Quick noob question about SMPS

[Mooly]

Using two or four SMPS of what are really unsuitable spec cobbled together isn't my idea of good design practice.

[carcass]

well, using national papers... (assuming the OP need for a smallish 30W 8ohm amp)
sqr(2*8*30)
vopeak=21.9V
sqr((2*30)/8)
~2.74A
Iopeak=2.75A
supply required=+- 25.9V@2.75A


easily managed using the smps calibration pots (the cheap ones found on ebay all seem to have it, this one for instance: 24V 10A DC Universal Regulated Switching Power Supply | eBay


And I found another well wroten article about it...here

ps it also as an alternative linear ps for "sensitive" minds... no pun intended

[frasco]

Interesting article, I've read it before, that's why I "knew" it could be done. He's using two 60W supplies though. Cool idea to integrate a cheap USB dongle too!

[carcass]

nice article yes, soft start for the smps, inductor filtering, thermal protection...the works, however doing the math for a 40W amp as he suggests one would need approx. 93W (29V@3.2A) to support the peaks, and as it's always best to have some headroom as we don't really know about the smps efficiency, double that to ~200W or just use two of the ones I've suggested before....

[frasco]

What about using LM1875 instead of LM3886 and power them with two 19V 3.42A laptop wall warts in a dual mono configuration? That would certainly fit my budget and 65W per channel should be fine for the LM1875. How's that for an idea?

[carcass]

sure if you want to try getting roughly 13-15W from it... don't forget some smoothing caps after those supplies try 2x2200uF 50V per rail for a start....normally those smps are indeed noisy, so that small inductor we've talked about doesn't hurt either.

go see the datasheet

[CBS240]

You can order a toroidal transformer kit for less than using multiple SMPS's strung together for a more reliable power supply. Most kits come with pre-wound and insulated primary/w thermal fuse. All you need do is wind the secondaries you need.