Introduction: "Joule Thief" Circuit in a Flashlight Bulb? Yes!!!
Investigating a Paradox:
Recently, I saw an "energy saving" LED flashlight for sale and it only used one 1.5 volt battery. I purchased this light and took it apart expecting to find a battery, bulb, switch and some kind of circuit on a board that would boost 1.5 volts to the higher voltage needed by any LED, especially a bright white-blue LED. I expected something similar to circuits used in my Instructable, "Joule Thief" circuits, crude to modern OR my Instructable, "Joule Thief" - no IC and no Transformer. I looked everywhere but only found a bulb, switch and a battery. This didn't seemed possible at first but then I wondered, could the "Joule Thief" electronics be entirely located in the flashlight bulb? Well, this possibility ruled out the use of any clunky, bulky toroid type of "transformer" used in the more popular "Joule Thief" circuits. It was time to try and cut open this bulb.
Well, isn't this amazing! Here is some kind of "Joule Thief" circuit so small it fits in the shell of a standard flashlight bulb. Especially notice the tiny and simple inductor along with the lack of any "toroid." The bulb had 1.5 volts and 0.2 watts stamped on it's metal shell. The brightness rating is 9 Lumens while the number of expected hours of use is 52 hours (In the past, I've seen 8 or 9 hours of use listed for incandescent bulbs).
And now the test. Did I wreck this LED circuit when I cut it out from it's casing? Here we have a direct hook up to a 1.5 volt battery. When the final connection was made, it lit up brightly. What a move forward this design is!!! The hardware isn't super friendly for Instructable People but it is not impossible either. I haven't "decoded" the circuit board yet as the layering looks tricky. And I just wasn't ready yet to risk destroying this cool light. Maybe I'll do this later or maybe someone else will do it...