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Accurate measurement method of IGBT turn-on delay time

Issuing time:2018-02-01 14:02
Keywords: IGBT devices, conduction characteristics, control chip

Source: Electronic enthusiasts

1, IGBT conduction delay time measurement principle

The accurate measurement of the IGBT turn-on delay time is obtained by measuring the time interval between the IG-BT control signal, the drive signal, and the turn-on current signal. The flow chart is shown in Figure 3. Through the signal processing isolation circuit, the control signal, the drive signal, and the on-current signal are input to the time measurement chip TDC-GP2. Among them, the control signal of IGBT is used as the input of the START port of the time measuring chip TDC-GP2, and the drive signal and the IGBT on-current signal are used as two pulse inputs of STOP1 and STOP2. The time interval between the START and STOP1 ports is the delay time between the control signal and the drive signal. The time interval between the START and STOP2 ports is the delay time between the control signal and the IGBT turn-on signal. The time difference between the two is the IGBT relative to the drive. The turn-on delay time of the signal.

flow chart

2, IGBT delay conduction time measurement system design

2.1 Measurement System Hardware Design

The system is mainly composed of a pulse signal sampler, a pulse input signal shaping circuit, a TDC-GP2 measurement circuit, an AT89S52 single-chip microcomputer, a liquid crystal display circuit, a power supply circuit, and a clock circuit. Each measurement channel of the TDC-GP2 provides an enable pin that can be independently set for channel selection. The TDC-GP2 requires a 2-8 MHz high-speed clock for calibration. The TDC-GP2 only needs to use the oscillator when performing time measurement, and it can automatically control the oscillator on time.

The hardware circuit connection of the entire system is shown in Figure 4.

Hardware circuit connection of the entire system

The whole system is divided into three parts: single-chip system module, TDC-GP2 measurement module and display module. TDC-GP2, as the core unit of system measurement, can directly measure the signal time interval, and display the time interval value on the liquid crystal display after processing by the single-chip microcomputer. Compared with the commonly used measurement methods, this method requires fewer peripheral devices, a simple circuit structure, and low power consumption.

2.2 Measurement System Software Design

The measurement unit is triggered by the START signal and stops when it receives the STOP signal. The time interval between the START signal and the STOP signal can be calculated from the position of the ring oscillator and the count value of the coarse value counter, and the measurement range can reach 20 bits. At 3.3 V and 25°C, the minimum resolution of GP2 is 65 ps and the RMS noise is about 50 ps (0.7 LSB). Temperature and voltage have a great influence on the propagation delay time of the gate circuit. Usually, calibration compensates for errors caused by temperature and voltage variations. In the calibration process, the timing of one and two calibration clock cycles measured by TDC is shown in Figure 5. The measurement range is limited by the size of the counter:

Tyy=BIN×26 224△1.8μs.

TDC measures the timing of one and two calibration clock cycles

After initialization, TDC-GP2 high-speed measurement unit starts to work after receiving the START pulse, and stops working after reaching the set number of samples or measuring overflow. The software design focuses on setting the TDC-GP2 operating mode and reading its internal measurement data as required. At the end of the measurement, the ALU starts processing the data according to the settings of HIT1 and HIT2 and sends the result to the output register. If calibration is not performed, the ALU transfers 16-bit raw data to the output registers; if calibrated, the ALU transfers 32-bit fixed-float data to the output registers. Then through the microcontroller AT89S52 processing, the LCD display reads the time interval data, the measurement process shown in Figure 6.

Measurement process

3, Conclusion

The system makes full use of the excellent features of the TDC-GP2 and is implemented through its high-precision time interval measurement function. Measurement of IGBT turn-on delay interval. The measurement range of the system is 2.0 ns to 1.8 μs. Its main performance indicators can meet the requirements for measuring the turn-on delay time of the IGBT and have certain practical value. Since the current signal of the IGBT is a high-frequency signal in the order of nanoseconds, in the subsequent circuit design, the anti-interference capability of the system will be further improved to meet the requirement of measuring the conduction delay time interval. In addition, the operating frequency of the single-chip microcomputer is relatively low. In order to further increase the working speed of the system and even add more additional functions, a control chip with a higher operating frequency may be considered as the control core of the system; at the same time, higher accuracy may also be used. The time interval measurement chip improves the measurement accuracy.
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