Power supply IGBT driver short circuit protection test method

　The main problem that IGBT needs to solve in application is how to provide relatively complete protection for IGBT in the case of overcurrent, short circuit and overvoltage. Overcurrent fault generally takes a little longer to cause the power supply to overheat, so its protection is solved by the main control board. Overvoltage generally occurs when the IGBT is turned off. The larger di/dt produces a higher voltage on the parasitic inductance, which requires a buffer circuit to clamp or appropriately reduce the shutdown rate. After a short-circuit fault occurs, a huge current will be generated instantly, which will quickly damage the IGBT. The overcurrent protection of the main control board is simply too late, and it must be protected immediately by the drive circuit or driver. Therefore, whether the short-circuit protection function of the driver is designed to be perfect is crucial to the safe operation of the power supply. It is necessary to test whether the short-circuit protection function of a drive circuit is perfect before using it. This article introduces two test methods.

　　1. The first test method

　　In the figure, the PWM signal is sent to the signal input end of the driver. After the fault, the restart capacitor Creset=10nF, Dhv is a high reverse voltage fast recovery tube, the current limiting resistor Rlimit=10-100R, and the capacitor C=10-470uF. The oscilloscope can monitor the input and output ends of the driver. If Creset is not connected, the output of the driver output is a pulse of about 1ms, that is, the IGBT is short-circuited once every 1ms. Considering that some IGBTs may still overheat and burn out in this case for a long time, after connecting 10nF Creset, it will be short-circuited once every 12ms, ensuring the safety of the IGBT. For the selection of the overcurrent action threshold setting resistor Rn, please select the appropriate resistance value according to the description of Rn in the description of the tested driver and the forward volt-ampere characteristic curve of the tested IGBT. In the switching power supply of the single-tube circuit, after connecting the appropriate Creset, the usual short-circuit signal feedback optocoupler can be omitted, and the Luomuyuan driver itself can ensure the safe operation of the IGBT, which is also one of the characteristics of Luomuyuan products.

　　2. The second test method

　　Similar to the first method, the only difference is that the IGBT is not always short-circuited, and points A and B are short-circuited manually. This short-circuit test is more severe than the first one, and has higher requirements for the driver, because it is impossible to connect the short circuit in one go, and it is actually a series of on-off processes. Luomuyuan's driver can ensure the safety of your IGBT. Note: Pay attention to personal safety during the experiment, and it is best to add an isolation transformer at the power frequency input.