kWh meter power supply with TNY254

Hi,

The polarity of the zener diodes Z1, Z2 and Z3 is incorrect in the schematic and capacitor C30 is connected to the anode of the secondary diode which should be connected to the other end of the transformer secondary winding.

Please verify your schematic. It appears as though the schematic does not match the board, could you please verify. Please compare your schematic to one of our design examples. using the link below:
http://www.powerint.com/en/design-support/reference-designs/design-examples

The following designs are similar to your circuit and I request you to compare your design with these circuits to see where components need to be terminated:

http://www.powerint.com/sites/default/files/PDFFiles/di124.pdf

http://www.powerint.com/sites/default/files/PDFFiles/der58.pdf

Regards

PI-Sarek

Thanks Sarek--I appreciate your prompt response.

Just to be sure that I am clear on your suggestions, particularly in reference to the capacitor connection, here is a modified schematic. Does this look like it properly reflects how the changes should be made?

Thanks

Doug

Yes the modification looks appropriate.

Zener Z3 anode also needs to be connected to the DC+ rail of the power supply which would be the top end of the transformer primary.

Currently your schematic does not show a tie dot to indicate a connection.

Regards

PI-Sarek

Hello Sarek--Thanks for your help.

We have checked the schematic and modified the power supply according to the attached .pdf. We have also tried some mitigation modifications, but are now convinced that the current design is not going to be readily salvageable. We have had some success in mitigating the higher frequency noise, but almost none with mitigating the lower frequency noise. Do you have any suggestions?

We are interested in possibly using your reference design for the DI-124: http://www.powerint.com/sites/default/files/PDFFiles/di124.pdf

Since it appears that layout of traces and components are very important when it comes to emissions, it will be very helpful if we can get the PCB layout of this reference design. Is that available? Can you point me to it or send it to me?

Thanks

Doug

Hi,

Yes, the layout is one of the most critical aspects of successful design of a switching power supply.

I would strongly encourage you to review the following application notes, if you are new to power supply design:

http://www.powerint.com/sites/default/files/product-docs/an15.pdf
http://www.powerint.com/sites/default/files/product-docs/an18.pdf

I have attached some design example reports for your reference.

Regards

PI-Sarek