Field effect transistors are semiconductor devices in which transients, as well as the magnitude of the output current, are controlled by changing the magnitude of the electric field. There are two types of these devices: with an isolated gate (in turn, they are divided into transistors with an integrated channel and with an induction channel) and with a controlled transition. Field-effect transistors due to their unique characteristics are widely used in electronic equipment: power supplies, televisions, computers, etc.
When repairing such a technique, surely every novice radio amateur faced the following question: how to check the field effect transistor? Most often, the verification of such elements can be encountered in the repair of switching power supplies. In this article, we will describe in detail how to do this correctly.
How to check a field effect transistor with an ohmmeter
First of all, in order to start checking the field effect transistor, it is necessary to deal with its "pinout", that is, with the location of the terminals. Today, there are many different versions of such elements, respectively, the location of the electrodes is different. Often you can find semiconductor transistors with signed contacts. For marking, use the Latin letters G, D, S. If there is no signature, then you need to use the reference literature.
So, having figured out the marking of the contacts, consider how to check the field effect transistor. The next step will be to take the necessary safety measures, because field devices are very sensitive to static voltage, and in order to prevent the failure of such an element, it is necessary to organize grounding. To remove the accumulated static charge, an antistatic grounding bracelet is usually worn on the wrist.
We should not forget that it is necessary to store field-effect transistors with closed leads. After removing the static voltage, you can proceed to the verification procedure. To do this, you need a simple ohmmeter. For a working element between all conclusions, the resistance should tend to infinity, but there are some exceptions. Now we will look at how to test an n-type field effect transistor.
Apply the positive probe to the gate electrode (G), and the negative probe to the source contact (S). At this moment, the shutter capacity begins to charge and the element opens. When measuring the resistance between the source and the drain (D), the ohmmeter will show some resistance value. In different types of transistors, this value is different. If you short the terminals of the transistor, then the resistance between the drain and the source will again tend to infinity. If this does not happen, then the transistor is faulty.
If you ask how to test a P-type field effect transistor, the answer is simple: we repeat the above procedure, only change the polarity. It should also not be forgotten that modern powerful field-effect transistors between the source and drain have a built-in diode, so it “rings” only in one direction.
Checking the field effect transistor with a multimeter
If you have a multimeter, you can check the field effect transistor. To do this, set the measuring device in the “ringing” mode of the diodes and enter the field element in saturation mode. If the transistor is N-type, then we touch the drain with a minus probe and a shutter with a positive one. A working transistor in this case opens. We transfer the positive probe, without tearing the minus one, to the source, and the multimeter shows some resistance value. After that, we lock the transistor: without taking the probe from the source, touch the shutter with a minus and return it to the drain. The transistor is locked and resistance tends to infinity.
Many hams ask: "How to check the field effect transistor without soldering?" Immediately answer that one hundred percent way does not exist. To do this, use a multimeter with an HFE pad, but this method often fails, and you can spend a lot of time in vain.