We all know such a device as an electromagnetic relay, it is used where it is necessary to control a large load with a small input current. But, like all relay mechanisms, it can not forever and relatively quickly fail, because it uses moving elements (usually a copper plate), and the contacts can burn out. In addition, when switching, a sound is made - clicks.
Modern industry now produces the so-called solid-state relay. It costs not much more than usual, but it copes with its task no worse, with its miniature size and silent operation. A good representative of the optical relay is the G3MB. It can be controlled with a voltage of 4-6 V, while the consumption is several mA. The load can be a device with a current of up to 2 A, with an alternating voltage of 75-265 V. The maximum voltage drop is only 1.6 V.
The principle of operation of a solid-state optical relay is simple: when a current is supplied to the LED, we force it to glow, the photon flux from it opens a special transistor in the middle of the device. Forward current of the light emitting diode 5-20 mA, maximum switching 50 mA. The overall dimensions of the reels are only 20.5 by 24.5 by 5.5 mm. The figure below shows a schematic diagram of connecting a g3mb relay with battery control, where the load is an incandescent lamp.
Cost: ~ 69