> -----Original Message-----
> From: John Payson [SMTP:supercat@CIRCAD.COM]
> Sent: Monday, January 11, 1999 6:03 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: The relay circuit
>
> |  Because you don't want to operate the relays from the same 5V
> |regulated line as the PIC, you don't really need 5V relays, but if
> you
> |already have them, you can use a series resistor for *each* to drop
> |whatever unregulated voltage you have, to 5V for the relay.
>
> What do you think of something like this circuit?
>
>      +Volts (e.g. 12V unreg)
>        |
>        +------------------.
>        |                  |
>       ||D                 |
>       ||D Relay           =
>       ||D                 ^ Diode
>        |                  |
>        +-----.            |
>        |     |            |
>       RES   CAP           |
>        |     |            |
>        +-----+------------'
>        |
>    [switched ground]
>
        [snip]

> Anyone here done anything like that?
>
        something quite similar, as a snubber
        circuit for transformers (as used in
        a SMPS). Except that the diode and
        resistor are in parallel, and the cap
        in series to supply rail:


              o   o
              |   |
             ---  |
             ---  |
              |   C
              |   C
          *---*   C
          |   |   C
          /   |   |
          \   =   |
          /   ^   |
          \   D   |
          |   |   |
          *---*---*
                  |
               (switch)


        you trade power dissipation in the switch
        for power dissipation in the resistor. it
        also slows the dv/dt of the (inductive)
        leakage spike.