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-   -   Adjustable High Voltage Power Supply (http://www.diyaudio.com/forums/equipment-tools/201329-adjustable-high-voltage-power-supply.html)

alfa88 27th November 2011 11:15 PM

Adjustable High Voltage Power Supply
 
Last month I fixed a guy's antique radio and was thoroughly intrigued by tube technology. In my stupidity, years ago, I traded a Heathkit HV power supply for a hard drive. I suppose because I didn't have the 'tube bug' back then.
I have a power transformer I pulled out of some old military equipment that has a 820Vct@100ma secondary, several 6.3 windings and a 5V winding. I'm hoping someone has some easy to build schematics where maybe I can turn that high voltage into a variable B+ and C power supply. I've seen several mosfet designs but they all seem to be fixed Voltage.

thaumaturge 28th November 2011 12:41 AM

Take a look at some commercial HV supply schematics. Should find some on the BAMA (boat anchor manual archive) site. HV supplies are rather tricky.
Doc

gootee 28th November 2011 01:58 AM

It seems like one of the high-output-voltage "booster" amplifiers could be used as a DC power supply, if it were DC coupled.

For example, there is a schematic for one in Figure 13 of AN18 at Linear Technology's site ( http://cds.linear.com/docs/Application%20Note/an18f.pdf ) that is a 1000V 15-Watt unipolar output stage that is powered by only a fixed +28V DC supply.

Control inputs of 0-10 Volts give outputs of 0-1000 Volts.

It would also work as a low-frequency AC supply or signal/function generator.

It seems to be artificailly limited to a slew rate of about 500 Volts per millisecond or a little more but that could be increased, at least a little bit.

There is a somewhat-similar schematic in Figure 10 of AN-272 from national.com ( http://www.national.com/an/AN/AN-272.pdf#page=1 ), that provides up to 1000V @ 300 mA output (300 Watts) and runs off of a +/-15V dual-polarity supply.

Cheers,

Tom Gootee

gootee 28th November 2011 02:34 AM

Bandwidth of that one from national.com in Figure 10 of AN-272 is similar to the one from linear.com, at 50 Hz. But if you need 500 kHz bandwidth, just look at the next one, in Figure 12, which goes to 350 V in one microsecond with the tubes shown but could be extended to several kilovolts by using different tubes and a higher-voltage fixed DC supply. However, as shown, it can only supply about 10 mA at 350 V.

Cheers,

Tom Gootee

thaumaturge 28th November 2011 09:43 PM

One trick I've seen used quite often on high voltage supplies is to feed the primary of the transformer with a variac for rough voltage out control. This reduces the differential voltage across the pass transistor. A pot mounted on the shaft of the variac sets drive voltage for course setting of base drive.
Doc

benc 4th January 2012 01:11 AM

I've used a LOPT (line output transformer) from a TV before to generate HT. You can pick these up new and cheap or raid some old TV's main board - basically they are flyback transformers.

Typically you will need to put an HT capacitor on the output as they tend to rely on the CRT's capacitance (which you won't have).

When i've done it in the past i've used a 555 timer to generate 15KHz low-duty cycle square wave (5-10%) to switch a fairly plain common-emitter power transistor, that sinks the primary to 0V. I' haven't bothered to regulate it and have varied the DC supply on one side of the primary to change the output V.

wrenchone 4th January 2012 01:57 AM

Why not just buy an electrophoresis power supply for the HV? The other voltages can be handled by standard bench supplies.

dangus 8th January 2012 11:33 AM

This might be a place to use an SCR or TRIAC. I designed a high-power constant current supply once, long enough ago that now I can't remember which side of the transformer the TRIAC was on. The controller used PID (mostly I). Output didn't need to be very clean since it was driving an electrolytic cell, but I stuck a huge computer-grade surplus cap in there. With a high-voltage supply you can use inductors to smooth things out. Possibly a "capacitance multiplier" active filter.

Elektor (if I remember correctly) published a pre-regulator for high voltage supplies sometime in the '80s that used phase control, so as to limit the drop across a linear regulator. I may have a photocopy of that article still. I tried using it in a project once, but it didn't work right away so I put in a variac on the primary and a fullwave rectifier and filter caps on the secondary. As it turned out, that's all the customer actually wanted.

Perhaps an ATX power supply transformer (or two) driven backwards. For high power, use the power supply portion of a car amp.


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