LED linear modulator

Posted on Feb 6, 2014

After constructing the Pulse Width Modulator for High Power LEDs I needed to build another LED modulator for another optical transceiver. For this project I decided to take a different approach and use solely linear techniques for the audio modulation. Like the PWM circuit, this circuit also uses the `precision current sink` to regulate set the LE

LED linear modulator
Click here to download the full size of the above Circuit.

D current but in addition to the linear modulator, a tone generator - based on the same source code as in the PWM circuit - was added to facilitate testing and aiming. In order to linearly modulate the intensity of an LED it is necessary to vary the amount of current flowing through the device rather than the voltage across it. It is fortunate that the luminous output of an LED is linearly proportional to the current flowing through it: At higher currents, the "current versus light output" curve "flattens" a little bit, but this results on only a very small amount (a few percent at most - see the sidebar below) of distortion and is unnoticeable in voice communications.

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