Relays: The Switch Masters of the Electronic World

1. Definition and working principle

• definition: An electrical control device that causes the output circuit to undergo predetermined on-off switching when the input excitation reaches a threshold.
• essence：Small current controls large currentThe automatic switch realizes the isolation and drive between the control and the load.
• Basic principles of electromagnetic
  1. The coil is energized → produces a magnetic field
  2. Attract the armature → contact action (normally open to close, normally closed to open)
  3. The coil is deenergized → the magnetic field disappears → the spring returns → the contacts return to their initial state

2. Basic structure

1. Coil: Electricity generates electromagnetic attraction
2. magnetic circuit: Iron core, armature, etc., provide a path for magnetic flux
3. reaction spring:Reset the armature and contacts when power is off
4. contact system：Normally open, normally closed, changeover contact, perform circuit switching

3. Main categories

• According to working principle:
  • Electromagnetic relay (most commonly used)
  • Solid state relay (SSR, non-contact, long life)
  • Reed relay, time relay, temperature relay, etc.
• According to contact form:
  • Normally open type (NO), normally closed type (NC), switching type (SPDT)
• By use:
  • Control relays, protection relays, signal relays, etc.

4. Core role

1. electrical isolation: The control loop is safely isolated from the high-voltage and high-current load loop.
2. signal amplification:Small signal controls high power load
3. automatic control: Automatically switch on and off according to preset conditions to achieve remote control and automation
4. Multi-channel linkage: A set of signals controls multiple circuits at the same time, improving system integration.
5. Security protection: Quickly cut off dangerous circuits in overcurrent, overload, undervoltage and other scenarios

5. Development Trend