12v to 5v SMPS?

Chris,

First, please ignore the idiot that has already responded. Anyone that spells friend as "freind" needs some serious help and schooling.

Depending on how much current you need, you may be able to get away with a simple linear regulator (like a 7805). With this approach, you will waste (in watts) 7V * current draw.

If this is too much wasted power (e.g., the 7805 would get too hot or the battery life would be compromised) then you must use a switching regulator. Digikey probably has one that will work, for you. Devices made by Artesyn, Power One, and Tyco come to mind.

Bob

You might check out the integrated switching regulators of Power Trends (now part of Texas Intruments, I believe). For example, one 5v 1A unit ("EA" style) is pin compatible with the popular 5v 1A 7805 linear regulator that Bob mentioned; DigiKey sells it (part# PT5101N-ND) for $12.25. A data sheet is available from Texas Instruments site.

Not all USB devices will charge with simply +5V on a USB connector. Some of them need a USB host to talk to, to authorise them to draw

This is actually the right thing for them to do, but causes problems with dumb chargers.

Oh cool. Thanks a lot for your help :) You've given me some ideas that I can go with. Also, the USB bit that Ian mentioned was something I hadn't considered.... I think I am going to build it and see how I get on..

Thanks again Chris

There was a thread on the most simple sm regs. Just google for: regulator nt sm. In short you dont need any IC, just 2 trs and a few passives.

NT

To meet +-0.25V@500mA?

I have decided to use the chip PT5101, cant remember the letter after that, but it's the horizontal one. It should arrive here tomorrow, then I'll hook it all up and get back to you and let everyone know how I got on.

It has a solar panel, which trickles charges a 6v SLA. Then there is a SPDT switch to switch between charging and dischaging. When set to discharging it will be connected to the PT5101 circuit (with the capacitor which is talked about in the datasheet for this component), which will give me 5V out. From here, there will be a female USB connector, so that I can connect my stuff in and hopefully charge it.

Thats my plan :)

Chris

ahh, usb port. It can be done, add a filter, tighten the v sensing, but I agree it would get more complex.

NT

A efficient 12V to 5V converter. Should be what you are looking for.

-- Best Regards, Lim Siong Boon

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