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Germanium transistor “joule thief” circuit

Project description

Long ago there was a sort of contest on 4hv forum – who can make a “joule thief” circuit that powers a blue LED, from a lowest possible voltage source. This is actually a quite difficult electronics problem, if no extra supply can be used to provide some sort of starting voltage for the converter. My attempt was a simple blocking oscillator based on a germanium transistor, which managed to light the LED with supply voltages down to 125mV, albeit at a very low efficiency. This allowed the LED to be lit from very small thermoelectric voltages – such as produced by a semiconductor Peltier heat pump from a portable fridge, when heated by hand or cooled on one side by an ice cube.

A demonstration, powered by a melting ice cube

A demonstration, powered by a melting ice cube

Schematics to come later.

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One Comment
  1. phil permalink

    Very impressive!! Would really love to see the cct diagram

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