The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: email@example.com (Tim Shoppa)
Subject: Re: White and blue dropping resistors
Date: 7 Dec 2002 08:09:51 -0800
NNTP-Posting-Date: 7 Dec 2002 16:09:51 GMT
NleahciM wrote in message news:...
> Tong Narak wrote in news:3DEC9B3C.51F3626D@fanwap.com:
> > Use a current regulator step down is better the super bright LED.
> > LM317 can do that with a 1.2v/0.020A = 60 ohms.
> > Limit at 20 mA for super bright LED.
> > note that each SuperLED forward voltage drop are not identical.
> > control Current is best when step down.
> Wait - can you clarify this? Let's say you wanted to power a super bright
> LED (is there a difference between a normal LED besides brightness?) from a
> 12V DC power source - so of course you would need to step down the voltage
> that the LED would see somehow. I always have just used resistors. Are you
> saying there's a more efficient/somehow better way?
A current regulator has advantages over a resistor if the DC power
source has poor regulation.
An example with a resistor:
If you knew the LED was rated only to 25mA and had
a voltage drop of 2V and the maximum DC input voltage was 14V, you'd pick a
(14-2)/0.025 = 480 ohm resistor; but you'd only get 12.5mA if the DC
voltage fell to 8V with that resistor, and the LED would be dimmer.
With a current regulator you could maintain the same current through the
LED while the DC voltage varies widely.
For a fixed DC voltage, a linear regulator and a resistor are exactly as
efficient as each other - the voltage drop times the current gets turned
The real gain in efficiency comes when you use a switching current
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup