Help Please i'm almost finished :-)

Discussion in 'General Electronics Chat' started by bmedeiros, Jan 30, 2009.

  1. bmedeiros

    Thread Starter New Member

    Jan 21, 2009
    3
    0
    i am presently using a 3V Micro machanical relay on my design... it works fine but i want to replace it with a somthing that is solid state so i get the clicking noise out of my head :eek: All i am doing is putting a 3V trigger to the relay... the in and out of the relay is hooked to one wire on a ethernet cable...the whole purpuse of the relay is to break and close the ethernet connection nothing more than that... i have started looking into transistors and other componets but not sure which way to go .... thanks for any help i can get :)
     
  2. Skeebopstop

    Active Member

    Jan 9, 2009
    358
    3
    you'll find that relays have a lower 'on' resistance, so are more suitable for high power applications, so long as the switching frequency is extremely low.

    in your situation, please consider a mosfet with a Vgs < 3V and a very low Rds. It should be NFET.

    Generally the higher frequencies of ethernet have them coming through isolation transformers etc.., so I recommend you do it on the other end of isolation to keep any higher frequency effects out.
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    I have never seen MOS which fully turn on with a Vgs of less than 5V. You can use BJTs or FETs.
     
  4. Skeebopstop

    Active Member

    Jan 9, 2009
    358
    3
    ooopsie, good call. I work in servo drives and MOSFET and IGBT seem to be 50% of the words out of my mouth, didn't even think twice :)

    Just make sure you stick any switches on the other end of the isolation transformer so the voltages are within range of your circuit. Voltages on the actual ethernet pipe could be anything, they are only differential to each other.

    I still think there must exist a 'small' low voltage relay which has next to no footprint and very quiet switching sound. I don't know why but using a discrete to act like a true circuit breaker bothers me.
     
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