Joule Thief

[gyulasun]

@gyulasun, I have one that will start without it ( the resistor ), without a switch as well, it's pictured here: http://www.overunity.com/index.php?topic=6123.msg165655#msg165655 and here http://www.overunity.com/index.php?topic=6123.msg166453#msg166453 as a recitation.

Ok,  it can start even without the R1 resistor indeed, induction and / or the charge/discharge of the series capacitor with L2 insures this when the battery voltage is connected, the transistor works as a kind of Class-C amplifier / oscillator.

Earlier you asked:

Quote from: jadaro2600 on March 28, 2009, 06:09:04 PM
I have a DMM, and it has a diode checking mechanism ..which, when placed across the appropriate leads on a diode, gives me a number ( usually a less than one as a decimal, such a 0.671 ).  Is this number the voltage drop I can expect to see across it?

Yes it is the forward voltage drop.  Many digital multimeters have a separate diode test setting either embedded in the resistance measuring range or next to it separately.  In this range the DMM is designed to display the voltage drop (not the forward resistance) in Volt, so your value of 0.671 is 0.671V for that diode, measured at a low (about 1mA) forward current via the diodes to be tested.  You can check the diodes between transistor electrodes (BE or CB) in this diode test setting too and in case of Germanium or Schottky diodes you can nicely see the differences in the forward voltage drops.

Re on you interesting observation you find a bit higher voltage across the upper capacitor:  I think the explanation is that between those two points the baterry voltage and the flyback voltage of L1 add up in series so in theory the extra voltage is just the value of the battery voltage minus the two voltage drops of the diodes leading to the upper capacitor.

rgds,  Gyula

[jadaro2600]

Re on you interesting observation you find a bit higher voltage across the upper capacitor:  I think the explanation is that between those two points the baterry voltage and the flyback voltage of L1 add up in series so in theory the extra voltage is just the value of the battery voltage minus the two voltage drops of the diodes leading to the upper capacitor.

rgds,  Gyula

This makes some sense, the reading was 105 volts on the upper and 100 volts on the right.

...there was some reverse bias, I could get the LED to light up in the opposite direction, but the polarity ... and the voltage as configured was giving my a very dimly lit LED.  I attribute that effect to the action of the collapsing field in the coil-to-base.

@all,

Has anyone come up with anymore results on the voltage difference between the secondary ( pickup ) and the ground?  I was reading that there were some boosted readings?

[xee2]

The following refers to a standard Joule thief circuit.

[jeanna]

Thank you xee2,

That is clear, sensible and simple.

IMO that is the best explanation of the bjt.

thank you,

jeanna

[nievesoliveras]

@jeanna

Howdy!

When you say 07,07,70 2(degree symbol)

What do you mean with the two and the degree symbol. What does that mean?

Thank you in advance.

Jesus