Joule thief?

http://joulethief.com/kit.php : It was from here that I built my first working joule thief. (I've found better ones now.) Anyways, last week, I got bored and tried to destroy an LED by feeding the circuit more and more power...I got to 18V (laptop charger adapter) and it still didn't bust. Why?

frimm6 years ago
 The joule thief does its work when the transistor turns off. With a higher than normal voltage, all you're doing is keep the transistor on much longer, which will do nothing but burn up power.

I suspect all you get is an uncomfortably warm coil.
For some reason the input voltage dose not greatly affect the output voltage but I have know idea why.
Re-design6 years ago
The coil must be limiting the current thru the led.  The transistors are also taking up some of the load.

Or maybe it's just a super-led!