NPN Transistor

Discussion in 'General Electronics Chat' started by Neyolight, Mar 1, 2012.

  1. Neyolight

    Thread Starter Member

    Dec 13, 2011
    54
    3
    Hi

    How does this simple NPN transistor work as an oscillator? I have it oscillating on breadboard but slightly confused about how it works....

    Can someone PLEASE explain it to me step by step!

    Pic attached....

    Thanks
     
  2. mlog

    Member

    Feb 11, 2012
    276
    36
    Oh, my. I haven't seen this one in a while -- a Colpitts oscillator. The resonant frequency is determined by the parallel resonant L-C combination -- the C part comes from C1 and C2 in series.
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,421
    3,357
    Check up Colpitts oscillator.

    http://en.wikipedia.org/wiki/Colpitts_oscillator

    An oscillator is not restricted to NPN transistors. A PNP transistor will work too with the proper modifications to the supply polarity.

    Basically, the LC network creates a phase shift of the signal from the output and feeds it back into the input. This causes the circuit to oscillate.
     
  4. mlog

    Member

    Feb 11, 2012
    276
    36
    I'm dating myself, but when I learned about Colpitts oscillators, it was with vacuum tubes. :)
     
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