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'[PIC] need to build a power regulator circuit'
2007\02\20@082047 by picnoob

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face

hi, i need to build a power supply for a pic, and an lcd(consumes about
250ma). The input must be a 9v battery, and output of 5v. what should i use
to build this supply? could i use this:
www.maplin.co.uk/module.aspx?detail=full&ModuleNo=46321&doy=20m2#more_info
LINK

if so, what caps do i use with it? a circuit diagram would be nice. i have
never built a regulator before, please help.
--
View this message in context: www.nabble.com/need-to-build-a-power-regulator-circuit-tf3260455.html#a9061539
Sent from the PIC - [PIC] mailing list archive at Nabble.com.

2007\02\20@084451 by Vasile Surducan

face picon face
On 2/20/07, picnoob <spam_OUTleeguy92TakeThisOuTspamgooglemail.com> wrote:
>
> hi, i need to build a power supply for a pic, and an lcd(consumes about
> 250ma). The input must be a 9v battery, and output of 5v.

I would like a few hundred myself...
http://www.voti.nl/wwpsu/index.html


what should i use
> to build this supply? could i use this:

NO, NO, not from England, didn't you heard about the chicken flu ? ...

> www.maplin.co.uk/module.aspx?detail=full&ModuleNo=46321&doy=20m2#more_info
> LINK
>
> if so, what caps do i use with it? a circuit diagram would be nice. i have
> never built a regulator before, please help.
> --
> View this message in context: www.nabble.com/need-to-build-a-power-regulator-circuit-tf3260455.html#a9061539
> Sent from the PIC - [PIC] mailing list archive at Nabble.com.
>
> -

2007\02\20@084810 by Wouter van Ooijen

face picon face
> hi, i need to build a power supply for a pic, and an
> lcd(consumes about 250ma).

That won't last long. can't you get rid of the backlight?

If it needs to be, I would probably power the PIC with an 78L05 and the
backlight with an LM317 (or maybe an LM2575).

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2007\02\20@155555 by Jinx

face picon face
>
www.maplin.co.uk/module.aspx?detail=full&ModuleNo=46321&doy=20m2#more
_info

"This device is an excellent choice for use in battery powered applications"

15mA quiescent current is not excellent

"Furthermore, the quiescent current increases slightly at dropout, which
prolongs the battery life"

I'll have to make a note of that - increasing drain on battery makes
battery last longer. And here's me squeezing circuits down to the uA
like a sucker

'noob, any (small) battery is going to take a beating with 250mA drain.
A 9V PP3 will last an hour. What will be better is a 4-pack of AAs, a
6-pack if you really must have 9V. Presumably the backlight is what's
eating the current - maybe have that as a pushbutton option ? The LCD
itself should draw only about 2-3mA

If you Google for TS2940CZ-5.0 or LP2940CZ-5.0 you should find
a data sheet easily enough. Maybe the 15mA Iq quoted by Maplin is
wrong - sounds high

If it isn't, I might go for a smaller regulator (or even a zener-regulated
transistor) like the 100mA LP2950-5.0, which has very low quiescent
current (75uA) and a bypass transistor to supply the other 150mA
when needed

2007\02\20@162222 by Jinx

face picon face

> NO, NO, not from England, didn't you heard about the chicken flu ? ...

England is going to get what's coming to it ;-)

http://www.nzherald.co.nz/section/story.cfm?c_id=5&objectid=10424822

We're screwed - Bruce Willis will be 80 years old

=================

http://www.voti.nl/wwpsu/index.html

'noob, apart from the obvious portability, is there a reason why it
has to be battery powered ?

2007\02\21@083425 by Byron A Jeff

face picon face
On Tue, Feb 20, 2007 at 05:20:45AM -0800, picnoob wrote:
>
> hi, i need to build a power supply for a pic, and an lcd(consumes about
> 250ma).

Are you sure it's 250 mA? For a PIC and an LCD that seems like a whole lot
of power.

> The input must be a 9v battery,

That simply does not compute with the above listed power requirement. On a
quick Google search the high capacity 9V that I could find were 595 mAh
and that's probably at a C/20 draw rate. At C/2 the battery would be dead in
about 10 minutes of operation.

So let me ask some questions:

1) What's the real power draw of the circuit? Are you sure that it's 250 mA?

2) What's the intended run time?

3) A 9V battery is the smallest battery power package you can use. Is it an
absolute requirement?

The point is that you've boxed yourself in with your requirements. You'll
have to either reduce your power draw, upgrade your battery power package, or
live with virtually no run time.

So where are you willing to compromise.

> and output of 5v. what should i use
> to build this supply? could i use this:
> http://www.maplin.co.uk/module.aspx?detail=full&ModuleNo=46321&doy=20m2#more_info

You cannot utilize a linear regulator in such an application. Linear regulators
work by burning up the excess voltage as heat. So you burn 50% of your power
right off the top.

If your 250 mA power requirement is legit then I would suggest something like
3 10000 mAh D cells as input to a LM2577 boost simple switcher. You can
find the data sheet here:

http://www.national.com/pf/LM/LM2577.html

At 90% efficiency you could get upwards of 35 hours of operation from such
a setup.

BAJ

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