# High voltage adjustable bipolar power supply

#### coinmaster

Joined Dec 24, 2015
502
Hello, I am trying to build a high voltage adjustable bipolar power supply with adjustable voltage and current up to 300v and 3A

I want it to be filtered and regulated with adjustable current. It's going to have to be an LC filter due to the high wattage requirement.
Unfortunately I can't think of any way to adjust the current without a potentiometer of an insane power rating.

Any ideas?

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#### crutschow

Joined Mar 14, 2008
26,035
You can use a series MOSFET to control the current, but you still have to dissipate the power. What's the maximum current and at what output voltage?
The only way to regulate current without significant power dissipation is to use some sort of rapid switching (SMPS) control.

#### coinmaster

Joined Dec 24, 2015
502
Maximum current is 3A at 300v.
Switch mode isn't an option.
Can you explain to me how exactly I would adjust the current with mosfets? My experience with solid state circuitry is limited and I can't think of a way to do it without using a high watt potentiometer.

#### coinmaster

Joined Dec 24, 2015
502
Actually make that 1.6 amps at 300v maximum.

#### coinmaster

Joined Dec 24, 2015
502
Wouldn't the resistors in that diagram need to be super high wattage?

#### Dodgydave

Joined Jun 22, 2012
9,862
Yes, if you want to limit current to 1.6amps, the resistor R2 will need to be 0.4ohms at 1.5W approx.

#### coinmaster

Joined Dec 24, 2015
502
I was thinking more like 480watts. 300v*1.6a=480w unless I'm missing something?
Also what about VR1? As an adjustable current shunt to ground I'd imagine it too would need quite a bit of power handling.

#### Dodgydave

Joined Jun 22, 2012
9,862
The voltage developed across R2 is 0.7V needed to turn on Q2, this will happen at approx 1.6amps.

#### crutschow

Joined Mar 14, 2008
26,035
In Dd's circuit, the resistors are just for setting bias voltage and current-limit levels.
The primary power dissipation occurs in transistor Q1. It must be capable of handling up to 480W.
That may require using several transistors in parallel on large heat sinks.

VR1 is for adjusting the output voltage level, but you don't need that if you are adjusting the voltage with the Variac shown in your schematic.

Do you need the current limit to be adjustable?