From: "Nucharin W. Jansen"
Subject: Re: Q. About ICs for Driving White LEDs
Date: Wed, 06 Nov 2002 04:32:14 +0700
Organization: C.S. Communications Co. Ltd.
NNTP-Posting-Date: Tue, 5 Nov 2002 21:32:17 +0000 (UTC)
To: Watson 'Atto Parsec' Name
X-Mailer: Mozilla 4.8 [en] (Windows NT 5.0; U)
I using MAX757 adjust voltage to 3.5V voltage regulator.
I can get 22uH inductor 1/4w ( look like resistor but green color )
The capacitor can use electrolye and don't worry about voltage ribble.
The problem is white LEDs itself!
Their are not the same voltage drop.
I parallel it up to 6 LEDs. These IC support 300mA output.
No reason the build smallest flashlight.
These IC can run down to 0.7v to 3.5v
Hope these help.
Watson 'Atto Parsec' Name wrote:
> I've looked over some of the different ICs for driving white LEDs, from
> Linear Tech, Maxim, National, Zetex, etc. I'm bewildered by all the
> choices, limitations, etc. I've looked over some articles that use them in
> projects, some using regular white LEDs and some using the super bright
> Luxeon Star LEDs. I've noticed that many are voltage regulated, which
> makes it necessary to do some form of current limiting before it gets to
> the LEDs. Some chips are constant current, for that very reason. I think
> that some boost circuits could be made current limited by reducing the
> charge pump capacitor or changing the inductor. I like the charge pump
> designs because they don't require an inductor which is often relatively
> difficult to find and often made by only one company. Of course it's not
> easy to find a small, low ESR cap in the 100 to 470 uF, 3V or 6V range
> either. But I suppose I could scrounge a few from a defunct CD-ROM or disk
> I'm looking for some advice from someone who has built some of these, to
> see what disadvantages they have, which don't always become apparent from
> looking at the data sheets. I've noticed that some chips run at 1 or 2
> MHz, which seems high and might cause some EMI, however it probably isn't
> very widespread. Also some ICs apparently have thermal shutdown. Any
> other such behavior?
> My email address is whitelisted. *All* email sent to it
> goes directly to the trash unless you put NOSPAM in the
> Subject: line. alondra101 hotmail.com
> Don't be ripped off by the big book dealers. Go to the URL
> that will give you a choice and save you money(up to half).
> http://www.everybookstore.com You'll be glad you did!
> Just when you thought you had all this figured out, the gov't
> changed it: http://physics.nist.gov/cuu/Units/binary.html