SEPIC, SMPS, LVR, :S which do I use?

[dannix]

I have a solar system (will have) I need both a +5v (1-1.5A) and +12v (2-3A) supply for some circuits, the input voltage will be between 10v-17v I therefore need some way to get 12v and 5v efficiently I dont want to use 7805's or 7812's as they waste so much.

So having read about I am left with SEPIC and SMPS

MAX649 or LM2937 seem to be talked about alot for 5v does anyone have a schematic for the best one?

What should I use for 12v? would it be better to increase the 12v load from 2-3A to 4A and feed the 5v regulator from that?

Are SEPICs better? what is the difference?

I don't know if ripple and all that other stuff is a problem I am supplying a thermostat, light sensor, volt / amp meter, LED array, fan and 15w heater.

any help is most apreciated

 

[boxer4]

multi-output Flyback SMPS, I suppose SEPIC is possible but I'm not sure about the feasibility of some of the components in it, specifically the high frequency capacitor in it.

There are some car ATX-compliant SM power supplies that you can probably directly use that have good efficiency.

Disclaimer: I'm not affiliated with this site, it just so happened to be the first one I saw on google:

https://www.mini-box.com/M1-ATX-90w-Intelligent-Automotive-DC-DC-Power-Supply?category=13

 

[dannix]

I was looking to make one not purchase one, but that isthekind of thing I was looking for, bit smaller however.

 

[Sceadwian]

Sepic is mearly another derivative of a basic SMPS design. Make is not going to be nearly as useful as finding a good core chip and designing around it.

 

[dannix]

I am happt to use a good core chip if I knew which that was and build around it as you say.

I found this while looking about the net

**broken link removed**

I was thinking I could chop out the -12v section as it is not required, It would be nice to increase output current for added overhead. Ignore the 5v section as well, it is not required as I was looking at the MAX649 for that, I need about 200mA min but would like overhead again.

 

[Optikon]

I am happt to use a good core chip if I knew which that was and build around it as you say.

I found this while looking about the net

**broken link removed**

I was thinking I could chop out the -12v section as it is not required, It would be nice to increase output current for added overhead. Ignore the 5v section as well, it is not required as I was looking at the MAX649 for that, I need about 200mA min but would like overhead again.

What's wrong with a buck-boost topology? These can be very efficient too. Find a controller that supports high efficiency at your load levels.

 

[dannix]

what topology was I looking at? I have never looked at SMPS before so im very new to it. What is buck-boost?

 

[Sceadwian]

dannix, try google and wikipedia, they're full of information about the buck-boost topology

 

[dannix]

dannix, try google and wikipedia, they're full of information about the buck-boost topology

hum, ok thanks.

 

[dannix]

From wiki the buck-boost is a step-up and step-down converter. Is that not the posted schematic above? it accepts a wide supply voltage. and is intended for a computer so I'm guessing its stable enough to use without having to look into harmonics and ripple and all that stuff I dont understand

I dont really know what im looking for as a controller IC, I always used 7805 etc This is what im asking for advice on.

 

[dannix]

Im looking LM3478 or maybe MAX668 anyone used these for 12v 2-3A in SEPIC (so the output is not reverse polarity)?

This is the MAX668 8-20VIN 12V 2.5A out https://www.electro-tech-online.com/custompdfs/2007/08/CB134.pdf

thoughts?