Practical Mosfet testing - diyAudio
 Practical Mosfet testing
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 26th June 2011, 09:37 AM #1 diyAudio Member   Join Date: Jan 2004 Location: GRASSE (France) Practical Mosfet testing Hi Friends, I refer to the Papa article "Practical Mosfet Testing for Audio" where he presents this diagram for testing theses devices: Uploaded with ImageShack.us 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,
 26th June 2011, 10:59 AM #2 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders 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. __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 26th June 2011, 12:47 PM #3 diyAudio Member   Join Date: Jan 2004 Location: GRASSE (France) 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 ...)
 26th June 2011, 04:04 PM #4 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders Power dissipation = Volts times Amperes = Amperes squared * Resistance = Volts squared divided by Resistance. P = V*I = I*I*R = V*V/R __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 26th June 2011, 04:34 PM #5 Banned   Join Date: Nov 2006 Location: Torpoint 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. Last edited by Andy5112405; 26th June 2011 at 04:39 PM.
 27th June 2011, 05:45 PM #6 diyAudio Member     Join Date: Sep 2006 Location: Graz, Austria 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 __________________ High Octane phono preamp Wiki
diyAudio Member

Join Date: Jan 2004
Location: GRASSE (France)
Thanks Andy, for the reply !

Quote:
 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...

 10th July 2011, 04:29 AM #8 diyAudio Member     Join Date: Apr 2011 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.
 10th July 2011, 08:25 AM #9 diyAudio Member     Join Date: Sep 2006 Location: Graz, Austria That's nice to hear! Having some equipment really helps in tuning amps! Enjoy! Hannes __________________ High Octane phono preamp Wiki

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