solar charging circuit, need explaination

Discussion in 'Homework Help' started by bug13, Mar 26, 2012.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    [​IMG]

    ref: http://forum.allaboutcircuits.com/showthread.php?p=469848#post469848

    I came across this circuit in this forum, and I don't understand it, I believe there is a missing link somewhere(some concept I don't know), can someone point me to the right direction? thanks

    basicly I don't understand the part with a transformer - transistor connection.
     
  2. jimkeith

    Active Member

    Oct 26, 2011
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    It is a self-oscillating boost regulator (actually non-regulator as there is no voltage feedback. It takes the low voltage solar cells 8 * 0.5V = 4V, uses this voltage to charge the primary transformer inductance--the secondary turns on the transistor harder so as to saturate the transistor (high current, low sat V zeltex transistor)--the current continues to increase until the transformer core saturates at which time the transistor drive substantially weakens and reduces the collector current, which reverses voltage polarity on both the primary and secondary--the transistor turns off and the inductance discharges into the higher battery voltage until the inductor is discharged--and then it starts over again--whew!
     
    Last edited: Mar 26, 2012
  3. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Thanks JimKeith, I got what you are saying, now I have new questions, what are those two capacitors do in this circuit?
     
  4. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    Bypass filters for AC, at the frequency of the oscillator they are effectively a short.
     
  5. jimkeith

    Active Member

    Oct 26, 2011
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    In addition to what nsaspook said, the input capacitor provides the peak current to saturate the transformer--the solar panel probably cannot do it--also keeps a steady DC current flow out of solar panel because the boost converter uses it in pulses so that during the transformer discharge cycle, the solar panel would be idle.

    The 2nd capacitor provides a low impedance return for the transformer winding that drives the transistor.

    An interesting experiment would involve trimming the transformer turns ratio for highest efficiency, and /or adjusting the base drive turns for the same.
     
  6. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    increasing efficiency is something interested me, but I don't what exactly do you mean to get better efficiency
     
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