design 1A current limiter for my 300V dc supply

[KUMARA SHP]

I am really in trouble in design 1A current limiter @ 300v dc output
I tried with some circuits
please check this circuit & tell me what should I change
in this max output is 100mA

 

[KUMARA SHP]

 

[(*steve*)]

At 1A that poor mosfet will be asked to dissipate 300W if you short the output. Without a massive heatsink, and possibly several paralleled mosfets, it's not going to happen.

Rather than parallel the mosfets you would probably parallel the entire current limit circuit, each one set up for maybe 1/4 of the current.

Also, while the idea is right, the exact implementation is not. The load is normally in series with the drain of the mosfet

The general rule is that the current limit is 0.7 / R. In your circuit R = 3R3, so the current limit is about 200mA

 

[Arouse1973]

I think the FETS ok the way it is, being a N type the input will be max 12V higher than the source clamped by the zener. You need to change the value of R2. Reduce the value to 0.5R and try that.
Adam

 

[KrisBlueNZ]

Also, the voltage regulation will be pretty poor - the voltage adjustment potentiometer is supplied from the unregulated voltage rail!

Edit: The MOSFET is connected as a source follower (common drain) so it will work, but the power dissipation is definitely an issue!

 

[KUMARA SHP]

I do not want to varie the voltage,so i removed pottentiometer,I reduced R2=0.6 & use 3 parallel mosfets, i hope it will work

 

[KrisBlueNZ]

You'd better have some pretty big heatsinks!