Quick guide to LED drivers

LED lighting requires a flow of consistent and constant electrical current at all times, at an exact voltage. Doing this also allows the LEDs to stay a consistent temperature; if an LED runs too hot, it may begin to malfunction and experience poor performance. LED drivers help LEDs achieve optimal conditions.

We spoke with Thomas Kent, manager of reliability at Eaton, about how LED drivers work.

What is an LED driver?

TK: LED drivers are similar to ballasts for fluorescent lamps or transformers for low-voltage bulbs: they provide LEDs with the electricity they need to function and perform at their best.

LEDs require drivers for two purposes:

• LEDs are designed to run on low voltage (12-24V), direct-current electricity. However, most places supply higher voltage (120-277V), alternating current electricity. An LED driver rectifies higher voltage, alternating current to low-voltage, direct current.
• LED drivers also protect LEDs from voltage or current fluctuations. Any change in voltage could cause a change in the current being supplied to the LEDs.

LED light output is proportional to its current supply, and LEDs are rated to operate within a certain current range. Therefore, too much or too little current can cause light output to vary or degrade more quickly due to higher temperatures within the LED, or thermal runaway.

In what applications are LED drivers used?

TK: LEDs that typically require an external driver include cove lights, downlights and tape lights, as well as certain fixtures, panels and outdoor-rated lights. These bulbs are often used for commercial, outdoor or roadway lighting purposes.

LEDs designed for household use contain internal drivers rather than separate, external drivers. Household bulbs usually include an internal driver, because this makes replacing old incandescent or CFL bulbs easier.

What are the types of LED drivers?

TK: There are two main types of external LED drivers: constant-current and constant-voltage. Each type of driver is designed to operate LEDs with a different set of electrical requirements:

• Constant-current drivers power LEDs that require a fixed output current and a range of output voltages. There will be only one output current specified, labeled in amps or milliamps, along with a range of voltages that will vary depending on the load (wattage) of the LED.
• Constant-voltage drivers power LEDs that require a fixed output voltage with a maximum output current. In these LEDs, the current is already regulated, either by simple resistors or an internal constant-current driver, within the LED module.

What are things to consider when selecting an LED driver?

TK: Once you’ve determined whether you need a constant-current or constant-voltage driver, there are a number of other factors to consider:

• The output current — Check the current requirements of the LED lights you’re using. If you’re using a constant-current driver, it will need to reflect that output.
• The output power — The output power is provided in watts. At a minimum, your LED driver should have the same output power as your LEDs.
• The output voltage — If you’re using a constant-voltage driver, it needs to have the same output voltage as your LED voltage requirements. If you’re using multiple LEDs, add the voltage requirements together to determine the output voltage your driver needs. If you use a constant-current driver, make sure the output voltage exceeds the requirements of your LED lights.

How does dimming play a role?

TK: Depending on their specifications, some LED drivers can also facilitate dimming and/or color sequencing for the LEDs they are connected to. Both constant-current and constant-voltage LEDs and drivers can be made with a dimming capability. Dimmable external drivers often require an external dimmer, or other dimming control devices specified on the product data sheet (namely TRIAC, Trailing Edge, or 1-10V dimmers) to function properly. Dimming works with building controls and occupancy sensors to create a more efficient and effective environment.

Evaluating and selecting an LED driver can be simple with the right know-how. An understanding of current vs. voltage and dimming considerations can help identify the important features essential to optimizing any lighting system performance.