our company try to use linkswitc-pl family to develop LED driver for 12 leds. I used RDR251 as based solution to develop schematics and PCB. Now i solder PCB and components and used transformer maded by myself which was calculated in PIXLs Designer software. Transformer is EFD20, Nprimary=87, Nsecondary=30 turns, air gap 0.86 mm (i used two parts of isolation in ferrite for both sides 0.4 mm thickness). Output voltage range is 20.7-40V.
First of all - i disconnect dumper, bleeder and other circuits for dimming. And tried to switch it on. It's started and stabilized current. PFC works very well - i maded FFT and see that there 50 Hz harmonic and other below 3-5% - so it's very good for me.
I leaved it for about all night to check overheating at full load - it's ok. I got efficiency about 76.54% now.
But there two problems which have to be solved now:
1. when i changing input voltage - there is no stability in output current and leds are flickering. Transformer is clickin (like a mouse) while i changind input voltage. Output current depend of input voltage too much - 0.29-0.37 A for all input voltage range. I want to increase transformer's number of turns in primary and secondary winding and increase air gap. I saw few messages where you recomend to use calculated value. But...
2. there are flickering with frequency 100 Hz at output with Pk-Pk value about 6.6 V. It's too much for lighting - flicker is bad for eyes and brain. I tried to increase output capacitance about 2 times and got 4.4 V Pk-Pk voltage ripple. As i understand 100Hz wave ripple associated with input voltage (there is no input capacitance).
3. I want to increase efiiciency to 85% (but understand that it'l be very hard)
Can you advice for me someting to solve problems which i described?