Petty Joule Thief

[minus3db]

You might be familiar with the original Joule Thief, a simple, homebrewable step-up converter often used to drive LEDs (with Vf of several volts) from a single 1.5V battery, or extract the last remaining juice from a battery that’s too dead for use in most real-world gadgets. The basic Joule Thief can suck power from low voltage sources where

Comments

[farniks]

the 555 timer chip has been around since the 70's and was designed for things like charge pumping. I guess it didn't work down to 300 mV (probably more like 5V) but I bet there are lower voltage versions of it around today that are not as hard to get as the Seiko.

Your diode in Figure 3 is gonna make the turn-on voltage pretty high. In practice do you guys use 0.2 V Schottky's or do you use some kind of synchronous rectifier?

[minus3db]

Yeah, hobbyists normally use a very low-vf diode there. This is basically the simplified "crystal radio" of the olden days with the earphone replaced by the boost circuit. Traditionally it was a germanium diode (0.3-0.4V) back in the day, now I think schottkys are the norm. I looked and there are actually synchronous rectifier circuits using the same (actually available) part I was going to mention:

Advanced Linear Devices has come out with a "zero-threshold" MOSFET that can be used to form oscillators from around the same voltage levels (~ 300mV) that run down to dozens of mV. That may be the better way to go (it beats chapped lips smelling of salesdouche), but I haven't gotten around to playing with it yet. Those parts are available in single units on Mouser though.