KA7OEI – LED Linear Current Modulator

May 19, 2011 | Amateur Radio, electronics | By: Mark VandeWettering

My silly experiment with an LED communicator naturally led me to looking up more complex (and better engineered) versions of the same kind of circuit. There are now cheap LEDs that can emit a watt or more of energy, and produce a prodigious amount of light. It seems like an area which is ripe for amateur experimentation (and just general mucking around) and could leverage some of my optical design skills as well. KA7OEI has some really good ideas and circuits for driving these kind of LEDs with as little distortion as possible, and will be definitely worth looking at:

KA7OEI – LED Linear Current Modulator.


Comment from niteshagr
Time 10/2/2011 at 7:56 am

could you please explain the working of the kA70EI-LED linear current modulator? it would be very kind of you if you post the schematic for the receiver section.

Comment from Mark VandeWettering
Time 10/5/2011 at 10:43 am

The link above fully explains the circuit much better than I can. It’s not too difficult: the linear current modulator converts a voltage into a proportional current. It does so by measuring the voltage drop across a 1 ohm resistor (since voltage = current / resistance, if resistance is one ohm, then if you read the voltage as 1 volt, it means a current of 1 amp is flowing through the resistor). This voltage feeds back into the inverting input of the op amp. The noninverting input is your signal. The output feeds the base of a transistor. With a bit of hand waving, the op amp slews to make sure the two voltage inputs are equal, which sets the current through the collector/emitter of the transistor to be the proportional current.

Check out the link above: it explains it all much clearer.

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