I got this Google Alert for a request for a JT schematic. The text of the original request and my reply are in the attached picture.
These request are quite common, and typical for the forums which discuss Joule Thiefs. It is an up front indication that the requester has no clue whatsoever about what the Joule Thief can do or that it will not “make my LEDs more efficient”, which is another typical misstatement.
I have speculated about how the requesters may have been misled to believe that the Joule Thief is the answer to their problem. One theory I have is that they see some Youtube video such as this one that makes the outrageous claim that the Joule thief can light up a string of hundreds of LEDs on Xmas tree lights “to full brightness” or something to that effect. What the simple math tells us is that it takes about a tenth of a watt to light up each LED “to full brightness”. So 300 times a tenth of a watt equals 30 watts. Simple, no? We will require about that much power to make a reasonable amount of light from the string of LEDs.
Somewhere there is this fundamental misunderstanding that we cannot get something for nothing. The added electronics are going to need some of the power, and what’s left is what’s going to be output to the circuit, the LEDs in this case. We can’t expect a Joule Thief to magically solve all of our problems.
When someone discusses a circuit, the reader should be informed of not just the circuit’s advantages, but also of its limitations and shortcomings. If they lack this information, they cannot make the correct decision on how suitable it is for their purposes.