Lately I've been playing around with different kind of leds, mostly with ones that are inside usual led bulbs. And when one led burns out, the whole lamp is useless - or is it?
I tested the rest of the smd-leds(in the bulb's pcb) with a simple voltage doubler, and yeah, it seems to be possible to run those 18-30V leds with lower voltage, like 9V.
But as usual, things got out of hand, and I had to find out, if there are ways to use them at even lower voltages. That's why I started to look for joule thief.
It's basically simple circuit like this:
There are dozens upon dozens of versions of it, but generally one thing appears to be common between them: toroidal bifilar coil. And they are pita to wrap, especially if one would like to experiment with different sizes:
Simpler, air core axial coils also work with joule thief, as some builders have done. That seems to be the case, as I tested it too.
Current circuit on breadboard:
Then somewhere came the idea to test instead with two separate 180uH inductors side by side:
It's weird, but it seems to work. To make sure, that the oscillation happens between those two coils, I pulled them slightly apart, and it stopped.
The results with current settings so far, with 3V led at 0,8V 48mA:
Three 15V(or perhaps rated at 18-20V like similar size 2835 leds) leds at 0,8V 54mA:
In both cases, the leds aren't overly bright, though. I tried increasing the voltage to 1V and above, but it starts to use excess amount of current, like 100mA or about as much as the source provides, even when there are no leds connected.
For testing, I used a bench psu, as at the moment I don't have batteries flat enough that would go down to 0,8V.