UCD3138A: use ucd3138A independently only with secondary

Hello,

Your question is that: Can you use UC7138 just to control DPWM falling edge, not the rising edge? If so, the answer is yes. You can tie CTRL to GROUND to disable rising edge which is related to primary side.

Thanks,

Sean

hello, thanks for your response, IF CTRL is tied to GND. who will decide the IN turn on edge?  only by the driver UCD7138? and also who decide the frequency.

UCD3138A controls DPWM rising edge, and UCD7138 just follows it. Also UCD3138A controls the frequency.

HI,sean, 

the point is that how to synchronous this DPWM with the current through the synchronous rectifier.

Hi, Lixin,

UCD7138 can sense body diode conduction time through DTC, and UCD3138A measures the conduction time, and then adjusts the SR pulse width. There is no need for external synchronization. UCD3138A controls the timing.

Regards,

Sean

hi, Sean.

yes, but it only adjusts the turn-off time, the turn-on edge is decided by the internal clock. how to make sure the turn-on is synchronous with SR. the EV board is an LLC topology, and the turn-on edge of the SR follows the turn-on of the primary DPWM. but I am not using it in LLC, I am using this controller on the secondary side of a wireless power transfer system. I cannot get information from the primary. how can I do to control the turn-on?

Hi, Lixin,

UCD7138 doesn't generate any gate drive signal. You may choose other SR driver which can produce the SR drive signal.

Thanks,
Sean

OK, I understand. thanks anyway