Protecting semiconductor devices
2025
The power semiconductor devices are turned "on" and "off" to converter and transfer energy from the source to the load. These devices are normally off. When the supply voltage is switched on, the device is in the off-state and withstands the supply voltage, ideally no current flows through the device. The rapid rate of the rise of the voltage across the device from zero voltage to the full supply voltage causes an internal current flow through the internal junction capacitance of the device and this may cause device failure. Due to the switching action of the devices, there are instances when one device is turning off while another device is turning on to maintain the continuity of the current flow. Ideally, when one device is turned off, another device should turn on immediately. However, practical devices have limitations and require finite time to fully turn on and turn off. As a result, a situation may occur when the voltage source is short-circuited during the turn-on and -off time intervals of the two devices. The rate of the rise of the current must be limited, not to exceed the device di/dt specifications. Also, a finite amount of power loss occurs across the semiconductor device due to the finite on-state resistance of the semiconductor device. The heat generated due to the power loss must dissipated to keep the junction temperature within the specified limits. These devices must also be protected due to the rising current under faulty conditions with the power electronic systems.