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Use NTC thermistor to detect temperature of IGBT
2018/10/18 02:10:48

IGBT is Insulated Gate Bipolar Transistor, it’s a composite full-controlled voltage-driven power semiconductor device which is made up by Bipolar Junction Transistor and Metal Oxide Semiconductor.

Currently, most of the IGBT Driver Boards don’t have overheat protection in the market , only installed a temperature sensor on the radiator near the IGBT module, the temperature signal is collected into the processor, the temperature of the radiator surface is calculated by sampling value to estimate the inside temperature of the IGBT; the temperature measured by this method is not very reliable, the installed position and thermal resistance of the temperature sensor on the radiator have great influence on the sampling value.

Nowadays, many IGBT manufacturers would encapsulate an NTC thermistor inside the IGBT module, which is used to measure the shell temperature of the module. This is not only high precision, but also very accurate, not affected by the installed location and other factors. The NTC thermistors researched, developed and produced by EXSENSE Electronics Technology Co., Ltd. have the characteristics of high precision, high sensitivity, high reliability, which could conduct the internal testing of the IGBT module better. This time, let’s introduce a IGBT temperature measurement method based on optical fiber.

As shown in the above picture, this method are including the following steps:

1st, making connection between the NTC thermistor and power supply through the three-terminal regulator, then use the resistor to in series partial pressure, make the electric current through the NTC thermistor is 4mA basically; collect the voltage signal on the NTC thermistor;

2nd, from V-F converting unit which has the converting chip and peripheral circuit, makes the voltage signal to frequency signal according to the ratio of 1V:1kHz;

3rd, from transmitting unit, converts frequency signal to optical signal first, then transmits optical signal to receiving unit through optical fiber;

4th, from receiving unit, restores the light signal to frequency signal first, then transmits frequency signal to control unit; Control unit is including a DSP chip TMS320F2812 with a CAP capture interface, CAP capture interface communicates with receiving unit;

5th, the control unit detects the frequency of the frequency signal first, then calculates the temperature of IGBT, the detection end.

This measurement method uses the optical fiber transmits signal, the ability of anti-electromagnetic interference is strong, which is suitable for the application in the electromagnetic interference in high requirement; The temperature of IGBT is detected by collecting the voltage of NTC thermistor, play a role of real-time monitoring, to avoid the IGBT overheating burned; The whole method is streamlined, the cost of hardware is lower, which can reduce application cost significantly.

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