diy solid state relay circuit schematic

Do It Yourself Solid State Relay

One advantage of solid-state relay (SSR) over conventional electro-magnetic relay (EMR) is its tear and wear free operation. S201S01 from Sharp is a good example.
Here is the circuit diagram of a DIY SSR project, which is in fact an isolated triac power controller.

The switching output from any dc circuit can be connected to pin 1 of opto-isolator (IC1) through a suitable current limiting resistor. Pin 2 of IC1 is grounded.
Pin 6 of IC1 is connected to one main terinal of Triac (T1) through resistor R1 and pin 4 drives the gate terminal of T1.

To limit the rate of change of voltage, a snubber circuit (R2-C1) is added across T1.
When current passes through the internal LED of IC1, internal diac is triggered and the diac provides the gate pulse to T1. Now T1 is fired to drive the ac mains operated load at its output.

After construction of the solid state relay on a common pcb, enclose the whole circuit in a very small ABS case. Now drill suitable holes to mount four labelled input and output terminals. Since switching is accomplished by triac T1, don’t touch the internal parts while AC supply is plugged in.

DIY Solid-State Relay Circuit Schematic

diy solid state relay circuit schematic


Related products: Electromechanical Relay | Solid State Relay


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  • RadYan

    What about using this chip and power triac at 24 VAC ?
    I need to switch 24 VAC valves.

  • Themisive

    This is a good idea, but I feel is limited to 230v only. I quite like the idea of an opto-isolator instead of a mains voltage coil and relay contacts, what I want really is one that will detect zero AC power and have as may contacts as possible, for instance I am building a unit that will need 2 x 12v relays, one is a 2 pole changeover and the other is a 4 pole changeover type.

    Can this circuit be modified to accommodate them? I would really like to use 230 – 240v input, but the relays I need are only 12v types.

    another circuit I did use until recently used a 240v relay with a 2 pole changeover, using banks of resistors, since they were used to bleed off EHT voltages – -1100v and +1200v, this worked well, and I am sure this circuit could be adapted for that, but the question remains, this is only a 240v changeover single pole type, I tend to use mufti-pole changeover relays, so how would I get around that.

  • Manoj Soorya

    Its a nice circuit……Great Perfomance. Good.

  • animesh

    hello, this concept is most important and here is the work done by you is greate , but i will try to make the SSR in PSIM( Power simulation software), so how can i do this. please reply as early

  • Andy

    What would be the best choice for the type of the snubber capacitor?
    Ceramic? Metal film?…?

    • breakthedawn

      Use only safe X-Type rated (self healing) capacitors. Other types may shorten up and blow your circuit or cause fire.

  • Surendra Rahalkar

    What will happen if phase and nuetral are reversed?

  • Sam

    This snubber, while it is not mentioned why it is required (the text only says “To limit the rate of change of voltage”, and not why this is necessary), with a simple calculation you find it is equivalent to ≈3MOhm, and this allows ≈15W thru the snubber when the external load is rated at ≈1000W (for 220V, 50Hz mains).
    Isn’t this a big waste of power when the device is expected to be completely shut off?

    • Sam

      Ooops! I made a multiplier conversion error.. 2 errors actually. Sorry…

    • Popescu Marian

      According to my calculations the capacitive reactance of C1 is 318309Ω = ~ 330kΩ => the current through it is 0.69mA thus the power dissipation is 0.15W.

  • AntonS

    Put a signal diode 1N4148 and a resistor in series with the MOC3021.
    R = (Vdc-0.6-1.15)/0.015 where Vdc is from say 5V to max about 30V DC.

    The internal LED cannot handle more than 3V if it is accidentally reverse that is why the 1N4148 is used.

  • dagg

    hi i am new to electronics, but i like this ssr, so i will try to build this circuit.
    But what is the wattage for r1,r2 and what is the voltage for c1?

    • piczim

      Please can you tell me what the wattage was of R1 and R2, Did you build the circuit and did it work?

  • Dan

    Is the input of this SSR DC?