Joule thief

376

13:06:10

Voltage from the battery (A) trickles through the transformer’s secondary winding (B) to the transistor’s base (C), opening the transistor’s collector path (D) partway. This energizes the primary winding (E) partway, storing up energy in a magnetic field which in turn induces current in the secondary, boosting the voltage back to the base, opening the transistor further … around and around. This feedback loop rapidly slams the transistor fully open. The transformer’s tiny ferrite core (F) rapidly saturates, at which point induction ceases, the base voltage drops again, the transistor slams shut, the magnetic field collapses and its stored energy is dumped to the LED (G). The cycle starts again, switching on and off about 50,000 times a second (50kHz) — more than fast enough to make the LED appear steadily lit.

published 9 years ago

thebugger

9 years ago

The explanation is perfect the circuit needs some tweaking. Start by decreasing the transformer's inductance. A small feritte core will have and inductance of a few mH. This has an inductance of 10H. This will affect the frequency. Othwr than that just look for joule thief circuits here in EC and see what might be wrong. Ah and adjuat the time frame too. Just add an AC source and increase/decrease its frequency to match the desired timw frame.

roops1967

9 years ago

Will work, ground it and reverse one of the windings

Vicentesocci

9 years ago

Umm, i may be wrong, but transformer cannot work with DC.

Ampjammer

9 years ago

Just ground it and up the voltage

roops1967

9 years ago

Ok almost there, drop the voltage and reverse the primary or secondary

rich11292000

9 years ago

You can put some dc on a transformer. It has to be derated.

thebugger

9 years ago

Transformer can't work with DC but can work with a modulated DC. The DC passes freely and somewhat biases the transistor while the AC passes through. The transformer's windings must be bifilar. That's ome of ypur errors the other one is the grounding is not present.

weezerr2183

9 years ago

So with the flashlight i built the LED is a three volt and the battery is a "dead" AA battery. Idk why it doesn't work on here.

weezerr2183

9 years ago

And the transistor switching on and off momentarily cuts the ground modulating the dc to make the Xformer work.

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