# Any simple ways of dropping voltage without disspating power.

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I need a very simple way of dropping 12V to 3V @50 ma without
dissapative losses, as the source 12V is very limited capacity.
Any switching regulator ICs that can do this with minimal external
components.

Re: Any simple ways of dropping voltage without disspating power.

Without dissipative losses is a big ask.

A simple circuit I've used for low power using an LM2936Z-5.0 and BC327
instead of the 7805 and BD242 is at
http://www.edn.com/article/CA220404.html

In my application, 13V @ 24 mA in -> 5V @35 mA out using a rather lossy
miniature inductor. 56% efficient -v- 40% from series regulation.

The author says she got 65% for 24V -> 5V and 75% for 24V -> 12V.

Re: Any simple ways of dropping voltage without disspating power.
On Sun, 19 Oct 2008 00:02:47 GMT, snipped-for-privacy@tpg.com.au (Mauried) put
finger to keyboard and composed:

If it's just a one-off, then get an old cigarette lighter DC adapter
for a mobile phone. Many are based on an MC34063 switching regulator.
If the voltage is not quite right, then reprogram one or both of the
feedback resistors. If you need one, I have lots of them. Free to a
good home, just pay me for postage.

- Franc Zabkar
--

Re: Any simple ways of dropping voltage without disspating power.
On Sun, 19 Oct 2008 13:54:08 +1100, Franc Zabkar

Many thanks, should have thought of this myself.
Got one around somewhere.

Re: Any simple ways of dropping voltage without disspating power.

You won't get a 100% efficient solution.
Around 95% is achievable using the right parts and topology though.
If you really want a minimal component solution, a DC-DC converter
module is probably your best bet. One with either a fixed 3V output
(not common), or programmable via a resistor. That way you get a known
efficiency with only a couple of parts. TI make a bunch of them as do
many others.

You don't mention cost, board area, prototype or production, or any
other parameters.

Dave.

Re: Any simple ways of dropping voltage without disspating power.
On Sat, 18 Oct 2008 21:36:14 -0700 (PDT), "David L. Jones"

90% is plenty efficient, just need to avoid linear dissapative
regulators.
Size isnt that important, but I was trying to avoid having to wind
inductors which are usually needed in switching buck regulators.
Ill try Francs idea of the cigar lighter .
As I dont need much power somehing small is all that needed.

Re: Any simple ways of dropping voltage without disspating power.

For that application, the inductor will be easy. Typically a few tens of uH
on a small toroid. You can buy prewound ones, eg. Altronics.

Re: Any simple ways of dropping voltage without disspating power.

You don't need to wind your own for apps like this unless you need
something exotic, plenty of suitable off-the-shelf ones.

Dave.

Re: Any simple ways of dropping voltage without disspating power.

Farnell do masses of suitable inductors ready wound. Trouble is the minimum
order charge if you have no account !

Graham

Re: Any simple ways of dropping voltage without disspating power.

Swiching regulators do this with the best efficiency but tend to use
quite a few parts, although for that low curent you may well get an IC
that requires few external parts.

Sometimes they're sold as potted 'blocks' too.

Sci.electronics basics and sci.electronics design might being you some
useful help.

Graham