As i had some free time this summer, I decided to bring back some of the popular designs i had created almost ten years ago with my recreational lighting company, Space Cat Advanced Lighting Systems. Around ten years ago when Luxeon LEDs were first hitting the market, I designed a 1 Watt LED driver circuit which uilized the Luxeon STAR-O LED which operated at 3V (it was a red LED) and 350mA. This was designed to be used for caving applications and powered via a single AA battery. The original assembly looked almost the same as this new design (used the same battery clips) but was about 1/2" longer to accomodate the larger LUXEON LED module. The exposed circuitry was also conformal coated for moisture protection. The circuit worked extremely well, although the LUXEON LED was quite large. So the first thing I did when redesigning my existing circuit was to use a smaller LED - in this case a Cree 1W X-Lamp, and to reduce the overall size of the board. The original size of the board had the same width, but was slightly longer (1/2") to accomodate the LUXEON LED. With the smaller Cree 1W LED, i was able to make the board the smallest size possible equal to the size of a single AA battery.
The original name for the LED driver i designed was the Hyperkatz LED Driver. However for this version I simply renamed it to a more generic Joule Thief name - as everyone and their grandmother seems to be calling any low voltage LED circuits Joule Thiefs regardless of how they are driven or how efficient they are. We also made some potted units of this same driver for another recreational lighting company as prototypes back in 2004. I've attached some photos of those original potted prototypes. The only difference with those, was that there was no switch and the LED had to be attached externally.
So back to this old 1W LED drive circuit. The circuit utilizes an programmable boost controller IC which operates from a single AA battery and utilizes a boost switching converter topology to boost the battery voltage of the single AA (down to 0.8V) up to approx. 4V to power the 1W Cree LED. Although not a Joule Thief in the traditional sense, it still will operate from a drained AA battery down to a voltage of 0.8V, although this circuit works best with a fresh AA battery.
This particular Joule Thief is designed for 1W White Cree LEDs, but can work for any number of high current LEDs. The boost circuit is designed to regulate LED current at 350mA or less. The onboard potentiometer can be used to vary the output LED current and therefore the brightness of the LED.