Power Transformer with secondary winding

Discussion in 'General Electronics Chat' started by tracecom, Oct 17, 2012.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
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    I have the power transformer shown in the attached schematic. The schematic is of a 12A, ≈13V power supply. From the schematic, it looks like there is one secondary, which supplies the output and another which supplies a regulator circuit. There are also two sets of rectifiers.

    Any additional information about this transformer and its use in this circuit would be appreciated.

    Thanks.
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    There is one secondary with multiple taps. The regulator is not designed to supply the output directly but is controlling a series pass element that actually supplies the load. The nominal output is supposed to be 13.8V which is common for Amateur Radio Transceivers.

    BTW Astron makes excellent power supplies -- I have several.
     
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  3. tracecom

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    Thanks. I actually used this power supply on my 2M rig, but it was damaged in a house fire and I pulled the transformer and a few other parts that seemed to be undamaged.
     
    Last edited: Oct 18, 2012
  4. Papabravo

    Expert

    Feb 24, 2006
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    Sorry about the fire -- that's a bummer.

    Physically it is much easier to fabricate a transformer with a single secondary winding than to have multiple secondaries. Suppose I want voltages of +5 and +12. I can use the single secondary with a carefully chosen tap point to get the AC voltages which I can regulate down to +5 and +12 depending on the dropout characteristic of my regulators.

    Although the main output is 13.8 V nominal there is no reason to run all of the ICs on the board at that voltage. I don't have a datasheet for the 723 but it probably has a VCC lower than 13.8. I once took a scope apart that had 4000 series parts with Vdd @ -800V and Vss @ -810V and they were happier than pigs in slop. This was done with multiple taps on a single secondary.
     
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  5. tracecom

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    Today, I finally got around to checking the transformer. With an input of 125.6 VAC, the no load output on the main winding is 37.2VAC and the no load output on the alternate (smaller wire) winding is 47.4 VAC.

    Not what I expected on a 13.8 VDC power supply. :confused:
     
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