Design of Triode Aging Test System Based on LabVIEW

For some power devices (power transistors, VDMOS, IGBTs, etc.), the ability to withstand cyclic stress can be tested by regularly energizing and de-energizing the components, and applying electrical and thermal stress cyclically. Based on the above principles, with the help of the visual programming language LabVIEW and the NI series sb RIO-9612 board, this paper designs a triode aging test system, which meets the test requirements of the national military standard GJB1036, and the sampling time of each station is not more than 4μs The sampling period of a total of 64 stations is no more than 300μs, which meets the requirements of fast control without losing accuracy. The sampling resolution of voltage and current reaches 12 bits, and the accuracy reaches 1%, thus controlling the junction temperature error of the device. At present, the system has been put into operation, and the experimental results have reached the needs of users, which has high practical value.

    With the increasing requirements for the quality of electronic products in aviation, aerospace, energy industry and other fields, the reliability of electronic products has received more and more attention. Electronic products encounter different environmental conditions during use. Under the stress of thermal expansion and contraction, electronic components with poor thermal matching capabilities are prone to failure, leading to electronic product failures and huge human and financial losses. The aging test of electronic components is to imitate the use state of the equivalent products. Through the test, the non-conforming devices are eliminated, and the quality of electronic products is effectively controlled in the early stage of processing to ensure the reliability and stability of the use of electronic products.

    In response to this situation of electronic components, we have developed an aging test system that can mainly target power devices (power transistors, VDMOS, IGBTs, etc.), by regularly energizing and de-energizing the components, and cyclically applying electrical stress and heat Stress, test its ability to withstand cyclic stress.

    1 working principle

    By energizing and heating the transistor, the transistor will work at the current constant power. After a period of time, the junction temperature of the device will continue to rise due to the heat generated by the transistor. After reaching the set value, the constant current source and the constant voltage source will be disconnected. Ventilate the device to lower its temperature to the set value. Repeat this process to calculate the heating time and cooling time of the device more accurately, achieving the purpose of intermittent testing. The basic working principle diagram is shown in 1.



    The thermal resistance of semiconductor devices is usually defined as:



    Where RθJX = the thermal resistance from the device junction to the specific environment (the substitute symbol is θJX) [℃/W];

    TJ = device junction temperature under steady state test conditions [℃];

    TX=reference temperature of the environment [℃];

    PH=equipment power consumption [W];

    The junction temperature of the device under test conditions can be expressed as:

    Tj=TJ0+△TJ

    Where TJ0 = the initial junction temperature before heating the device [℃];

    △TJ = device junction temperature change

    The temperature sensitive parameter (TSP) is used to express the change in junction temperature, the formula is:

    △TJ=K×△TSP

    Among them △TSP=change of temperature sensitive parameter [mV];

    K=The constant defining the relationship between TJ and TSP [℃/mV];

    Temperature sensitive parameters can be expressed as:

    TSP=Ie×-4Vce

    Among them Ie = constant current source value added at the time of cooling measurement [mV];

    Vce=junction voltage value of the device [mV];

    The K coefficient is the relationship between junction temperature and junction voltage. The K coefficient of the retainer is constant. The coefficient of K is different for different devices. It can be found in the data of the test device or given by the manufacturer. The calculation formula can be expressed as:



    Among them, TJ1 and TJ2 are the junction temperatures at two moments, and Vce1 and Vce2 are the junction voltages corresponding to the junction temperature.

    2 System architecture

    The system adopts the structure of PC + sbRIO-9612 + main control board + drive board + aging board, as shown in Figure 2, the PC and 9612 communicate through the network port, and the 9612 and the main control board through the digital I/O port Communication, sbRIO-9612, main control board, and drive board are powered by a switching stabilized power supply. The program-controlled power supply provides working power for the devices on the burn-in board. 16 differential ADs are used to collect the current of the device under test on the burn-in board. Signals such as voltage and power supply temperature. The system uses sbRIO-9612 plus an expansion board to form a lower computer as the main control board of the system; the main control board and the drive board use bus communication, and the main function of the drive board is to convert the 20 pairs of differential signals from the main control board (hardware implementation) For the driver board FPGA, use 20 signals to communicate with the sbRIO-9612. The sbRIO-9612 realizes the on and off of the power supply, constant current source, and drain/source by controlling the registers in the FPGA to establish a power cycle and appropriate sampling conditions. The hardware schematic diagram is shown in 3.





    The drive board and the burn-in board are respectively connected by two docking sockets, and the current and voltage sampling signals are transmitted back to the sbRIO-9612 board for AD conversion and then sent to the host computer.

    3 Work process and realization

    3.1 Introduction to LabVIEW

    LabVIEW is a program development environment. It uses the graphical programming language G to create the source program in the flowchart. The LabVIEW FPGA module extends the LabVIEW graphical development platform to the field programmable gate array (FPGA) based on the NI reconfigurable I/O (RIO) architecture hardware platform. ).

    3.2 Work flow

    At the beginning of work, the host computer sends control commands to sbRIO-9612 according to the TCP/IP protocol. After receiving the instructions, according to the host computer operations, sbRIO-9612 sends the corresponding instructions and related parameters to the main control board, and the main control board controls the drive The board executes instructions, and then controls the aging board to perform related operations.

    sbRIO-9612 is mainly composed of two parts, FPGA part and RT part; in the division of work, due to the speed requirements of the system, including fan control, program-controlled power supply control, temperature and frequency reading, ADC acquisition, DAC transmission number , Differential data transmission and other modules are allocated to the fast FPGA part for execution, and the slower RT part mainly implements the analysis of the upper computer instructions, the aging work control and the data transmission work of the lower computer to the upper computer. LabVIEW FPGA work flow chart is shown as in Fig. 4.



    3.3 Realization of the work process

    3.3.1 Overview

    Before the work starts, first connect to the lower computer. After the connection is successful, call the self-check module to perform self-check on the burn-in board that will be tested. After the self-check is successful, the upper computer sends the parameters to the lower computer, and then sends it to start control Command, the lower computer polls the control command word of each board. After the board starts to work, it will send the heating current, measurement current and programmed voltage required for the work to the driver board through the serial data transmission module, and load it to the corresponding driver board through the driver board. On the aging board, heat the device and record the time at this time, which is the heating start time. When the difference between the current time and the heating start time is greater than or equal to the on time, stop heating, turn on the fan, record the heating end time, and start AD collection , Calculate the junction temperature according to the collected current and voltage, send the value back to the upper computer, and the upper computer draws a curve according to the temperature change. When the difference between the current time and the heating end time is greater than or equal to the off time, the cooling is completed and the measurement is ended, and the next cycle is entered. After the number of cycles is reached, the board is placed in an idle state.

    3.3.2 Realization of accuracy and switching speed

    1) High-speed ADC acquisition

    The SbRIO-9612 integrates an AD acquisition chip. The 16-bit AD can guarantee its sampling resolution of 1‰. At the same time, the conversion time of 4μs guarantees the AD sampling speed; in order to eliminate the influence of common mode noise, 32 channels of AD Converted to 16 differential inputs, each channel continuously takes 8 values each time during acquisition and the average value is the result of this acquisition. At the same time, it is switched with the high-speed switch used in the aging board to ensure the accuracy requirements of the acquired data. The figure below shows the current junction voltage of the NMOS tube (model IRFP460) and the tube junction temperature measured at the current moment through LabVIEW at a set measuring current of 10 mA and a programmable voltage of 12 V. The room temperature is installed in each block The temperature sensor on the aging board is 17.3 20 6 degrees Celsius. It can be seen from Figure 5 that the values of 16 channels collected by AD begin to fluctuate after three decimal places, which ensures that the calculated value of △Vf is after the decimal point. The two began to fluctuate.



    The system can complete the collection of all station junction voltages within 20μs after the heating state is switched to the measurement state. In order to meet the requirements of fast acquisition, when writing the program, taking into account the high real-time problem of ADC, the acquisition part is allocated to the sbRIO-9612 FPGA Finished, the Onboard Clock of sbRIO-9612 is 40 MHz, which is a cycle of 0.025μs. When writing the FPGA program, the ADC acquisition configuration (that is, the switching command execution of the switch) and the acquisition data are placed between two adjacent frames of the sequence structure , Taking into account the switching time, add 1μs waiting in the middle to ensure the reliability of the data, and then start data acquisition, the ADC acquisition part of the program is shown in Figure 6.



    2) Differential data transmission

    This module realizes the communication between sbRIO-9612 and FPGA. The communication method is asynchronous bus access. Data is sent and received through serial DAC. The so-called serial DAC is under a certain clock (clock cycle is 80 MHz). Perform serial data transmission at a fixed timing. First assign the address to the port. The address is a total of six bits, namely A0-A5. The upper four bits are the address bits (control board number), and the lower two bits are the driver board register addresses; then Put the data on the data bus, the data format is U8, set WR/RD high, then: DR position is low, keep two clock cycles, DR is set high, complete the serial DAC write data; similarly, set the address first when reading data On the bus, WR/RD is set low, DR is set low, maintaining two clock cycles, the data reading is completed within two cycles, and DR is set high to complete the serial DAC reading data. The entire communication module realizes the control of SbRIO-9612 to FPGA in accordance with the communication protocol.



    4 Experimental results

    When the ambient temperature is 25°C, the temperature rise is 80°C, the heating constant current source is set to 50 mA, the constant voltage source is set to 5 V, the on time is set to 2 300 s, and the off time is set to 7700 s. In the timing mode, every time The junction temperature diagram is obtained by sampling every 50 ms, as shown in Figure 9. At the end, the temperature is basically difficult to reach the initial 25°C due to the increase in the surrounding temperature, but the temperature is reduced to the allowable range of error. In the figure, the red line is drawn by the temperature change data measured by the sensor attached to the back of the NMOS tube, and the black line is drawn by the data calculated from the collected data through the junction temperature calculation formula. In comparison, the sensor's measured data change The trend is consistent with the calculation result data change, which shows that the measurement result is accurate.



    5 concluding remarks

    The article introduces an aging test system on SbRIO-9612, using LabVIEW to realize the work of controlling an aging test system. The system achieves the accuracy and resolution of scheduled data acquisition, and meets the requirements of rapid acquisition and rapid control. In practical applications, it has reached a very high level. Good results have high practical value.