# Could this MOSFET Tester actually work ?

Thread Starter

#### Lumenosity

Joined Mar 1, 2017
634
I assume the LED is supposed to light up if the Mosfet is good?

#### LowQCab

Joined Nov 6, 2012
1,183
MOSFETS can be damaged, and yet still "test" good.

I wouldn't bother with making this Board,
it only "demonstrates" the operation of a FET,
it does not provide any parameter or performance information.
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Thread Starter

#### Lumenosity

Joined Mar 1, 2017
634
Would it be possible or feasible to design a relatively simple circuit that could test most N-Channel Mosfets more effectively?

#### KeithWalker

Joined Jul 10, 2017
1,933
Would it be possible or feasible to design a relatively simple circuit that could test most N-Channel Mosfets more effectively?
Yes. Why not.
The most simple practical one would have a variable supply for the gate to source voltage and a fixed suppl;y with a series resistor connected across the source and drain. Inexpensive panel digital volt meters could indicate gate to source voltage and drain to source voltage.

#### LowQCab

Joined Nov 6, 2012
1,183
Then there's testing Current,
which will require that the FET be properly mounted to a substantial Heat-Sink.

The best plan is to learn, and practice, safe handling habits, and storage habits,
then always start with a known, high-quality-supplier of Name-Brand-Parts,
Study the Spec-Sheet carefully,
and define all the terms You don't understand,
don't "re-use" scavenged-parts in a critical, or highly-stressed application.

If You do all this stuff, there's basically no need to "test" Transistors in the first place.
Start with a new reputable Part, and believe the Spec-Sheet,
install it, and it will work as expected.
( this assumes that the Circuit has been properly calculated, and simulated, first )
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#### dl324

Joined Mar 30, 2015
13,268
Would it be possible or feasible to design a relatively simple circuit that could test most N-Channel Mosfets more effectively?
If you make it useful in a general way, you'll end up with a curve tracer.

Thread Starter

#### Lumenosity

Joined Mar 1, 2017
634
If you make it useful in a general way, you'll end up with a curve tracer.
I had to look that up.
Interesting. That looks like a piece of equipment I'd see in Mr. Carlsons Lab

That said....I found this......
https://www.ebay.com/itm/154515935339?hash=item23f9de106b:g:0kkAAOSwD15g305v

Description:
This circuit will perform similar to a Huntron Tracker. (The Tracker manual can be helpful understanding the Lissajous Patterns.) The circuit also has a voltage output so you can measure Zener diode voltages. The circuit also has a High and Low sensitivity. and an external pot can be added as a gain control. The circuit is very sensitive and built with High quality parts.
PCB Size =50mm x 70mm / 1.9" x 2.7"

This is a great tool that can even be added to an old Oscilloscope to have a stand alone Curve tracer. DIY Kit.

#### dl324

Joined Mar 30, 2015
13,268
Interesting. That looks like a piece of equipment I'd see in Mr. Carlsons Lab
If you bide your time, you can find curve tracers on eBay from well known manufacturers for a reasonable price. I bought one last November for < $50: Most sellers are expecting$200-700.

#### Ian0

Joined Aug 7, 2020
3,459
You can test a MOSFET with a multimeter to see if it is likely to work.
Measure continuity between gate and source with the BLACK lead on gate for an N-channel device, (RED lead on gate for a P-channel device). If there is any continuity throw it in the bin.
This leaves the gate charged negative - then test between source and drain with on the diode tester - you should find a diode with a forward voltage drop of around 0.55V with its cathode connected to the drain. If you have continuity in both directions it is faulty. If you have no continuity in either direction it is faulty.

Now measure continuity between gate and source with the RED lead on the gate for an N-channel device, (BLACK lead on gate for a P-channel device). If there is any continuity throw it in the bin.
This leaves the gate charged positive - then test between source and drain - there should be continuity in both directions.

(This might not work if you have a multimeter with a low test voltage and a high Vgs(th) MOSFET, but it works with all the multimeters I've tried)

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