UCC35706: Power management forum

Sreenivasan M

Prodigy 80 points

Part Number: UCC35706

HI,

I have Designed Forward converter 240W using UCC35706, Mode1, PWM frequency 130KHz,Dmax=0.65

Input : 180V AC to 240V AC / 50Hz

Output : 24V DC / 10A

a) For purpose of testing i have connected 12V DC External supply

b) Maximum output voltage is raising only to 6V & OSC pin (RC) is resetting.

unable to measure output switching voltage / PWM frequency.

regards

M.Sreenivasan

mBil:919880037604

over 2 years ago

0 Hong Huang over 2 years ago

TI__Guru 74115 points

Hi,

a) Please provide your schematics.

b) What was input voltage, and output load current? Please provide the OUT (pin 7) and ILIM (pin 1) waveform.

0 Sreenivasan M over 2 years ago in reply to Hong Huang

Prodigy 80 points

Hi,

Design Input: 240W Forward Converter

Vin min = 220V DC (180V AC/50Hz)
Vin max = 345V DC (265V AC/50Hz)
Vin(shutdown) = 210V DC
Vo = 24V DC
Io = 10A
F= 130KHz
Mode = 1
Dmax = 0.65

Observed zero volts Across ILIM & GND.

unable to attach schematic & waveforms in this forum, pl send your email id.

regards

M.Sreenivasan

msvasan@iepl.in

0 Hong Huang over 2 years ago in reply to Sreenivasan M

TI__Guru 74115 points

hong_huang@ti.com

0 Hong Huang over 2 years ago in reply to Hong Huang

TI__Guru 74115 points

Hi,

What is the IC FB pin waveform along with Vout = 6V? Please provide the waveforms with horizontal scale in 1ms/div and 10us/div.

Also can you try increase VDD to 13V so to make sure the IC is on UVLO on.

0 Hong Huang over 2 years ago in reply to Hong Huang

TI__Guru 74115 points

Hi,

I am summarizing the status of this support here. Basically your test shows the ILIM threshold (200mV) is very well exceeded which it looks the root cause to make the very narrow pulses in your test. When no power stage (no transformer) then the pulse width becomes normal. So you would need to resolve that ILIM threshold trigger to make peak < 200mV.

The layout needs to be optimized to reduce the noise.

If you need to help to review your layout please provide the layout design files.

0 Hong Huang over 2 years ago in reply to Hong Huang

TI__Guru 74115 points

Hi,

As we are in communication through email for the layout review, I will close this thread. If you have other support need, you can create a new thread.