Selection of Capacitors for Power supply(II)

Surge voltage protection

Modern power semiconductor devices with high switching frequency are vulnerable to potentially damaging voltage spikes. Surge voltage protection capacitors (such as EPCOS B32620-J or B32651.56) that span both ends of power semiconductor devices protect semiconductor devices by limiting peak voltages by absorbing voltage pulses. The surge voltage protection capacitor becomes an important member of the power component library.

The rated voltage, current value and switching frequency of semiconductor devices influence the selection of surge voltage protection capacitors. Because these capacitors bear steep DV/DT values, thin film capacitors are the appropriate choice for such applications.

When the rated voltage is as high as 2000VDC, the typical capacitance rating is between 470 PFN and 47NF. For high-power semiconductor devices, such as IGBT, the capacitance can be as high as 2.2 μ m F, and the voltage is in the range of 1200 VDC. Capacitors cannot be selected solely on the basis of capacitance / voltage values. The required DV/DT value should also be considered when selecting surge voltage protection capacitors.

The dissipation factor determines the power dissipation inside the capacitor. Therefore, a capacitor with a lower loss factor should be selected as a replacement.