On 2005-10-19 07:13:06 +1000, "Meindert Sprang"
said:

"Gordon Wedman" wrote in message
news:Naa5f.17849$y_1.2003@edtnps89...
Meindert, Terry, Chris
Thanks for the info. Didn't know they would take something simple and
complicate it. Switched to save power? How much power are we trying to
save anyway?

Ok, I'll do some math: A typical high-power LED draws 500 mA at 3V. If I use
a ballast resistor to connect this LED to a battery at 12V, 9V will drop
across the resistor at 500mA, which produces 4.5Watts of heat, which is
quite substantial. The total power drawn from the battery is 6 Watt.

With a switched regulator, there is (hardly) no voltage drop, so the power
the LED uses (3V * 500mA = 1.5Watt) is the same as the power drawn from the
battery. So more efficiency and the regulator also compensates for varying
battery voltage which results in longer LED life. LEDs are quite picky on
the proper voltage. 1/10th of a volt more than specified can shorten their
lifespan from 50,000 hours to a few 100. This regulator prevents this.

Meindert

Don't forget that the LED is a current device. By that I mean light
output is a function of forward current. Hence to get even illumination
from multiple LEDs it is imperative that each LED be driven via a
current regulated source. It is not sufficient to parallel them up in
series with a dropping resistor.

Sometimes simple things are complex.

--
Regards,
John Proctor VK3JP, VKV6789
S/V Chagall