I have designed and built a prototype with the aid of PI Expert Designer tool according to the following characteristics:
- Vinput = 85-305Vac
- Voutput / Ioutput = 12Vdc / +700mAdc
I also attach you the schematic of the converter, which was taken from DER-528 application note (14 W Non-Dimmable, High Efficiency (>86%), Power Factor Corrected Isolated Flyback LED Driver Using LYTSwitchTM-5 LYT5226D) as a starting point to design my own converter.
The problem is the converter is not started up once the line input voltage is connected.
In fact, between 30Vac-60Vac the converter tries to start up and the output leds are blinking but not lightning continuosly which in returns means the converter is not really started up and operating well.
For this voltage range, output voltage is near the output led (Vf 12 aproximately) and the auxiliary winding is triying to reach the high level, which is set up at 20Vdc, but never reaches it because of blinking.
So, I assume the converter is not started up because of some OVP input or output protection, but after reviewing the RL and Roc resistances designed with the PI Expert, the value is correct.
The OVP voltage output protection is set up in 14,9Vdc and I have tested that this level is never reached at all.
I cannot understand what is going wrong in my design, I have tried some tests but nothing changes this behaviour.
I tried to remove Cdc and leave alone Rdc1 and Rdc2, but it does not change the status of the converter.
The most disturbing fact is that when I check the voltage in the Line Sense (L) pin with a tester probes, the converter starts up and operates correctly (12V-670mA but only for 60-140Vac aproximately) and when I remove the probes the converter switches off again.
Concerning this measurement, I actually do not know where I should have to connect the tester probe for the return point. It should be connected to Source (S) pin or to -Vdc line reference?.
Whichever the place chosen for connecting the return probe, the converter starts up and the voltage measurement is less than 1,8Vdc. I also realized that when this voltage is near 2Vdc the converter is switched off.
In summary, could you please explain to me this abnormal operating condition? I cannot see the mismatching point between spreadsheet calculations from PIExpert and the prototype I designed.
Need technical support.