Dpdt relay circuit

Discussion in 'Power Electronics' started by Angela.ca, Aug 24, 2017.

  1. Angela.ca

    Thread Starter New Member

    Oct 27, 2016
    4
    0
    Hi,
    I want to use a dpdt relay to switch between two power supplies for a load and found a reference in an old book. Can anyone explain the connections of x and x_bar, I understand A+B would be power supply 1, and C+D would be power supply 2. Have I got that right? Are the x and x_bar the connections similar to the coil connections in an ic relay? Also, to modify this to a dpst, I just leave cr4 and cr8 unattached? I think I still need Q2 and Q4, or is there a way to get rid of other components?

    Thanks for all inputs!
     
  2. crutschow

    Expert

    Mar 14, 2008
    19,793
    5,538
    That circuit will only work for very specific conditions of voltage and current.

    What are the maximum currents and voltages involved?

    Can you use a mechanical for this or do you want it to be solid-state?

    Do the power supplies share a common ground?
     
  3. Angela.ca

    Thread Starter New Member

    Oct 27, 2016
    4
    0
    Hi crutschow,
    The supplies are both within a few hundred mV of 5V and carrying between 1.5-2A, I just need them to come from different sources, same ground. Solid state ic's are rare in spdt, dpdt able to carry this much current, and mechanicals are too large. I'd like to understand this circuit to see how small I can get it.
    Thanks!
     
  4. crutschow

    Expert

    Mar 14, 2008
    19,793
    5,538
    The simplest way to switch between the two supplies is likely using a P-MOSFET for each voltage.

    Will the switch have to block in both directions, i.e. will one supply ever be significantly different in voltage from the other?

    What are the two supplies and why do you want to switch between them?
     
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