Practical Mosfet testing

[Nounours18200]

Hi Friends,

I refer to the Papa article "Practical Mosfet Testing for Audio" where he presents this diagram for testing theses devices:

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I would just like to know:
-what is the recommended wattage for the resistors ?
-same for the V+ voltage (approx) ?

What kind of regulated power supply do you use ?..

Thanks,

 

[AndrewT]

Calculate the dissipation for each resistor.
Then use a resistor rating that is at least double the required dissipation. If possible use 10times the dissipation for minimal resistance change.

 

[Nounours18200]

Thanks Andrew, but if I were able to calculate this, I would not have asked the question ...😀
(I just begin building power amps, my experience/expertise relates only to other kind of devices (DAC, etc), so I am an idiot here ...)

 

[AndrewT]

Power dissipation = Volts times Amperes = Amperes squared * Resistance = Volts squared divided by Resistance.

P = V*I = I*I*R = V*V/R

 

[Andy5112405]

Assume that the MOS-FET has failed and that it is a short circuit.

The variable voltage supply can be almost anything +24V is a good place to start.

R3, R4. R5, R6. R7. R8 are then directly connected across the 24V PSU.

From that you can use Andrew T's calculations to work out current and power ratings.

WORST CASE R3 or R6 are in circuit with the other side SHORT CIRCUIT.

V**2 / R = 24 x 24 / 10R = 57W.

I've got 10R 100W resistors for sale on E-Bay at 99p each at the moment.

 

[h_a]

Are you sure you need the full circuit? I mean it provides a lot of functionality and for example its possibility to test for transconductance might not be applicable to you as you would need a signal generator and an oscilloscope.

Hannes

 

[Nounours18200]

Thanks Andy, for the reply !

Are you sure you need the full circuit? I mean it provides a lot of functionality and for example its possibility to test for transconductance might not be applicable to you as you would need a signal generator and an oscilloscope.

I have a signal generator and an oscilloscope , (you can laugh: i have received them last week and they are still in their box 😛😛) but i am not sure I will conduct all these tests in the near future, as I just start my F5 assembly...

 

[digits]

Lol, I also got me a new scope and sig gen, so far all I have done is found the signals 🙂> Thank god for autoset.

 

[h_a]

That's nice to hear! Having some equipment really helps in tuning amps!

Enjoy! Hannes