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Registered Member #3451
Joined: Sun Nov 28 2010, 11:13PM
Location: United States
Posts: 100
Hi, everyone. I found this schematic of an efficient joule thief online:
I grabbed all the parts and prototyped the circuit on my solderless breadboard; LEDs do light up, and my multimeter measures 3 volts. However, when I pulled the transistor out, the reading didn't change. I glanced at the circuit again and realized that the LEDs were simply connected to the battery terminals, albeit with the 10T coil's resistance. The transistor is essentially useless because it's not even being turned on! My other 2N4401s show no difference.
I get the feeling that I'm doing something painfully wrong. Have I misinterpreted the schematic?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi,
Well the circuit is a boost converter, hence it can't reduce the voltage if you run it from 3V, and might likely blow either the led's or the transistor if you do. LED's would be ran from voltage source which is very bad for them, and the transistor is biased pretty hard to supply voltage so if oscillation stops it will act as a short.
Try running it from 1.5V and see the difference :)
Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
The whole idea behind the joule thief is to suck that last bit of energy out of half dead cells which electronic devices think are completely empty, hence the name "joule thief"
These devices are said to kep a LED lit down to 0.8 or even 0.5V.
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Understanding a Joule Thief
