Hi experts,
The customer has came across the problem that the UCC28704 can't work normally in their flyback circuit.
Circuit parameter and test condition:
1. Vin_flyback= 24V, Vout_flyback = 24V.
2. Flyback circuit are using IGBT for it's switch mos, Vgs_min= -9V, Vgs_max= 15V.
3. Dual output and transformer is 100uH, 25:25:25.
The phenomena is that:
When flyback is on-power, pin Vdd will drop from 21V to 7.6V, and you can see there is 3 ripples appeared.
Measured we have tried:
1. C10 value is changed below 30pF or not used;
2. R19 = 0Ω;
3. C28 is not used.
4. Confirmed the transformer's connection way.
Result:
Problems not be solved. There still no Vgs for flyback's IGBT.
Next step:
Maybe the soft start is not be triggered.
Could you help support on this topic ? There is a little urgent, thank you.