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Need SS Design for Vibrator ckt

Discussion in 'General Electronics Discussion' started by BCISam, Mar 30, 2013.

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  1. BCISam

    BCISam

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    Mar 29, 2013
    Vintage radio-tried commercial vib; input current smoked it. Need design for robust Six volt sync SS Vib ckt. want to fit back in Vib can.
     
  2. duke37

    duke37

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    Jan 9, 2011
    Please give more details of what you wish to do.

    Are you going to use the original transformer?
    What frequency was the transformer run at?
    What is the transformer core, ferrite or Si-iron laminations?
    What is the input current and voltage?
    What is the output current and voltage?
    How big is the can?
    What is the original circuit?

    I made a vibrator replacement some time ago and have just made a 12V to 300V invertor to drive a 62 set.. The vibrator replacement would go inside a vibrator can, the invertor uses a TV LOPT transformer core and will not go inside the can (it is inteded to replace a rotary convertor) but it may be possible with a pot core.


    I will look up the earlier circuit and find a pretty picture.
     
  3. duke37

    duke37

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    Jan 9, 2011
    Here is a circuit for 12V input, A couple of diodes from the drains of the fets to supply the chip would be necessary for 6V input.
     

    Attached Files:

  4. duke37

    duke37

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    Jan 9, 2011
    And here is a picture.
     

    Attached Files:

  5. BCISam

    BCISam

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    Mar 29, 2013
    Thanks Duke; Answers to your questions:
    Transformer replaced;Runs @115Hz; core is laminated; input is 6.3V @ 4.5A;Output is 330V;Size is ~ 15/8 In. dia. ;X31/2 in. Ht.
    Original ckt in Delco Model R-705, Neg Ground, Vibrator (dual sets of points) used as a chopper for input 6 VAC and 2nd set used to rectify xformer output.
    I'm not real sure about the use of diodes to convert ckt to 6V; could you clarify?
     
  6. duke37

    duke37

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    771
    Jan 9, 2011
    The circuit is running slowly so the fets could be fed directly from the 4047.
    The timing components for the 4047 should be sized for 120Hz or so. The frequency must not be so low as to put the transformer into saturation.
    F=1/(4.4*R*C)

    Normal fets need more than 6V to turn on fully, 10 or 12V is good. Feeding the 4047 from the drains via diodes gives about twice the input voltage. It is only necessary that the fets should be able to pass some current at 6V input to start.

    You will need a bridge rectifier on the output to replace the second set of contacts, this can be made from individual diodes (1N7007) or from a moulded bridge (SKB1.5?).

    You should check that the fets do not get hot and you may need some extra capacitors on input and output if you get interference.

    The original vibrator will have a dead time as the contacts change over. There is often a capacitor to tune the primary so that the voltage reverses ready for the next contact to be made. This capacitor will not be needed.

    A fuse is always a good thing. Polarity is critical, you may want to fit a fat diode to ground after the fuse so that the fuse blows if the polarity is connected wrongly.
     

    Attached Files:

    • Inv.png
      Inv.png
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  7. BCISam

    BCISam

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    Mar 29, 2013
    Hey duke37: Thank you for the help!
     
  8. duke37

    duke37

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    Jan 9, 2011
    Two things.
    1. In my sketch, I connected the fets to one output of the 4047. This is of course wrong. They should be connected to P10 and P11.

    2. If your new transformer is a replacement for a synchronous vibrator, then it will have a centre tapped output so only two HT diodes will be needed.

    Let us know how you get on.
     
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