UCC2894: Snubber and voltage clamp circuit for secondary diodes

Hi Umamaheswararao,

The RC snubber circuit values are typically determined by measuring the ringing frequency of the voltage across the diodes.

If you have an estimate for this ringing frequency you can follow the steps outlined here: Power Tips: Calculate an R-C snubber in seven steps - Power management - Technical articles - TI E2E support forums to calculate the necessary components. 

You may also have to tweak some of the values once you have a prototype developed and can measure the ringing frequency without the snubber.

Thanks,

Joseph

Hi Joseph,

Thank you for the reply. Can you please send some reference document for the clamping circuit as well.  It will be helpful for the off-line applications. 

Regards

Umamaheswararao

Hi Umamaheswararao,

For the clamping circuit, what are you trying to clamp? Is it more of a DC clamping circuit, or one used in the case of transient voltage spikes?

If you are trying to provide protection to the diodes from transient voltage spikes, I would recommend looking at TVS diodes to place in parallel with the rectifier diode so that it clamps any large voltage spikes.

Thanks,

Joseph

Hi Joseph,

Thank you. 

Actually, I want add clamping circuit at the secondary side rectifier diode (Secondary RCD clamp)  to limit the transient voltage oscillations. 

Regards

Umamaheswararao

Hi Umamaheswararao,

The RCD snubber would have a form similar to this:

You will need to tune the R and C values to match the desired damping for your application.

This app note: AN-776 20 Watt Simple Switcher Forward Converter (Rev. A) (ti.com) gives some guidance on calculations for the RCD snubber for the primary side switches. However, it is not as common to use snubbers on the secondary side rectifiers of the Active-clamp forward.

I have also seen many different variations of the RCD snubber based on desired behavior of voltage clamping and rise rate limiting.

Thanks,

Joseph