What Is a Micro Relay?
A micro relay is a compact device among relays, designed to switch electric circuits on and off in response to external signals. Smaller than typical relays, they range in size from a few centimeters to just a few millimeters, making them ideal for space-constrained applications such as control systems and electronic equipment.
Notable for their high-speed switching capability, micro relays are suitable for applications requiring rapid signal processing and timing control. They are reliable in operation and have a long service life. However, due to their small size, their current capacity is limited. For large current control, larger relays should be considered.
Uses of Micro Relays
Micro relays find applications in various fields:
1. Electronic Devices
In smartphones, they control circuits and are used for functions like camera auto-focus or speaker switching. Office automation equipment, like printers, also uses micro relays for controlling paper feed and cartridge positions.
2. Automobiles
Widely used in automobiles, these relays manage window operations, switch headlights, and control bright mode settings. Automobile door lock systems also depend on Micro Relays for locking and unlocking mechanisms.
3. Medical Equipment
In medical devices like electrocardiographs, micro relays are used to acquire and process signals. They also play a role in sphygmomanometers, helping to control pressure sensors and switch display devices.
Micro Relay Principle
Comprising a coil, contacts, and springs, micro relays are enclosed in a resin or other insulating material casing for protection.
1. Coil
These relays often use electromagnetic coils made from thin conducting wires that generate a magnetic field to operate the contacts when electrified.
2. Contact Point
Contacts, made of electrically conductive metals like gold, silver, and copper, control the electrical flow.
3. Spring
Springs in micro relays apply the necessary pressure to the contacts, ensuring reliable switching between open and closed states.
How to Select a Micro Relay
When selecting a micro relay, consider the following:
1. Coil Voltage
Choose a micro relay with a coil voltage that matches your system’s operational voltage, ranging from low voltage options like 3.3 VDC or 5 VDC to higher voltage models at 12VDC or 24VDC. Select relays with built-in protection diodes to handle back EMF currents that could affect other devices.
2. Contact Current
Assess the contact current, the maximum current that the relay can handle. Due to their compact size, most micro relays have a low current rating, typically 2A or less. Exceeding this rating can cause contact welding or other malfunctions.
3. Connection Method
Micro relays can be integrated into circuits through various methods. Socket connections using pins are common, but there are also surface-mountable products.
4. Number of Poles and Contact Configuration
Consider the number of poles (number of contacts) and contact configurations, which include a-contact (normally open), b-contact (normally closed), and c-contact (a combination of the two).