how to balance +12v and-12v in a smps?
- Thread starter vajanda
- Start date
I had same problem with different chip from (Power integrations), and I had no success to make it working at all. even PI themselves gave no solution to that problem, eve you may find my discussion with them at the PI forums.
After digging into the web, I found a Russian solution for that problem, witch is to use the feedback as it is, and to increase the output voltage for example up to +-30VDC, then insert your voltage regulators there, and you are done.
I had no time to test that circuit, however, same issue and same problem was clearly indicated in Fairchild Chips, the confirm there is a voltage variations , because of feedback.
I don't know how these companies just manufacture these chips without testing such circuit.
Good luck
A PWM IC can only regulate 1 voltage. It's really annoying but it's not the fault of the IC manufacturer. At some point it has to come back to a single control point, the duty cycle, so how can 2 independant things be regulated by adjusting one thing which is common to both. You can wind output inductors on a common core to improve cross-regulation, or you could differentially sense across both of them, to regulate the differential voltage at the expense of not being able to regulate either one referenced to ground.
There are various other techniques for cross-regulating multiple outputs. It's always a trade off in one way or another. This is a really good article from ON Semiconductor:
Multi-Output Flyback Off-Line Power Supply
It's about flyback converters but remember a multi-winding flyback transformer is actually multiple inductors wound on the same core, not a transformer.
There are various other techniques for cross-regulating multiple outputs. It's always a trade off in one way or another. This is a really good article from ON Semiconductor:
Multi-Output Flyback Off-Line Power Supply
It's about flyback converters but remember a multi-winding flyback transformer is actually multiple inductors wound on the same core, not a transformer.