Hi,
I am trying to design a PFC circuit (370V, 1kW) using the UCC28019. A prototype single-layer board has been made for this purpose and calculations were done as per design note SLUC069. Initially, a couple of 60W bulbs (parallel) were placed in series with the input of the board, and the Output was observed. The mains is a 240V source. The NTC thermistor was heating to quite an extent along with input bulbs glowing brightly (slow flickering).
I then tried to provide it with a variable input through an autotransformer without the series bulb and that ended up blowing the thermistor and the MOSFET (all leads were short). This process was repeated again but now monitoring the gate waveform and found out that the gate PWM becomes almost close to 100% once the input crosses the VIN enable threshold level which in our case was around 85V. Before reaching this level, the gate was low.
I also tried removing the MOSFET and replace the IC and then operate it with varying input and found out that the same thing happens as above with some of the pin voltages being
VCOMP = 7.55V, VSEN = 1.57V, VINS = 2.08V, ISEN = 0, VCC = 11.85V and ICOMP = 1V.
The Inductor waveform (wire through toroid core) shows that the PWM (65kHz) to be in kind of a burst mode followed by a slow switching waveform (~12Hz) which is visible through the flickering of the input bulb. There are also some spikes on the waveform when the PWM is active which makes me believe that perhaps the overcurrent (PCL) might be triggering. The images are of PWM and slow flickering respectively,
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The gate waveform is as follows,
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The PWM triggers after every 20m sec (T = 80m sec, 12.5Hz) as seen above.
Note: A 60W Incandescent bulb has been used as a load. The component values in light blue are the ones that are used in the circuit.
Here's the schematic of the PFC board
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inductor waveform with visible bursts of PWM
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Any kind of help or suggestion is highly welcomed and appreciated,
Regards,
Ashwin619.