LR8 high volltage linear regulators
Piglit
external pass elements in a similar way as their low voltage (LM317)
cousins in order to increase the available current ?. Looking for an
adjustable (50..350volt /150ma) regulator to run from a 400v raw
supply, and the Supertex part looks ideal except for the 10ma rating,
and strangely, current boosting is not mentioned in the apps notes. Any
better parts out there ?.
M
Winfield Hill
>
> Is there any reason that Supertex LR8 regulators cannot be used with
> external pass elements in a similar way as their low voltage (LM317)
> cousins in order to increase the available current?
Are you aware of the inherent difficulty in stabilizing high-
side current-amplification circuits? The regulator has an
internal high-gain feedback loop, whose gain drops 20dB/decade
with frequency, with an associated 90-degrees phase shift.
. ,--- S D -----------,
. | G _______ |
. | | | | |
. ---+-/\/\-+---| |--+-+----+----
. |_______| | _|_
. adjust | | --- Cout
. gnd -- pot --/\/\--+--/\/\--' |
. gnd
The external amplifier, a P-channel MOSFET or PNP transistor
(although a PNP is not preferred because it suffers from severe
SOA limitations), adds voltage gain inside the feedback loop.
This gain also drops by 20dB/decade with frequency, and has an
associated phase shift, due to the high capacitance load on the
output. Recall that Gain = gm * load In this case the load
is a reactance that drops with frequency and has a 90-degree
phase lag.
The high gain and combined phase shifts in a feedback loop with
two poles, as we call it, can lead to high-frequency oscillation.
In the case of an LM317, this possibility is moderated by the
high speed of its error amplifier and by a fortunate assist from
the internal self-resistance of the large electrolytic output
capacitor. This resistance, called esr, adds a pole-canceling
zero essential to the safe operation of this type of circuit.
Evaluating this scene for an LR8, we can suppose that its error
amplifier does not have the speed possessed by the LM317, and may
therefore be more susceptible to oscillation. We observe the
LR8's transient response is considerably slower than the LM317.
You can add a little series resistance to isolate the capacitor
and move the zero to a lower frequency, solving the oscillation
problem. This comes at the expense of degraded load regulation,
with a voltage drop outside the feedback loop, but that may be
acceptable in some high-voltage regulators.
. ,--- S D -----------,
. | G _______ |
. | | | | |
. ---+-/\/\-+---| |--+-+--/\/\--+----
. |_______| | _|_
. adjust | | --- Cout
. gnd -- pot --/\/\--+--/\/\--' |
. gnd
BTW, when testing circuits like this for stability, be sure to
test with the fill range of load currents, that's because gm and
therefore gain, increases nearly proportional to current. It's
useful to use the regulator's response to load-current steps to
evaluate its loop stability, looking for ringing, etc. One other
comment, Spice modeling will not work for such a circuit, unless
you correct your power MOSFET model for sub-threshold operation.
> Looking for an adjustable (50..350volt /150ma) regulator to run from
> a 400v raw supply, and the Supertex part looks ideal except for the
> 10ma rating, and strangely, current boosting is not mentioned in the
> apps notes.
One attractive possibility is to beef up the regulator's current
capability with an N-channel power MOSFET source follower, rather
than a P-channel high-side amplifier. First, this greatly reduces
the danger of oscillation, also very important, you can get bigger
N-type than P-type high-voltage power MOSFETs,
. ,---/\/\---- D S ----,
. | _______ G |
. | | | | 680 |
. ---+--| LR8 |---++-/\/\-+--+--
. |_______| | _|_
. | | --- Cout
. ,--/\/\--+--/\/\--' |
. | gnd
. '--- pot --- gnd
Although the source follower lowers the output voltage by an
uncertain load-dependent amount, typically three to four volts,
this isn't so painful for high-voltage regulators, where you
will no doubt have an output voltage-monitor meter anyway.
A power resistor in the MOSFET's drain can help reduce its
heating at high currents, and provide a crude current limit.
You can also easily add a true current limit,
.
. ,---/\/\---- D S -+-/\/--,
. | G | |
. | | B |
. | _______ +- C E ---+
. | | | | |
. ---+--| LR8 |---+-+--/\/\---+--+--
. |_______| | _|_
. | | --- Cout
. ,--/\/\--+--/\/\---' |
. | gnd
. '--- pot --- gnd
This is best done by adding two resistors to make a "foldback"
current limit, which reduces the maximum current during a short
circuit, where the highest power dissipation would occur. At
high voltages, with Vout up near Vin, Icl = Vbe/Rs primarily
determines the current limit, but at lower Vout, R4 and R5
subtracts from Vbe in the equation. You can choose R4/R5 to
reduce the current limit for a short to half or even 1/3 the
full level. This protects Q1, substantially reduces the heat
sink size, and may eliminate the requirement for a fan.
. High-voltage high-current regulator
. Q1
. ,- Rp -+----- D S ----------,
. | | G |
. | '- R5 -- | ---+-- R4 --+
. | | | |
. | | B Q2 |
. | _______ +- C E --, Rs
. | | | | | |
. --+---| LR8 |---+-+-- R3 --+--+--+--- Vout
. Vin |_______| | _|_
. | | --- Cout
. ,-- R1 --+-- R2 ---' |
. | gnd
. '--- pot --- gnd
One other thing, be safe and add a protective 10V zener across
Q1's gate to source.
> Any better parts out there?
I was a fan of Intersil's HIP5600, a bipolar linear IC, which
sadly was discontinued some time ago. But I still use it in
my designs, drawing sparingly from a lifetime-supply purchase.
--
Thanks,
- Win
Piglit
Winfield Hill wrote:
> Are you aware of the inherent difficulty in stabilizing high-
> side current-amplification circuits? The regulator has an
> internal high-gain feedback loop, whose gain drops 20dB/decade
> with frequency, with an associated 90-degrees phase shift.
> Thanks,
> - Win
Great answer (kinda restores faith in usenet), thanks Win.
cheers
M
(Looking forward to the next edition of "The Art..")
Winfield Hill
>
> Winfield Hill wrote:
>> Are you aware of the inherent difficulty in stabilizing high-
>> side current-amplification circuits? The regulator has an
>> internal high-gain feedback loop, whose gain drops 20dB/decade
>> with frequency, with an associated 90-degrees phase shift.
> (snip comprehensive reply)
>
> cheers
As you can see, I compared two ways of enhancing high-voltage
low-current three-terminal programmable regulators, one with
excess gain inside the feedback loop, and a second without but
with hopefully-modest output voltage errors. There's a third
attractive approach using low-voltage high-current regulators,
like the LM317 or LM317L, and cascoded series voltage-dropping
MOSFET(s) that always present the low-voltage LM317 with about
7V more than its output, for safe cool operation. I, and others,
have written about these in earlier s.e.d. posts, complete with
ASCII drawings. Here's an example from January 7th, 2002,
From: Winfield Hill (hi...@rowland.org)
Subject: Re: regulated power supply 50 volt to 400 100mA
Date: 2002-01-07 15:27:16 PST
Radioman wrote:
>
> I am looking for a schematic for a regulated power supply
> 50 volt to 400 volt that can deliver 100mA or more.
The ST VB408 etc., parts that Xenos suggests are nice, but
they may be hard to get. You may be interested in a simple
high-voltage regulator that uses standard LM317 or LM317L
chips plus an easy-to-get reliable high-voltage MOSFET.
600V FET _____ LM317L 5 to 500V
IN o----+----, ,-+-----+--| |--+---+----+---o OUT
| | | | s | | | | | | to 100mA
| _|_V_|_ | |_adj_| 1.2k | |
2.2M ----, | | | | | 0.47uF
1/2 W | '-||--+-----+ | ===
| | , 68pF | | | 630V
'--------+---|<|-----------|---' |
' 10V zener | 2.7 ohms
500k |
pot gnd
|
gnd
The FET needs a very serious heat sink, because 450V at
100mA is 45 watts, and under a short circuit condition the
LM317L may allow even more current to flow. You can add
a single-transistor foldback current limit if you want.
Add a 1n4002 diode backwards across the LM317 if you plan
on ever shorting out the input filter-storage capacitor.
(Always use drain resistors with high-voltage capacitors.
And always approach the open circuit with one hand behind
your back.)
The LM317L needs as much as 2.5mA to operate, and the 1.2k
resistor only takes 1mA, so this sets a 1.5mA minimum load
requirement. (BTW, the VB408 has a 1.2mA minimum load spec.
Note, you could use 470-ohms instead of 1.2k, but this would
require a 200k pot with up to 1W of dissipation, instead of
the 0.4W maximum dissipated in the 500k pot when its set to
about 400k for +400V out.)
---------
> (Looking forward to the next edition of "The Art..")
Groan.
--
Thanks,
- Win
Jeremy Morgan
Phil Hobbs
(sci.electronics.design) is older than Google. The short answer is,
"You can't do it on the Google Groups web interface."
Unfortunately Google collapses multiple space characters into one, which
destroys schematics and other ASCII art.
Ditch Google Groups and use a real newsreader such as Thunderbird or
Seamonkey.
You can get a free Usenet account from eternal-september.com. Setting
it up is pretty simple--you'll be on the air in half an hour.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
Carlos E.R.
not using Google Groups as you do.
You need to display them in a terminal using fixed width fonts, as I do.
Not a web browser. And download them from an Usenet server that contains
that old thread, not from Google Groups. I don't know any that has that
old content.
For those on Usenet, it is this thread:
https://groups.google.com/g/sci.electronics.design/c/MM5_wQtm0ds
--
Cheers, Carlos.
Carlos E.R.
> On 2023-03-09 07:25, Jeremy Morgan wrote:
>> On Monday, 31 July 2006 at 00:57:28 UTC+1, Winfield Hill wrote:
>> Please can anyone explain to me how to read the ASCII schematics in
>> this post? Thanks
>>
>
> Welcome to Usenet, which has been around since 1979. This group
> (sci.electronics.design) is older than Google. The short answer is,
> "You can't do it on the Google Groups web interface."
>
> Unfortunately Google collapses multiple space characters into one, which
> destroys schematics and other ASCII art.
>
> Ditch Google Groups and use a real newsreader such as Thunderbird or
> Seamonkey.
>
> You can get a free Usenet account from eternal-september.com. Setting
> it up is pretty simple--you'll be on the air in half an hour.
servers probably don't.
Mine doesn't, or my client expired it.
--
Cheers, Carlos.
Phil Hobbs
2003. (I splurged and got 180G for $25, so I should be reading SED till
about 2523 AD. ;)
Supernews also has stuff back to 2003.
The Internet Archive has mbox files of a number of groups going back
about that far, including this one.
At the moment I have some Seamonkey config problem that I haven't
bothered tracking down, that prevents me from _posting_ via Astraweb,
but it works fine via Supernews or ES.
Fred Bloggs
Haven't done it in a while because all the traffic is verbiage, so I can't really say it still works.
John May
Jeremy Morgan
@JohnMay Your suggestion re: View source worked a treat thanks. I was able to paste it into a text editor in Windows. Using a monospaced font (Courier) made everything line up OK and I was able to make sense of the schematics.
John Larkin
fixed.
That circuit is probably the one on page 609 of Win's book, AoE 3rd
Edition Improved. Everyone should have that book, and the X-chapter
supplement (to which Phil and I made modest contributions.)
Given your requirements, we could play with HV regulator ideas here.
Jan Panteltje
<robin_...@es.invalid> wrote in <3d1pdjx...@Telcontar.valinor>:
>On 2023-03-09 13:37, Phil Hobbs wrote:
>> On 2023-03-09 07:25, Jeremy Morgan wrote:
>>> On Monday, 31 July 2006 at 00:57:28 UTC+1, Winfield Hill wrote:
>......................****
>
>>> Please can anyone explain to me how to read the ASCII schematics in
>>> this post? Thanks
>>>
>>
>> (sci.electronics.design) is older than Google. The short answer is,
>>
>> Unfortunately Google collapses multiple space characters into one, which
>> destroys schematics and other ASCII art.
>>
>> Ditch Google Groups and use a real newsreader such as Thunderbird or
>> Seamonkey.
>>
>
>Yes, but the other problem is getting that ancient post. Most Usenet
>servers probably don't.
>
>Mine doesn't, or my client expired it.
but only of articles and postings I found interesting.
I wrote it around year 1998 as Linux replacement for Free Agent,
https://panteltje.nl/panteltje/newsflex/index.html
Version 1.5.5 is from 2002...
Some older code and data got lost, or maybe on that old PC in the attic?
Anyways its still going strong.
Don
> Jeremy Morgan wrote:
Readable version of Win's followup:
<https://crcomp.net/misc/lr8.php>
<snip>
> It would be readable in a fixed-pitch font, with some line wraps
> fixed.
>
> That circuit is probably the one on page 609 of Win's book, AoE 3rd
> Edition Improved. Everyone should have that book, and the X-chapter
> supplement (to which Phil and I made modest contributions.)
>
> Given your requirements, we could play with HV regulator ideas here.
with ideas presented on page 608 - 609.
What! Wait. Win's circuit went to pot as they say. So it's no good,
right John? LOL.
Regardless, this thread illustrates the virtues of hosting your own
usenet archive instead of outsourcing it to the slop served by Big Tech.
Danke,
--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
John Larkin
>John Larkin wrote:
>> Jeremy Morgan wrote:
>
>Readable version of Win's followup:
>
><https://crcomp.net/misc/lr8.php>
>
><snip>
>
>> It would be readable in a fixed-pitch font, with some line wraps
>> fixed.
>>
>> That circuit is probably the one on page 609 of Win's book, AoE 3rd
>> Edition Improved. Everyone should have that book, and the X-chapter
>> supplement (to which Phil and I made modest contributions.)
>>
>> Given your requirements, we could play with HV regulator ideas here.
>
>Close, but no cigar. Although Win apparently cooked up the above circuit
>with ideas presented on page 608 - 609.
> What! Wait. Win's circuit went to pot as they say. So it's no good,
>right John? LOL.
Carlos E.R.
> On Thursday, March 9, 2023 at 12:25:36 PM UTC, Jeremy Morgan wrote:
>> On Monday, 31 July 2006 at 00:57:28 UTC+1, Winfield Hill wrote:
>>> Piglit wrote...
>>>>
>>>> Winfield Hill wrote:
>> Please can anyone explain to me how to read the ASCII schematics in this post? Thanks
>
> If you're prepared to faff-about highlight the ascii schematic lines and (if using firefox) right click and select view source. Copy to vim and replace the <br> with returns (%s/<br>/\r/g).
--
Cheers, Carlos.
Don
ehsjr
> John Larkin wrote:
>> Jeremy Morgan wrote:
>
> Readable version of Win's followup:
>
> <https://crcomp.net/misc/lr8.php>
>
(It deserves more than a plus 1, maybe a
plus 1 times the number of characters in
Win's schematic. :-) )
Ed
Phil Hobbs
That's your unobtainium Allen Bradley carbon unit there.
Anthony William Sloman
> On 2023-03-09 18:43, ehsjr wrote:
> > On 3/9/2023 11:17 AM, Don wrote:
> >> John Larkin wrote:
> >>> Jeremy Morgan wrote:
> Yikes. The poor pot is going to have to dissipate 500 mW and drop 500V.
> That's your unobtainium Allen Bradley carbon unit there.
A cermet part would work fine. The trouble with carbon film is the negative temperature coefficient of resistance. Treat them wrong and you can form a low resistance hot channel in the film. I've seen it done with a 10k carbon film resistor, and - worryingly - the resistor still measured 10k afterwards, though there was a thin dark line in the paint over where the hot channel had been.
--
Bill Sloman, Sydney
ehsjr
> On 2023-03-09 18:43, ehsjr wrote:
>> On 3/9/2023 11:17 AM, Don wrote:
>>> John Larkin wrote:
>>>> Jeremy Morgan wrote:
>>>
>>> Readable version of Win's followup:
>>>
>>> <https://crcomp.net/misc/lr8.php>
>>>
>>
>> +1
>>
>> (It deserves more than a plus 1, maybe a
>> plus 1 times the number of characters in
>> Win's schematic. :-) )
>> Ed
>>
>
> Yikes. The poor pot is going to have to dissipate 500 mW and drop 500V.
> That's your unobtainium Allen Bradley carbon unit there.
>
> Cheers
>
> Phil Hobbs
>
link that contained the schematic, not the circuit.
But I sure didn't make that clear.
Ed
John Larkin
https://www.dropbox.com/s/ak7lvemwbd4sj48/HV_Pos_Reg.jpg?raw=1