Energy Losses in Semiconductor Devices of PWM DC/DC Converters

All the above relationships are obtained under the conditions of ideal power electronic devices, ideal inductor and capacitor energy storage elements and ignoring line impedance, that is, they are obtained under the conditions of ignoring the loss of Buck PWM DC/DC converter. Therefore, the input power Pi is equal to the output power Po, and the converter efficiency η=Po/Pi=1. But in fact, power electronic devices, inductor and capacitor energy storage elements, etc. are not ideal, they are lossy. For high-power Buck step-down PWM DC/DC converters, it is extremely important to reduce losses and improve efficiency, which not only saves energy, but also reduces heat, reduces the size and weight of the switching power supply, and improves reliability.

For Buck step-down PWM DC/DC converters, since various devices and wires have losses, the loss of semiconductor devices has the greatest impact on converter efficiency. It is usually calculated based on average loss: the loss Pv of the switch tube V includes the conduction loss Pv (ON) and the switching loss Pv (s), and the loss PD of the diode D includes the forward conduction loss Pv (on) and the switching loss PD (s). For the convenience of analysis, the switching loss that has a small impact on efficiency can be ignored.