Symmetrical power rails with two identical SMPS

Posted by: -_nando-_ on 03/02/2011

Hi there,

I intend to use two indentical, high power, PSUs to power an audio system. So, I would need simmetrical power rails.

I would like to know if the attached schematic as it is, is correct. I already did it previously, but I didn't have multiple outputs, just one simetrical power rail. So, the way it is now, can I tie together GND and GND1 without any problems, or should I AC couple them instead?

Thank you in advance!

Best Regards,

Fernando

Files

dual_psu.png (53.64 KB)

Comments

If the outputs of each power supply are isolated, I do not see why you can not connect them the way you show. Electrically the circuit will work.

Hi PI-Worf,

Thank you very much. I just wanted to make sure instead trying and maybe burning it!

By the way, this power supply uses the TOP260. Can I replace it with TOP261 directly, without any transformer / diodes modification? The feedback loop works for both, that I know for sure.

Best Regards

The TOP261 has a larger current limit than the the TOP260. So you need to adjust the resistor connected to the X pin of the TOPSWITCH for the peak of the DRAIN current limit to be the same as for the TOP260 design. In other worse, you need to increase the value of the X pin resistor to reduce the current limit and make it the same as in the TOP260 design. This is the only change you need to do.

The X pin is actually tied to the ground, I'm not using current limit because it won't be exceeded by the load, in this case, should I just leave it as it is?

Thank you!

add a resistor to the x pin, make the ILIMIT to be the same as the smaller device

I've just finished the SMPS.

I changed the design for the TOP261, I found it pretty much more adequate for this power, up to 160W. The troublesome part was to re-work the transformer's gap to reduce the primary inductance and also kill the EMI emissions that were interfering on the SMPS regulation.

I had to use 100R + 22pF snubber from drain to source and from the 1st clamping diode to the drain. Also I had to change the main output snubber from 330R + 22pF to 27W 1W + 1nF 1KV. That was a BIG improvement in emissions.

After all that, she's really doing fine and it is incredbly 85% efficient putting out 140W at 127VAC. Awesome for a Flyback, what you think? Nice work Power Int, very neat product. Can't wait to use the Hyper TFS!