English
中文Relay is an electrically controlled switch device, commonly used in the control circuit of electronic equipment. Relay usually consists of one or more electromagnetic coils and a set of mechanical contacts for connecting or disconnecting the circuit. It uses the principle of electromagnetic induction to control the flow of large current with small current, thereby achieving control and protection of the circuit. Relay is one of the indispensable components in modern electrical control systems.
1. Principle of relay
The core parts of the relay are electromagnetic coil and contact. The electromagnetic coil is wound by wire. When the current is connected, a magnetic field is generated, which closes or disconnects the contact. There are control terminal and output terminal on the pin of the relay. The state of the output terminal can be controlled by powering on or off the control terminal.
When the control terminal is powered on, the current passes through the electromagnetic coil, and the iron core in the coil is attracted by the magnetic field. With the attraction of the iron core, the contacts are closed, a path is formed between the output terminals, and the current can flow.
When the control terminal is powered off, the magnetic field in the electromagnetic coil disappears, the iron core loses its magnetism, and the contacts are disconnected due to the action of the return spring, the path between the output terminals is disconnected, and the current stops flowing.
2. Classification of relays
Relays can be divided into two types according to the contact type: normally closed contacts and normally open contacts.
(1) Normally closed contacts: When the relay is not in operation, the contacts are closed and the circuit is on and off. When the control end is powered on, the contacts are disconnected and the circuit is disconnected. This is the most common type of relay.
(2)Normally open contacts: When the relay is not in operation, the contacts are disconnected and the circuit is disconnected. When the control end is powered on, the contacts are closed and the circuit is closed. This type of relay needs to be used in specific applications.
According to the working principle, relays can be divided into two types: electromagnetic relays and solid-state relays.
(1)Electromagnetic relay: It works on the principle of electromagnetic induction. Its contacts are closed and opened by the attraction of the iron core and the action of the spring. Since the contacts of the electromagnetic relay are mechanically connected, it can withstand large currents and is widely used.
(2)Solid-state relay: It uses the characteristics of semiconductor materials for control and achieves output through photoelectric isolation. Solid-state relays have no mechanical parts, are more durable, and the contacts are not easily affected by vibration and corrosion, but the load-bearing capacity is relatively small, and it is mainly suitable for low-power control.
3. Working mode of relay
Relay has two working modes: single switching type and double switching type.
(1)Single switching type relay: The relay has one contact. When the control end is powered on, the contact is closed and the circuit is connected; when the control end is powered off, the contact is disconnected and the circuit is disconnected. This type of relay is often used to control normal switching circuits, such as household lighting.
(2) Double switching type relay: The relay has two contacts, usually one contact is normally closed and the other contact is normally open. When the control end is powered on, the normally open contact is closed, the normally closed contact is disconnected, and the circuit is closed; when the control end is powered off, the normally open contact is disconnected, the normally closed contact is closed, and the circuit is disconnected. This type of relay is often used in circuits that require dual control, such as car headlight control.
4. Application of relays in different fields
The application of relays is very extensive, covering various fields such as electricity, communications, chemicals, transportation, and medical care. Some common relay applications are listed below.
(1) Power system: Relays play a role of protection and control in power systems. They can be used for overcurrent protection, undervoltage protection, overvoltage protection, earthquake protection, etc.
(2) Electrical control systems: Relays can be used to control motors, such as starting and stopping elevators, fans, water pumps and other equipment.
(3) Communication equipment: Relays are used in the communication field for switching power supplies, repeaters, circuit switching, etc.
(4) Subway systems: Relays are used in subway systems to control signal lights, open and close station doors, etc.
(5) Household appliances: Relays are often used in household appliances to control lights, air conditioners, televisions, washing machines, etc.
In the PCB (Printed Circuit Board) wiring design of relays, the width of the trace is a very important factor.
First, the width of the relay PCB trace has an important impact on the current carrying capacity of the circuit. The wider the trace, the greater its current carrying capacity, because the increase in width reduces the trace resistance. When the relay is switching high currents, the wide trace can reduce the resistance to the connection loss between the power supply and the load, thereby improving the efficiency and stability of the entire circuit. On the contrary, if the trace width is narrow, it may cause current overload to cause line failure, or even cause dangers such as fire.
Second, the width of the relay PCB trace also affects the current concentration effect. A wider trace can accommodate more current and reduce local trace resistance, thereby reducing the risk of current concentration in the narrow part of the trace. Excessive current density may cause local overheating, melting, and even pad peeling of the trace. Therefore, according to the current requirements and wiring area of the relay, choose the appropriate trace width to ensure uniform current distribution and improve the reliability of the circuit.
Trace width also affects the heat dissipation performance of the relay PCB. Wider traces have a larger heat conduction area and can dissipate heat more effectively. In high-power relay circuits, due to the large Joule heat generated by the current passing through the trace, appropriately selecting wide traces can reduce the temperature rise and keep the circuit within the operating temperature range. However, in lower power relay circuits, in order to optimize the PCB layout and reduce the circuit area, the trace width can be appropriately reduced to reduce cost and space.
In addition, the trace width is also important for the electromagnetic compatibility (EMC) of signal transmission. Wider traces can reduce the self-inductance and capacitance of the line, reduce impedance mismatch and reflection during signal transmission, reduce interference and noise, and improve signal integrity. Therefore, in high-frequency relay circuits and sensitive signal transmission, appropriately increasing the trace width can improve the system’s anti-interference and anti-noise performance.
Finally, the selection of relay PCB trace width is also constrained by manufacturing process and cost. During the PCB manufacturing process, trace width has a direct impact on the possibility of short circuits and poor connections of wires. If the trace is too narrow, it may cause short circuits or insufficient wire spacing due to manufacturing deviations, thus affecting the normal operation of the circuit. In addition, wider traces may increase board area and raw material consumption, increasing costs. Therefore, when determining the trace width, it is necessary to comprehensively consider manufacturing process and cost factors.
In summary, the width of the safety relay PCB trace has an important impact on circuit performance and reliability. Appropriate selection of trace width can improve the circuit’s current carrying capacity, current concentration effect, heat dissipation performance, signal integrity and anti-interference ability. However, the selection of trace width also needs to consider manufacturing process and cost factors. Therefore, in safety relay PCB design, engineers should reasonably select trace width according to specific application needs and design requirements to ensure circuit stability, reliability and cost-effectiveness.
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