Today I experimented with the components for the surface mount version of the Joule Thief.  The experiment involved trying a different combination of  transistors and resistors. Finally I have settled on the values for the production version of the surface mount JT PCB. When this board is completed it will be one of the smallest JT circuits available and should measure around 0.276″ x 0.276″ x 0.118″ (7mm x 7mm x 3mm)

The final prototype was capable of running from input voltages of 600mV to 2.1V , it could drive two series white LEDs with a voltage as low as 600mV and they were still giving off a decent amount of light. At 600mV input the current draw was 6mA, at 1.5V in the current draw was  about 70mA, and at 2.1V the current draw was a little over 100mA.

The amazing thing was without the LEDs connected I was seeing peak voltages >100V with the 2.1V input voltage. Running this circuit without a load is not recommend because it was exceeding the absolute max voltage rating of the collector to emitter of the transistor.

I was using OSRAM Hyper PointLEDs that are rated for about 800mcd, and they are tiny at 1.9mmx3.5mm. See the LW P4SG Datasheet, these LEDs and many other LEDs will be available for purchase in the products section when the commerce section of the MSH website goes live later this year.

The next step of this project will be to experiment on the printed circuit board. I still have to order parts for the surface mount version so I expect to do some more lab work on this in a couple of weeks.

I spent time laying out the thru-hole Joule Thief PCB today. This board is designed so that you can experiment with different component values so I made the board as rugged as possible so that the parts can be removed and replaced many times without worrying about damaging the PCB (so long as good soldering practices are followed). This board measures 0.775″ x 0.795″ (19.7mm x 20.2mm).  This kit will be offered with complete parts or as individual components. The introductory price for the individual PCB will be $2.99 or as a complete kit with a toroid core, 80 inches of magnet wire (40inches red, 40 inches green), a transistor, an ultra bright white LED and resistor for about $5.99