UCC28780: How to delay PWMH or increase t_D(PWML-H) ?

Julien MENAGE

Part Number: UCC28780

Hello,

As you can see on the scope picture below, I think the PWMH needs to be delayed in order to get the High Side transistor in ZVS.

CH1 : Vgs of SR mosfet
CH2 : Vgs of high-side mosfet
CH3 : Current in primary of transformer
CH4 :Voltage at switching node

Tests conditions : Vin = 140Vdc, Vout = 22Vdc, Pout = 20% of Pmax

Is it possible ? Because it seems that at low Vin, it is fine but when the voltage goes up, the losses are too high for the cooling.

Thanks for your help

over 4 years ago

0 Pye Naing over 4 years ago

TI__Prodigy 590 points

Hello,

Your thread has been assigned. You should be receiving a reply shortly.

0 Jaden Ning over 4 years ago in reply to Pye Naing

TI__Expert 7080 points

Hi Julien,

You can add a RC filter on the input of high side drive , in this way , you can get a delay of PWMH. since it also bringing turn off delay . please minor increase RTZ pin resistor (maybe 10% increase is a start point) to compensate the turn off delay of high side .

Thanks

0 Julien MENAGE over 4 years ago in reply to Jaden Ning

Prodigy 200 points

Hi Jaden,

Thanks. I will try today.

Julien

Power management

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UCC28780: How to delay PWMH or increase t_D(PWML-H) ?