LNK500 start up problem

Posted by: pre on 05/12/2010

Hi,

i have done a SMPS design with the LNK500 device. Schematic equals the one in EPR-16, figure 5 with a few changes. My design is for 24V output, transformer datasheet is attached. The following changes were made:

1) R1 increased to 21k
2) C3 increased to 1uf
3) D6 changed to MURS160
4) C5 higher voltage rating

If no load connected to the output, the power supply starts without problems and the output reaches about ~30V. After successful start i can connect a 24V/100mA lamp as load and the output drops to desired output voltage of about 24V. Thats OK. But when i switch on the power supply with the load connected it didnt start. I tried to increase C3 but without success. Can you give me any hints regarding my problem.

Thanks.

Best Regards

Files

096905_b.pdf (58.57 KB)

Comments

Does the power supply start up into an appropriately sized (240 ohm) resistive load?

Hi Wesley,

thanks for your reply. I just connected a 230Ohm Resitor and switched on the power supply. It didn't start and output voltage was about ~2V. I then tried different AC input voltages and noticed, that with about 80V AC the power supply starts after a delay of ~1sec after switching it on.

Best Regards
PRE

Hi Wesley,

did my remarks help you ? Or should I do some additional measurements ?

Best Regards

It would be great to get an answer. Thanks.

Best Regards