UCC28780: UCC28780

user5781628

Part Number: UCC28780

Hi,
In figure 27 in datasheet, it shows three moment for "ZCD through VAUX" in LPM burst period.
In my understanding, "ZCD through VAUX" refers to QL turn on. So there will be two ZCD moment in each burst period due to only two times of QL turned on.
Why it shows "ZCD through VAUX" at the moment that the magnetizing current drops to zero in this figure?

How to understand the third "ZCD through VAUX"?

BR
Eleven Chen

over 6 years ago

0 Benjamin Lough over 6 years ago

TI__Mastermind 27105 points

Hi Eleven,

ZCD through VAUX refers to zero current detection using the AUX winding. It is detecting when the magnetizing current is 0A or when the magnetizing current drops to 0A. This is why you see "ZCD through VAUX" at the moment the magnetizing current reaches 0A.

Best Regards,
Ben Lough

0 user5781628 over 6 years ago in reply to Benjamin Lough

Intellectual 970 points

Hi Lough,
You know, for the first two ZCD detection is used to turn on PWML.
When magnetizing current drops to 0A, there will be the third ZCD. what is the purpose of the third ZCD?

BR

0 Benjamin Lough over 6 years ago in reply to user5781628

TI__Mastermind 27105 points

Hi Eleven,

RUN changes from high to low on the last ZCD.

Best Regards,

Ben Lough

0 user5781628 over 6 years ago in reply to Benjamin Lough

Intellectual 970 points

Hi Lough,
Is there any other purpose of the last ZCD?
Thanks.

BR

0 Benjamin Lough over 6 years ago in reply to user5781628

TI__Mastermind 27105 points

Hi Eleven,

The last ZCD is indicating that the current has dropped to 0A. You will see RUN change from high to low and the controller will enter its low power wait state.

Best Regards,
Ben Lough

Power management

Power management forum

UCC28780: UCC28780