Re: EMC Filtering question

In article <[EMAIL PROTECTED]>
           [EMAIL PROTECTED] "David Fussell" writes:

> Hi,
> 
> I am in the process of adding a relay driver board as a 'daughter
> board' to an existing design/enclosure. I have to take the (isolated)
> relay contact connections to a new connector in the enclosure, for
> connection to (goodness knows what in) the outside world.
> 
> I'd like to take some precautionary measures to attenuate any h.f.
> that may propogate into my enclosure via the relay contact wires, but
> I'm unsure as to what is the best practise for this- The connector is
> PCB mounting, and so the usage of ferrite beads might be difficult.
> Any suggestions?


        *-----------*-------*----------*
                    |       |
                   ----     -
                    /\     | |
               D1  /  \    | | R1 (100R)
         (1N4004) ------   | |
                    |       -
                    |       |
                    |     ----- C1 (0.1uF)
                    |     -----
                    |       |
      *-------------*-------*-----------*

Add the above circuit across each relay coil and place a suitably rated
VDR across each contact that exits to the outside world. You might also
look at a series inductance and parallel capacitance on the contact.
You may need to play around with the values a a bit to suit your 
situation. Some relay manufacturers have application notes that will
be useful to dig out and review for improvements to the above.

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