• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

High Voltage Regulator Design

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#3
One thing I was thinking of is youk now how you can hook a normal lm317 and have it switch transistor in series to run at higher voltages. Well I was also wouldering if it can switch igbt because I have igbt rateed at 1600vdc at 10 amps that would do for any regulator anyone would need here.

Nick
 
#8
For that service, I would just use the lm317 as is, nothing else required. 50mA at 200V won't come close to overwhelming it for heatsinking. Sure, just one accidental short and the 317 is toast, but who cares, they are cheaper than all the do-hickeys on a Maida regulator. I have a simple 317 regulator in my 160V B+ 6922 preamp and it is still going strong for a year or two now.

EDIT: Forgot to mention, if your design assumption is 15% mains variation, which is way-overdesigning for the homes I have lived in, that's only 30V for a 200V B+, less than the 40Vdiff rating of an LM317 or the 60Vdiff rating of an LM317HV. It'll work fine unless you are trying to burn a lot of voltage.
 
#10
You may use simple source follower like one discussed recently,
or this one for better regulation and slow start:

bc348bplus.jpg
 
#11
I'm using this regulator (from earlier in this thread) :

http://www.tech-diy.com/POWER/HV_Supertex/local_hvregulator.gif

to regulate ~430v plate supply voltage down to 200v at a few mA for the screen, and it works fine.

I wanted to try regulating the plate voltage as well, so I could adjust it. Using the same regulator circuit, but bringing 430v down to 390-400v at <100mA. Same circuit, etc, but this one keeps burning out the BU208 pass transistor. The regulator chip is unharmed. I have a diode across the emitter and collector as shown, and the diode isn't burning out. Any idea what might be going on? There's a 47uF capacitor across it later on, am I drawing too much current charging this capacitor? Seems unlikely since the the transistor is rated for several amps, and doesn't even have a chance to get warm.


A secondary question - For safety and convenience, I'd like to use a relay to positively switch the plate and screen voltages. Maybe even use a time delay to turn them on after the filaments warm up. Can anyone point me to a source of a reasonable sized relay with contacts rated for >450v _DC_ ? I can't find any at the usual sources because nobody seems to list them by contact voltage ratings.
 
#13
nhuwar said:
One thing I was thinking of is youk now how you can hook a normal lm317 and have it switch transistor in series to run at higher voltages.
Nick
Click to expand...

Just float the adjustment terminal above ground with a zener of the appropriate voltage, so that your desired output voltage is within the LM317's adjustment range.

That's the easiest way to turn an LM317 into a high voltage device. Devices like TL783 ^^^^ make it easier because of their wide voltage spread.

To get more current, wrap a pass transistor around the three terminal regulator.
 
#15
qq said:

A secondary question - For safety and convenience, I'd like to use a relay to positively switch the plate and screen voltages. Maybe even use a time delay to turn them on after the filaments warm up. Can anyone point me to a source of a reasonable sized relay with contacts rated for >450v _DC_ ? I can't find any at the usual sources because nobody seems to list them by contact voltage ratings.
Click to expand...

First, I recommend bypassing the adjust pin of the LR8N3 regulator.

Second, switching 450 VDC is a daunting task (well, not daunting, but it isn't trivial either) -- remember that as the relay contacts come into proximity they behave like a capacitor, when they get minutely close a spark will bridge the gap -- less a problem in switching A.C. If you are going to switch D.C. use a relay snubber like a Mallory Quencharc.

Elsewhere I have shown how to use a pair of HV MOSFET to do the trick.
 
#16
First, I recommend bypassing the adjust pin of the LR8N3 regulator.
Click to expand...

I'm not sure what you mean. Bypassing it to where/with what?

Second, switching 450 VDC is a daunting task (well, not daunting, but it isn't trivial either) -- remember that as the relay contacts come into proximity they behave like a capacitor, when they get minutely close a spark will bridge the gap -- less a problem in switching A.C.
Click to expand...

Yeah, that's the problem. I just wanted to have a standby switch that would kill plate and screen but leave the heaters on, but they're all from the same transformer so I can't just switch the primary. But DC arcs persist in switches/relays, of course.

If you are going to switch D.C. use a relay snubber like a Mallory Quencharc.



Elsewhere I have shown how to use a pair of HV MOSFET to do the trick.
Click to expand...

If such a pair of mosfets were to fail, they would fail in a conducting state, no?
 
#17
Bypass the adjust pin with 10uF rated at the output voltage +33%

I can't recall a ham radio tube linear amp in which the plate voltage is controlled by a relay unless it is done so on the primary side. While we are talking a couple kiloVolts at 500 mA, the same safety principle should apply for audio gear.

You can use synchronous rectification of the power diodes -- a little tricky but the method has been described in Audio Amateur and is available on the International Rectifier website.
 
#19
qq said:


what would cause a pass transistor used this way to burn out?
i can't figure out what i'm doing wrong.
Click to expand...

That's a pretty broad question; you could have used a bad part, used an NPN device instead of a PNP (depending on supply polarity), exceeded specs for your device, wired it wrong .....
 
#20
qq said:


what would cause a pass transistor used this way to burn out?
i can't figure out what i'm doing wrong.
Click to expand...


I guess I can't understand why you would have D1 in that circuit you linked to unless it's required for that regulator, which is a type I am unfamiliar with. That's not your problem, but it seems unnecessary.

A 100pf capacitor can't possibly hold enough charge to worry about protecting the regulator from it, unless this is an unusually sensitive regulator chip.

Don't you normally want a bit of resistance, say 5 to 10 ohms, between the input to the pass device and the input to the regulator, or, in other words, the pass device sees the full B+, but the regulator sees the B+ after it goes through the small resistance?

Again, this is a regulator chip that I am not familiar with.
 
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