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
MOC 3021 is only suitable in countries that use 120 Volts…
MOC3020 Series consists of gallium arsenide infrared emitting diodes,optically coupled to a silicon bilateral switch.They are designed for applications requiring isolated triac triggering.Recommended for 115/240 Vac(rms) Applications. Refer Datasheet : http://www.kitsrus.com/pdf/moc3021.pdf
The MOC3020 Series consists of gallium arsenide infrared emitting diodes,optically coupled to a silicon bilateral switch.They are designed for applications requiring isolated triac triggering.Recommended for 115/240 Vac(rms) Applications. Refer Datasheet :www.kitsrus.com/pdf/moc3021.pdf
Is the input of this SSR DC?
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?
Please can you tell me what the wattage was of R1 and R2, Did you build the circuit and did it work?
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 biased.so that is why the 1N4148 is used.
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?
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.
Ooops! I made a multiplier conversion error.. 2 errors actually. Sorry…