Joule Thief

[Pirate88179]

As far as I know, when you check a diode you should get a high resistance in one direction and low resistance in the other direction. This is using the resistance reading on the meter. Now that they have a diode setting on most meters, I'm not really sure of the meter circuitry that gives you the reading. I would think that the diodes that give you the same reading both ways are questionable.

Good point.

Bill

[crowclaw]

Good point.

Bill

This theory is correct. A standard silicon diode has a forward voltage drop of 0.7v while a standard schotky diode has a lesser value. Their reverse resistance for all intensive purposes can be viewed as open circuit. Certain diodes work better in switching circuits especially at higher frequencies and power levels. Ultra fast and fast recovery types are worth experimenting with many of these are frequently used in PSU's surprising what you can retrieve from scrap.

[crowclaw]

 This is my EMPT (electro magnetic power transfer) circuit using a standard JT  configuration. An empty plastic paint tin cut to make two 10" rings 2" wide.
14 turns of insulated stranded hook up wire for the secondary. The primary feedback is two turns around the outside over the secondary. This configuration produces pulses of approx 160 volts @ around 20Khz. The source = 1.5 volts using a BC547 transistor. The pick up coil is wound the same as above except no feedback winding. The distance between the coils = 5" to give light as seen but will remain lit up to around 9_10". The base resistance uses a 5k control but a 100R together with a 10R or less in series would be better to limit the base current. See Pics. Have fun

[crowclaw]

PIc two showing bottom and top coils spaced by tape reels

[crowclaw]

Notice the scope shot of the JT CE junction showing positive going pulses and not AC in this case.
This demonstration shows the magnetic flux lines from the first coil transfering through the air to the  second pick up coil and lighting up the LED.