I have designed 20 watt led driver based on TNY280 switch with additional current control circuit in secondary. Unfortunately some of the drivers have flicker problem at start up for almost 20 seconds (mostly when input voltage is higher than 220 Volts). The output voltage has 200 mV fluctuation in 100 Hz (the supply frequency is 50 Hz). I have changed every part of the board but only TNY280 change affects the ripple.
When I monitored the EN/UV pin of the TNY280 it was full of low frequency spikes! The idea was putting a low ESR capacitor on the pin. In the amazing way it works! And the fluctuation and flickers are vanished.
So I wanted to know what really goes on? Where this 100 Hz ripple come from? Is my idea true? Is there any other way to solve the problem?