Joule Thief is not working

Discussion in 'General Electronics Chat' started by GeorgeElectronics10, Jun 13, 2015.

  1. GeorgeElectronics10

    Thread Starter New Member

    Jun 13, 2015
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    I made a Joule Thief recently and it worked -on a protoboard- but now it does not work, it gives the same voltage from the batteries, I apply like 2V and the white LED does not light up, I have no idea of what might be the problem, the coil is about 12 turns, the LED is 3.5V 100 mA. Also I have used a 3.2V 20mA LED and it´s the same.
     
  2. ian field

    Distinguished Member

    Oct 27, 2012
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    Unless you use one of the standard form oscillators to drive the inductance - nothing much will happen.

    The most common type of Joule thief is usually the blocking oscillator - which I believe may be a variant of the Hartley oscillator.

    If you were using a 1.5V cell, I'd say; wind about 15T for the collector winding, twist out a tapping point and continue winding the same way for another 12T. The tap is the Vcc feed and the end of the 12T goes to the base via a 15 - 100R resistor. The flyback pulses on the collector should easily light a white LED.

    For higher voltage supply, you need to bias the transistor differently; first the 2 windings have to be isolated from each other and secondly they have to be correctly phased for the oscillator to work. The 12T base winding must be ground referenced and fed to the base via a DC blocking capacitor. Then you have to add a start up resistor from base to Vcc to get the transistor started.

    Another common Joule thief is the basic astable multivibrator with a single inductor replacing one of the collector load resistors - but you have to dimension the CR timing components to suit the coil you use to get efficiency.
     
  3. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Please post a schematic or a link to same:)

    TTFN
    HP
     
  4. ian field

    Distinguished Member

    Oct 27, 2012
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    The simplest Joule thief is only 5 components - including LED and single cell power source.
     
  5. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    I'll take your word for it!:cool: - Even so 'debugging' assistance would be greatly augmented via apprehension of the specific circuit in question:)

    Best regards
    HP
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    The internet is literally cluttered with the basic blocking oscillator type Joule thief schematics - the astable variety aren't exactly scarce.
     
  7. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Just so!:) -- All the same I hesitate to advise sans details specific to the OP's circuit "one man's human's Joule Thief....." and all that:D

    TTFN
    HP
     
  8. GeorgeElectronics10

    Thread Starter New Member

    Jun 13, 2015
    2
    0
    Thanks, I put it again on the protoboard and it works :)
     
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