UCC28511: Two transistor forward converter

Ivan Blaskovic

Part Number: UCC28511

Dear all,

I am designing PFC and two transistor forward converter with UCC28511 controller. PFC works well, but I have problem with forward converter. When I remove MOSFETs, gate signals are present, but when i put MOSFETs back on PCB, there is no any signal on gate of forward converter. I am driving these MOSFETs with pulse transformer and FAN3122 controller. Do you have any idea what am I doing wrong?

Ivan

over 5 years ago

0 John Griffin1 over 5 years ago

TI__Mastermind 34465 points

Hello Ivan
The FAN3122 is a low side driver only so you must have some other method of driving the high side forward switch.
When you disconnect the driver section attached to the GT2 output pin of the UCC28511 do you see a gate drive ?

Regards
John

0 Ivan Blaskovic over 5 years ago in reply to John Griffin1

Prodigy 40 points

Hello John,

When I disconnect the driver section, there is a gate signal on GT2 pin. You can see gate drive circuit below.

0 John Griffin1 over 5 years ago in reply to Ivan Blaskovic

TI__Mastermind 34465 points

Hello Ivan,
I dont see anything amiss with the schematic.
You know that the UCC2851 is working properly and the FAN3122 appears to be wired up properly.
You probably need diodes from the OUT pins up to VCC and to GND.
This will protect the output section of the FAN3122 from inductive ringing .
You should maybe disconnect the gate driver transformer and see if this is overloading the driver.
It could be the transformer is saturating and not suitable for this duty cycle and frequency.
Regards
John

0 Ivan Blaskovic over 5 years ago in reply to John Griffin1

Prodigy 40 points

There was (and still is) a problem with current and voltage feedback loop. I got some voltage on the output but it was too high and I can't regulate it. Thank you for your time and suggestions.

Best regards,

Ivan

Power management

Power management forum

UCC28511: Two transistor forward converter