PWM dimmable LED driver

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Hi All,

 

I have developed a PWM dimmable LED driver using TOP249. Circuit has single stage pfc. I'm switching the FET connected in series with LED to achieve dimming. Circuit is working fine when no dimming is applied. But when I apply dimming, peak current shoots up and LED starts flickering.

Since I'm working in a proprietary company, I am not at liberty to share the schematic of my circuit.

Can anybody suggest the reason and/or solution for this?

Hi,

We do not have your schematic so we will guess the possible cause of your problem.

Single stage PFC is very slow loop response therefore a dynamic load of 0 to 100% load in the output will cause instability.  FET connected in series with LED is not the right approach.  PWM dimming in a single stage approach can be done by converting the PWM signal into analog signal and then control the output current level accordingly.

Follow this approach in this DER:

http://www.powerint.com/sites/default/files/PDFFiles/der263.pdf

Share some waveforms, PWM frequency, output current, loop response to give us more understanding.

Regards,

PI-Jono 

I cannot use the approach shown in der-263 as changing the current in LED changes the color temperature of LED. So PWM switching is the only option available. Office is closed today. I remember following data:

1. PWM frequency = 1kHz

2. Output voltage = 29V (No Load. LED voltage is approx. 24V)

3. Current Limit = 2.8A(Peak) (At full load due to ripple caused by pfc, avg current is approx. 2.1A)

4. Whenever flicker happens, output voltage distorts from pure sine wave. It has alternatively 1 high peak and 1 low peak.  Also flickering happens over a certain range of dimming which varies from piece to piece. But generally between 50% to 70% all piece has flicker.

 

I will share the waveform on monday when I reach the office.