Is that a joule thief?

[Groundloop]

Hi Groundloop,  Thanks for sharing that figure 8 circuit.  I think I've got everything to build it except the diode.  I've got a C5778 transistor with 1600v 15A ratings and it's a high speed NPN that I think will work fine to replace the NTE2354 and a 225 watt rheostat should handle the variable resistor  
While looking in a folder of saved info from you I found the diagram below from you from 2011 but I can't seem to find any message thread tied to it.  Do you have any idea where I might find more about it?

e2matrix,

I finally got time to download and study the data sheet for your 2SC5778 and you can NOT use that
transistor in the Figure-8 circuit. The reason is that the 2N5778 has an internal diode over the collector
emitter wires. The transistor also have a internal resistor between base and emitter. You need to find
a high voltage power NPN transistor that does not have any internal "extra" components.

GL.

[Groundloop]

Today I did a test with two depleted 8,4 Volt 120mA rechargeable Ni-Cad batteries.
I did connect the two batteries in series and the start voltage was almost 9 volt.
(Less than 4,5 Volt in each battery, totally drained.) I have connected the batteries
to the JT posted above. I have found that it is almost impossible to fully drain a
rechargeable Ni-Cad battery to zero volt. It will always gain some small value after
a prolonged short circuit. So I assume that rechargeable Ni-Cad batteries has the
same "self charge effect" as electrolytic capacitors have. I know that my JT will run
fine down to approx. 2 Volt. So it will be funny to see if the "self charge effect" in the
batteries will keep the LED lit for some prolonged time. Expriment started 21.04.2013
at 1500 local time. Measured voltage was 8,9 Volt. Now I must let the JT run and see
when (or if) the LED will go totally dim.

GL.

[Groundloop]

Now (22.04.2013 1600) the JT circuit has run over 24 hours. The voltage in the two series
batteries has dropped to 3,72 Volt, but that was expected. The LED is still giving out
a good "night light" level. Both batteries is very close to the "self charge" level where
the "self charge" should kick in. I know from earlier tests that it is almost impossible
to fully drain a battery to zero volt. The battery always "want" to have some small
level of charge. So I will let the circuit run and see what happen.

GL.

[Groundloop]

Now we are into day 3 of the run down test. The combined battery voltage is now 2,87 Volt.
The LED still has enough light to be useful for night lighting. The frequency of the oscillator
has been constant at approx. 479KHz during the run and has not changed much since the
start of the run. A 9 Volt rechargeable battery (Ni-Cad is actually 8,4 Volt) has 6 cells inside
connected in series. Since I have connected two such batteries in series then we have 12 single
cells in series. So each battery cell is now at 0,2391 Volt. Remember that we started the run
with two drained batteries. It is my theory that it is impossible to fully drain a battery to
zero Volt because of the battery "self charge effect". So by theory at some point in the
discharge curve of the battery we should see that the voltage stops dropping. Where this
voltage point is at is unknown right now so I will keep the circuit running until there is no
more useful light in the LED. To be continued...............................

GL.

[Groundloop]

Now (23.04.2013 1500) the battery voltage is 2,83 Volt.
LED still providing enough light to be a "night light".
Only 0,04 Volt battery voltage drop in 9 hours.

GL.