This cycle happens so fast that the human eye resolves these pulses as a constant light source. The field then collapses, inducing current that travels through and lights the LED, instead of traveling through the collector-emitter path, at a voltage higher than the battery can provide by itself.Īfter the field collapse, and the LED’s momentary lighting, the process starts over again. When the core becomes saturated, not able to further increase its magnetic field, the induced voltage goes away, closing the emitter-collector gate. This, in turn, allows electrons to flow through the other coil, increasing the magnetic field and inducing even more voltage to the base. ![]() This creates a magnetic field and provides voltage on the base to open the collector-to-emitter path of the transistor. When the circuit starts up, voltage is applied to the transistor's base through the inductor. ![]() The 10mH coupled inductor pictured here works, but makes an audible noise. Coil cut in two here forms a coupled inductor. Low voltage required to keep this joule thief LED running. If you’re buying a device specifically for this use, however, you’ll want to pick up a coupled toroid. You can also hand-wrap your own ferrite core, which can be useful if you find one to recycle. The coupled toroid shown was made by cutting a single winding inductor into two and scratching off the insulation with sandpaper. In the image below, you can see this type of circuit lighting a red LED at a mere. ![]() Once connected, you can power an LED with a voltage drop well beyond the cell’s rating, even when it’s mostly discharged. Coupled (2 separate windings, 4 connections) toroid inductor-2mH (millihenry) and 10mH tested, many others will workĬonnect components per the schematic below:.Battery, rated at (or discharged to) ~.To build this, you’ll need the following components:
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