DC-AC Solid State Relay or SSR - del30008

These are Thyristor, Triac and Zero-Crossing Optocoupler based Relays. They do not have wear-tear. But they dissipate some heat. They are rugged but have to be used with external snubbers when switching highly reactive loads. The designs shown here are for heaters and non-inductive loads. They were sealed in thermally-conductive epoxy.

It is more expensive than a relay. But is good for on-off time-cycling proportional control. The control circuits are here Analog Circuits. This is a DC Control AC Load SSR, This Solid state relay is the most popular and standard. See the datasheet Motorola MOC3041 pdf. These circuits is based on such application notes. This was made by me in nice numbers for plastic and rubber molding machine, temperature controllers.

If you have a proportional controller and you need a 2-3 second cycle time, using relays is not good, they will not last. Here SSR wins, with resistive heaters it will work very well.

These can turn 230V AC equipment on and off. The output is like a NO normally open contacts of a relay and have to be in series with the Load like any other switch. This should not be used for large inductive loads like big motors. The Q1 transistor limits the current thru the LED by providing an alternate path for more current. The DC input can be from 3V to 20V. The Triac can be chosen depending on current in the load.