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    This universal triac controller circuit with optocoupler solves the problem that triacs have when functioning at low temperatures (triac needs higher gate current) by adding a transistor at the output of the optocoupler circuit.
    The transistor amplifiers the trigger pulse coming from the optocoupler and the gate current is high enough to trigger the triac in all temperature cases.

    How does the circuits works?

    The base of the transistor is driven by the OC. C2 works as capacitive bias resistance to avoid power losses and it also helps avoid DC loading of the supply line. The switch current is limited by R3. D1 works as one-way rectifier while C1 works as ripple filter.
    D2 stabilize the rectified voltage to 15 V.

    T1 conducts when the OC sends a pulse to its base. C discharges through the collector-emitter line. The trigger current is limited by R2 to around 40 mA.
    The discharge current time of C1 is less than 1 ms.

    The RC circuit R4 and C3 protects the triac from voltage spikes.
    This is very important in all inductive loads.

    Triac Optocoupler Controller Schematic

    universal optocoupler triac controller circuit schematic

    ask a question

    16 Responses to "Universal Triac Control with Optocoupler"

    1. Does it Work?

    2. hi
      does it support cfl lamps?

      thanks in advance…

    3. Good day :) can i ask for an application for this circuit? Thank you

      • hello.can i ask , what should be input for the opto copler? is it voltage or resistance? if volt.how many volt?

    4. The input is a current to drive the LED–approx 5 to 10mA. To change it to a voltage, add a series resistor. For example, the drive voltage is 5V–of this, 2V is dropped across the LED and the remaining 3V is dropped across the resistor. R = E/I = 3V/10mA = 300Ω

    5. hi i can’t find 2sb358.
      Is there any equivalent to 2sb358?

      thank you.

      • sorry 2sb328 i meant…

      • Jim Keith says: on November 13, 2012 at 4:39 am

        I do not know how this 50year old PNP germanium transistor got into the circuit–it is not even the correct polarity–should be NPN. Actually, almost any NPN silicon transistor will do the job.

      • Hello sir, so if the transistor should be an NPN type, to which side the emitter point ? towards the triac gate or the opposite direction. Thanks

    6. above circuit work with kitchen machine ac motor 600w/60hz/230ac if not tell me the change needed to create circuit

    7. What kind is the driver signal?
      I mean:
      – DC Voltage
      – pulsed (DC) Voltage

    8. Hi I got a circuit from this site similar to the one shown below used to operate an electric fan based on temperature. The circuit is similar to the one below but when I connect practically it does not function. Kindly show me where there is a problem

    9. What is the max current can be taken on load, for instance can I replace the circuit instead of relay for boiler?

    10. ferenc-lengyelgmail-com says: on April 19, 2016 at 10:25 pm

      Is it possible to use this circuit for dimming? Need some modification or just drive with input current?


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