What do these 3 components do together?

Discussion in 'General Electronics Chat' started by Amenably_Amendable, Feb 11, 2008.

  1. Amenably_Amendable

    Thread Starter Member

    Jan 21, 2008
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    Let's say you have a NPN BJT
    Connected to the Collector you have a diode connected via the anode
    Connected to the Emitter you have ground
    And, you have a capacitor connected from the cathode end of the diode to ground.

    So you have a "loop"

    N_____DIODE_______(load/output)
    P--------------CAP
    N--------------_____
    _____________Ground
    I'm assuming the BJT is acting like a switch somehow but I'm not exactly sure..
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Well, if you additionally connected the base to the capacitor/cathode junction, you'd have a full-wave rectifier bridge.

    See the attached.

    [ETA] well, you changed things from a PNP to an NPN, but there's no real point in changing my schematic. Go back to your original post.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Actually, you'd have more than just a rectifier bridge; you'd have an unregulated positive DC power supply - with your original PNP configuration.

    Your NPN configuration has a mistake; it wouldn't work with the anode to the collector; it would have to be the cathode to the collector. With that correction, and the addition of an AC supply on the collector and a connection from the base to the anode/capacitor junction, you have an unregulated negative DC power supply.

    I also forgot to mention that in the attached schematic, your proposed circuit was on the left, and an equivalent circuit using diodes instead of a transistor is on the right; similar to the one attached to this post.
     
  4. Amenably_Amendable

    Thread Starter Member

    Jan 21, 2008
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    Thanks for your responses.. Actually it's more something like this (see attachment) I don't know if the values are correct.. but I was wondering what this configuration did..

    Also, sorry for the confusion.. the input (from the base) does not feedback to the output!

    Does it keep the output voltage constant somehow? I'm not interested in the details.. just the theory behind this type of configuration..

    Thanks!
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
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  6. SgtWookie

    Expert

    Jul 17, 2007
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    What scubasteve said ;)

    You made no mention of an inductor before you posted the schematic.

    No, the circuit by itself would not be self-regulating; and would require a driver circuit to turn the transistor on and off.
     
  7. Amenably_Amendable

    Thread Starter Member

    Jan 21, 2008
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    WOW that is exactly it! Thanks guys!:)
     
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