App Note: Boost converter that works with voltages down to 0.5v


EDN Network covers the design of a very low voltage boost converter. The circuit in question is an LED flashlight designed to power 2 LEDs from voltages as low as 0.5V. The circuit uses an integrated constant current boost converter LT192, though for a cheaper design look no further than the Joule Thief.

Via Electronics Lab.

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  1. It “works” with 0.5V by powering the circuit with two dead batteries in series so you get more than 1V supply.

  2. The EDN article sounds pretty optimistic. Run old batteries down to 0.5V? This will need a replaceable 2xAA battery holder since you’ll probably be dealing with rust later on… Say you run 2 white LEDs at ~7V (series) and 20mA. With 2AAs, it will start with ~2.5X boost. At 0.5V per AA, >7X boost is needed. Nearly-exhausted AAs supplying 140mA? Only if the no-load voltage is quite a bit larger than 0.5V. 90% alkaline cell capacity down to 0.9V suits me just fine ;-)

  3. My bad, 140mA is the average current desired for normal light levels. The peak draw, according to simple boost equations, would be 280mA, and that would be asking a lot of an alkaline cell at 0.5V, which would sag pretty badly. IMHO, normal light levels is pretty much out of the question at 0.5V. Would the rosy scenario in the EDN article actually work for such exhausted batteries? Colour me skeptical.

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