Based on RDR-189 design sample(PLC810 and TNY275), I made a AC/DC moudle to get a 27VDC power.
If without load, it can be power on and its output was normal(26.8-27.2V). Then I can add loads on it(from 1-8A) and its output voltage was steady, just a little dropped(from 27.0V down 26.2V).
But when I connected a load(resistance load) first, current just 1A-3A, then switched on the power, the output dropped too much, it may be only 4-6V something like that. Also I can hear a high HZ noise from the PCB board, not sure where it came from.
What is the problem? Please help.