Curious about white LED circuit

I bought a few surplus pc boards that contain 29 LEDs and some resistors.

13" long x 2" wide.

The wiring seems odd, there are two circuits repeated.

The first: two series LEDs in series with a 560 ohm resistor.

The second: one LED in series with a 820 ohm resistor.

These two circuit are in parallel with each other.

This is repeated all across the board for 29 LEDs.

I'm running it on 7 Volts and it's bright enough for my purpose.

Each 560 ohm has 1.4 volts across across it. 2.5 ma

Each 820 ohm resistor has 4.1 volts across it. 5 ma

It only has one power connection.

Any thoughts about why this was made like this?

I have the board mounted under the top of my computer desk. My keyboard is on a slide out shelf the gets lit by the LED board. It lights up the keyboard for me in the morning before I've turned on other lights.


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I have no idea about why there are two separate circuits repeated unless it is related to wanting 29 LEDs and not 30. (I am assuming from your description that there are ten 2 LED circuits, and nine 1 LED circuits. Which is not the best from an efficiency stand point.)

From the resistor values, I am guessing that the circuit was designed to operate from 12 volts. With an LED voltage drop of 3 volts, you would have about 10.8 mA going through the LEDs in both circuits.


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Dan Coby

Ya, it all seems a bit strange, but I paid $1 and it does it's job fine. When I was testing it, I did run it up to 12 volts and it is very bright. I found a 6.2V wall wart and used that for power. Mikek

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"amdx" schreef in bericht news:4e347$4fb2dceb$18ec6dd7$ snipped-for-privacy@KNOLOGY.NET...

White and white are not always the same as white. The taste of white that a white LED produces depends on its physical properties and the current that flowa through it. So this particular combination might have been designed to produce a special white for some purpose. I ever saw a bunch of white LEDs with some lonely red and green ones between them just to produce the white that was required.

petrus bitbyter

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petrus bitbyter

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