How to measure the quality of an IGBT module

Date：2024-03-15 13:57:24Views：7

IGBT (Insulated Gate Bipolar Transistor) is a composite fully controlled voltage driven power semiconductor device composed of BJT (bipolar transistor) and MOS (insulated gate field-effect transistor), which combines the advantages of high input impedance of MOSFET and low on/off voltage drop of GTR. The saturation voltage of GTR decreases, the current carrying density is high, but the driving current is high; MOSFET has low driving power, fast switching speed, but high conduction voltage drop and low current density. IGBT combines the advantages of the above two devices, with low driving power and reduced saturation voltage.

IGBT is very suitable for application in converter systems with DC voltage of 600V and above, such as AC motors, frequency converters, switching power supplies, lighting circuits, traction drives, and other fields. Figure 1 shows an N-channel enhanced insulated gate bipolar transistor structure, with the N+region referred to as the source region and the electrodes attached to it referred to as the source. The N+zone is called the leakage zone. The control region of the device is the gate region, and the electrodes attached to it are called gates. The channel is formed close to the boundary of the grid area. The p-type region (including p+and p-1 regions) between the leakage and source (where the channel is formed) is called a subchannel region.

The p+region on the other side of the drain region is called the drain injector, which is a unique functional region of IGBT. It forms a pNp bipolar transistor together with the drain region and sub channel region, acting as an emitter, injecting holes into the drain, conducting conductivity modulation, and reducing the on state voltage of the device. The electrode attached to the leakage injection area is called a drain electrode. The switching function of IGBT is to form a channel by applying a forward gate voltage, providing base current to the pNp transistor, and making the IGBT conductive. On the contrary, adding reverse gate voltage eliminates the channel, cuts off the base current, and turns off the IGBT. The driving method of IGBT is basically the same as that of MOSFET, which only needs to control the input pole N for one channel of MOSFET, so it has high input impedance characteristics. After the formation of MOSFET channels, holes (minority carriers) are injected from the p+base into the N-layer to modulate the conductivity of the N-layer, reduce its resistance, and enable the IGBT to have a low on state voltage even at high voltages.

A convenient method for detecting the quality of IGBT

1. Judging polarity

Firstly, set the multimeter to R1K gear. When measuring with a multimeter, if the resistance value between one pole and the other two poles is infinite, and after switching the probes, the resistance value between that pole and the other two poles is still infinite, then it is judged that this pole is a gate (G). Measure the remaining two poles with a multimeter. If the measured resistance value is infinite, replace the probe and measure the resistance value to be smaller. In a measurement with a smaller resistance value, it is judged that the red probe is connected to the collector (C); The black probe is connected to the emitter (E).

2. Judging good or bad

Set the multimeter to R10K, 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 zero. Touch the gate (G) and collector (C) simultaneously with your finger, and the IGBT is triggered to conduct. The pointer of the multimeter swings towards the direction with lower resistance and can stand to indicate a certain position. Then touch the gate (G) and emitter (E) simultaneously with your fingers, and the IGBT will be blocked, causing the pointer of the multimeter to return to zero. At this point, it can be determined that IGBT is good.

3. Any pointer type multimeter can be used to detect IGBT

When judging the quality of an IGBT, be sure to set the multimeter to R10K, as the internal battery voltage of the multimeter below R1K is too low. When detecting the quality, the IGBT cannot be conducted, making it impossible to determine its quality. This method can also be used to detect the quality of power field-effect transistors (p-MOSFETs).

Inverter IGBT module detection:

Set the digital multimeter to the diode test mode and test the forward and reverse diode characteristics between the IGBT modules c1e1 and c2e2, as well as between the gate G and e1 and e2, to determine if the IGBT module is intact.

Taking the six phase module as an example. Remove the wires of the U, V, and W phases on the load side, use a diode test gear, connect the red probe to p (collector c1), and measure U, V, and W in sequence with the black probe. The multimeter displays the maximum value; Turn the pen upside down, connect the black pen to p, and measure U, V, and W with the red pen. The multimeter displays a value of around 400. Connect the red probe to N (emitter e2), measure U, V, and W with the black probe, and the multimeter will display a value of around 400; The black probe is connected to p, the red probe measures U, V, and W, and the multimeter displays the maximum value. The forward and reverse characteristics between each phase should be the same. If there is a difference, it indicates that the performance of the IGBT module has deteriorated and should be replaced. When the IGBT module is damaged, only a breakdown short circuit occurs.

The red and black probes measure the forward and reverse characteristics between gate G and emitter E respectively. The values measured by the multimeter twice are both the maximum, indicating that the IGBT module gate is normal. If there is a numerical display, the gate performance will deteriorate and this module should be replaced. When the forward and reverse test results are zero, it indicates that the detected phase gate has been broken and short circuited. When the gate is damaged, the voltage regulator protecting the gate on the circuit board will also break down and be damaged.