| Si C Schottky diode is a kind of semiconductor of wide bandgap and high backward voltage that could endure high current. Its rectified current can be up to thousands amperes while forward voltage is only about 0.4V, but its reverse recovery time is only a few nanoseconds. Now it is in wide application, including high-frequency and low-voltage switching power supply, high current rectifier diodes, protection diodes, it can also be used as secondary power rectifier in color TV, high-frequency power rectifier and so on. Si C Schottky diode recently is developing more and more fast, and its operating power is also growing. The cooling package of Si C Schottky diode is one of the most important factors that associated with the device temperature rise and thermal resistance, the Si C Schottky diode device reliability is based on thermal resistance and temperature rise. With growth of the power of the Si C Schottky diode, heat will be a key issue that needs to be resolved, so the measurement of thermal resistance and temperature, optimization package is essential for its future development. In this paper, the PN junction diode junction voltage and temperature are related, we built high-power Si C Schottky diodes thermal resistance measurement system combining with the structure function method, the establishment of the thermal resistance measurement platform by engineering methods that can clearly analyze the different layers of Si C Schottky diode structure thermal heat transfer path..In this paper, Si C Schottky diode being tested is high-power devices of forward package which means the negative legs of the device components and the brass heat fan are connected, while backward package means the positive legs of the device components and the brass heat fan are connected. To the heat sink of the copper holder of the lower surface device, different packages have different directions of current, we define the direction of current of forward package as forward current and the direction of current of backward package as backward current. The high power laser device being tested is corresponding to the backward current thermal resistance tester, but the previous thermal resistance tester is not alright for measuring the forward-packaged devices like Si C Schottky diode. Because of the heat fan is directly connected with the temperature platform, study shows that: This connection will produce a voltage difference between the negative legs of the Si C Schottky diode and the ground, and it will seriously affect the accuracy of the thermal resistance measurement.We redesigned the circuit, enabling to test the forward package device and the backward package device through the working mode selection section. With previous method, we designed the circuits for the forward current part and its software and equipment and so on, and we integrated the two current direction system together for the new thermal resistance tester. In this paper, we select the forward current working mode for the Si C Schottky diode, and the backward current working mode for the laser device. This avoids the impact of the voltage difference between the Si C Schottky diode and the ground.The way to work it out:Firstly, we designed this thermal resistance tester that has forward current and backward current working mode for the Si C Schottky diode and the laser device, and the electrical circuit design include logic module circuit design and matching chassis design. Its function module circuit design is composed of working mode selection circuit, working circuit, testing circuit, switching circuit and amplifying circuit; and the logic module circuit design is based on an asynchronous serial communication protocol of FPGA, and it is composed of control section, baud rate generator, serial transmission section, serial receiving portion, and through the way of transferring the serial data into parallel executable command to enable communication with computer, and ultimately controls the switching circuit and the heating circuit, and to a variety of real-time acquisition of voltage and current feedback information to the computer for the purposes of monitoring.Secondly, we programmed the FPGA to convert the serial digital signal into recognizable signal for the A/D converter, then A/D converter would outputs a constant voltage signal to make sure testing and working circuit producing constant current, with the switching circuit, we can control the heating time, and to switch working mode into testing mode.By writing programs and supporting software, the digital signal is converted by a serial computer to be sent to the FPGA DAC recognizable signal, digital-analog converter outputs a constant voltage signal, the constant current circuit and the test circuit through the heating output, with the state of the switch circuit heating circuit turned on and off to control the heating time of the device under test, the device under test when the temperature rises to steady state heating circuit is turned off to cut off the heating device under test which is used to power heating current, and switch to the temperature rise can be ignored for testing low-power current.Thirdly, with the structural function algorithm for data processing after the data is obtained by capture card from the amplifying circuit and is transmitted to the computer, we obtained the thermal data.Fourthly, we completed tester package design and engineering practice, after the completion of all hardware and software debugging, complete chassis cooling and so on.Finally, with the electrical method we did a research on Si C diode thermal resistance. And we understand the Si C diode heat transfer path.The result of this research will help to improve the level and the function of commercial and technical semiconductor thermal resistance tester which has practical significance and application value in the domain of the semiconductor thermal resistance testing. |
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