UCC28950: Snubber capacitor at PSFB Primary

Anoop kumar N

Part Number: UCC28950

Hello experts,

snubber capacitors are genarally placed across the half bridge to support high frequncy ripple current demand. In PSFB primary half bridge whether we require this snubber capacitors ? Since the current drawn from the supply is always lagging because of the transformer leakage and shim inductance, so do we need to provide capacitor across dc link to improve di/dt ?

Thanks and regards

Anoop kumar N

over 2 years ago

0 Mike O' over 2 years ago

TI__Guru* 86106 points

Hello,

I am reviewing your inquiry and will get back to you shortly.

Regards,

0 Mike O' over 2 years ago in reply to Mike O'

TI__Guru* 86106 points

Hello,

Can you send me a schematic of where you are placing the snubbers?

Regards,

0 Anoop kumar N over 2 years ago in reply to Mike O'

Intellectual 998 points

C7,C8,C13,C14 required ?

0 Mike O' over 2 years ago in reply to Anoop kumar N

TI__Guru* 86106 points

Hello,

I am revenging your inquiry and will get back to you shortly.

Regards,

0 Mike O' over 2 years ago in reply to Mike O'

TI__Guru* 86106 points

Hello,

Those capacitors are actaully across the H Bridge and are not snubber capacitors. C3 and R3 is a snubber circuit and C3 would be the snubber capacitor. I don't think you need C13 and C14 on the output. However, C7 and C8 will lower the total ESR seen by the bulk input capacitance. This is commonly done in power supply design.

I did notice that your current sense transformer is in series with the transformer. It is not recommended that you do this do this because during large signal transients the DC current will not be sensed correctly and cause control issues. It is recommended that you put the CT before the H Bridge. The data sheet gives recommendations for proper transformer placement of the CT.

Regards,

Power management

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UCC28950: Snubber capacitor at PSFB Primary