The supply problem of PFC chip PFS726
We prepare to design a 400W LED driver, and using PFS726 as a PFC stage, LCS708 as a LLC stage.
I take responsibility for the PFC part. The designed PFC726 and power supply circuit is attached in files.
The power supply of PFC726 is a flyback based on TNY284.
The PFC circuit boosted up to 380VDC without load, but pulled down to 290VDC with light load (<10W).
I tried DC regulated power supply (Agilent N5746A). The air-break switch of whole lab tripped.
I tried a old computer power supply that manufactured in the 1990s. It works well with heavy load (power resistors,400W), but the LED flashed when connected to the LLC stage.
I think isolated power such as flyback is not suitable because the G pin is connected to the power ground in the chip.
Can you give me some advice?
Comments
I removed the LLC stage, the problem remains unsolved.
Connecting external power, the PFC+LLC works well. The output voltage of PFC is 360VDC when the LED is 400W.
Connecting TNY284 based flyback power, the output voltage of PFC pulled down to 290VDC.
I tried a resistor load of TNY284 power, which can reach 100mA.
sounds like the problem is based on TNY section. You can probe the TNY output votlage to debug.
Do you have your TNY spreadsheet to share wit hus so we can review the desing?
to debug, you can remove the LLC stage and just test the PFC stage. You can use external power supply to power the PFS VCC throught your on board regulation circuit. You schematic looks ok. if no load, PFC can supply 380V bus, with 10W load, it drops to 260V, it is abnormal. You might want to check the FB circuit and layout, make sure it is not around the transformer area.