UCC27624DGNEVM: 2-switch flyback topology. UCC27624-Q1 to drive SiC mosfet

Flyback transformer

LP= 2930uH
Leakage Inductance = 40uH

N1:150
N2=10
Naux=20

Hey,

Thanks for reaching out to TI with your questions regarding the UCC27624.

We have the following Application Note that discusses operation in a pulse transformer:

Why use a Gate Drive Transformer?

Please measure OUTA and OUTB at the pins of the gate driver to better understand the condition that the driver is in during this.

In addition to the 0.1uF capacitor on VDD, it would be advised to put a 1uF in parallel there as well placed close to the gate driver as advised by the power supply section of the datasheet.

Thank you,

William Moore

My main problem is the oscillation occurring in the MOSFET's drain-source voltage. Can you help me with this?

Hey,

Yes, I see that the D-S voltage is causing issues. But, understanding what OUTA and OUTB are doing at this time will provide guidance as to what is going on in the system. Please provide these waveforms under this condition as well as the VDD waveform.

Thank you,

William Moore

VDD startup supply: 24V, there is no problem

Vaux VDD IC PİN:



OUT A and OUT B signal:





OUT (gate signal )AND MOSFET Vds

Hey,

There is a lot of ringing and noise on the OUTx signals. This should be mitigated because as you see with the OUT and Vds waveforms, as OUT rings back up the MOSFET appears to begin conducting again.

One way to help mitigate this ringing is to increase gate resistance. Have you tried that? Also, please take a look at this FAQ on output overshoot mitigation tactics.

[FAQ] What happens when output overshoot or undershoot occurs and how to address it?

Thank you,

William Moore

Hey,

Are there any updates or further questions regarding this?

Thank you,

William Moore

Hi,

I think the main problem is the Miller plateau. To reduce the Miller plateau, I will try to decrease the transformer leakage inductance. In the circuit, I tried reducing the Rgate resistance to mitigate the Miller plateau issue that occurs when the MOSFET transitions to the turn-off state, but it was not completely resolved. Do you have any other suggestions?

Transformer specifications:
Lp = 2930 µH
Lleak = 40 µH max, 22 µH typ
Np = 150, Ns = 10, Naux = 20