Relay Switch Circuit
A relay switch circuit works by transferring electrical power through the contact between two terminals. This transfer occurs through the use of an electromechanical or solid state relay. Both types of relays have various specifications and are used for different purposes. When selecting the best switch for your application, you should weigh the pros and cons of both types.
While many electronics hobbyists use the expensive relay modules that cost several dollars, it is possible to build a relay switch circuit on your own using inexpensive components. The price of a relay module can be as low as $2 or $0.70. A relay switch circuit requires some calculation and the right components. Once you know how to calculate component values, you can create a circuit that will work for you.
The coil of a relay is usually surrounded by wires that have a fixed resistance. The resistance should range from one hundred to five hundred ohms, and the side terminals of a relay should be of a similar resistance. A multimeter is useful in this regard, as the resistances on both sides of a relay should be close to each other.
The coil of a relay operates only when it receives a current or voltage. A transistor is connected in series between the relay coil and the supply terminals. When this condition is met, the transistor acts as an open circuit, while when it’s not, it acts as a closed circuit. This can damage a switching NPN transistor.
How to Build a Relay Switch Circuit
When a relay is switched on, the current flows through the coil. This creates an electromagnetic field that attracts an armature, which is made of a ferromagnetic metal. The armature also has a spring to return it to the open position. A multimeter must be set in resistance measurement mode to properly read this information.
The common collector follower configuration is useful when you need a circuit with low input and high output impedances. When the coil is on, the current flows through the base of C1. When the relay is off, the current flows through the other end of the coil. The circuit will repeat until the opposite condition occurs.
Relay circuits are very useful because they can control electrical circuits with different current and voltage. Compared to thermistors, these circuits do not require any additional power from the supply and can operate with a low current. They are also compatible with tiny DC power sources and can be fabricated on a small PCB.
Relays can be either single pole or double pole. The difference between the two types depends on the type of load. For example, a fluorescent light typically consumes 1 A. A double pole relay, on the other hand, will change a connection.