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Without resistors

Discussion in 'General Electronics Discussion' started by pidja105, Jan 6, 2016.

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  1. pidja105

    pidja105

    106
    1
    Oct 16, 2015
    Hello,
    I'm building inverter and I am using transformer from PC power supply,and can I makr that without resistors with attached schematics?
     

    Attached Files:

  2. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    PC power supplies normally use high frequencies and a ferrite cored transformer. These can not produce 50 or 60Hz.
    The resistors are necessary to limit the transistor current and they will not last long without them.
    The frequency will depend on the transformer parameters and will be square wave. This may not suit you.
     
  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    651
    May 8, 2012
    Why PNPs? High power NPN's are far more common. No Base - Emitter Caps either. How does it oscillate without them? o_O

    Chris
     
  4. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    The circuit oscillates with the feedback through the resistors, they are crucial to the operation.
    Normally capacitors are used for feedback and there are resistors to give the base current. In this case, the circuit switches when the transformer saturates so I suspect that it will be hard on the transistors and low in efficiency.

    A better circuit uses two transformers, one a power transformer running in its linear mode and one small transformer supplying the low voltage base drive running into saturation (and getting hot).

    The fasion seems to be to use fets which have a low resistance when switched on, these have to be driven with a small circuit.

    Trevor
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    651
    May 8, 2012
    Trevor, thanks for the T.O.O. Seems like the OP's image is a crap shoot design.

    Chris
     
  6. BobK

    BobK

    7,682
    1,687
    Jan 5, 2010
    It would probably oscillate, but I expect the frequency would be dependent on the inductance of the transformer and perhaps even the load. Not likely a good design.

    Bob
     
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