At 11:38 AM 3/15/2004 -0700, you wrote:
>At 08:34 AM 3/15/2004, Andre Miller wrote:
>>Thanks for the circuit diagram!
>>
>>I still have one question though, how do I connect the AC supply and the 5V
>>DC supply together?
>>
>>Say I have a 24V transformer, which will drive the load, and I rectify /
>>regulate this to drive the PIC. Where is 'ground' in this case for the
>>rectified/regulated supply and where is ground for the two AC wires coming
>>out of the transformer? And do I just connect these two grounds together?
>>
>>Sorry if you've answered this already. (And apologies about my poor ASCII
>>art!). Are there any connections missing from the below schematic? And would
>>it work like that? I know the supply is missing some filter/smoothing caps.
>>
>>                                  7805
>>                    A   K       ,----------.
>>-------)-+----------|>|---+----|IN  G  OUT|------ +5V to PIC
>>  24V AC  }               CAP   `----+-----'
>>-------)------+-----------+---------+------------ GND to PIC
>>          |    |       470 uF 50V
>>          |    |               ____
>>          |    |  ------------|____|-------------- Trigger from PIC
>>          |   _|_/              Rg
>>          |   V_A
>>          |    |
>>          C|   |
>>Solonoid C|   |
>>          C|   |
>>          |    |
>>          +----+
>
>Easy - don't use a bridge rectifier.  Use a single diode as a half-wave
>rectifier.  Look at it this way: the PIC and its associated circuitry does
>not consume much current (5 - 20 mA).  You can tolerate a lot of ripple
>going into the regulator with no problems.

You just double the capacitor value and you'll have the same ripple as
with a FW bridge rectifier. Here's what I think Dwayne is talking about.
Of course if you had an opto-isolator you could use the bridge.
You should not use the 7805 in the above circuit, BTW, it's far too tight on
maximum input voltage.

                     +----------------------------+
                     |              Vdd           |
                     |               |            |
                     |               |            |
                   o-+    +----------+----+-------+  --+
                          | +     5.1|    |      _|_/  |
                         --- 470uF   - / ---     V_A  .-.
                 24VAC   --- 50v   / ^   ---      |   | |
                          |-   ___   |    | 0.1uF |   | | Rg
                   o---|<-+---|___|--+----+       |   '-'
                   |   1N4004       ===           |    |
                   C|               GND           |    o
                   C|                             |  To PIC
                   C|                             |  or collector
                   |                              |
                   +------------------------------+


>Most of my 24 Vac stuff doesn't even use an IC regulator - just a simple
>series resistor / zener shunt regulator.

I'm just doing one with a tiny ~1MHz buck regulator. But it needs a few
watts, not just 100mW.

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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