Share: IGBT detection method

IGBT has three electrodes, which are called gate G (also called control electrode or gate), collector C (also called drain) and emitter E (also called source)

1. Use an analog multimeter to judge the field effect tube

(1) Using resistance measurement method to distinguish the electrodes of junction field effect transistors

According to the phenomenon that the forward and reverse resistance values of the PN junction of the field effect tube are different, the three electrodes of the junction field effect tube can be distinguished. Specific method: Set the multimeter on the R×1k file, choose two electrodes, and measure the forward and reverse resistance values respectively. When the forward and reverse resistance values of certain two electrodes are equal and are several thousand ohms, the two electrodes are the drain D and the source S respectively. Because for the junction field effect transistor, the drain and source are interchangeable, the remaining electrode must be the gate G. It is also possible to arbitrarily touch the black test lead (red test lead) of the multimeter to one electrode, and the other test lead to contact the remaining two electrodes in turn to measure the resistance value. When the two measured resistance values are approximately equal, the electrode touched by the black test lead is the grid, and the remaining two electrodes are the drain and source respectively. If the resistance values measured twice are both large, it means that the PN junction is reversed, that is, both are reverse resistances. It can be determined that it is an N-channel FET, and the black meter pen is connected to the grid; if it is measured twice The resistance values are very small, indicating that it is a forward PN junction, that is, a forward resistance, which is judged to be a P-channel field effect tube, and the black meter pen is also connected to the grid. If the above situation does not occur, the black and red test leads can be exchanged and tested according to the above method until the grid is judged.

(2) Use resistance measurement method to judge the quality of FET

The resistance measurement method is to use a multimeter to measure the resistance value between the source and drain, the gate and the source, the gate and the drain, the gate G1 and the gate G2 of the field effect tube, and the resistance value indicated in the field effect tube manual Whether it is consistent to judge the quality of the tube. Specific method: first set the multimeter to the R×10 or R×100 gear, and measure the resistance between the source S and the drain D, usually in the range of tens of ohms to several thousand ohms. The resistance of the tube is different), if the measured resistance is greater than the normal value, it may be due to poor internal contact; if the measured resistance is infinite, it may be an internal disconnection. Then put the multimeter in the R×10k file, and then measure the resistance between the grid G1 and G2, between the grid and the source, and between the grid and the drain. When the measured resistance values are all infinite, then It means that the tube is normal; if the above-mentioned resistance values are too small or a passage, it means that the tube is broken. It should be noted that if the two grids are broken in the tube, the component substitution method can be used for detection.

(3) Estimating the amplification ability of the field effect tube with the induction signal input method

Specific method: Use the R×100 range of the multimeter resistance, connect the red test lead to the source S, and the black test lead to the drain D, and apply a 1.5V power supply voltage to the field effect tube. At this time, the resistance between the drain and the source indicated by the needle value. Then pinch the grid G of the junction field effect transistor with your hand, and add the induced voltage signal of the human body to the grid. In this way, due to the amplification of the tube, both the drain-source voltage VDS and the drain current Ib will change, that is, the resistance between the drain-source electrodes has changed, and it can be observed that the hands of the watch have a relatively large swing. If the hand-squeezed grid hand has a small swing, it means that the tube’s magnification capability is poor; if the hand swings too much, it indicates that the tube’s magnification capability is large; if the hand does not move, it means the tube is broken.

According to the above method, we use the R×100 file of the multimeter to measure the junction FET 3DJ2F. Open the G pole of the tube first, and the measured drain-source resistance RDS is 600Ω. After pinching the G pole with your hand, the needle swings to the left. The indicated resistance RDS is 12kΩ. The needle swings more widely, indicating that the tube is good. , And has a larger amplification capability.

There are several points to be explained when using this method: First, when the test field effect tube is pinched with the grid by hand, the multimeter needle may swing to the right (resistance value decreases), or it may swing to the left (resistance value increases). This is because the AC voltage induced by the human body is relatively high, and different FETs may have different working points when measuring with the resistance file (or work in the saturated or unsaturated zone). Tests have shown that the RDS of most tubes increases. , That is, the hand of the watch swings to the left; the RDS of a few tubes is reduced, which makes the hand of the watch swing to the right. Regardless of the direction of the hand movement, as long as the hand movement amplitude is larger, it means that the tube has a larger amplification capability. Second, this method is also applicable to MOS field effect transistors. But it should be noted that the input resistance of the MOS field effect tube is high, and the induced voltage allowed by the grid G should not be too high, so do not pinch the grid directly by hand. It must be used to hold the insulated handle of the screwdriver and touch it with a metal rod. Touch the grid to prevent the human body's induced charges from being directly added to the grid, causing grid breakdown. Third, after each measurement, the G-S poles should be short-circuited. This is because there will be a small amount of charge on the G-S junction capacitor, which builds up the VGS voltage, which may cause the needle to not move when the measurement is performed again. Only the short-circuit of the charge between the G-S electrodes can be done.

(4) Use resistance measurement method to identify unmarked field effect transistors

First, use the method of measuring resistance to find two pins with resistance value, that is, the source S and the drain D. The remaining two pins are the gate G1 and the second gate G2. Write down the resistance value between the source S and drain D measured with the two test leads first, adjust the test leads and then measure, and write down the measured resistance value. The larger resistance value is measured twice, and the black test lead is connected. The electrode of is the drain D; the red test lead is connected to the source S. The S and D poles distinguished by this method can also be verified by the method of estimating the amplification ability of the tube, that is, the black test pen with large amplification capability is connected to the D pole; the red test pen is grounded to 8 poles, two The test results of both methods should be the same. After determining the positions of the drain D and source S, install the circuit according to the corresponding positions of D and S. Generally, G1 and G2 will also be aligned in sequence, which determines the positions of the two gates G1 and G2. Thus, the sequence of D, S, G1, G2 pins is determined.

(5) Determine the size of transconductance by measuring the change of reverse resistance value

When measuring the transconductance performance of the VMOS N-channel enhanced field effect transistor, the red test lead can be connected to the source S and the black test lead can be connected to the drain D, which is equivalent to adding a reverse voltage between the source and the drain. At this time, the grid is open, and the reverse resistance of the tube is very unstable. Select the ohm range of the multimeter to the high resistance range of R×10kΩ, and the voltage in the meter is higher at this time. When you touch the grid G by hand, you will find that the reverse resistance of the tube changes significantly. The greater the change, the higher the transconductance of the tube; if the transconductance of the tube under test is very small, use this method to measure When, the reverse resistance value does not change much.

Two, the use of field effect tube matters needing attention

(1) In order to use the field effect tube safely, the limit value of the power dissipation of the tube, drain-source voltage, gate-source voltage and current, etc. cannot be exceeded in the circuit design.

(2) When using various types of FETs, they must be connected to the circuit strictly according to the required bias, and the polarity of the bias of the FET must be observed. For example, there is a PN junction between the source and drain of the junction field effect transistor, the gate of the N-channel transistor cannot be positively biased, and the gate of the channel transistor cannot be negatively biased, and so on.

(3) Because of the extremely high input impedance of MOS field effect transistors, the lead pins must be short-circuited during transportation and storage, and metal shielding packaging must be used to prevent external induced potential from breaking down the grid. Pay special attention to the fact that the MOS field effect tube cannot be placed in a plastic box, and stored in a metal box. At the same time, attention must be paid to the moisture-proof tube.

(4) In order to prevent the induction breakdown of the FET grid, all test instruments, workbenches, soldering irons, and the circuit itself must be well grounded; when soldering the pins, solder the source first; before connecting to the circuit , All the lead ends of the tube should be kept shorted to each other, and the shorting material should be removed after welding; when removing the tube from the component rack, ensure that the human body is grounded in a proper way, such as using a grounding ring; of course, if it can Using advanced gas-heated electric soldering iron, it is more convenient to solder the field effect tube, and to ensure safety; when the power is not turned off, the tube can not be inserted into the circuit or unplugged from the circuit. The above safety measures must be paid attention to when using field effect tubes.

(5) When installing the field effect tube, pay attention to the installation position to avoid close to the heating element; in order to prevent the tube from vibration, it is necessary to fasten the tube shell; when the pin lead is bent, it should be 5 mm larger than the root size To prevent bending of the pins and causing air leakage.

For power-type FETs, there must be good heat dissipation conditions. Because the power-type FET is used under high load conditions, it is necessary to design enough heat sinks to ensure that the shell temperature does not exceed the rated value, so that the device can work stably and reliably for a long time.

In short, to ensure the safe use of field effect tubes, there are many things to pay attention to, and the safety measures adopted are also various. The majority of technical personnel, especially the majority of electronic enthusiasts, must proceed according to their actual conditions. Take practical measures to make good use of field effect transistors safely and effectively.

Three, VMOS field effect tube

VMOS field effect transistor (VMOSFET) is abbreviated as VMOS tube or power field effect tube, and its full name is V-groove MOS field effect tube. It is a high-efficiency, power switching device newly developed after MOSFET. It not only inherits the high input impedance of MOS field effect tube (≥108W), small drive current (about 0.1μA), but also has high withstand voltage (1200V), large working current (1.5A-100A), and high output power (1～ 250W), good linearity of transconductance, fast switching speed and other excellent characteristics. It is precisely because it combines the advantages of electron tubes and power transistors into one, it is being widely used in voltage amplifiers (voltage amplification up to thousands of times), power amplifiers, switching power supplies and inverters.

The VMOS field effect power tube has the advantages of extremely high input impedance and large linear amplification area, especially its negative current temperature coefficient, that is, when the gate-source voltage does not change, the conduction current will follow the tube temperature. As it rises and decreases, there is no pipe damage caused by the "secondary breakdown" phenomenon. Therefore, the parallel connection of VMOS tubes is widely used.

As we all know, the gate, source, and drain of a traditional MOS field effect transistor are on a chip where the gate, source, and drain are roughly on the same horizontal plane, and the working current basically flows in the horizontal direction. The VMOS tube is different. Two major structural features can be seen from Figure 1: The metal gate adopts a V-groove structure; second, it has vertical conductivity. Since the drain is drawn from the back of the chip, the ID does not flow horizontally along the chip, but starts from the heavily doped N+ region (source S), flows into the lightly doped N-drift region through the P channel, and reaches the drain vertically downwards. Extreme D. The direction of the current is shown by the arrow in the figure, because the cross-sectional area of the flow is increased, so a large current can be passed. Because there is a silicon dioxide insulating layer between the gate and the chip, it is still an insulated gate MOS field effect transistor.

The main domestic manufacturers of VMOS FETs include 877 Factory, Tianjin Semiconductor Device Fourth Factory, Hangzhou Electronic Tube Factory, etc. Typical products include VN401, VN672, VMPT2, etc.

The method of detecting VMOS tube is introduced below.

1. Judgment grid G

Set the multimeter to R×1k to measure the resistance between the three pins. If it is found that the resistance of a pin and its two pins are both infinite, and it is still infinite after exchanging the test leads, it is proved that this pin is the G pole, because it is insulated from the other two pins.

2. Determine the source S and drain D

It can be seen from Figure 1 that there is a PN junction between the source and the drain. Therefore, according to the difference between the forward and reverse resistance of the PN junction, the S pole and the D pole can be identified. Use the exchange meter pen method to measure the resistance twice, among which the lower resistance value (generally several thousand ohms to ten thousand ohms) is the forward resistance. At this time, the black test lead is S pole, and the red one is connected to D pole.

3. Measure the drain-source on-state resistance RDS(on)

Short-circuit the G-S pole, select the R×1 gear of the multimeter, connect the black test lead to the S pole, and the red test lead to the D pole, and the resistance should be a few ohms to more than ten ohms.

Due to different test conditions, the measured RDS(on) value is higher than the typical value given in the manual. For example, use a 500-type multimeter to measure an IRFPC50 VMOS tube with R×1 file, RDS(on)=3.2W, which is greater than 0.58W (typical value).

4. Check the transconductance

Place the multimeter in the R×1k (or R×100) position, connect the red test lead to the S pole, and the black test lead to the D pole. Hold a screwdriver to touch the grid. The needle should deflect significantly. The greater the deflection, the greater the transconductance of the tube. high.

  Precautions:

(1) VMOS tubes are also divided into N-channel tubes and P-channel tubes, but most of the products are N-channel tubes. For the P-channel tube, the position of the test leads should be exchanged during measurement.

(2) There are a small number of VMOS tubes with protection diodes between G-S, items 1 and 2 in this detection method are no longer applicable.

(3) At present, there is also a VMOS tube power module on the market, which is specially used for AC motor speed controllers and inverters. For example, the IRFT001 module produced by the American IR company has three N-channel and P-channel tubes inside, forming a three-phase bridge structure.

(4) The VNF series (N-channel) products on the market are ultra-high frequency power FETs produced by Supertex in the United States. Its working frequency is fp=120MHz, IDSM=1A, PDM=30W, and a common source small signal low frequency span Guide gm=2000μS. It is suitable for high-speed switching circuits and broadcasting and communication equipment.

(5) A suitable heat sink must be added when using a VMOS tube. Take VNF306 as an example. After the tube is equipped with a 140×140×4 (mm) radiator, the power can reach 30W.

(6) After multiple tubes are connected in parallel, due to the corresponding increase of the inter-electrode capacitance and distributed capacitance, the high-frequency characteristics of the amplifier are deteriorated, and the high-frequency parasitic oscillation of the amplifier is easily caused by feedback. For this reason, there are generally no more than 4 composite tubes in parallel, and an anti-parasitic oscillation resistance is connected in series on the base or grid of each tube.

A simple way to check the quality of insulated gate bipolar transistors (IGBT)

1, to determine the polarity

First, set the multimeter to the R×1KΩ block. When measuring with the multimeter, if the resistance between one pole and the other two poles is

Infinity. After the test pen is replaced, the resistance between this pole and the other two poles is still infinite, then this pole is judged to be the grid (G). Use a multimeter to measure the remaining two poles. If the measured resistance is infinite, the measured resistance is smaller after changing the test leads. When the measured resistance is small, it is judged that the red test lead is connected to the collector (C); the black test lead is connected to the emitter (E).

2, judge good or bad

Set the multimeter to the R×10KΩ block, connect the black test lead to the collector (C) of the IGBT, and connect the red test lead to the emitter (E) of the IGBT. At this time, the pointer of the multimeter is at the zero position. Touch the gate (G) and collector (C) with your finger at the same time. At this time, the IGBT is triggered to turn on, and the pointer of the multimeter swings in the direction of lower resistance, and can stand and indicate a certain position. Then touch the gate (G) and emitter (E) with your finger at the same time. At this time, the IGBT is blocked and the pointer of the multimeter returns to zero. At this point, it can be judged that the IGBT is good.

3, matters needing attention

Any analog multimeter can be used to detect IGBT. When judging whether the IGBT is good or bad, be sure to
The multimeter should be set to the R×10KΩ gear. The internal battery voltage of the multimeters below the R×1KΩ gear is too low, and the IGBT cannot be turned on when the quality is detected, and the quality of the IGBT cannot be judged. This method can also be used to detect the quality of power field effect transistors (P-MOSFETs). Inverter, soft starter, PLC, human-machine interface, low-voltage electrical appliances, electrical automation engineering, constant pressure water supply equipment, music fountain control system, inverter maintenance, etc.