Need variable high voltage power supply

[ksquared]

I'm trying to find a design sample for a simple variable high voltage power supply. I need 0 -> 600 volts DC at around 50 to 60 ma max. The supply is easy. The variable part has me searching. I have a design that uses a vacuum tube but I'd rather go with semiconductors. I have access to some rather large IGBTs if that helps. I'm building a capacitor leakage tester.

 

[flat5]

A Variac is a useful shop accessory.
Put it ahead of your step up transformer.

Autotransformer - Wikipedia, the free encyclopedia

 

[ksquared]

Variacs are great tools but I'm thinking of something along the lines of a semiconductor version of a subset of an old Sprague TO-6. Assume I have a rectifier that can supply 600vdc at up to 60ma or so. What I want to do is vary the output voltage from zero (or nearly zero) up to 600 volts with a pot. Regulation is not desired. A Variac seems a bit much for this app.

Although now that you have me thinking about it, perhaps someone makes small ones? A 0.5 amp Variac would be fine and not much bigger than a big pot. Hmm...

 

[Hero999]

The smallest variac I've seen is 0.75A @ 230V

What's the mains voltage where you live?

If it's 230V, just put a diode voltage doubler after the variac to give you 0 to 253√2 = 716VDC (most variacs go up to the input voltage plus 10%).

Do you need isolation?

If so add an isolation transformer.

if you want isolation

 

[crutschow]

If you regulate the 600V at 60mA with a series transistor, the maximum transistor power dissipation would be 36 watts. You would need to mount the transistor on a fairly large heatsink. You would also likely need to add some sort of short circuit protection to avoid zapping the transistor.

A variac (driving a high voltage transformer if needed) would seem to be the simplest approach.