Relay

Relay is a kind of electronic control device with control system (also called input circuit) and controlled system (also called output circuit), which is usually used in automatic control circuits, and is actually a kind of automatic switch controlling larger current with smaller current. Therefore, it plays the role of automatic regulation, safety protection, conversion circuit in the circuit.

Relay relay characteristics

Relay input signal x When the continuous increase from zero reaches the action value xx when the armature starts to absorb, the output signal of the relay immediately jumps from y=0 to y=ym, from break to contact from break to open. Once the contact is closed and the input x continues to increase, the output signal y will not change. When the input quantity x drops from some value greater than xx to xf, the relay begins to release and the normally open contact breaks. We call a relay a relay and also the input and output characteristics of a relay.

Relay operating principle and characteristics

Relay working principle and driving circuit

Electromagnetic Relay Working Principle and Characteristics

Electromagnetic relays are generally composed of an iron core, coil, armature, contact reeds and so on. As long as a certain voltage is added to both ends of the coil, a certain current will flow through the coil, resulting in an electromagnetic effect. Under the action of electromagnetic attraction, the coalescing force will overcome the tension of the return spring to inhale the core, thus driving the coalescing force to inhale the moving contacts and static contacts (normally open contacts). When the coil is de-energized, the electromagnetic suction will also disappear, and the reaction force of the spring will return to its original position, releasing the moving contacts and the original static contacts (normally closed contacts).

This suction and release achieves the purpose of guiding and cutting off in the circuit. For the normally open and normally closed contacts of the relay, you can distinguish between the static contacts that are disconnected when the relay coil is not energized, called normally open contacts, and the static contacts in the on state, called normally closed contacts.

Circuit Principle

When the input changes to a certain value, the relay is a contactor (or circuit) or break AC DC small capacity control circuit.

Relay operating principle and drive circuit

By the permanent magnet to maintain the release state, plus the operating voltage, electromagnetic induction attraction and repulsion cohesion and permanent magnet, resulting in downward movement, and ultimately reach the suction state.

Transistor driven drive circuit

Relay working principle and drive circuit

It is recommended to use a transistor to drive the relay NPN triode. The specific circuit is as follows:

When a high level is input, the transistor T1 saturates and conducts, the relay coil is energized, and the contacts are absorbed.

When the input low level, the transistor T1. relay coil is de-energized, the contact is disconnected

The role of each component in the circuit:

Transistor T1 is the control switch

Resistor R1 mainly acts as a current limiter and reduces the power consumption of transistor T1.

Resistor R2 makes the transistor T1 reliable cutoff

Diode D1 reverse current for the relay coil in the transistor from on to off to provide leakage path, and its voltage clamped on the bit 12V

Integrated Circuit Driver Circuit

Relay operating principle and drive circuit

Currently, the use of integrated circuits with multiple driver transistors can simplify the design process of printed boards that drive multiple relays.

When the 2003 input is high, the corresponding output port outputs a low level, the relay coil is energized at both ends, and the relay contacts are absorbed; when the 2003 input is low, the corresponding output port is highly resistive, the relay coil is de-energized at both ends, and the relay contacts are disconnected.

Relay working principle and driving circuit

24V Relay Driver Circuit

Relay Series RC Circuit: This form is mainly used in circuits where the rated operating voltage of the relay is lower than the supply voltage. When the circuit is closed, the relay coil generates a potential that prevents the current in the coil from increasing, thus prolonging the suction time and shortening the circuit by connecting the RC suction time in series.

The principle is that the instant the circuit is closed and the capacitor C voltage can not be changed suddenly, can be regarded as a short-circuit, which will be higher than the rated operating voltage of the relay coil power supply voltage is added to the coil, thereby accelerating the increase in the current in the coil, so that the relay quickly suction. After the power supply is stabilized, capacitor C does not function and resistor R acts as a current limiter.

Selection of the rated operating voltage of the relay

The rated operating voltage of a relay is the most important technical parameter of a relay. When using a relay, the operating voltage of the circuit (i.e. the circuit where the relay coil is located) should be considered first.

The rated operating voltage of the relay is 0.86. Please note that the circuit must not exceed the rated operating voltage of the relay, otherwise the relay coil will be easily burned out.

In addition, there are some integrated circuits, such as the NE555 circuit can directly drive the relay, while some integrated circuits, such as the COMS circuit output current is small, drive the relay before the need to add a level of transistor amplifier circuit, should be considered that the transistor output current should be greater than the rated operating current of the relay.

Transistor Driving Circuit

When a transistor is used to drive a relay, the emitter of the transistor must be grounded. The specific circuit is as follows:

Relay Operating Principle and Driving Circuit

Principle Introduction

NPN Transistor Driver: Transistor Driver: T1 When the base input is high, the transistor saturates and conducts, the collector becomes low, so the relay coil is energized and the contact RL1 When the transistor T1 When the base input is low, the transistor cuts off, the relay coil is de-energized and the contact RL1 is disconnected.

Furunda Relay

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