Due to increasing energy regulations, most people are familiar by now with the long life spans and energy savings associated with LEDs, or light-emitting diodes. However, many are not aware that these innovative light sources use specialized devices called LED drivers to operate. LED drivers (also known as LED power supplies) are similar to ballasts for fluorescent lamps or transformers for low-voltage bulbs: they provide LEDs with the correct power supply to function and perform at their best. Below, we discuss when you need an LED driver, why you need an LED driver, and what type of driver you may need.
When Do I Need an LED Driver?
Every LED light source requires a driver. The question should be whether or not you need to purchase one separately. Some LEDs already include an integrated driver within the bulb. LEDs designed for household use (bulbs with E26 / E27 or GU24 / GU10 bases and that run on 120V) typically already include a driver. However, low voltage LED light sources, such as some MR- bulbs (MR GU5.3s, MR8s, and MR11s) and tape light, as well as certain fixtures, panels, or outdoor-rated lights, usually require a separate driver. When an LED that requires a separate driver stops working before the end of its rated lifetime, it can usually be saved if the driver is replaced.
Why Do I Need an LED Driver?
- 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’s main purpose is to rectify higher voltage, alternating current to low voltage, direct current.
- LED drivers also protect LEDs from voltage or current fluctuations. A 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 (measured in amps). Too much or too little current can therefore cause light output to vary or degrade faster due to higher temperatures within the LED.
In sum, LED drivers serve two purposes: to convert higher voltage, alternating current to low voltage, direct current, and to keep the voltage or current flowing through the circuit at its rated level.
What Type of LED Driver Do I Need?
There are two main types of external LED drivers, constant-current and constant-voltage, as well as a third type of driver called an AC LED driver which will also be discussed. Each type of driver is designed to operate LEDs with a different set of electrical requirements. When replacing a driver, the old driver’s input/output requirements must be matched as closely as possible. Key differences are detailed below.
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. In the example to the right, the current output is 700mA, and the output voltage range is 4-13V DC (volts of direct current).
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. These LEDs require one stable voltage, usually 12V DC or 24V DC. In the example to the left, the output voltage is 24V DC, and the output current is a maximum of 1.04A.
AC LED Drivers
AC LED drivers are actually no-minimum load transformers, meaning they could technically operate low-voltage halogen or incandescent bulbs as well. LEDs, however, cannot operate with conventional transformers because conventional transformers were not made to detect the low wattage of LEDs. In other words, LEDs have such a small electrical load that regular transformers do not register that they’re wired to a bulb at all. AC LED drivers are typically used with bulbs that already contain an internal driver that converts the current from AC to DC, so an AC LED driver’s job is to register the low wattage of LEDs and step down the voltage to meet the bulb’s voltage requirements, usually 12 or 24 volts. AC LED drivers are typically used to power 12-24V AC input LED MR16 bulbs, but they can be used for any 12-24V AC input LED bulb. The LED bulb datasheet must be carefully examined; if the LED bulb requires DC voltage input, it cannot be used with an AC LED driver.
We’ve now discussed when, why, and what type of LED driver you need. Next time, we’ll discuss the many other factors involved in choosing LED drivers, such as dimmability, IP-rating, UL class 1 or class 2 designations, efficiency, and power factor.