How to judge the polarity and quality of IGBT FET? Its working principle and detection method

Date：2022-03-16 17:49:13Views：1146

IGBT (insulated gate bipolar transistor), also known as insulated gate bipolar transistor, is a composite fully controlled voltage driven power semiconductor device composed of BJT (bipolar triode) and MOS (insulated gate field effect transistor). Its input pole is MOSFET and output pole is PNP transistor. Therefore, it can be regarded as a Darlington transistor with MOS input. It combines the advantages of high input impedance of MOSFET and low on voltage drop of GTR. It has the characteristics of easy driving, large peak current capacity, self turning off and high switching frequency (10-40 kHz). It has gradually replaced thyristor and GTO (gate turn off thyristor). It is a new generation of power electronic devices with the fastest development at present.

It is widely used in small volume and high efficiency variable frequency power supply, motor speed regulation, ups and inverter welding machine.

Working principle of IGBT

IGBT is controlled by grid (g), emitter (E) and collector (c). As shown in Figure 1, the switching function of IGBT is to form a channel by adding forward gate voltage to provide base current to PNP transistor and turn on IGBT. On the contrary, add the reverse gate voltage to eliminate the channel and cut off the base current to turn off the IGBT. As can be seen from Fig. 2, if a driving positive voltage is applied between the gate and emitter of the IGBT, the MOSFET is turned on, so that the collector and base of the PNP transistor form a low resistance state and the transistor is turned on; If the voltage between the gate and emitter of the IGBT is 0V, the MOSFET is cut off and the supply of the base current of the PNP transistor is cut off, so that the transistor is cut off.

If the voltage between the gate and emitter of IGBT, that is, the driving voltage is too low, the IGBT cannot work stably. If it is too high or even exceeds the withstand voltage between the gate and emitter, the IGBT may be permanently damaged. Similarly, if the voltage between the collector and emitter of IGBT exceeds the allowable value, the current flowing through IGBT will exceed the limit, resulting in the junction temperature of IGBT exceeding the allowable value. At this time, IGBT may also be permanently damaged.

IGBT polarity judgment

When testing IGBT, pointer multimeter shall be selected. First, turn the multimeter to R × 1K Ω gear, use a multimeter to measure the resistance between each pole. If the resistance between one pole and other poles is infinite, and the resistance between this pole and other poles is still infinite after changing the probe, this pole is grid (g). Use a multimeter to measure the resistance value between the other two poles. If the measured resistance value is infinite, the resistance value is small after changing the probe. When the measured resistance value is small, the red probe contacts the collector (c) and the black probe contacts the emitter (E).

Judgment of IGBT quality

When judging whether IGBT is good or bad, pointer multimeter must be selected (the internal battery voltage of electronic multimeter is too low), or 9V battery can be used instead. First, turn the multimeter to R × 10K Ω gear (R) × At 1K Ω gear, the internal voltage is too low to turn on the IGBT). Connect the black probe to the collector (c) of the IGBT and the red probe to the emitter (E) of the IGBT. At this time, the pointer of the multimeter is at the zero position. Touch the grid (g) and collector (c) with your finger at the same time. At this time, the IGBT is triggered and turned on. The pointer of the multimeter obviously swings and points to the direction with small resistance value and can be maintained at a certain position. Then touch the grid (g) and emitter (E) with your fingers at the same time. At this time, the IGBT is blocked and the pointer of the multimeter returns to zero. In the detection, the above phenomena are consistent, and it can be determined that the IGBT is good, otherwise there is a problem with the IGBT.