I have a regulated 500 VDC power supply (actually shows 545 V on voltmeter) that we wish to use to test a DC-to-AC inverter (designed for feeding dc from solar panels into the power grid). We need a minimum of 150 mA to get the inverter to activate. Without a current limiter, our power supply just pushes as much current as it can until the 1.5A fuse (on the ac side) blows. I would like to add an external circuit to limit the current to 200 mA. Most of what I have found searching around is for much lower voltage supplies. Could anyone point me to resource or suggest a circuit?

 

Not a surprise there; to get 150mA stepped down from 545V would require about 82W power dissipation from a linear solution.

Sounds like you need a high voltage switching supply solution. Don't happen to have one in my back pocket at the moment.

International Rectifier has a number of application notes on their website for HV switcher applications.

National Semiconductor might have some resources for you.

 

II would like to add an external circuit to limit the current to 200 mA.

The following is a quick and dirty setup to do just that. You first need to find a N-Ch MOSFET which is rated 800V or higher and has a power PW of over 100W. The current requirement is 1A or more.

Two additional component are needed and they are a 9V battery(can be permanently connected between source & gate as there is no current drain) and a current sensing resistor.

The MOSFET must be mounted properly on a heatsink as the worst case heat dissipation can be as high as 90W should the output load is shorted.

Here is a simulation of the setup. Current is the same for load of 1Ω to 1000Ω.