Matching MOSFET's for Aleph 2

[Thago]

I bought a series of IRFP240 and IRF9610 that I want to match for my Aleph 2 project.
I want to follow the how-to document from Mr. Pass himself: http://www.passdiy.com/howto/matching.htm

My question: I have a lab power supply that can be adjusted to a given voltage and current, for example 15V and 5 mA (IRF9610) and 15V and 20mA (IRFP240). Do I need the setup with a 2.2kohm resp. 560kohm resistor, as described in the how-to document? Or could I connect the power supply directly to the mosfet's, and measure the voltage between the gate and the source?

[jackinnj]

Originally posted by Thago
I bought a series of IRFP240 and IRF9610 that I want to match for my Aleph 2 project.
I want to follow the how-to document from Mr. Pass himself: http://www.passdiy.com/howto/matching.htm

My question: I have a lab power supply that can be adjusted to a given voltage and current, for example 15V and 5 mA (IRF9610) and 15V and 20mA (IRFP240). Do I need the setup with a 2.2kohm resp. 560kohm resistor, as described in the how-to document? Or could I connect the power supply directly to the mosfet's, and measure the voltage between the gate and the source?

If you trust your power supply, and it will really will dial down the current to these levels you can go for it.

If you don't trust your power supply you can make a simple current limiter with an LM317 -- connect a resistor from output to adjust whose value is:

R = 1.25 / I

When matching it's important (well, at least I think it's important to keep the time and temperature constant.

[RoboMan]

Originally posted by Thago
Do I need the setup with a 2.2kohm resp. 560kohm resistor, as described in the how-to document? Or could I connect the power supply directly to the mosfet's, and measure the voltage between the gate and the source?

You must include a resistor as indicated in the document and you should set the current of your power supply to a level much higher than the required current to make sure the current limiting circuit does not affect your measurement. No current limiting is required from your power supply. Current is limited by the resistor.

The purpose is to measure the voltage of the MOSFET, not the voltage of your supply.

[jackinnj]

quod erat demonstratum:

[Thago]

Thx for replying!

Why is I(rms)=0 in the second case (current source)?