Different characteristics between optocouplers and solid-state relays

What is an optocoupler relay?
Optocoupler relay is a type of solid-state relay. Generally, relays are mechanical contacts that rely on passing current through a coil to become magnetic magnets that attract the contacts, thereby controlling the on state. The working principle of optocoupler relay is similar to optocoupler (in fact, it is the same when looking at the equivalent circuit diagram).
Solid state relay
Solid State Relay (SSR) is a contactless switch composed of microelectronic circuits, discrete electronic devices, and power electronic devices. Isolation devices were used to achieve isolation between the control end and the load end. The input terminal of solid-state relays uses small control signals to directly drive high current loads.
What is the difference between optocoupler relay and solid-state relay?
Optocoupler relays belong to solid-state relays. Generally, electromagnetic relays rely on current passing through coils to turn the iron core into a magnetic magnet that attracts the armature, thereby causing the relevant contacts to operate and control the on/off of the load. However, optocoupler relays do not have contacts and their working principle is somewhat similar to optocouplers.
The internal light-emitting diode is used to emit light to the photoelectric element, which receives the light and controls the output field-effect transistor to turn on or off. Optocoupler relays also have another type of thyristor rectifier (SCR) output, which has a larger load current than field-effect transistors. The latter can reach several amperes, while the former can reach tens of amperes.
Compared to electromagnetic relays, optocoupler relays have an infinite lifespan due to the lack of contact induced wear, and also have characteristics such as no sensation and no switching sound. Like electromagnetic relays, they can control various loads (light bulbs, light-emitting diodes, heaters, motors, etc.).
When the battery applied to the input terminal of the optocoupler relay is released in the output conducting state, the light emitting diode at the input terminal will stop emitting light because the photoelectric element no longer has light shining, and the voltage of the photoelectric element will drop. When the voltage supplied from the photoelectric element starts to drop, the charge on the field-effect transistor is rapidly discharged through the control circuit, causing the field-effect transistor to no longer conduct, the load to be disconnected, and the light bulb to not emit light. The time consumed in this process is called the reset time.
In the output cutoff state, when the battery is applied to the input terminal of the optocoupler relay through a current limiting resistor, the light-emitting diode at the input terminal will emit light, and the announced light will shine on the opposite photoelectric element. The photoelectric element converts it into a corresponding voltage according to the intensity of the light, and controls the circuit to charge the gate of the field-effect transistor. When the gate voltage reaches the turn-on voltage of the field-effect transistor, the field-effect transistor starts to conduct and the light bulb emits light. The time consumed in this process is called action time.
Due to the use of optoelectronic coupling between the front and rear stages, the insulation resistance Riso between the input and output is very large, usually as small as 1000M ohms.
The maximum value of forward current is about tens of milliamps. In practical applications, it should not exceed the maximum value in the data manual, otherwise the lifespan of the light-emitting diode will be shortened or even damaged.