What Are Relays?
Relays are electrically operated switches that use an electromagnet or solid-state mechanism to open or close contacts, allowing a low-power control signal to switch a high-power load circuit. Types include electromechanical relays (general purpose, power, latching), solid-state relays (SSR), reed relays, and time-delay relays. LCSC stocks 8,000+ relay SKUs from 100+ manufacturers.
Relays — Definition and Sub-Categories
A relay is an electrically operated switch. In an electromechanical relay, a coil energizes an electromagnet that mechanically moves contacts. In a solid-state relay, semiconductor devices (triacs, MOSFETs) perform the switching function with no moving parts, offering faster switching and longer life.
|
Sub-Category |
Function |
Key Parameters |
|
General Purpose EMR |
Electromechanical switching for moderate loads |
Coil voltage, contact rating, configuration (SPDT/DPDT) |
|
Power Relays |
Heavy-duty switching for high-current loads |
Contact current (10–80A), coil voltage, life cycles |
|
Solid-State Relays |
Semiconductor-based switching, no moving parts |
Load type (AC/DC), current rating, control voltage |
|
Reed Relays |
Fast, small relays using magnetic reed switches |
Switching speed, contact rating, size |
|
Latching Relays |
Maintain state without continuous coil power |
Set/reset coil voltage, contact rating, power consumption |
How to Choose: Relays Selection Guide
Choose relay type based on load characteristics. Electromechanical relays (EMRs) offer galvanic isolation and handle both AC and DC loads with low contact resistance. SSRs are better for frequent switching, long life, and silent operation but generate heat under load. For battery-powered designs, latching relays save power by maintaining state without continuous coil current. Always verify contact ratings exceed your load’s voltage and current with a safety margin.
Relays Comparison
|
Relay Type |
Contact Life |
Switching Speed |
Best For |
Limitation |
|
EMR (general) |
100K–1M cycles |
5–15 ms |
General switching, low cost |
Mechanical wear, noise |
|
SSR |
Virtually unlimited |
<1 ms |
Frequent switching, silent |
Heat generation, leakage current |
|
Reed Relay |
1M–10M cycles |
0.5–2 ms |
Signal switching, fast |
Low current capacity |
|
Latching |
100K cycles |
5–10 ms |
Battery applications |
More complex drive circuit |
Why Source Relays from LCSC Electronics
LCSC stocks 8,000+ relay SKUs from manufacturers including Omron, Hongfa, Songle, and Goodsky. The catalog spans from miniature signal reed relays to 80A power relays for industrial switching.
Frequently Asked Questions
Q: What is the difference between an EMR and SSR?
Electromechanical relays (EMRs) use physical contacts moved by an electromagnet — they offer true galvanic isolation and near-zero on-resistance but wear out mechanically. Solid-state relays (SSRs) use semiconductors — they’re faster, silent, and last longer but have voltage drop across the switching element (generating heat) and small leakage current when off.
Q: How do I drive a relay from a microcontroller?
MCU GPIO pins can’t drive relay coils directly (insufficient current). Use a transistor (NPN BJT or N-channel MOSFET) as a switch between the GPIO and relay coil. Always add a flyback diode (1N4148 or 1N4007) across the coil to suppress the voltage spike when the coil de-energizes.
Q: What is a latching relay?
A latching relay has two stable states and stays in its last-switched position without continuous coil power. A brief pulse sets or resets the relay. This saves power in battery-operated systems like smart home switches and metering equipment.
Q: What relay do I need for AC mains switching?
For switching AC mains (120V/240V), use a relay rated for at least your load current at the mains voltage, with appropriate safety certifications. A 10A/250VAC general purpose relay handles most household loads. For motor or inductive loads, derate the contact rating by 30–50% due to inrush current and arcing.