PMP41009：UCC28740

cks Chen

Part Number: PMP41009
Other Parts Discussed in Thread: UCC28740,

Hello, I am debugging a self-designed flyback switching power supply with an input of 90-900VAC and an output of 24VDC. I use the UCC28740 chip and adopt the relevant power supply circuit from the PMP41009 design. Why is it that when the input is 220VAC, the voltage after rectification is 328VDC, the measured voltage at the HV pin is 12V, the chip fails to work normally, and the voltage at the VDD pin is only 1.3V? No changes have been made to the circuit. Below are the relevant power supply circuit from the PMP41009 design and the power supply schematic diagram of my input voltage after rectification. The turns ratio of the transformer is 20:5:6, $R_{vs1} = 160 k Ω$ , $R_{vs2} = 24 k Ω$ .Could you please advise on how to solve this problem?I also asked this question last Monday, but when replying to your inquiry, I couldn’t upload images or send messages at all, and it’s only now that I can do so.

2 天前

0 FRANK1 1 天前

TI__Genius 14690 points

感谢您对TI产品的关注！
已经收到了您的案例，调查需要些时间，感谢您的耐心等待

0 Links 12 小时前

TI__Mastermind 31030 points

Hi,

1. Double check the resistance of R1~R4

2. Remove P6KE300A and short R1~R4, check the VDD voltage, and power up UCCC28740. UCC28740 HV pin ABS voltage is 700V, make sure the voltage after rectification is lower than 700V when do this testing.

3. Place P6KE300A back to check the HV voltage

0 cks Chen 12 小时前回复 Links

Prodigy 60 points

I have performed the following operation before: I removed the P6KE300A, short-circuited resistors R1 to R4, and connected the HV pin directly to the rectified circuit. At this time, the input voltage was 387VDC after rectification, the voltage at the HV pin was 10.5V, and the voltage at the VDD pin was 1.4V—there was no change. Reconnecting the P6KE300A also resulted in no change. Is this phenomenon related to the values of RVS1 and RVS2?

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PMP41009：UCC28740