How to test MOSFET with a multimeter? - Page 1
Forum section: electronics / beginners

author: Jane
author_rank: Frequent Contributor
timestamp: September 26, 2024, 08:57:32 am
content: I tried to use this method:Testing an N-channel MOSFET:Step 1: Discharge the Gate (turn off the MOSFET)Place the black probe (COM) on the Source (S) and the red probe on the Drain (D). The multimeter should show no continuity (high resistance or "OL" – open line).Then, touch the black probe to the Source (S) and the red probe to the Gate (G). This discharges any stored charge in the Gate, turning the MOSFET off.Step 2: Charge the Gate (turn on the MOSFET)Now, place the red probe on the Gate (G) and the black probe on the Source (S). This charges the Gate and turns the MOSFET on.Step 3: Check for Drain-Source ContinuityAfter charging the Gate, place the black probe on the Source (S) and the red probe on the Drain (D). If the MOSFET is functional, the multimeter should now show low resistance or some continuity.Step 4: Discharge the Gate AgainTo turn the MOSFET off again, place the black probe on the Gate (G) and the red probe on the Source (S). Afterward, place the black probe on the Source (S) and the red probe on the Drain (D) – the multimeter should now show no continuity (high resistance).Is this method correct?I can not measure low resistance, after openning the MOSFET - see step 3. Does it mean my multimeter does not provide enough voltage to open the MOSFET?I tried with 4468 MOSFEThttps://alltransistors.com/adv/pdfview.php?doc=ao4468.pdf&dire=_aosemiThank you for advice.

author: PGPG
author_rank: Frequent Contributor
timestamp: September 26, 2024, 09:46:31 am
content: You didn't said anything how is voltage used by your multimeter to measure resistance (I assume you set it to measure resistance) related to voltage needed to switch this exact MOSFET on.To simple test MOSFET I would connect it (with resistor in D) to 10V and then will connect G to 0 and 10V.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 26, 2024, 09:51:32 am
content: Watch this video by our memberw2aewand it should all be clear to you, of how to test the MOSFET

author: Jane
author_rank: Frequent Contributor
timestamp: September 26, 2024, 09:55:43 am
content: I used Diode mode on my multimeter but as I wroteQuote

author: MrAl
author_rank: Super Contributor
timestamp: September 26, 2024, 11:48:19 am
content: Hello,For MOSFETs that will be switched you just have to supply a voltage and a load, and a gate voltage to turn it on.The gate voltage varies though per device. Some only need 5v while others need 10v or higher.In some cases you may want to check the Drain to Source resistance. Then you would have to use a heavy load and high current drain to source and then check the voltage drop across the drain and source.These would be the basic tests. You could do more advanced tests if you need to.

author: Jane
author_rank: Frequent Contributor
timestamp: September 26, 2024, 12:47:38 pm
content: At present I need to check if mosfet is good or faulty in a laptop. What method is good enough for that?

author: PGPG
author_rank: Frequent Contributor
timestamp: September 26, 2024, 01:02:01 pm
content: Quote from: Jane on September 26, 2024, 12:47:38 pmTill now we had mosfet not connected with anything.Now it looks that it is in circuit. True?If true then why you assume charge at gate stays there.

author: Jane
author_rank: Frequent Contributor
timestamp: September 26, 2024, 01:35:23 pm
content: I tried to test a mosfet both in a circuit and desoldered. The same result

author: PGPG
author_rank: Frequent Contributor
timestamp: September 26, 2024, 04:55:35 pm
content: Quote from: Jane on September 26, 2024, 01:35:23 pmOne mosfet that you are not sure if not broken or you tested the test method on mosfet you know is correct?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 26, 2024, 05:20:00 pm
content: Normally a DMM does not output enough voltage to charge a MOSfet to the point the gate opens.A simple (and probably good enough) check is:1. With one probe short Gate and Source.2. Measure whether the body diode is present (i.e. conducts in one direction, is open in other direction).3. Measure resistance between gate and source. (Should be open).I think that already takes care of most failure modes.

author: Jane
author_rank: Frequent Contributor
timestamp: September 26, 2024, 07:53:52 pm
content: @PGPG: Yes, mosfet should be good@Doctorandus_P:QuoteCan you please explain 2? The diode between Drain and source? Do you mean in diode mode to check ?

author: Jane
author_rank: Frequent Contributor
timestamp: September 27, 2024, 02:55:14 pm
content: Can anyone here explain a way of testing of MOSFET he uses during repairs?