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Toggle switch using SSR with MOSFET

Prodigy 250 points

Replies: 5

Views: 557

Dear Experts,

I try to use a SSR instead a toggle relay to switch the polarity of a railway DCC signal at a RailSwitch middle contact. This digital signal is AC 18V, the maximal current is 3A
Inspired by the TIDUC87A document I create following circuit. The gray toggle switch is only to show what I want to realize.
It works perfect if only one SSR is implemented ( left OR right side ) but no function if both SSR are connected.

My Questrion:
Is there an integrated ( and cheep ) ready to use circuit available for a AC SSR toggle switch?
Whats wrong with this circuit?

  • Dear Experts,

    I see the issue here now. Take the reverse diodes of Q1 to Q4 in account the opposite MOSFET will create a short. Example: switch Q1 & Q2 ON the reverse diode of Q3 will short the signal line via Q1.

    So now my hope is to find a full integrated solution. Otherwise I have to go back to mechanical relais which is bad in size and price as well as reliability.

    best Regards
    Karsten
  • In reply to Karsten Kankowski:

    Karsten, What is speed of your communication, How quickly you will need MOSFETs to turn on and off?

    Regards

    Miro

  • In reply to Miro Oljaca79:

    Dear Miro,
    As the switch is not syncronized to the digital signal the speed is not important. The signal is 1 für 58µs high and 58µs low and for logic 0 116µ high and 116µs low. The slew rate is only 2.5V/µs.
    The digital information is repeated, so lost a datagram while switching is no problem.

    regards
    Karsten
  • In reply to Karsten Kankowski:

    Hi Karsten,

    That is good, requirements are not too hard. Looking at your schematic it looks to me that you are making short circuit between DCC+ and DCC-. Is that correct?

    What is maximum current that you are expecting and what is voltage that you are expecting between DCC+ and DCC-?

    Miro

  • In reply to Miro Oljaca79:

    Dear Miro,

    Thanks a lot for your interest!
    I try some different versions to control both side of MOSFET SSR with common ground. But this do not work related to the reversi diodes. So I have to spend 5 more parts and two independent ground lines. Now it´s working fine. But it seemed to be near the same costs and PCB space like a mechanical relay. My hoe was to find a more integrated solution.

    The max current is less than 3A for which I chose now the IRLL024N because its reverse diode can drive 3.1A continous current. The SPDT switch using my solution with discrete parts do not create a short between DCC+ and DCC- . It is used for a mobile train railswitch which need a "polarisation" to ensure that the mobile train see allways a voltage different between its wheels.

    I attach my solution here: may be someone is intereste in such a solution.

    Thanks a lot again for your interest and questions!
    Best Regards
    Karsten

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