Have you ever heard of a MOSFET? It’s a sort of transistor derived from metal oxide semiconductor FET, in case if you didn’t know. Switch mode power supply and many other circuits utilize fet transistors as part of a circuit. Mosfet failure and leakage are extremely high in a circuit and you need to know how to correctly test it.
In today’s article, we will discuss more about this unusual sort of transistor and find out how to check Mosfet with multimeter.
I’ll start with the most basic method of testing a MOSFET transistor. You’ll need to take the device out of the circuit, so if it’s on a PCB and you’re unsure about de-soldering, I have a step-by-step instructions here.
It’s the simplest method since you:-
1. It is not necessary to know what sort of MOSFET you have (N channel, P channel, enhanced or depleted)
2. You do not need to know the pin out of the device being tested.
3. You do not need to fiddle with holding the device and test probes into various pins while you’re trying to read the multimeter. Then worrying if you have the probe on the proper leg.
4. It’s much faster, especially if you have several to test.
MOSFET: What exactly are they?
MOSFETs are devices in which the variation in voltage determines the device’s conductivity. It’s a semiconductor device, which belongs to the FET family.
MOSFET is also termed IGFET or insulated-gate field-effect transistor. Nonetheless, the name MOSFET is used since various devices are produced using gate electrodes of metal oxide and Si for semiconductors.
You will detect three-terminal devices in a MOSFET that contains a gate terminal, a drain, and a source. Voltage-controlled devices are those in which the current flowing between the drain and the source is proportional to the input voltage.
It’s also worth noting that MOSFET is an innovative FET designed to overcome the limitations of FET. As you can see, FETs have a high drain resistance, a delayed function, and a low input impedance. Meanwhile, MOSFETs have a lower capacitance value and a higher input impedance than MOSFETs.
Because of their capacity to modify conductivity in response to applied voltage, MOSFETs are extensively used in signal amplification and switching. Because of its tiny size, it is also normally used in transistors in digital circuits. The voltages applied change the channel width. The greater channel width also improves the device’s conductivity.
How does it perform the function?
MOSFETs are voltage-controlled field-effect transistors that differ greatly from JFETs. The gate electrode, you see, is electrically isolated from the primary semiconductor by a thin layer of insulating material.
The greatest feature is that the insulated metal gate is similar to a capacitor plate with a high input resistance. Because of the gate’s isolation, there will be no current flow into the MOSFET from the gate.
When a voltage is provided to the gate, the width of the drain-source channel, through which charge carriers pass, is quickly adjusted. Simply said, the greater the width of the channel, the better the device conducts. Isn’t it incredible?
MOSFETs are typically used differently from other standard junction FETs.
MOSFETs are useful for power amplifiers due to their infinitely high input impedance. The devices are ideally matched to high-speed switching applications as well. Other integrated circuits (ICs) with tiny MOSFETs are widely used in computers.
Furthermore, because the oxide layer is very thin, the MOSFET might be destroyed by accumulated electrostatic charges. MOSFET devices do not often perform as well as other types of FETs in weak signal radio frequency.
How TO Check Mosfet With Multimeter
Digital multimeter is the best device to check the Mosfet with a multimeter We use the K1058 and the IRFP240 as examples of N-channel MOSFETs that may be checked with an ordinary digital multimeter using somewhat various procedures.
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How to Evaluate N-Channel Mosfets
1) Adjust the diode range on the DMM.
2)Place the Mosfet on a dry hardwood surface on its metal tab, printed side up, leads pointing towards you.
3) Short the mosfets gate and drain pins using a screwdriver or meter probe. This will initially
keep the device’s internal capacitance entirely drained.
4) Now, connect the meter’s black probe to the device’s source and red probe to its drain.
5)On the meter, you should see a “open” circuit indicator.
6) While maintaining the black probe in touched with the source, take the red probe from the drain and briefly touch it to the gate of the Mosfet before returning it to the source.
7) This time meter will indicate a short circuit (sorry, not short-circuit rather “continuity).The findings from points 5 and 7 confirm that the Mosfet is functional. This method should be repeated several times for good confirmation.
You will need to reset the MOSFET by shorting the gate and drain lines with a meter probe each time you perform the above method.
How to Evaluate P-Channel Mosfets
The testing processes for P-channel will be the same as for 1, 2, 3, 4, and 5, but the polarity of the meters will vary. Here’s how to go about it.
1) Adjust the diode range on the DMM.
2) Place the Mosfet on a dry wooden surface on its metal tab, with the printed side facing you and the leads pointing in the same direction.
3) Short the P-gate mosfets and drain pins with any conductor or meter probe. This will initially allow the device’s internal capacitance to drain, which is required for the testing process.
4) Now, connect the meter’s RED probe to the device’s source and the BLACK probe to its drain.
5) The meter will show a “open” circuit reading.
6) Next, without taking the RED probe from the source, remove the black probe from drain and contact it to the gate of the Mosfet for a second, then bring it back to the drain of the Mosfet.
7) This time the meter will display a continuity or a low value .
That’s it; this will validate that your Mosfet is working properly. Any other reading will indicate a bad Mosfet.
If you have any more questions about the processes, please leave them in the comments area.
Simple Mosfet Tester Jig Circuit
If the above-mentioned testing process with a multimeter is not convenient for you, you may rapidly construct the following jig to examine any N channel Mosfet effectively. Once you’ve built this jig, you can plug the mosfets necessary pins into the G, D, and S sockets. After that, simply click the push button to validate the Mosfet status.
If the LED only lights up when you press the button, your Mosfet is OK; otherwise, it is a faulty or malfunctioning Mosfet.
The LED’s cathode will be connected to the drain side or drain socket.
Conclusion
To summarize, a MOSFET is a voltage-controlled device with three terminals: source, gate, and drain, as opposed to an emitter, collector, and base in a bipolar transistor. By providing a voltage to the gate, it generates an electric field that regulates the current flow across the channel between the source and drain. There is no current flow from the gate into the MOSFET.