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Nov 20, 2013, 07:12 AM
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Flashlight part 2





Took another swing at the flashlight problem. The easiest way to make it more efficient was to boost the voltage to 9.9V & power 3 LEDs in series. 5 strings of 3 LEDs would suck 200mA. Bucking it down to 3.3V would take 600mA, a real challenge for a tiny inductor.

Made an exact, miniaturized copy of the microphone boost converter from 2 years ago & changed the target voltage to 9.8V. In the worst case of boosting 6V to 9.8V with 200mA, the MOSFET hit 60C & the diode hit 60C.

In reality, the lowest input voltage is 6.6V, at which point the battery is destroyed. The nominal voltage is 7.4V. The actual current for the 15 LEDs ended up being 170mA. 4 strings ended up using 30mA & 1 string ended up using 50mA.

Powering 15 LEDs with the boost converter now takes 400mA. Using the linear regulator, it took 600mA to power 10 LEDs. The battery should last 2 hours instead of 1. That's the power of the boost converter. You can always buy a more stable boost converter that does it in a lot less space, but that comes with a $15 tag.






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