Introduction
Traffic lights are deployed in outdoor environments, and the complete system comprises an AC power supply unit, an MCU main controller, a traffic flow detection module, and multi-channel LED signal displays. Equipment damage is easily caused by surge impacts resulting from thunderstorms or power grid switching disturbances, thereby disrupting traffic flow and creating safety hazards.
Therefore, implementing systematic protection against lightning strikes and surges is a crucial aspect of traffic signal equipment design that cannot be overlooked.
I. Key Electrical Risks Facing Traffic Lights
- Induced Lightning Surges
While traffic lights are rarely struck directly by lightning, nearby strikes generate powerful electromagnetic pulses. These pulses couple into the equipment via 220V AC power cables and traffic detection signal lines, inducing transient high voltages of several thousand volts.
Such high-energy surges can cause dielectric breakdown in power supply PFC and DC-DC converter chips, burn out the MCU main control unit, or directly destroy LED signal displays, resulting in equipment failure.
- Power Grid Switching Surges
Voltage spikes can occur on power supply lines due to grid switching operations or the startup and shutdown of nearby high-power equipment. Repeated surge impacts accelerate the aging of power supply components, shorten the overall lifespan of the traffic light unit, cause intermittent malfunctions, and increase long-term on-site maintenance costs.
- Damage from Residual Surges on the Low-Voltage Side
Even if the power supply front-end absorbs the majority of a surge, residual transient voltage can still propagate to downstream low-voltage circuits.
MCUs, traffic detection modules, and LED components are highly sensitive to transient overvoltage. Residual surges can cause open-circuit failures in LEDs and anomalies in main control logic, leading to erratic signal light behavior or individual LEDs failing to illuminate.
- Surges Introduced via Signal Lines
Signal lines for traffic detection modules are exposed to the outdoors; surges can travel along these lines to the main control MCU, causing control unit failure and preventing the traffic light from adjusting its timing logic based on traffic flow conditions.
II. Semiware’s Tiered Protection Design Approach
A tiered protection strategy is recommended: implement primary high-energy discharge at the AC power input, secondary clamping at the power conversion stage, and precision protection for low-voltage LEDs and signal interfaces. This approach dissipates surge energy layer by layer, preventing total system failure caused by the breakdown of a single protection point.
- AC Power Input: Discharging High-Energy Lightning Surges
The power inlet is the primary entry point for surges; a combination of a Ceramic Gas Discharge Tube (GDT) and a Metal Oxide Varistor (MOV) is the preferred solution.
Recommended Components:
🔹 SG2R08B600A (20kA) / SG2R08B600 (10kA) Gas Discharge Tube (GDT)
Features low parasitic capacitance (only 1.5pF) and high current-handling capability. It conducts rapidly upon the arrival of a lightning surge, shunting massive surge currents to the ground. It is suitable for primary protection on the power side and can be selected based on specific needs—ranging from high-lightning-risk areas to standard urban projects.
🔹 14D561K Metal Oxide Varistor (MOV)
560V operating voltage; withstands 4500A surge current and absorbs 150J of energy.
The GDT and MOV combination suppresses residual voltage and mitigates the "follow current" risk associated with GDTs. This protects downstream PFC and DC-DC power circuits, preventing high-voltage breakdown of power management chips.
- LED Signal Load: Targeted LED Open-Circuit Protection
After passing through the power conversion stage, residual voltage spikes can directly impact the LED display. LED arrays are susceptible to open-circuit failures in individual beads due to transient surges, which can cause the entire signal light circuit to fail.
Recommended Component:
🔹 PLED06F: A 6V LED protector in an SOD-123FL package, specifically designed for LED circuit protection.
If an open-circuit fault occurs in an LED branch, the protector quickly bypasses the fault, ensuring the remaining LEDs stay lit. The device utilizes an SMD package for easy PCB integration, making it ideal for mass production.
- Signal Detection Circuit Protection
Signal lines for traffic flow detection modules are also susceptible to surge coupling.
Recommended Component:
🔹 Select a low-capacitance gas discharge tube (GDT) to protect the signal interface.
This component discharges surge energy without interfering with the normal transmission of traffic detection signals, ensuring the MCU can accurately collect traffic data and enable intelligent traffic light timing.https://en.semiware.com/applications/traffic-lights/
III. Reference Design Block Diagram for Traffic Light Circuit Protection
Conclusion
For traffic signal systems, surge protection enhances the reliability of traffic signal equipment against transient events and reduces unnecessary field failures.
Semiware provides circuit protection components for traffic lights and traffic signal systems. If you are designing a new traffic signal system or seeking suitable protection devices for an existing design, please contact us to discuss your circuit requirements and component selection.
Learn more about Semiware's traffic light protection solutions:
