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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
How could this be possible? I have a small solar cell that puts out .5 volts in full sun, and .3 under slightly shady conditions. It's output current is 500 mA.
I tried a joule thief...but that didn't work. Any other ideas?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
The TPS61202 (see Sulaiman's link) can work down to 0.3v input with 5v output. It can't start up from 0.3v, it needs a higher voltage already on the output to bias the switch FETs, but if you're charging cells then you've got that anyway.
I did come across a better device (but of course can't find it now) that IIRC would work down to 30mV input, for stepping up Peltiers and themrocuple outputs. This used a FET bridge round the inputs to a step-up transformer, again it needed an existing several volts on the output to bias the FETs. Was it made by Linear Technology?
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
JFETs can be used for super low voltage oscillators as well.
Their on resistance isn't great, so it wouldn't be too good for efficiency ... but you could make an oscillator with 2 JFETs in series to create a bootstrap voltage for a plain old boost converter, after the output voltage is sufficient for the boost converter to run you pinch off the second JFET and stop the oscillator.
PS. I wouldn't be surprised if that is close to how the Linear IC works, start up with JFETs and then transition to MOSFETs.
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How to step up .3 - .5 volts of electricity to 5 volts?
