From: Tong Narak
Subject: Re: Driving an LED from 9v battery
Date: Thu, 21 Nov 2002 14:06:12 +0700
Organization: C.S. Communications Co. Ltd.
NNTP-Posting-Date: Thu, 21 Nov 2002 07:06:16 +0000 (UTC)
X-Mailer: Mozilla 4.8 [en] (Windows NT 5.0; U)
It look like that you need a perfect chip IC or circuit.
Everybody want it perfect world.
You need buck and boost IC.
If u can control voltage, u can control the current.
( Your LEDs are normal RED LED ? )
In practical, forward voltage with each LED aren't
identicle. we accept 20% tolerant when seeing with human eyes.
So u can use Buck and boost constant voltage regulator.
Search at maxim-ic.com or TI.com
There are a lot of ICs for 6-12VDC input.
Hope these help.
Walter Harley wrote:
> I really appreciate all the help you folks have provided for me lately.
> Here's another question: I'd like to drive from one to four LED's, from a
> source with voltage as high as 12v and as low as 6v (basically, a 9v
> battery, occasionally supplemented by a poorly regulated wall-wart). I want
> constant brightness (= constant current) over the whole voltage range, and I
> want maximum possible efficiency, to preserve battery life. Need to keep
> the cost and parts count under control, need to keep the circuit physically
> small, and I need to keep audio-band noise low. The circuit will be
> incorporated into a variety of small battery-powered audio processors.
> I'm thinking that one of the many small switching converters or charge pumps
> would be right. But hunting around on the web sites I can't seem to find
> which one: most seem to be oriented to stepping up from small voltages,
> rather than stepping down, and I'm not sure I'm searching with the right
> terminology. Can someone point me in the right direction? Or, perhaps
> there's a better solution to my problem?