Electronic – Protecting low voltage high C capacitor with high voltage low C capacitor

capacitorpower supply

With regards to "catching" very high voltage transients on a DC power supply, is it possible to use a small, high voltage capacitor with a current limiting resistor to catch the transient in order to protect a much lower voltage, larger capacitor in parallel? Or will the transient destroy the lower voltage capacitor regardless? I assume that the high voltage capacitor and current-limiting resistor will have to be sized appropriately to be able to absorb the total energy of the transient.

Example circuit:

parallel capacitors

Best Answer

It's not clear how exactly you intend to connect the two capacitors. If they are in parallel, then they will see the same voltage, which then needs to be safe for the low voltage capacitor. If you are filtering the spike first thru a resistor and the high voltage capacitor, then another resistor to the low voltage capacitor, it may work depending on the time constants, the max spike voltage, and the total spike voltage-time integral.

Unless you are very sure about the exact characteristics of the spikes, this is probably a bad idea. How about clamping with a zener or transzorb or something instead?