+/-15V share regulation
Dear PI-Experts,
My +/- 15V 120W TOP258EN power supply works well with the balanced load. But once the negative load was removed, the negative o/p was rose up to -23V. I did add a 30V zener in series with a 10ohm resistor to the + & - o/p that similar to der191 but in vain. Is there any method to avoid that and improve the cross regulation of a negative voltage.
Thank you very much.
Brgds,
Jun.
===================================
Winding order? VOR? Schematic
Posted: Mar 19, 2010 | 14:53 PM Reply .Hi,
There are many factors that affect cross-regulation of outputs. I suggest you read through AN-22 http://www.powerint.com/sites/default/files/product-docs/an22.pdf to help you find a solution that fits your needs.
What tolerance on the -15 V output do you realistically expect? What type of feedback are you using on the +15 V output?
Lowering your VOR and making sure the two windings are well coupled will help you achieve your regulation goals. To this end, placing the windings physically close together, choosing wire gauges that cause the windings to cover the entire bobbin width and other good transformer construction practices with help you accomplish this.
If you do not have strict efficiency or no-load input power requirements using a preload resistor (a resistor that is always drawing current from the output) can help keep the output in regulation. Also you can use a zener and series resistor to act as a linear regulator to help but again this will hurt your no-load and efficiency performance.
Posting your schematic and transformer construction will help me make better suggestions too.
Hope this is helpful!
-Wesley
PI-Wesley | 74 posts
Comments
Hi PI-expert,
I just found der43 fits my application. It use a PNP transitor 3609 to make the -Ve voltage sharable to regulate. But I don't know what value the bias resistor should be. Pls help. Thanks,.
Thanks PI-Wesley,
I did read AN22 already but I can't find one suitable for negative voltage cross regulation. I did try share regulation by adding a resistor on the negative side, but this does not work for negative voltage. Attached is the schematic.
The design actually works very well when both positive and negative o/p are on load at the same time (light to heavy load). As it is only feedback/regulated on the +15V o/p using TL431. The problem is when one of the load is disconnected suddenly, I mean on heavy load. i.e. If the load on +15V is disconnected, the p/s will loss regulation. I think this is normal. But if only the -15V load is disconnected, the -15V o/p will stay at high end, i.e. -23V. I think this is normal too since the +15V is on high load. What I want is clamping the -15V from high end to a reasonable level. I also tried using a 30V zener clamp but this doesn't work too. The zener gets very hot indeed. Is my connection wrong? Pls comment.
Thanks a lot.
Brgds.
Jun