Buck Converter

It really depends on what current you need at the output and what efficiency you require.

It may turn out that a simple resistor dropping the voltage may be all that's needed, maybe a neon to stabilise the output at approx 90 volts??

More information is needed please.

John.

Hi. Thank you for your kind answers. The efficiency should be at least 85% and the output current is up to 8A. Which circuit topology is recommendable and which components should be in the control circuit.

Answering your question...

YES

there are ICs that do this whole task with a few external components in what they call PWM mode.

In effect the load is connected to the 325 volts DC and switched on and off on a variable duty cycle as soon as the outut rises above the desired voltage. swicy rate caan be 50,000 to 100,000 hertz.

LC filters remove the pulses from the line and the parts are sized to the estimated demand.

poke around here

http://www.google.com/search?hl=en&q=pwm+%2B%22buck+regulator%22&btnG=Google+Search

i searched in google but couldnt find anything suited for 325V Input and 8A output.

What you need is not a Buck converter, but an SMPS. At the given voltage 8A current means a lot of heat, You can assemble an SMPS or even can buy one, they are cheap and relaible too.

I agree with you Holmes, if its for high current, 8 amps, almost all SMPS accept dc inputs and 325 volts is perfectly acceptable for a 230 volt input SMPS, so it would be cheaper and more reliable to buy one off the shelf for your purpose.

John.

could you give me a link for a cheap smps.

Nahhh its too expensive, i would like to build a cheap Buck converter circuit with one or 2 IGBTs. The Load will not change and will be always the same. I dont want to use a transformer or some expensive, just a relative simple circuit. If the efficiency is over 90%, i dont think it gets too warm.

Have a look at www.powerint.com.

They have a range of single chip converters for switching voltages of up to 700V DC.

Its only for rough information for you as the power range goes only up to 290W. But based on these single chip solutions you can add a power stage extending the internal switchers capability to those currents you want.

good luck
uwe

Hi I looked at the Website but couldnt find the chip you mentioned with 290W power. Could you give me the part number or link.

Thank you

Hoki

It`s their TOP250Y or F which are said to be able to.
Regards Uwe