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Joule robber - a better joule thief.... Answered

I had a look at some of our 'ibles for the famous Joule Thief circuit.
While checking a few of the creations and checking their performance I noticed a massive flaw:
Only LED's with very low power consumptions can be used.
After some trial and error I was able to create a slightly modified version that not only lights white and blue 5mm LED's but also the very powerful Cree Led's - the later would require a suitable transistor to handle the load.
I only used a salvaged BC556 transistor, so the LED starts working at around 0.5V, brightness is adjustable within certain limits to cater for the battery state.
So instead of using a limited circuit that basically just doubles the input voltage with the focus of extreme low power consumption, my circuit is aimed on single cell battery lamps that might need more power.
Using a very low voltage transistor with minimal losses would still provide a power source for batteries that are under 0.5V, while using a bigger transistor like Tip142 or 2N3055 and a modified transformer can drive a CFL lamp from two AA batteries, single cell if you don't mind a warm transistor.
Biggest improvement however is that I don't use a toroid core, which makes winding so much easier :)
I am not too good in drawing circuits and prefer the direct solder method for my prototypes but if there interest I would take the time to make some pics and draw a circuit for an Instructable.
But with so many similar circuits already out there I wanted to get some feedback first.



4 years ago

I would be keen to see that. Can see some good purpose in that


4 years ago

I don't think it is a flaw that joule thiefs are usually made to run low power LEDs but more of a design restraint. You are trying to suck out the last bit of juice in a battery that is not enough to drive your device like a flashlight or portable radio. Your CFL lamp might run for a few minutes whereas a single LED light would last a lot longer. If you have a warm transistor, that is also wearing away at whatever power you can extract.