Output voltage undershoot in flyback based power supply

[Libin]

Hi Friends,
I made one flyback converter and observed voltage undershoot(negative spike) at 12Vdc output rail (12VDC voltage is dropping to 7V for small duration of 2 to 3 nanosecond) frequency of undershoot is same as switching frequency.
Give me some tips for eliminating voltage undershoot in flyback based power supply.

Best regards
Libin

 

[vilela]

Libin, could you show us the circuit?
A capacitor employed as a high frequency filter may be a solution, but it is hard to tell without seeing.

 

[wky]

Could it be a measurement problem ? Such as noise pickup by the scope probe ?

 

[Libin]

Dear Vilela,

Thanks for your response, please refer the attached schematic.
regards
Libin