Relay is operated by an electric switch. The current flowing through the relay coil creates a magnetic field that pulled the lever and change the switch contacts. Coil current can be on or off so relays have two switch positions, and most have double throw (changeover) switch contacts as shown in the diagram.
Relays allow one circuit to switch a second circuit that can be completely separated from the first. For example, a low voltage battery circuit can use a relay to switch a 230V AC electrical circuits. There is no electrical connection inside the relay between the two circuits, magnetic and mechanical link.
Flows through the relay coil is relatively large, typically 30mA for a 12V relay, but can be as much as 100mA for relays designed to operate from low voltage. Most of the IC (chip) can not provide this current and the transistor is usually used to reinforce the small IC current to a larger value is needed for the relay coil. The maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils directly without amplification.
SPDT or DPDT relay usuallly but they can have more sets of switch contacts, for example, with 4 sets of relay changeover contacts are available. For more information about the switch contacts and the term used to describe them please see the page on the switch.
Most relays are designed for PCB mount, but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay.
Catalog of suppliers must demonstrate that the connection relay. Coil will clear and it may be connected either way around. Relay coils produce a 'spike' brief high voltage when they are turned off and this can destroy transistors and ICs in the circuit. To prevent damage you must connect a protection diode on the relay coil.
Animated image shows the relay coil and work with the switch contacts. You can see a lever on the left is pulled by a magnet when the coil is activated. This lever to move the switch contacts. There is one set of contacts (SPDT) in the foreground and another behind them, making the relay DPDT.
Flows through the relay coil is relatively large, typically 30mA for a 12V relay, but can be as much as 100mA for relays designed to operate from low voltage. Most of the IC (chip) can not provide this current and the transistor is usually used to reinforce the small IC current to a larger value is needed for the relay coil. The maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils directly without amplification.
SPDT or DPDT relay usuallly but they can have more sets of switch contacts, for example, with 4 sets of relay changeover contacts are available. For more information about the switch contacts and the term used to describe them please see the page on the switch.
Most relays are designed for PCB mount, but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay.
Catalog of suppliers must demonstrate that the connection relay. Coil will clear and it may be connected either way around. Relay coils produce a 'spike' brief high voltage when they are turned off and this can destroy transistors and ICs in the circuit. To prevent damage you must connect a protection diode on the relay coil.
Animated image shows the relay coil and work with the switch contacts. You can see a lever on the left is pulled by a magnet when the coil is activated. This lever to move the switch contacts. There is one set of contacts (SPDT) in the foreground and another behind them, making the relay DPDT.
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