Hello,
I'm debugging an active clamp forward converter using LM5026, with the following parameters:
- Vin = 54V
- Vout = 48 V
- Pout = 250W
- Inductor 240 uH
- f_sw=130k
- Cclamp = 30n
- N mosfet : Infineon IPB117N20NFD
- P mosfet: ON Semi. FQD4P40
Transformer parameters:
- n = 2.5
- Magnetizing inductance 140uH
- Leakage inductance ~0.6 uH
The problem is that a voltage ringing appears at the gate of the N mosfet during toff. The oscillations are so high that it seems that the transistor is switched on several times during the oscillations, leading to current oscillations at the clamping capacitor. This has become an EMI issue at radiated emissions, as the oscillations have a frequency of approximately 100 MHz.
I attach an oscillator image, CH1 is Vds and CH2 is Vgs of the main mosfet.
Any help will be appreciated,
Thank you,