Hello,
I would like to ask questions regarding UCC28782.
I am checking the behavior of ZVS.
The measured waveform is shown below.
(question 1)
Is the low-side current waveform operating normally?
(Question 2)
Low-side Vds waveform is not ZVS.
Is there any way to improve this behavior?
Is it because the settings per Rsws Csws are not optimized?
(Measurement condition)
VIN:AC100V
VOUT:5.1V
IOUT:12A
Best regards,
Hi Kaji-San,
Thank you for reaching out.
1. The current waveform looks ok. I think what you are seeing is the primary side - lower side switch + clamp current. The resonance time of the clamp duratio is less than the QH turn on time and this is expected. You might want to adjust the Clamp capacitor.
2. The non ZVS is due to fact that 1/2 * Lm * (Im-)^2 energy is not sufficiently high to discharge the switch node capacitance energy 1/s * Csw * (Vds)^2. You might want to check if this condition is met for ZVS to be met.
Regards,
Harish
