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Question: Choosing/Using an SSR

Discussion in 'Electronic Basics' started by [email protected], Oct 6, 2007.

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  1. Guest

    I'm working on a circuit to replace a wired remote control unit with
    an RF remote. The existing remote is nothing more than 3 push buttons
    that connect a 5V supply voltage to ground via a 470 ohm resistor
    (remote connected via some RJ-11 connectors and a phone cord. The
    buttons are UP count, Down Count, and Reset.

    I'm having some trouble interfacing the RF remote circuitry with the
    wired remote interface. My plan is to use 3 SSR's in place of the
    existing push button switches. The RF remote works great, and lights
    up test LED's just as I would expect when push buttons on the
    transmitter are pushed. My next step was to replace the LED's with
    the SSRs. I chose the SHARP PR22MA11NTZF to do the job. I connected
    pin 2 to ground, and 1 to my output. Then I hooked up pin 6 and 4 to
    my continuity tester and hit the buttons on my transmitter.
    Everything looked like it was going smoothly. The SSR was behaving
    just like the switch. When I held the buttons down, I got a solid
    buzz, when i hit them fast, i got short blips. Then I replaced the
    continuity tester with the wires I wanted to short (+5V from the
    circuit i am driving, and Gnd (via a 470 ohm resistor).

    Here is where my problem was noticable. I push the button one time,
    it latches the SSR, causes the circuit to count as expected, but then
    never unlatches, so even after i release the button my circuit keeps
    counting. I'm assuming I have either chosen the wrong SSR, or need
    different circuitry somewhere as it behaves as if the current flowing
    through the SSR after the initial button press is holding the switch
    on, when I want it to turn off when the drive logic turns off.

    Any ideas? If someone could point me in the right direction for a
    more appropriate SSR, or SSR circuitry that would be great. Thank you
    in advance for any assistance you can provide.
     
  2. This relay is intended for AC loads. Its output device is a
    latching thyristor that relies on the current zero crossing
    twice per AC cycle to reset it to a nonconducting state.
    http://document.sharpsma.com/files/pr22ma11_e.pdf

    Your test meter does not draw enough current for the
    thyristor to latch on, but your intended load does.

    You need an SSR intended for DC loads (mosfet output or
    photo transistor) If your load current is a few
    milliamperes, you may get by with an ordinary opto isolator
    like one of these:
    http://rocky.digikey.com/WebLib/Toshiba/Web Data/TLP331,332.pdf
     
  3. John Fields

    John Fields Guest

     
  4. John Fields

    John Fields Guest

     
  5. Jamie

    Jamie Guest

    That's how they work.
    once current is moving through the SSR's, they stay latched until the
    current drops below the holding point.
    if you're dealing with DC volts, use logic type fets.
     
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