitter must be there for fast
turn offs that will generate negative voltage in cases where it will
zener the Base-Emitter, you don't want that to happen.
With this circuit, you can use very small zeners. Select the proper
transistor to handle the power.
Jamie
mike
Apr 20, 2012, 10:22:45 PM4/20/12
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a component of a bad design.
There's something comforting about a pre-regulator circuit that doesn't
explode instantly when you short the output to ground.
George Herold
Apr 20, 2012, 10:36:58 PM4/20/12
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boot.
George H.
Jamie
Apr 20, 2012, 10:47:20 PM4/20/12
to
If it really matters to you, I use that circuit in many, many!
clamping protecting circuits for HI-Pot test equipment and HV protection
clamps and regulators to increase the handling current on zeners.
It works as advertised. Never had one of those fail unless there was
some incoming that exceeded the NPN transistor. If that being the case
then there is something else wrong and shouldn't be doing that.
Also, that circuit is very common from old school. I am not the first
one to use that and it's been used in countless designs. So go tell them
they are wrong, too! If it would make you feel any better, you could put
a R in series with the zener, but really, all that is going to do is
slow it down a bit.
Jamie
Tim Williams
Apr 21, 2012, 3:02:42 AM4/21/12
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Probably a few microseconds. Hot spots and junction heating are the
limiting concerns. Regular zeners I don't think are going to be rated for
peaks, but TVS rated diodes do.
As for preregulators, I recall Jeorg telling a story of a similar
application where a 2N2222 was mysteriously going PFFT, BANG, while being
well within limits according to most instruments. A higher bandwidth scope
indicated ~nanosecond pulses which were invisible on lesser instrumentation
and, with amplitudes of ~1A peak, where more than sufficient to cause
troubles.
As Mike said, a current-limited solution is an excellent idea. Even a good
BJT circuit may not respond to nanosecond pulses, but a ferrite bead and
hearty ceramic cap will take care of that kind of stress.
That said, filtering is always the best idea. Good bypass never hurts, and
good filtering turns a spikey challenge into a mere bumpy ride.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
"panfilero" <panf...@gmail.com> wrote in message
news:9f37100c-30a1-43f9...@c4g2000yqj.googlegroups.com...
limiting concerns. Regular zeners I don't think are going to be rated for
peaks, but TVS rated diodes do.
As for preregulators, I recall Jeorg telling a story of a similar
application where a 2N2222 was mysteriously going PFFT, BANG, while being
well within limits according to most instruments. A higher bandwidth scope
indicated ~nanosecond pulses which were invisible on lesser instrumentation
and, with amplitudes of ~1A peak, where more than sufficient to cause
troubles.
As Mike said, a current-limited solution is an excellent idea. Even a good
BJT circuit may not respond to nanosecond pulses, but a ferrite bead and
hearty ceramic cap will take care of that kind of stress.
That said, filtering is always the best idea. Good bypass never hurts, and
good filtering turns a spikey challenge into a mere bumpy ride.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
"panfilero" <panf...@gmail.com> wrote in message
news:9f37100c-30a1-43f9...@c4g2000yqj.googlegroups.com...
mike
Apr 21, 2012, 6:12:05 AM4/21/12
to
you took offense to me being more conservative.
I never found fault with your using a zener diode, synthesized or otherwise,
in an application where a zener diode was appropriate.
I did suggest, in an earlier post, that using a zener, synthesized or
otherwise, in this application might not be optimal.
If a current spike shorts the zener, synthesized or otherwise,
it likely takes out the power supply it's protecting...and maybe
it takes out the whole board. Compound that with
an attempt to use a 1/2W zener with 1A current pulses.
I am NOT comforted by that design.
I stand by my assertion that it can be beneficial to take a step back,
look at the big picture
and try a different topology rather than patch up a brute-force
design that has limitations by adding more brute to the force.
We can't do that, because the big picture was never presented by the OP.
All I can do is suggest caution.
John S
Apr 21, 2012, 12:04:57 PM4/21/12
to
nospam
Apr 21, 2012, 12:32:49 PM4/21/12
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Jamie <jamie_ka1lpa_not_v...@charter.net> wrote:
>why not simply use a transistor to boost the handling of the
>zener circuit?
Then he will just post asking about transistor pulse current ratings.
>why not simply use a transistor to boost the handling of the
>zener circuit?
Extra annoying when he links an excellent datasheet with clear abs max
current, power, junction temperature limits, and transient thermal
impedance graphs.
upsid...@downunder.com
Apr 21, 2012, 1:07:30 PM4/21/12
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On Fri, 20 Apr 2012 13:36:49 -0700 (PDT), panfilero
<panf...@gmail.com> wrote:
>I need a 30V zener to drop the a high voltage of 100V down to 60V so I
>can use it with a switch mode power supply chip.
Why not use a different switcher, rated for 100 V ?
<panf...@gmail.com> wrote:
>I need a 30V zener to drop the a high voltage of 100V down to 60V so I
>can use it with a switch mode power supply chip.
It does not make sense to burn 30 % (or should it be 40 %:-) of the
available power in a resistor (zener) and then use a switcher to go
down to whatever voltages are needed ?
The total system efficiency will be better with a 100V switcher :-)
John Fields
Apr 21, 2012, 4:57:06 PM4/21/12
to
On Sat, 21 Apr 2012 17:32:49 +0100, nospam <nos...@please.invalid>
wrote:
---
Bingo!
--
JF
wrote:
Bingo!
--
JF
John Fields
Apr 21, 2012, 5:08:58 PM4/21/12
to
>I need a 30V zener to drop the a high voltage of 100V down to 60V so I
>can use it with a switch mode power supply chip. So while this
>circuit is in use the zener will be exposed to current pulses from the
>switching, these current pulses are in the neighborhood of 1A.
.
>can use it with a switch mode power supply chip. So while this
>circuit is in use the zener will be exposed to current pulses from the
>switching, these current pulses are in the neighborhood of 1A.
.
.
---
What's the quiescent current through the Zener, how long do the pulses
last, and how often do they occur?
--
JF
mike
Apr 21, 2012, 9:11:40 PM4/21/12
to
A person is certainly free to ask a specific question and get a specific
answer.
BUT
You can often judge the experience (I was gonna say competence. That's the
right word, but would ignite the ethernet and we don't want that.) of
the person asking the question by the form and words used.
When the big red flags go up, it can be helpful to the person to
elaborate...whether they like it or not. The side effect is that we
turn on each other, but that's just the way of the web.
In my opinion, there is NO pulse width that allows 40W of peak power
in a 1/2W device to be considered an acceptable design...none.
And it's difficult to filter the current pulses. You start adding
caps and discover that something else blows up when you crowbar the
100V supply. Are we comforted by the fact that most designers wouldn't
consider that a problem?
Without context, we're left with only common sense to guide us.
Ignoring the 10V discrepancy in the question, someone stated that
the zener could sustain 17mA if you didn't derate it. For many single
chip switchers, the duty factor is closely related to the ratio of input
and output voltages. Narrow 1A spikes seem out of place.
I would prefer a design that didn't have 'em.
Yes, it's possible for a system integrator to be in a situation where they
have to mate two bad designs. That's why you need your BEST engineers
doing the integration.
One of the jobs of a project manager is to stamp out tunnel vision.
Everybody needs to be aware of the big picture...not an expert, but aware.
Communication is key.
I used to tell engineers at the first project meeting that I was gonna
personally test the design before the second prototype phase.
The list of abuses would contain
Crowbar the power supplies.
Any connector that could be put on the wrong socket or backwards or
off-by-one on the right socket would be tried and the power turned on.
Bunch of other single-point failures that could happen in manufacturing.
You could have heard the whimpering and wailing in the next county.
Probably increased the cost a few pennies too. But the concept propagated
to other parts of the design so engineers considered more than just what
happened when everything was working right.
Yes, you can easily come up with single-point failures that can't be
protected against
and will reduce the project to a smoldering lump.
The key point is that MANY, MOST can be mitigated by paying attention.
Enough rant...
Back to the current situation.
More context would be helpful.
If we were voting based on what's been divulged, I'd bet that this is
a disaster waiting to happen. I refuse to be comforted by the fact
that most designs are faulty in ways that could have been easily
avoided by paying attention. Excuses are cheap. Field failures aren't.
Tim Williams
Apr 22, 2012, 3:50:17 AM4/22/12
to
"mike" <spa...@gmail.com> wrote in message
news:jmvlsl$ood$1...@dont-email.me...
Back in the toob days, horizontal sweep outputs were actually rated for this
service. Typical datasheet reads 30W plate dissipation (abs. max.,
continuous service), 260W short circuit during startup only. This rating
today would be labeled as something like "single pulse non-repetitive", with
a maximum pulse width of a leisurely 60 seconds or so.
Admittedly that's a peak-to-average ratio of not quite 10, rather than 80.
Tubes are essentially limited by dumb joule heating until voltages cause
vacuum breakdown or ion bombardment destroys the cathode; the peak could be
much higher for shorter periods, but the cathode will saturate before you
reach the actual pulsed thermal limit of the electrodes themselves.
There are plenty of other examples in semiconductors, anyway.
If your statement were unconditionally true, real switching circuits would
essentially never work. A transistor (optimistically) rated for ~500W, will
easily see, under hard inductive switching, power pulses over 20kW peak.
That's a peak-to-average ratio of 40 right there. If you count against the
actual continuous power rating, it could be 100W (ratio of 200) for typical
heatsinking, all the way down to just 1-2W without any heatsink at all (for
a ratio of a whopping 1000!).
Clearly, there is SOME pulse width that allows a peak-to-average ratio over
80 to be considered an acceptable design, for some component types.
Real engineers don't go by hearsay, they actually run experiments and think
for themselves.
news:jmvlsl$ood$1...@dont-email.me...
> In my opinion, there is NO pulse width that allows 40W of peak power
> in a 1/2W device to be considered an acceptable design...none.
Well, why not?
> in a 1/2W device to be considered an acceptable design...none.
Back in the toob days, horizontal sweep outputs were actually rated for this
service. Typical datasheet reads 30W plate dissipation (abs. max.,
continuous service), 260W short circuit during startup only. This rating
today would be labeled as something like "single pulse non-repetitive", with
a maximum pulse width of a leisurely 60 seconds or so.
Admittedly that's a peak-to-average ratio of not quite 10, rather than 80.
Tubes are essentially limited by dumb joule heating until voltages cause
vacuum breakdown or ion bombardment destroys the cathode; the peak could be
much higher for shorter periods, but the cathode will saturate before you
reach the actual pulsed thermal limit of the electrodes themselves.
There are plenty of other examples in semiconductors, anyway.
If your statement were unconditionally true, real switching circuits would
essentially never work. A transistor (optimistically) rated for ~500W, will
easily see, under hard inductive switching, power pulses over 20kW peak.
That's a peak-to-average ratio of 40 right there. If you count against the
actual continuous power rating, it could be 100W (ratio of 200) for typical
heatsinking, all the way down to just 1-2W without any heatsink at all (for
a ratio of a whopping 1000!).
Clearly, there is SOME pulse width that allows a peak-to-average ratio over
80 to be considered an acceptable design, for some component types.
Real engineers don't go by hearsay, they actually run experiments and think
for themselves.
mike
Apr 22, 2012, 5:14:20 AM4/22/12
to
for such use???
Couldn't agree more.
Apparently, you've never got the panicked call from production,
"hey mikie, your product is exploding. The parts have the right part
number, but they're a different color. Incoming inspection says
they meet the spec. Lead time on the old parts is 20 weeks.
We've got enough of the old parts in rework to last 'till Wednesday.
FIX IT!!!??"
Or the call from purchasing, "hey mikie, your idiot engineer wants
to add a 40W pulse power spec on a jellybean 500mW part.
The vendor just laughed at me. Whatdayawannado???"
Or you've never had to explain safe operating area to an engineer
who wanted to use a transistor at max voltage and
current simultaneously.
I have a lot of experience with what engineers do.
Product designers expect the product to sail through manufacturing
and be trouble free in the customer's hands. Sometimes, that
means overruling what "engineers" "think".
Go back a couple of weeks and review the thread on "slightly reverse
biased tantalums". Perfect example of allegedly rational engineers
arguing that it's OK to do something irrational.
Abusing a part WAY, WAY beyond its specification when there
are conservative alternatives is bad business.
Message has been deleted
Spehro Pefhany
Apr 22, 2012, 1:09:07 PM4/22/12
to
On Sun, 22 Apr 2012 09:41:15 -0700, the renowned Fred Abse
<excret...@invalid.invalid> wrote:
>On Sun, 22 Apr 2012 02:14:20 -0700, mike wrote:
>
>> Or you've never had to explain safe operating area to an engineer
>> who wanted to use a transistor at max voltage and
>> current simultaneously.
>
>Apparently a usage of the word "engineer" with which I am unfamiliar.
>
>Where I come from, engineers are experienced graduates who design and
>develop equipment that works, and is suitable for purpose. They know about
>SOA, and where to find the relevant data.
They probably didn't learn about SOA in University.
>"Product designers" are people who decide what sort of pretty box it's to
>go in.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
<excret...@invalid.invalid> wrote:
>On Sun, 22 Apr 2012 02:14:20 -0700, mike wrote:
>
>> Or you've never had to explain safe operating area to an engineer
>> who wanted to use a transistor at max voltage and
>> current simultaneously.
>
>
>Where I come from, engineers are experienced graduates who design and
>develop equipment that works, and is suitable for purpose. They know about
>SOA, and where to find the relevant data.
They probably didn't learn about SOA in University.
>"Product designers" are people who decide what sort of pretty box it's to
>go in.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Jeroen
Apr 22, 2012, 4:13:12 PM4/22/12
to
On 2012-04-22 18:41, Fred Abse wrote:
> On Sun, 22 Apr 2012 02:14:20 -0700, mike wrote:
>
> On Sun, 22 Apr 2012 02:14:20 -0700, mike wrote:
>
>> Or you've never had to explain safe operating area to an engineer
>> who wanted to use a transistor at max voltage and
>> current simultaneously.
>
>> who wanted to use a transistor at max voltage and
>> current simultaneously.
>
> Apparently a usage of the word "engineer" with which I am unfamiliar.
>
> Where I come from, engineers are experienced graduates who design and
> develop equipment that works, and is suitable for purpose. They know about
> SOA, and where to find the relevant data.
I knew one, long ago. It was just around the time power MOSFETs
>
> Where I come from, engineers are experienced graduates who design and
> develop equipment that works, and is suitable for purpose. They know about
> SOA, and where to find the relevant data.
became common, even though they were still expensive. He was
testing some and he had a whole heap of devices that "didn't
conform to specs". You'd think that after a pop or two he'd
start to wonder if he'd misunderstood something, but not this
one.
Oh well, I thought it was funny. No idea what's become of him.
Popping GaN transistors somewhere, probably.
Jeroen Belleman
k...@att.bizzzzzzzzzzzz
Apr 22, 2012, 5:07:23 PM4/22/12
to
power spec says you can't do that (unless it's an IRC part ;-). SOA is about
transitioning between the two safely. ;-)
One project I was sucked into turned out to be a SOA problem that the more
senior engineer in the group designed in. Because of some completely
avoidable design decisions, he put freewheeling diodes across contactors
instead of across the transistors driving them, some 20' away. In one series
of mainframes the wiring inbetween was just "black wire" (basically a wad of
individual 24GA wires) which was quite inductive. Oops. The other two models
used twinlead or trilead between the two points, which was quite capacitive.
No problems with them. One brand of drivers (Motorola) would go through
secondary breakdown and fry, causing the contactors to fail closed and the
magic smoke to roll out of some ballast resistors. Not so good. I proved
that Sprage devices would never fail (without avalanching first), so that was
the fix. Not the best, but it worked.
>I have a lot of experience with what engineers do.
>Product designers expect the product to sail through manufacturing
>and be trouble free in the customer's hands. Sometimes, that
>means overruling what "engineers" "think".
>Go back a couple of weeks and review the thread on "slightly reverse
>biased tantalums". Perfect example of allegedly rational engineers
>arguing that it's OK to do something irrational.
>Abusing a part WAY, WAY beyond its specification when there
>are conservative alternatives is bad business.
Tim Williams
Apr 23, 2012, 12:29:56 AM4/23/12
to
"mike" <spa...@gmail.com> wrote in message
news:jn0i5l$98l$1...@dont-email.me...
> Go back a couple of weeks and review the thread on "slightly reverse
> biased tantalums". Perfect example of allegedly rational engineers
> arguing that it's OK to do something irrational.
Ah, but you see.. I would never insult the word "rational" by using it to
> biased tantalums". Perfect example of allegedly rational engineers
> arguing that it's OK to do something irrational.
describe most of the engineers here :)
Michael A. Terrell
Apr 24, 2012, 8:42:55 PM4/24/12
to
"k...@att.bizzzzzzzzzzzz" wrote:
>
> I proved
> that Sprage devices would never fail (without avalanching first), so that was
> the fix.
--
You can't have a sense of humor, if you have no sense.
John Fields
Apr 25, 2012, 8:09:28 PM4/25/12
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