Or the Linear Technology LT1111 if your current requirements aren't too high
(300mA?)

The application note has some example circuits and you can get a 12-28v to
5V 300mA output with 5-7 components.

Also look at the LT1173, LT1070, LT1071.

There are heaps of these types of chips out there. I don't know about
prices.

You can also get pre-made SIP/DIP modules. eg NME1205 (12V -> 5V).

A word of warning, you may want to add a L/C filter after the switcher to
kill some of the noise it generates.

Alternatively you could use a 5V wall wart and a 5V -> 12V switcher to get
the power for the LCD (assuming it doesn't use much current). It may even be
possible to use "switched capacitor" voltage doubler to get nearly 12V for
the LCD and be "close enough".

Ash.

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Byron A Jeff
> Sent: Tuesday, 17 July 2001 11:19 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]:Voltage Reg vs Switcher
>
>
> On Tue, Jul 17, 2001 at 08:57:40AM -0400, Robert E. Griffith wrote:
> > I have a design that uses a 12v wall wart power supply
> because an LCD needs
> > the 12v.  The main circuit runs on 5v and 3v.  In the
> prototype I have a 5v
> > regulator (LM340TS) dropping the 12v to 5v and a 3v
> regulator (TPS7230QP)
> > that drops 5v down to 3v. This device will be on all the time.
> >
> > I have a heat sink on the 5v reg and it gets hot. I want to
> put the finished
> > circuit in a project box with vents but no fan.
> >
> > My question is: is there an easy, low cost, solution to
> implementing a
> > switcher to drop the 12v to 5v? Is this done? The 3v reg
> does not provide
> > much power so it is not a problem.
>
> Easy? yes. Low cost? Depends on your price range. Take a look
> at the National
> semiconductor Simple switcher series. Requires little more
> than a coil, diode,
> and a cap. But the total cost will be in the $10 range.
>

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