Asked by: Dulcerina Klockenkampertechnology and computing digital audio
Can a MosFet be tested in circuit?
Last Updated: 24th May, 2020
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Similarly one may ask, do MOSFETs fail open or closed?
The short answer is I would expect a MOSFETtofail as an open circuit due toover-temperatureconditions. This wikipedia article suggests that:Increase indrain-to-source resistance. Much of the MOSFETheating athigh currents is in the leads - which can quite easilyunsolderthemselves without the MOSFET failing!
One may also ask, what causes a MosFet to fail? The cause of this failure is a veryhighvoltage, very fast transient spike (which may be positiveornegative going). If such a spike gets onto the drain ofaMOSFET, it gets coupled through the MOSFETsinternalcapacitance to the gate. Once that has happened, theMOSFETexplodes in a cloud of flame and blacksmoke.
Accordingly, how do you test a transistor in a circuit?
Hook the positive lead from the multimeter to the totheEMITTER (E) of the transistor. Hook the negative meterleadto the BASE (B) of the transistor. For an goodNPNtransistor, you should see “OL” (OverLimit).Ifyou are testing PNP transistor, the metershould showa voltage drop between 0.45V and 0.9V.
How can we test transistor using analog multimeter?
Connect the base terminal of the transistor totheterminal marked positive (usually coloured red) onthemultimeter. Connect the terminal marked negative orcommon(usually coloured black) to the collector and measuretheresistance. It should read open circuit (there should beadeflection for a PNP transistor).