UCC28056: ZCD threshlod detection

fred cheng

Prodigy 140 points

Part Number: UCC28056

Hi team.

when in DCM,

which voltage here is the threshold voltage that trigger when to start TDCM?

Is it VZCBorise or VinSyn ?

over 3 years ago

0 Ray DiCecco over 3 years ago

TI__Genius 11350 points

Hi Fred,

VInSyn is used to detect zero crossing (which occurs at the DCM threshold, or CrM).

VZCBoRise is used to determine when the line-in is above 85Vac.

Regards,

Ray

0 fred cheng over 3 years ago in reply to Ray DiCecco

Prodigy 140 points

Hi Ray,

Vinsyn is not fixed but dynamic,

would you help elaborate how it works?

0 Ray DiCecco over 3 years ago in reply to fred cheng

TI__Genius 11350 points

Hi Fred. Please give me a couple of days to respond to this thread. Thank you for your patience.

0 Ray DiCecco over 3 years ago in reply to Ray DiCecco

TI__Genius 11350 points

Hi Fred,

I apologize for the delay. I didn't realize I had typed the response below but never clicked the "Reply" button. This was just brought to my attention.

Vinsyn(α) is the average drain voltage for one switching cycle. This average of the rectified input waveform is going to change depending on where it is being sampled. However, the inductor current is zero during each switching cycle when the voltage on ZCD is equal to Vinsyn(α).

Regards,

Ray

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UCC28056: ZCD threshlod detection