Need help with design

[Y2KEDDIE]

Experimenting with "vintage" radio circuits I find myself in need of various high voltage supplies,typically in the range of 250 to 650 VDC.

I have several industrial type transformers designed to boost 120 to 220 VAC and, 220-440 VAC, at several amps. These were used for running light , lighting and small single phase motors from a 3 phase motor control center. Physically they are 6X6X8" in size. I have quite a few.

I've been able to build unregulated supplies by wiring the primaries in series and secondaries in parallel combination. Resulting in 120V input, 220/440/880 output. With rectification and filtering I can get (1.414X) : 311 ,622, and 1244 VDC unregulated at several amperes.

What I would like to build is a series pass element regulator circuit to yield: 100V, 250-275, 350-375.400-775, etc, variable output at 0.5 to 1 ampere.

I found a circuit using a Supertex LR8 High Input Voltage Adjustable # terminal Linear Regulator and a TK9J90E MOSFET as a pass element. I'm not sure if these parts are still obtainable (obsolete), but I need something , if not similar.

With 311,622,1244 VDC fixed, a lot of voltage drop would be needed to occur requiring a lot of heat sinking. Never the less my quest, if practical, is to find a circuit to accomplish this.

Has anyone else tried this? Are there more practical components /circuit designs available?

Thanks,
Eddie

 

[Harald Kapp]

I've been able to build unregulated supplies by wiring the primaries in series and secondaries in parallel combination

Sure? Not primaries in parallel and secondaries in series?

 

[duke37]

At 1A you will be dissipating a lot of heat even with a small voltage drop.
Consider using an appropriate transformer tap to minimise the drop.
Chose a lowish voltage supply and then use a switch mode boost circuit to get the higher voltages.

 

[Harald Kapp]

You can use a variable autotransformer on the primary side to adjust the primary voltage and thus the secondary voltage. This method incurs rather small losses.

 

[Y2KEDDIE]

Sure? Not primaries in parallel and secondaries in series?

My bad, I meant primaries in parallel, secondary in series.

Yes, I could buy a tapped transformer with the exact voltages, but I want to use what I have.

Yes, I’ve used Auto transformers (power-stat) in a single voltage supplies. My goal is to build a multi voltage supplies. One particular supply example: I need 110v@100 mA regulated, 275v@150mA regulated, and 800v@500 mA un regulated. I would like to use two 120: 440 transformers, which I have in my stock.

Switch mode would work, but again: I wish to use the transformers I have in stock, and keep it linear.

With the secondaries in series I can get the 800V-1200v. I can use one secondary as a tap for the 110 and 275v, but I need to drop the voltage/regulate.

A simpler way to approach this: how can I get 110 v and 275 v regulated from a 622vdc supply?

The goal is a circuit similar to a low voltage supply where they use a single transformer /rectifier supply with multiple solid state regulators to achieve multiple voltages.