Or using centre tap for fullwave rectifier :-


                 metal frame grounded        ____
       Neutral     to Earth                 |    |
          +----------+  ---->|-----+---+-----7805|----+----o
                     |  |  Diode   | + |    |____|    | +
                     C||C         ###  |      |      ###
                     C||C         ---  |      |      ---
                     C||C          |   |      |       |
                     C|||          |   |      |       |
                     C||+-----+----+----------+-------+--------+
                     C|||     |        |
                     C||C    ===       |
                     C||C  Earth       |
        Hot          C||C              |
          +----------+  |----->|-------+
                             Diode
RP





                    Spehro Pefhany
                    <speff@INTERLO        To:     PICLIST@MITVMA.MIT.EDU
                    G.COM>                cc:
                    Sent by: pic          Subject:     Re: [OT]: Transformer connections
                    microcontrolle
                    r discussion
                    list
                    <PICLIST@MITVM
                    A.MIT.EDU>


                    27/01/03 13:48
                    Please respond
                    to pic
                    microcontrolle
                    r discussion
                    list






At 07:28 PM 1/26/2003 -0500, you wrote:

Correction!: I left out the diodes.


The secondary can be grounded to earth, but not the primary. Here, an ASCII
schematic:


                 metal frame grounded        ____
       Neutral     to Earth                 |    |
          +----------+  -----|>|---+---------7805|----+----o
                     |  |          | +      |____|    | +
                     C||C         ###         |      ###
                     C||C         ---         |      ---
                     C||C          |          |       |
       120VAC        ||||          |          |       |
          +----------+||+-----+----+----------+-------+--------+
                     ||||     |    | +        |       | +      |
                     C||C    ===  ###         |      ###      ===
                     C||C  Earth  ---        _|__    ---      GND
        240VAC       C||C          |        |    |   |
          +----------+  |----|<|---+--------|7905|----+----o
                                            |____|

      LEAVE 120 or 240 unconnected




Your new transformer:



                 metal frame grounded        ____
       Neutral     to Earth                 |    |
          +----------+  -----|>|---+---------7805|----+----o
                     |  |          | +      |____|    | +
                     C||C         ###         |      ###
                     C||C         ---         |      ---
                     C||C          |          |       |
                     C|||          |          |       |
                     C||+-----+----+----------+-------+--------+
                     C|||     |    | +        |       | +      |
                     C||C    ===  ###         |      ###      ===
                     C||C  Earth  ---        _|__    ---      GND
        Hot          C||C          |        |    |   |
          +----------+  |----|<|---+--------|7905|----+----o
                                            |____|




>Maybe I got lucky, heh.

Maybe it wasn't a center tap, but rather a screen. This is copper tape
or a winding between primary and secondary for shielding purposes.

If the wire was green and measures open circuit to all other wires, that's
probably what it is.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the
reward"
speff@interlog.com             Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog  Info for designers:
http://www.speff.com

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