02 Sep Structure and Inspection of IGBT Tube for Induction cooker

The Insulated Gate Bipolar Transistor (IGBT) is a high voltage, high speed, high power device that combines the high current density of the BJT and the advantages of a voltage-excited field-controlled device such as a MOSFET.

Currently, there are IGBT tubes made of different materials and processes, but they can all be regarded as a MOSFET input followed by a bipolar transistor amplification of the composite structure.

In the induction cooker circuit, N-IGBT is often used, and its shape and graphic symbols are shown in Figure 1.

The IGBT tube has three electrodes, called the gate G (also known as the control pole or gate), collector C (also known as the drain) and emitter E (also known as the source).

The IGBT tube in the induction cooker is the key device to achieve low voltage to high voltage, small current to high current control, and it is one of the important components of the resonant circuit. Through its switching effect, the changing current can be converted into magnetic

1. I GBT tube detection

( 1) Under normal conditions, the three electrodes of IGBT tube are not on each other.

①judge the polarity. Put the multimeter in R × 1 kΩ file, the black pen is fixed on a pin, the red pen is connected to the other two pins, observe the measured data; transfer the two pens, the red pen is fixed on the original black pen connected to the pin, the black pen is connected to the other two pins, if the resistance measured twice is infinity, the fixed pen is connected to the pin for the gate. The remaining two pins are measured with a multimeter, if the measured resistance is infinity, the resistance measured after the pen is adjusted to a smaller value; in the resistance of a smaller measurement, the red pen is connected to the drain, the black pen is connected to the source.

②judge good or bad. Put the multimeter in R × 1 kΩ file, with the black pen connected to the drain of the IGBT tube, the red pen connected to the source, at this time the multimeter should be infinity. Touch the gate and drain with your finger at the same time, when the IGBT tube is triggered on, the pointer of the multimeter swings to the direction of the smaller resistance value, and can be stabilized at a certain value. Then touch the source and gate with your finger at the same time, when the IGBT tube is blocked, the pointer of the multimeter back to infinity. At this point, you can judge the IGBT is good.

Note: When making the second measurement, you should first short the source and gate.

( 2) choose a digital multimeter with a multimeter (diode file) of the red pen connected to the emitter of the IGBT tube, the black pen connected to the collector, the measured value of about 450 Ω; on the contrary, the red pen connected to the collector of the IGBT tube, the black pen connected to the emitter, the measured value should be infinity. And the control electrode and collector, emitter between a certain resistance value.

Note: When the IGBT tube with damping (included), there will be E-C pole conduction, C-E pole resistance infinity, that is, normal. When replacing the IGBT tube, the following issues should be noted.

As the IGBT tube work in high voltage, high current state, high operating temperature, easy to damage, in the actual maintenance of induction cooker failure, IGBT tube damage accounted for more than 70%. Therefore, in the maintenance of replacement should pay attention to the following two points.

①IGBT tube of the main parameters should be large rather than small, 2000 W induction cooker below the maximum current of 20 ~ 25 A IGBT tube, 2000 W or more induction cooker can use the maximum current of 40 A IGBT tube.

② Distinguish whether the IGBT tube contains a damping diode, the IGBT tube containing a damping diode can be replaced by an IGBT tube without a damping diode; if the IGBT tube without a damping diode is replaced by an IGBT tube containing a damping diode, a fast recovery diode should be connected between the drain and source of the newly replaced IGBT tube. The most commonly used IGBT tubes are FGA25N120, SGW25N120, H20T120, H20R120, etc.