How to test a field effect transistor?

Как проверить полевой транзистор

In powerunits or uninterruptible power supplies, field effect transistors often break down. Checking the field  transistor is important and, in some cases, one of the first steps in repairing the equipment.

How to test a FET with a multimeter?

For a simple check of the field effect transistor, it is necessary to perform the actions according to the scheme.

How to test a field effect transistor

Inspected FET is IRFZ44N.

  1. The black probe (-) is connected to the drain (D), and the red one is connected to the source (S) – the transition value of the built-in oncoming diode will be shown on the screen. This value must be remembered.
  2. Remove a red probe from the source and touch the shutter (G) – so we partially open the FET.
  3. Return the red probe back to the source (S). See that the value of the transition has changed, it has become slightly smaller – the field-effect transistor has partially opened.
  4. Transfer black probe the drain (D) to the shutter (G) – to close the field effect transistor.
  5. Return the black probe back and observe that the indication of the transition has returned to the original – the field transistor has completely closed.

How to test a field effect transistor sheme

The shutter of the working FET should have a resistance equal to infinity.

Done, field effect transistor is in working order.

The described procedure is meant for the n-channel field, the p-channel is tested similarly, only the polarity of the probes needs to be changed.

To test the FET, small circuits to which the field transistor is connected can also be used. Such a method will give a quick and accurate diagnosis. But if there is no need for frequent field inspections or not to feel like to mess around with the circuit, the described method of testing the FET with a multimeter will be an excellent solution to the task.

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