LNK408 LED driver is flickering at low brightness

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Flickering at low brightness

 

I use the LNK408 in a LED driver and it shows subtle flickering when dimmed to low brightness. The feedback current is approx. 50-60uA to get low output power. I tried various modifications to stabilize all control currents into the chip but I it didn't change much. Even with feedback current, supply current (BP) and V-pin current drawn from a battery it's still there. At mains I tried it with an incandescent lamp parallel to the dimmed LED supply but without success. Flickering frequency is from 1-10 Hz and it's only a little modulation of the output current but you can see it and won't be accepted by the customers.

Could you please help with a potential root cause or test to identify the root cause.

 

Best regards

bimota_toni 

The low frequency shimmer at minimum conduction angle might be coming from the line and also because of not constant firing angle from the dimmer or noisy line. You can try to increased the damping and/or increase the output capacitance to minimize this problem.