(Issue: May 2017)

Replacing LED Drivers

By Craig DiLouie, CLCP, LC

 LED driver with label shown. The programmed tune level for this driver is 1300mA.
Image courtesy of Universal Lighting Technologies.

The majority of LED lamps and luminaires use an electronic driver that provides the same basic functions as a fluorescent ballast. It converts incoming AC to DC and drives current to the LEDs.

Standardization makes fluorescent ballast replacement simple. If a ballast fails, a replacement that matches the previous ballast’s characteristics and is compatible with the lamp is selected and installed. If the ballast is dimmable, a ballast compatible with the dimming method is selected.

Like fluorescent ballasts, LED drivers also fail. For the majority of luminaires, the driver is installed inside the luminaire. If the luminaire is serviceable, the driver can be replaced in the field. Some feature quick disconnects for easy servicing. The replacement driver should be high quality -- providing high efficiency, good reliability and stable output.

Otherwise, the new driver should function the same as the driver it is replacing. This requires the maintenance technician to select a driver offering the same performance characteristics while having a form factor allowing it physically to fit in the same space within the luminaire. Mismatching can result in performance and safety issues. In some cases, the issue is immediately apparent, such as the LEDs failing to light. In other cases, it may not be apparent, such as a Class A driver in a residential application causing interference with TV reception.

The problem is LED drivers are not standardized, which means drivers are not interchangeable. There is little effort being put toward standardizing drivers because luminaire manufacturers want a wide range of options from driver manufacturers. Similarly, LED modules are not standardized and vary widely in regards to light output, efficacy and chip layout, all of which determine the appropriate drive current. Many indoor LED drivers are programmed at the factory to deliver a specific drive current for the specific connected LED module.

The many available driver-LED module pairings and form factors, coupled with short product cycles, can make driver replacement challenging. When replacing an LED driver, ideally replacement will be straightforward with all required information printed on the driver label and a factory-tuned replacement driver readily available from the same manufacturer.

Driver types and characteristics
The industry categorizes LED drivers according to a range of characteristics:

Output characteristics: Driver performance depends on how well the output voltage or current is matched to the LEDs.

Constant-voltage drivers operate LED modules requiring a fixed voltage, typically 12 or 24VDC. They are typically used in applications where the LED load is unknown, such as track and sign lighting.

Constant-current drivers operate LEDs requiring a constant current such as 350mA, 700mA or 1A. They are used in the large majority of LED general lighting.

Input characteristics: The replacement driver must operate properly on the supply voltage. Most drivers are universal 120-277V, 50-60Hz. Some require a fixed or single voltage.

Electrical safety rating: Class 1 drivers operate on high voltage and are used in the majority of outdoor LED products. Class 2 drivers operate on low voltage and are used in the majority of indoor LED products.

Programmability: Drivers may be programmed or tuned to set a maximum output for the LED load. This allows precise pairing between the driver and LED module, which results in a precise lumen and wattage package. The industry is moving toward programmable drivers, which allow luminaire manufacturers to reduce the number of drivers they use and distributors the number they need to stock. The majority of drivers used in indoor luminaires is tunable, while most outdoor drivers currently are not. Besides maximum output, some drivers also allow programming of dim levels and dimming curves. Programming typically occurs at the factory, though some products allow field programming using special tools.

Electromagnetic interference (EMI): Drivers may be rated as Class A for nonresidential or Class B for residential applications.

Dimming interface: The majority of LED products is dimmable and designed to accept control input via an interface, typically 0-10VDC, digital (e.g., DALI) or phase-control. Digital and 0-10V drivers feature a set of low-voltage control leads similarly to a digital or 0-10V dimmable fluorescent ballast. Drivers with a phase-control interface do not, as the control signal travels along power wiring.

UL Class P
In January 2016, UL announced the Class P LED Driver Program. This program defines evaluation and testing guidelines for standardized LED driver constructions and ratings, allowing luminaire manufacturers to source alternate LED drivers without having to recertify their products. By further addressing the temperature considerations of an LED luminaire system, the Class P LED Driver Program allows luminaire manufactures greater flexibility in LED driver substitution.

Luminaire manufacturers using an LED driver certified under the program may source multiple LED drivers without the need to resubmit for UL testing and recertification. This helps ensure continuity in the supply chain if an LED driver manufacturer discontinues a part. Manufacturers can provide their end users with multiple options for supply voltages, dimming, and other LED driver features.

Driver replacement
In 2016, the National Electrical Manufacturers Association (NEMA) published LSD-74, Considerations of Field LED Driver Replacement. This whitepaper offers recommendations for driver replacement.

Take a photo of the driver labeling, ensuring that the information on the label is legible. Of particular interest is the programmed current (tuned) level on the label. Then take a photo of the LED module, which will provide substantial visual information that may be needed. Consult the luminaire label and installation instructions for information about the system and replacing the driver.

Replacement can be straightforward if using the same manufacturer driver. Selecting the same model number and programmed current (tuning) from the driver label will ensure a proper match to the modules in the luminaire. 

If using a different manufacturer’s driver, NEMA advises contacting the luminaire or LED module manufacturer to determine the module’s rated current. These manufacturers may list suitable replacement drivers with their characteristics. If the type of LED module is unknown, the photo of the module may help.

Note that tuning can be difficult to replicate across manufacturers, as tuning values typically do not transfer between them. The result may be a current that is too high or low, which can make the luminaire appear bright or dim compared to other luminaires in the space.

Field tuning entails using tools and process that may be unique to the manufacturer of the driver. Typically, it is not recommended. Some driver manufacturers offer quick-shipping of factory-tuned drivers.

Download NEMA LSD-74-2016 at NEMA.org

Craig DiLouie, CLCP, LC, principal of ZING Communications, Inc., is a consultant, analyst and reporter specializing in the lighting and electrical industries, and a regular contributor to LM&M. You may contact Craig at cdilouie@zinginc.com.