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I can't get SCR's to work

Discussion in 'Hobby Electronics' started by Jason S, Sep 22, 2005.

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  1. Jason S

    Jason S Guest

    Has anyone been having issues with SCR's (silicon controlled rectifiers)?

    I've been trying a couple of different ones, and they just won't work for

    I've viewed some schematics with SCR's in them, and it seems you can just
    connect them up like transistors... seems simple. A resistor connects to
    the gate of the SCR, and you connect a load (such as an LED). So why
    wouldn't they work? Is there a trick to it? I've tried connecting them
    both ways and still nothing.

    I am using a 12V supply. I've tried various resistor values (for the gate)
    such as 10K, 2K and 1K. Attempting to trigger it fails.

    I've tried a couple of SCR's from Jaycar Electronics, namely the C106B and
    C106Y. I can't even get an LED to light up!! Can anyone make a
    suggestion? It seems I am just wasting money on these dumb devices.
    [] 560R
    Trigger (+) -----====------SCR
    Resistor |
  2. Phil Allison

    Phil Allison Guest

    "Jason S"

    ** You real sure you know where the Anode, Cathode and Gate leads are ??

    ............. Phil
  3. Ken Taylor

    Ken Taylor Guest

    Here's an example test circuit - what you are doing seems to be correct
    though maybe the resistor value is incorrect. I don't have the data sheet
    for yours on hand, but the circuit referenced gives 270 Ohm as the resistor
    value. Have you tried one that low?

  4. Martin

    Martin Guest

    2 things I can think of -

    1) is the SCR and LED connected the right way around?
    2) is the current drawn by the LED sufficient to latch the SCR on?

    Try this circuit below it should show you if the SCR is working. Use a
    normally open push button switch to trigger the SCR and once triggered the
    12V globe should continue to illuminate even after the trigger voltage is

    +12V --------------------
    | |
    | |
    | 12V 6W globe
    | |
    | | anode
    / -----
    \ R \ /
    / -
    | gate / | cathode
    | _|_ / |
    - ------- -------- |

    R = 270 ohm

    If this circuit works then the problem with your LED circuit is either
    component polarity or insufficient current draw.
  5. Jason S

    Jason S Guest

    thanks guys. its fine now.

  6. budgie

    budgie Guest

    Fess up, wot'd you change?
  7. Jason S

    Jason S Guest

    well i didn't realise the SCR's anode, cathode and gate are in different
    order compared to that of a transistor. I always assumed the gate was the
    middle pin. Ha ha. I laughed it off, but I'm relieved now. I've never
    worked with SCR's before.... First time for everything!! ;-)
  8. Phil Allison

    Phil Allison Guest

    "Jason S"

    ** So you were starting from SCRatch ??

    ............ Phil
  9. Martin

    Martin Guest

    Tranny with an anode, cathode and gate?? :)

    You'll find that transistors have their pins in different orders as well.
    Some will be Collector, Emitter, Base whilst others are Collector, Base,
    Emitter... and so on..

    Sounds like you could make use of a transistor reference guide that has the
    pinouts included.....
  10. Jason S

    Jason S Guest

    u could say that.
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