MOS FET detection methods and precautions for discrimination

A mos transistor is a metal oxide semiconductor transistor or metal insulator used for field effect semiconductor. MOS tube source and drain can be interchanged, both of which are N-type regions formed in P-type backates. In most cases, these two regions are the same, and even if both sides are switched, the characteristics of the device will not be affected. This type of device is called symmetry. This article has collected and organized some materials, which are expected to have great reference value for readers.

1、 Advantages and disadvantages of MOS field utility transistor judgment

1. Identifying the electrical level of junction type field effect transistor using resistance measurement method

The three electrical levels of a junction type field effect transistor can be distinguished based on the PN junction forward and reverse resistance values of the field effect transistor. Specific method: Set the multimeter to R × On 1k gear, select any two electrical stages and measure their positive and negative resistance values respectively. When the forward and reverse resistance values of the two electrical stages are the same and are thousands of ohms, the two electrical stages are respectively the drain electrode D and the source electrode S. For junction type field effect transistors, the drain and source electrodes can be exchanged, and the remaining electrical stages must be gate G. You can also touch the black pen (red pen can also be) of the multimeter at will, and the other pen contacts the other two electrical levels to measure their resistance. When the resistance values measured twice are similar, the electrical level contacted by the black pen is the gate electrode, and the other two electrical levels are the drain and source electrodes. If the resistance values measured twice are large, it indicates the reverse resistance of the PN junction, which can be determined as an N-channel field-effect transistor with a black pen connected to the gate; If the resistance value measured twice is very small, it is a positive PN junction, that is, a positive resistance, determined as a P-channel field-effect transistor, and the black pen is also connected to the gate. If there is no such situation, you can replace the black and red probes as described above for testing until the gate electrode is determined.

2. Distinguishing the Mass of Field Effect Transistors by Measuring Resistance

How to judge the advantages and disadvantages of field effect transistors? The first method of measuring resistance is to use a multimeter to measure the resistance values between the source and drain electrodes, the gate and source electrodes, the gate and drain electrodes, and the gate G1 and G2 of the field effect transistor. To do this, first place the multimeter in R × 10 or R × In gear 100, the measured resistance between the source electrode S and the drain electrode D is typically between tens of euros and thousands of euros (according to the guidelines, the resistance values for different types of pipes vary). If the measured resistance exceeds the standard value, it may be due to poor internal contact; If the measured resistance value is infinite, it may be an internal pole break. Then place a multimeter in R × Measure the resistance between grid electrodes G1 and G2, grid electrode and source electrode, and grid electrode and drain electrode at 10k. When the measured resistance values are infinite, it indicates that the pipeline is normal; If the measured resistance value is too small or the channel is too small, it indicates that the pipeline is damaged. It should be noted that if the pipeline interrupts both gates, the component replacement method can be used for inspection.

3. Estimating the Amplification Ability of Field Effect Transistors Using Inductive Signal Input Method

How to Judge the Advantages and Disadvantages of Field Effect Transistors: Using a Multimeter Resistance R × At gear 100, connect the red lead to the source electrode S, and connect the black lead to the drain electrode D. Add 1.5V power supply current to the field effect transistor. At this time, the pointer indicates the drain source resistance value. Then pinch the gate G of the junction type field effect transistor with your hand and add the human body induced voltage signal to the gate. In this way, due to the pipe amplification effect, the leakage voltage VDS and leakage current IB will change, that is, the resistance between the leakage and leakage electrodes will change, and it is observed that the pointer shakes greatly. If the shaking of the gate pointer is small, it indicates that the pipe amplification ability is poor; The large shaking of the pointer indicates a large amplification capacity of the pipeline; If the pointer doesn't move, the pipe is broken.

According to the above method, we use the R value of the multimeter × 100 gear, junction type field effect transistor 3DJ2F. First, open the G-pole of the tube and measure the leakage resistance RDS to 600 Ω. After gripping the G-pole, the pointer swings to the left. The marked resistance RDS is 12k Ω, and the pointer swings greatly, indicating that the tube is good and has a large amplification capacity.

When applying this method, the following points should be noted: First, when the test FET holds the gate electrode, the multimeter needle may shake to the right (resistance value decreases) or to the left (resistance value increases). This is because the AC current induced by the human body is relatively high, and different field effects may be caused by different operating points (or working in saturated or unsaturated regions). Experiments have shown that most pipeline RDS increases, which means the pointer swings to the left; A few pipes have reduced RDS, causing the pointer to shake to the right. However, no matter what direction the pointer swings, as long as the pointer swings significantly, it proves that the pipeline has a greater amplification ability. Secondly, this method is also applicable to MOS field utility transistors. However, it should be noted that the input resistance of MOS field utility transistors is very high, and the allowable induced voltage of gate G should not be too high. Therefore, remember not to pinch the grid with your hands. Be sure to hold the insulating handle with a screwdriver and touch the gate electrode with a metal rod to prevent body induced charges from directly adding to the gate electrode, causing the gate electrode to penetrate. Third, at the end of each measurement, there is a short circuit between G-S electrodes. This is because the G-S junction capacitor is filled with a small amount of charge, creating a VGS voltage, which may cause the pointer to not move during the second measurement, and can only discharge the short circuit of the G-S electrode charge.

4. Identification of unmarked field effect transistors using resistance measurement

How to judge the advantages and disadvantages of field effect transistors? First, by measuring the resistance, find two pins with resistance values, namely the source electrode S and the drain electrode D. The remaining two legs are the first gate G1 and the second gate G2. Write down the resistance value between the source electrode S and the drain electrode D measured with two electric pens, exchange the electric pens for another measurement, record the measured resistance value, and measure the larger resistance value twice. The electrical level connected with the black electric pen is the drain electrode D; The source electrode S is connected to the red probe. Using this method to identify the S and D electrodes can also be verified by estimating their pipeline amplification capacity, that is, connecting a black pen with a larger amplification capacity to the D electrode; The red probe is grounded to 8 poles, and the inspection results should be the same. After determining the position of drain electrode D and source electrode S, install the circuit according to the corresponding position of D and source electrode S. Generally, G1 and G2 will also be aligned successively to determine the positions of the two gate electrodes G1 and G2, and then determine the pin order of D, S, G1, and G2.

5. The magnitude of transconductance is determined by measuring the change in the reverse resistance value

How to judge the advantages and disadvantages of field effect transistors? When measuring the transconductance characteristics of VMOSN channel enhanced field-effect transistors, you can use a red lead to connect electrode S and a black lead to connect drain electrode D, which is equivalent to increasing the reverse voltage between the source and drain electrodes. At this time, the gate electrode is open, and the reverse resistance value of the tube is very unstable. Select the ohmic profile of the multimeter in R × At 10k Ω high resistance level, the voltage in the meter is high. When experts touch the gate electrode G, they will find that the reverse resistance value of the pipeline has significantly changed. The greater the change, the greater the transconductance value of the pipeline; Once the transconductance of the measured pipe is small, the reverse resistance value does not change much.

2、 Precautions for MOS field utility transistor judgment

1. VMOS pipes are also divided into N-channel pipes and P-channel pipes, but the vast majority of products belong to N-channel pipes. For P-ditch pipes, the position of the pen should be exchanged during measurement

2. There are a few VMOS transistors and maintenance diodes between G-S. Items 1 and 2 of this test method are no longer applicable

3. Currently, there is also a VMOS transistor power module on the market for AC motor speed regulators and inverter applications. For example, the IRFT001 module manufactured by IR Corporation of the United States has three N-channel and P-channel tubes, forming a three-phase bridge structure

4. The VNF series (N-channel) products currently sold on the market are ultra high frequency power field effect transistors manufactured by Supertex Company in the United States. Their maximum output power is FP=120mHz, IDSM=1A, PDM=30W, and common source small signal low frequency transconductance gm=2000 μ S. Suitable for high-speed switching circuits, broadcast and communication equipment

5. When using VMOS pipes, you must add appropriate heat sinks. Taking VNF306 as an example, pipeline installation 140 × one hundred and forty × After a 4 (mm) radiator, the high power can reach 30W.