IGBT, MOSFET, BJT. No solution to this problem!

Thread Starter

Matter45

Joined Dec 13, 2012
32
Hi internet

got a slight problem. To keep things simple, I have 3 parts. Resistor, capacitor and a transistor arranged like this:

upload_2017-11-1_18-43-7.png

Very simply, all it does is once the capacitor is full, the transistors emitter collector or drain/source resistance becomes zero.

for safety reasons, the transistor needs to have a break down voltage of 400v+. It also needs to be able to handle 10 amps @ 100 degrees Celsius.

List of problems:
  • cant use N channel mosfet, unable to get the gates voltage above 250v to keep it on.
  • seaching for P channel mosfets proves to be difficult.
  • Cant use IGBT, same problem as the N channel mosfet, unless there is a P channel version
  • Using NPN/PNP means power loss of 5w or more. Furthermore, its hard to find a high voltage, high amp PNP/NPN with high gain 100 or more
I would love to find an affordable P channel mosfet, Vds 400v and 10 amps @ 100 degrees Celsius.

Unless there is anything else out there that I have not educated myself into? Thyristor?
 
Last edited:

Thread Starter

Matter45

Joined Dec 13, 2012
32
Cheers dendad. This seems to be the way to go.

1W Isolated? Seems spending $5 on the 1w power supply plus the N channel mosfet is an expensive solution?

I wonder if there are cheaper solutions?

And yes you are correct, speed is not an issue.
 

dendad

Joined Feb 20, 2016
4,452
You could just use a relay.
I think $5 is pretty cheap really.
Some old Ethernet cards have isolated power supplies on them and those old cards are just junk now.
 

dl324

Joined Mar 30, 2015
16,846
got a slight problem. To keep things simple, I have 3 parts. Resistor, capacitor and a transistor arranged like this:
Didn't see the problem mentioned.

You don't give a part number for the JFET and we don't know how it's gate is being driven.
 

Thread Starter

Matter45

Joined Dec 13, 2012
32
Rather than tell us the problem with your proposed solution, tell us what you are trying to achieve and why -- and maybe there is a better approach.

It looks like you may be trying eliminate inrush current on the cap. If so, is an inrush current limiter perhaps a better solution?
BOOYA! Thank you joeyd999

I will look into inrush current limiters.

Thanks internet!
 
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