Normal relays and solid-state relays (SSRs) function, especially useful for student-friendly presentations or training kits:
Normal Relay
(Electromechanical Relay)
Working Principle:
- Operates
using electromagnetism.
- When
current flows through the coil, it creates a magnetic field.
- This
magnetic field pulls a mechanical armature, closing or opening the
contacts.
- The
switching action is physical, producing a clicking sound.
Key Components:
- Coil
(electromagnet)
- Movable
armature
- Mechanical
contacts
- Spring
mechanism
Pros:
- Can
switch both AC and DC loads.
- Provides
galvanic isolation.
- Easy
to understand and troubleshoot.
Cons:
- Mechanical
wear and tear over time.
- Slower
switching speed.
- Generates
electrical noise (sparking at contacts).
Solid-State Relay (SSR)
Working Principle:
- Uses
semiconductor components (like triacs, thyristors, or transistors).
- Input
signal activates an opto-isolator (LED + photodetector).
- The
photodetector triggers the switching device to control the load.
- No
moving parts—switching is purely electronic.
Key Components:
- LED
(input side)
- Photodetector
(isolator)
- Triac
or transistor (output side)
- Heat
sink (for high-power SSRs)
Pros:
- Fast
switching and silent operation.
- Long
lifespan (no mechanical parts).
- Ideal
for frequent switching applications.
Cons:
- Typically
load-specific (AC or DC).
- May
require heat dissipation.
- Slight
leakage current when "off".
Quick Comparison Table
|
Feature |
Normal Relay |
Solid-State
Relay |
|
Switching Mechanism |
Mechanical (armature) |
Electronic (semiconductors) |
|
Speed |
Slower |
Faster |
|
Noise |
Audible click |
Silent |
|
Durability |
Limited (wear & tear) |
High (no moving parts) |
|
Isolation |
Galvanic |
Optical |
|
Applications |
General-purpose |
High-speed, industrial |