DIY SSR ( solid state relay )

Hello friends,
First of all, you should caution work with 220 can be killer
we can control 220v device by using a relay there are two kinds of relays :
1- electromagnetic relay
2- solid-state relay
A solid-state relay (SSR) is an electronic switching device that switches on or off when an external voltage (AC or DC) is applied across its control terminals. It serves the same function as an electromechanical relay, but has no moving parts and therefore results in a longer operational lifetime. SSRs consist of a sensor that responds to an appropriate input (control signal), a solid-state electronic switching device that switches power to the load circuitry, and a coupling mechanism to enable the control signal to activate this switch without mechanical parts. The relay may be designed to switch either AC or DC loads. Packaged solid-state relays use power semiconductor devices such as thyristors and transistors, to switch currents up to around a hundred amperes. Solid-state relays have fast switching speeds compared with electromechanical relays, and have no physical contacts to wear out. Users of solid-state relays must take into consideration an SSR’s inability to withstand a large momentary overload the way an electromechanical relay can, as well as their higher “on” resistance
Buffer & isolation:
This circuit for MOC3021 Opto Triac you can replace the switch with a microcontroller or transistor or anything else generate a small signal
Opto-Triac as you can see it consist of two parts infra-red led & triac
تنزيل (1)
we will see this couple several times in electronics, the led will take the signal that comes from your UC or transistor or sensor then send it as an IR wave the second will receive the IR wave then allow the current goto gate of Triac ( the triac in Opto-Triac) the triac will work as a switch and allow current to flow

the second part is triac

bidirectional triode thyristor or bilateral triode thyristor[citation needed]) is a three-terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericized trademark.

TRIACs are a subset of thyristors (analogous to a relay in that a small voltage and current can control a much larger voltage and current) and are related to silicon-controlled rectifiers (SCRs). TRIACs differ from SCRs in that they allow current flow in both directions, whereas an SCR can only conduct current in a single direction. Most TRIACs can be triggered by applying either a positive or negative voltage to the gate (an SCR requires a positive voltage). Once triggered, SCRs and TRIACs continue to conduct, even if the gate current ceases, until the main current drops below a certain level called the holding current.

Gate turn-off thyristors (GTOs) are similar to TRIACs but provide more control by turning off when the gate signal ceases.

The bidirectionality of TRIACs makes them convenient switches for alternating-current (AC). In addition, applying a trigger at a controlled phase angle of the AC in the main circuit allows control of the average current flowing into a load (phase control). This is commonly used for controlling the speed of a universal motor, dimming lamps, and controlling electric heaters. TRIACs are Bipolar devices.
Triac BT136 will work as a switch allow current move-in bidirectional when the gate is triggered by Opto-Triac,v1 is a plug, you can replace L1 with any blub
Full circuit:

The link:

feel free to ask me any question:


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