Why low value cap is placed in parallel to diode in SMPS?

[saurav_sdpl]

In power supply design SMPS we often see a low value cap placed in parallel to diode, both at primary and secondary side.

what is the real purpose for this.

 

[darla1]

Re: low value cap

for snubbing action

 

[babbage]

low value cap

in order to kill the high-freq ring

Added after 1 minutes:

u can serach the related application information-subber circuit from TI.

 

[raptor1981]

low value cap

this capacitor is used to filter out the high frequency AC component present in the output of the line. We can prove this as followingly " As the impedance of a capacitor is dependent on the frequency of the applied signal so for a pure DC this will behave as short circuit where as for a signal having a frequency component it will be a short circuit " . Thus forcing the signal to mave into ground.