How to test mosfets in parallel circuitry

[Schorsch87]

Hey guys,

I have the question mentioned in the title. Is it possible to get the bad mosfet within a parallel circuit?

I think i read something about a current limited supply and look which of the transistors is getting hot?

Would this work without destroying another parts on the board?

Best reagards

[budm]

Re: How to test mosfets in parallel circuitry

Test it off the board if the reading looks bad when test it on board.

[Schorsch87]

Re: How to test mosfets in parallel circuitry

One of the right 4 couples on the picture is bad. I measure a short. So it would be best to solder them off. Maybe it's not the last one which is bad

[budm]

Re: How to test mosfets in parallel circuitry

It is not easy narrowing down the bad parts when they are connected in parallel. You can use low voltage high current source to find out which one will get hot.

[CapLeaker]

Re: How to test mosfets in parallel circuitry

or an ultra sensitive ohm meter.

[Schorsch87]

Re: How to test mosfets in parallel circuitry

You can use low voltage high current source to find out which one will get hot.

This is what I wanted to hear. Maybe I will try this.

Thanks you.

[budm]

Re: How to test mosfets in parallel circuitry

Since the MOSFET has body Diode you will want to make sure that you connect the power supply in the reverse polarity of the body diode in case the shorted MOSFET blown open circuit when the power supply is connected to it.

[rievax_60]

Re: How to test mosfets in parallel circuitry

The Gates usually have individual series resistors. Comparing G-D and G-S resistance usually finds the faulty MOSFETs.

[sententia]

Re: How to test mosfets in parallel circuitry

You can also use the millivolt range of you DMM (or diode testing), most of DMMs have, and measure the smallest voltage drop to ground while supplying a safe voltage (for that rail) from a current limited supply, 0.25A should be ok.

However this is to find the shorted one and not to check if a fet is good....

[ReeceyBurger123]

Re: How to test mosfets in parallel circuitry

I sometimes use my esr meter to find which device had lowest resistance across lol

[TechGeek]

Re: How to test mosfets in parallel circuitry

It is not easy narrowing down the bad parts when they are connected in parallel. You can use low voltage high current source to find out which one will get hot.

As in 5VDC@100A?

[budm]

Re: How to test mosfets in parallel circuitry

1~2V 5A, just enough to heat up the shorted parts, we do not want to explode the parts and causes more damages to other part when it goes open circuit.

[ReeceyBurger123]

Re: How to test mosfets in parallel circuitry

As in 5VDC@100A?

Lol thats 500w across a shorted device, think it might smoke a little would probably melt the bloody probes used to test

[TechGeek]

Re: How to test mosfets in parallel circuitry

lol

[goontron]

Re: How to test mosfets in parallel circuitry

Lol thats 500w across a shorted device, think it might smoke a little would probably melt the bloody probes used to test

dont knock it till you try it! i dumped 1800w (12v @ 150A) through a 24v circuit to find a short. Shorted ceramic disk cap was glowing orange!