How to tell if a MOSFET is good or bad?

MOSFET. The method of judging the quality of the transistor is the same.

Completely different, taking an N-channel MOSFET as an example, it is done as follows:

1.Multimeter.

Diode gear;

2.The red pen is connected to the D pole, and the black pen is connected to the S pole, which should be impassable; The reverse amount is connected to the due pressure drop;

3.The red pen is connected to the G pole and the black pen is connected to the S pole, which should also be impassable, but this step is very important, the G pole has been charged, and the tube has been opened at this time;

4.The red pen is connected to the D pole again, and the black pen is connected to the S pole, and there should be a pressure drop of a few tenths of a volt at this time, indicating that the tube has been opened;

5.The pen remains motionless, touches the three poles of the tube with your fingers, discharges between g and s, and turns off the tube. D, S is not connected again.

If all the above processes are correct, then you can be sure that the tube is good.

If it is a P-channel MOSFET, you can exchange the red and black pens of the multimeter.

The method of judging a transistor is the same.

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Hello pro refer to the detection method of the FET: hit the digital multimeter to the diode file, touch the three pins of the FET with two meter pens at will, a good FET should only have a reading once when measuring, and the value is about 300-800, 2, if there is only one reading measured in the final measurement results, and when it is 0, the multimeter must be short-connected with the pin of the FET, 3. Re-measure once, if a group of readings of about 300-800 are measured, the tube is also a good tube. 4. Turn the multimeter to the diode file, measure the D, S pole and G and S pole with the two meters of the multimeter to see if the reading between the two poles is very small, if this value is below 50, it can be judged that the effect tube has been broken down Field Effect Transistor, also known as Field Effect Transistor, is a semiconductor device that uses the electric field effect of the control input loop to control the output loop current.

Conducted by a majority of carriers, also known as a unipolar transistor,[1] it is a voltage-controlled semiconductor device. There are two main types (junction FET-JFET) and metal-oxide semiconductor FET (MOS-FET). FET has the advantages of high input resistance (10 7 10 15), low noise, low power consumption, large dynamic range, easy integration, no secondary breakdown, and wide safe working area, and has become a strong competitor of bipolar transistors and power transistors.

Compared with bipolar transistors, MOSFETs have the following characteristics. (1) The MOSFET is a voltage control device, which controls the I D (drain current) through V GS (gate-source voltage); (2) The current at the control input end of the FET is very small, so its input resistance (10 7 10 12) is very large. (3) It uses most carriers to conduct electricity, so its temperature stability is good; (4) the voltage amplification coefficient of the amplification circuit composed of it is smaller than the voltage amplification coefficient of the amplification circuit composed of the triode; (5) The FET has strong radiation resistance; (6) Because it does not have the scatter noise caused by the diffusion of electrons in chaotic motion, the noise is low.

The working principle of the MOSFET is "the ID of the channel flowing between the drain and the source, and the gate voltage control ID of the reverse bias formed by the PN junction between the gate and the channel". More precisely, the width of the path through which the ID flows, i.e., the cross-sectional area of the channel, is controlled by the change in the reverse bias of the PN junction, resulting in the depletion layer propagation change. In the unsaturated region of vgs=0, the expansion of the transition layer is not very large, and according to the electric field of VDS applied between the drain and the source, some electrons in the source region are pulled away by the drain, that is, there is a current ID flowing from the drain to the source.

The excessive layer that expands from the gate to the drain forms a part of the channel as a blockage type, and the ID is saturated. This state is called pinching. This means that the transition layer will be a part of the channel.

Measure the voltage between the source and gate of the FET with a multimeter voltmeter, and when the FET is normal, the voltage between the source and the gate should be within the specified range, otherwise the FET is damaged. 2.Dynamic current test method:

When the FET is normal, the voltage between its gate and source causes current to pass through the tube, the current value should be within the specified range, and when the tube is damaged, the voltage between the gate and the source does not produce enough current. 3.Capacitance test method:

The capacitance of the MOSFET can be tested by using the capacitance level of the multimeter, and when the leakage capacitance is abnormally large or even infinite, it shows that the control voltage is insensitive to changes, which is a typical manifestation of the failure of the FET. The FET is a kind of semiconductor component, and its characteristics are slightly different from ordinary diodes, transistors and other devices, so it is necessary to be familiar with its basic characteristics and test methods when testing. In addition, it is necessary to use professional test instruments for MOSFETs to correctly judge their performance and correctness.

Hu Chabi, the above is mine, I hope these contents can help you, thank you for your understanding and support, I will continue to work hard.

Summary. The quality of a FET can be determined by a variety of test methods. Here are some of them:

1.Verify that there is on-on: Set the multimeter to the multimeter, place the test electrodes on the source and drain, and the test rod should show zero resistance when powered on.

If the test rod shows a different number, it means that the FET cannot be turned on. 2.Verify Resistance:

Connect the test electrode between the source and drain, and connect the test rod to the grid. If the test table shows an infinite resistance, the FET is broken down or damaged and needs to be replaced. 3.

Verify Gate Threshold: A voltage is applied to the gate in a voltage gradient and the gate voltage is recorded. When the FET is saturated, the voltage between the source and drain is recorded, and the current at saturation is calculated.

The gate voltage should fall within the specified range. If the voltage is out of range, the FET will not work properly.

The quality of the FET can be determined by a variety of test methods. Here are some of them:1

Verify that there is on-on: Set the multimeter to the multimeter, place the test electrodes on the source and drain, and the test rod should show zero resistance when powered on. If the test rod shows a different number, it means that the FET cannot be turned on.

2.Verify the resistance: Connect the test electrode between the source and the drain, and connect the test rod to the grid.

If the test gauge shows an infinite resistance, the FET is broken down or damaged and needs to be replaced. 3.Verify Gate Threshold:

A voltage is applied to the gate in a voltage gradient fashion, and the gate voltage is recorded. When the FET is saturated, the voltage between the source and drain is recorded, and the current at saturation is calculated. The gate voltage should fall within the specified range.

If the voltage is out of range, the FET will not work properly.

FETs have a high ingress impedance, so they are widely used in circuits. When measuring FETs, special care needs to be taken to avoid electrostatic discharge, which can cause damage to the FETs. When testing FETs, be sure to use the correct test power supply and measurement equipment to ensure the accuracy of the test results.

In addition, special care needs to be taken to avoid operating the FET at high temperatures, which can often cause damage to the FETs. If the FET needs to be replaced, care should be taken to select the correct model. <>

The method of measuring the quality of the MOSFET is as follows:

It is to use a multimeter to measure whether the resistance values between the source and drain, gate skin and source, gate and drain, gate G1 and gate G2 of the MOSFET are consistent with the resistance values indicated in the FET manual to judge the quality of the tube.

Specific method: firstly, put the multimeter in R 10 or R 100 gear, measure the resistance between the source S and the drain D, usually in the range of tens of ohms to thousands of ohms (it can be seen in the manual, the resistance value of various types of tubes is different), if the measured resistance value is greater than the normal value, it may be due to poor internal contact; If the measured resistance is infinity, it may be an internal pole break.

Then put the multimeter in the R 10K file, and then measure the resistance value between the gate G1 and G2, between the gate and the source, and between the gate and the drain. If the above resistance values are measured too small or are pathways, it means that the tube is bad. It should be noted that if two gates are broken in the tube, the component substitution method can be used for detection.

According to the phenomenon that the positive and reverse resistance values of the PN junction of the MOSFET are different, the three electrodes of the junction MOSFET can be distinguished. Specific method: Dial the multimeter on the R 1k file, select two electrodes, and measure their forward and reverse resistance values respectively.

When the positive and reverse resistance values of two electrodes are equal and are several kiloohms, then the two electrodes are drain d and source s, respectively.