dual mode usage
I plan to use the Lnk304 in a non-isolated configuration as describe in the datasheet with 10V output in parallel with another DC supply at 15V. In other words, the capacitor for 10V and for 15V are the same. so, while the other supply is in function, the Lnk304 doesn't have an input anymore and the 15V is seen at his output. I have tested this configuration and it works fine. Does PI engineer see any problem of using this configuration for mass production.
Comments
I joined a functionnal bloc of the usage I am doing with the LNK304. There are two supplies, a power steal circut and an AC-DC converter using the LNK304. Both outputs are connected together on the same capacitors. The LNK304 is configure to output at 10V and the power steal circuit is configure to output at 15V. When the power steal circuit is in use, the input of the LNK304 is close to 0 volt and the output is 15V supplied by the power steal circuit. When the AC voltage comes back on, the LNK304 restarts and the power steal circuit stops supplying. Does this configuration can lead to any kind of problem?
From your basic description, I can't see any major concerns. However, I can forsee some *potential* problems depending on how you've setup the feedback circuitry and how the hand-off between the two supplies works.
The block diagram you attached still doesn't give me much in the way of details. If you're concerned about posting your schematic in the forum, you're welcome to private message me and send it to me directly. Having the schematic, layout, PI Expert files, etc, would give me a lot more information so that I can answer your question better.
-The Traveler
Yes I am concern about posting my schematic, however I managed to modify it so nothing confidentiel is shown. I hope this will be enough. If not then you should send me an email adresse to private message you more.
The feedback is as the schematic. The hand-off between the two supplies happens when the voltage between line1 and line2 drops close to zero (LNK to other supply) or comes back to its original value of 120V or 240V (other suplly to LNK).
Tousi -
Thank you for the schematic. It's much more helpful than the quick sketches!
In general, you'll probably be ok with your design. I do have a couple thoughts and general concerns:
-You might want to do something similar with the LNK302 supply like you're doing with D2 to isolate the two power supplies from each other. Even with LNK302 not having an input, it's possible the output from the second supply could provide enough current to start up the LNK302 controller and have it switch occasionally.
-Another reason for adding the isolation diode would be to keep the second supply from seeing the LNK302 inductor and bulk caps. You might run into some unexpected LC circuit oscillations.
-Make sure there won't be any operating conditions that would result in the FB or BP pin max voltages being exceeded (9V max).
-Depending on your application, you might have to play with the differential inductor in your LNK302 circuit. There is the possibility of EMI getting transmitted back from your load (or your second PSU) through to the mains input of the LNK302 supply.
If you have any other questions, please let me know.
-The Traveler
I'm not quite following your explanation of how you intend to use the LNK304 in your design. Can you give me some additional details, a schematic, sketch, etc?
-The Traveler