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About the detailed working principle of the relay, the working principle of the driving circuit

About the detailed working principle of the relay, the working principle of the driving circuit

August 15 , 2023 0

Relay is an electronic control device, it has a control system (also known as the input circuit) and the control system (also known as the output circuit), usually used in automatic control circuits, it is actually a smaller current to control a larger current of an "automatic switch". Therefore, in the circuit plays a role in automatic regulation, safety protection, switching circuits.

Relay Relay Characteristics
When the input signal x of a relay is increased continuously from zero to the value xx at which the armature starts to engage, the output signal of the relay immediately jumps from y=0 to y=ym, i.e., the normally open contact goes from broken to open. Once the contacts are closed and the input x continues to increase, the output signal y will no longer change. When the input x drops from a value greater than xx to xf, the relay starts to release and the normally open contact opens. We call this characteristic of the relay the relay characteristic, or the input-output characteristic of the relay.

Principle of operation and characteristics of relays

1, the working principle and characteristics of electromagnetic relay

Electromagnetic relay is generally composed of iron core, coil, armature, contact reed and so on. As long as the coil ends plus a certain voltage, the coil will flow through a certain current, resulting in electromagnetic effect, the armature will be attracted in the electromagnetic force under the action of overcoming the return of the spring tension suction to the iron core, thus driving the armature's moving contacts and static contacts (normally open contacts) suction. When the coil is powered off, the electromagnetic suction also disappears, the armature will return to its original position under the reaction force of the spring, so that the movable contact and the original static contact (normally closed contact) release. This suction, release, so as to achieve the purpose of conduction in the circuit, cut off. For the relay "normally open, normally closed" contacts, can be distinguished in this way: the relay coil is not energized in the disconnected state of the static contacts, known as "normally open contacts"; in the on state of the static contacts known as "normally closed contacts The static contact in the on state is called "normally closed contact".

2、Circuit Principle

2.1 Brief Introduction to Relays

Basic Concept
Relay is a kind of small capacity control circuit which connects or breaks AC and DC when the input quantity changes to a certain value.

2.2 Principle of operation

The magnet is kept in the released state, and when the operating voltage is added, electromagnetic induction causes the armature and magnet to produce attraction and repulsion torque, generating a downward movement to reach the suction state.

3、Transistor Driver Drive Circuit

3.1 Circuit schematic

When a transistor is used to drive a relay, an NPN triode is recommended. The specific circuit is as follows:

　　Brief description of the operating principle
　　When input high level, transistor T1 saturates and conducts, relay coil is energized, and contacts are closed.
　　When the input is low, transistor T1 cuts off, the relay coil is de-energized and the contact is disconnected.
　　3.2 Role of each component in the circuit
　　Transistor T1 is the control switch.
　　Resistor R1 mainly plays the role of current limitation and reduces the power consumption of transistor T1.
　　Resistor R2 makes the transistor T1 reliable cutoff.
　　Diode D1 reverse current, for the transistor from conduction to turn off when the relay coil to provide a drain path, and its voltage clamped at +12V.

4、Integrated Circuit Driver Circuit

Integrated circuits with multiple driver transistors are now used, and the use of such integrated circuits simplifies the process of designing printed circuit boards to drive multiple relays. The main integrated circuits used by our company to drive relays are now the TD62003AP.

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 engaged;
When the 2003 input is low, the corresponding output port is in high resistance state, the relay coil ends are de-energized and the relay contacts are disconnected.

24V Relay Driving Circuit

Relay in series with 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 due to the self-inductive phenomenon will generate an electric potential to hinder the increase of the current in the coil, thus prolonging the suction time, series connection on the RC circuit can shorten the suction time. The principle is that the instant the circuit is closed, the capacitor C can not be considered as a short circuit, so than the rated operating voltage of the relay coil will be higher than the power supply voltage added to the coil, thereby accelerating the current in the coil to increase the speed of the relay to quickly close. After the power supply is stabilized, capacitor C does not function and resistor R acts as a current limiter.

II. Selection of the rated operating voltage of the relay

The rated operating voltage of a relay is one of the main technical parameters of a relay. When using a relay, you should first consider the operating voltage of the circuit (i.e., the circuit in which the relay coil is located), and the rated operating voltage of the relay should be equal to the operating voltage of the circuit in which it is located. The rated working voltage of the relay should be equal to the working voltage of the circuit in which it is located, which is generally 0.86 of the rated working voltage of the relay, and it should be noted that the workpiece voltage of the circuit in which it is located should never exceed the rated working voltage of the relay, otherwise the relay coil will be easily burnt. In addition, some integrated circuits, such as the NE555 circuit can directly drive the relay work, while some integrated circuits, such as the COMS circuit output current is small, you need to add a transistor amplifier circuit to drive the relay, which should be considered transistor output current should be greater than the rated operating current of the relay.

1. 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:

2, principle introduction

NPN transistor drive: when the base of transistor T1 is input high level, the transistor saturation conduction, the collector becomes low level, so the relay coil is energized, contact RL1 is absorbed. When the base of transistor T1 is input low level, the transistor cuts off, the relay coil is de-energized and contact RL1 is disconnected.