Joule Thief

[xee2]

@ altrez

I posted this some time ago.

[altrez]

@ altrez

I posted this some time ago.

Thank you so much for the re-post!

-Altrez

[crowclaw]

Can someone explain the concept of parasitic capacitance a bit more ( or at least how this pertains to the joule thief ).

Hi jadaro2600,

Parasitic capacitance is a situation that often exists as an unwanted result of electronic components placed within close proximity to each other.
Circuit board tracks, wires and inductors can effectively form capacitive elements similar to the plates of a capacitor. The resultant capacitance set up by surrounding electrostatic fields can seriously effect the performance of electronic circuits creating instability, frequency deviations in oscillators and many other undesirable effects. Two conductors placed side by side or wound as a as a coil posses a natural capacitance due to the fields set up as current flows through them. Circuit designers have to take into account  these capacitive effects especially in the design of HF oscillator circuits where the spacing between the windings of a coil is paramount to it's circuit performance. The JT circuits posted here in particular can produce varying results from this phenomena alone.  Unfortunately electronic principles and explanations can be very difficult to put across in terms that can be easily understood and I'm probably not the best when it comes to explaining things... so I hope I've managed to help you here!     

[stprue]

@all

Koolers circuit works great!  Here are a few pic and a video is soon to follow.

1.5v
Draw .07ma
7 LEDS
Transistor 2N3904

[crowclaw]

The spikes refer to the high voltage transient pulses that are produced when an electrical current flowing through an inductor is switched on and off. The resultant back EMF (electro magnetic field) due to the calapsing field at switch off  produces a resultant voltage in excess of the voltage that created it. This is a very brief theory. Think of the transistor used in a JT circuit as a simple off/on switch connected in a series with an inductor which is being turned off and on at a rapid rate. The on time compared to the off time is infact quite short and so appears as a positive spike resembling a needle as seen on an oscilloscope screen, this positive transition represents the time the transistor is switched on and because of it's extremely short on period compared with it's relatively long off period is one of the main reasons this type of circuit draws such a low current from the source battery. There are several scope shots within this thread showing the wave form produced by this type of circuit. By the use of a feedback coil winding to the base circuit the transistor can be automatically switched on and off at a re occurring frequency dependant on the various component elements which make up the complete circuit. This switching action thus gives rise to a  series of high output voltage pulses or spikes. LED's are relatively high impedance and low current devices and work well across the output of the JT. By clever manipulation of the available energy
various other ideas have also been put forward by other contributor's.