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March 20th, 2012 - Adventures in Engineering — LiveJournal
The wanderings of a modern ronin.

Ben Cantrick
  Date: 2012-03-20 22:10
  Subject:   The simple and easy single transistor NPN constant current sink for driving LEDs.
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  Tags:  simple circuits

I constantly see people on Reddit /r/ece, /r/electronics, etc asking for advice on how to drive LEDs. It happens at least once a week. The classic approach is to take the input voltage, subtract the LED's forward voltage, and then use V = IR to compute the appropriate resistor. And that does work.

But there's another way. In my opinion, a better way.Collapse )

Here it is:


Click on the image to open circuit simulation in a new window/tab. (NOTE: Requires Java capable browser.)

Simple, no? The only thing you need to know is how to calculate the resistor. Here's the formula:

Rbase = 100 * ((Vconstant - 0.65) / Iconstant)

Read more...Collapse )
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