Relationship between du/df and load current

The du/dt generated by power switching devices is one of the main sources of interference in switching power supplies. The magnitude of |du/dt| generated by IGBT and power MOSFET when turned on and off is different. This is a problem that must be paid attention to when analyzing and dealing with interference in power electronic devices and systems. The figure is the test result of an IGBT voltage-type bridge inverter circuit. Figure (a) shows that as the load current increases, the value of |du/dt| generated by the shutdown increases, while Figure (b) shows that the change in load current has little effect on the |du/dt| of the turn-on. Both experiments and analysis show that due to the different |du/dt| generated when turning on and off, the interference pulses generated by the outside are also different.

Figure 1. Relationship between voltage jump and load current during IGBT switching operation