Power Match

How the LEDs are driven is as important as the diodes themselves.
This 12 V, 60W constant voltage driver from Principal LED has two channels, accepts input current of 2.2A at 120VAC or 0.9A at 277VAC and has a five-year warranty.

While watching the men’s Wimbledon tennis final between Roger Federer and Novak Djokovic, I realized the best games in terms of power, technique and talent are played between well-matched opponents. Likewise, LED drivers, also known as power supplies or transformers, should be well-matched with their LEDs to ensure excellent performance over a long haul.

The driver is like the ballast in fluorescent lighting; it regulates the voltage and current to the LED modules to ensure safety and consistency. LED drivers must be matched to the modules to prevent LED overdriving, which shortens lifespan, or underdriving, which limits brightness. In signage, water damage and overheating can cause premature failure. Drivers should be installed in well-ventilated areas where the driver-case temperature will not exceed its rated operating range. Drivers installed in cabinets should be accessible and mounted well above the cabinet bottom, where moisture can accumulate.

LED drivers are available in two forms, constant voltage and constant current, which are not interchangeable. Constant-voltage drivers take input from the mains (100-277 VAC), transform the AC to DC current and step down the voltage to provide a single, low-DC output to the LEDs, typically 12 V or 24 V. The driver’s output voltage should be compatible with the LED-input voltage. Constant-voltage drivers will maintain output voltage regardless of load current, as long as it remains below the driver’s rated level. Constant-current drivers are designed for a fixed load. Because of the variable nature of signage, constant-voltage drivers are often used.

The power requirement of your sign depends on the sum total of the power required by the LED modules and driver efficiency. A channel letter product may specify the power per module, which you multiply by the number of modules to get a total. Then scale-up this number by dividing the total power by 0.8. If the sign requires 80W, which divided by 0.8 gives 100W, and two 60W drivers could be used.

The environment of the sign is reflected in the IP rating of the LEDs and driver. For outdoor signage IP67 or IP68 is common, while IP54 is often used indoors. The numbers indicate protection level from dust (first number) and water (second number). While drivers for outdoor environments are more expensive, some installers might choose them for indoor signage because of certain design features.

Finally, the manufacturer’s warranty should match the warranty of the LEDs. Also, look for the Class 2 designation, which ensures current will not exceed 5 amps. 12 V drivers must be 60W or under per channel and 24 V drivers must be 96W or under per channel to prevent electrical shock and fire. Local safety or electrical inspectors typically check for Class 2 drivers and look for approval by Underwriter Laboratories (UL) or Intertek (ETL).