A power supply or driver is an electronic device that supplies energy to an electrical load in order to convert one form of electricity to another and control the electrical current. Most residential, commercial and industrial lighting systems require a power supply to regulate the electrical current to the lamp or fixture. In this post we will discuss the three main types of lighting power drivers: ballasts, transformers and LED drivers.
Ballasts are required for fluorescent and HID light sources. They provide the right voltage to start the lamp and then regulate the electrical current to the lamp while it is running. Without a ballast to regulate the current, the lamp would draw too much power, then overheat and burn out. To get the full rated life output and rated lamp life from a fluorescent lighting system, the ballast must match the requirements of the lamps used in the fixture.
There are two main categories of ballasts: electronic and electromagnetic. Electromagnetic ballasts were used in the original fluorescent lamps and were later replaced in some cases by electronic ballasts. Electromagnetic ballasts are still used in outdoor fluorescent fixtures such as sign lights and for HID lamps. There are a wide range of ballast types depending on the luminaire and requirements of the lighting system.
Types of fluorescent lamp ballasts include:
Instant start – They power the lamp through high voltage without needing to heat the filament, making them more energy efficient and good for lamps that are on a lot.
Rapid start – They use low voltage to preheat the filament until the lamp starts, making for a short delay in starting. They are recommended when you have frequent on/off switching.
Dimmable ballast – In fluorescents, these ballasts – which are mostly electronic - have the ability to maintain electrode heat to excite the gas in the lamp even when input voltage is varied.
Programmed start – These electronic ballasts heat the lamp cathodes before the lamp ignites. They allow for frequent switching and are good for use with occupancy sensors.
Hybrid – Also called cathode-disconnect ballasts, use a magnetic core and coil transformer and electronic switch for the electrode-heating circuit, making them cheaper than electronic ballasts.
A lighting transformer is a device used to convert electrical energy from a higher to a lower voltage or vice versa. While they were first invented in the nineteenth century and have become more sophisticated, they still perform the same basic function of transforming voltage or electrical current for various purposes.
Lighting transformers are most often used in residential, commercial, industrial and outdoor applications to convert standard line voltage (110 to 240 volts) into a lower voltage (12 to 24 volts). This lets you supply power to specialized low voltage lighting systems such as recessed lights, pendant lights, outdoor lights or swimming pool lights.
Dimmer switches are a type of lighting transformer used to scale back or turn up the voltage to make a light dimmer or brighter.
Lighting transformers need to be placed close to the lighting load and can power more than one lighting load.
Main types of lighting transformers include:
Electromagnetic Transformers – Rely on the relationship between magnetism and electricity to transform voltage and current.
Electronic Transformers – Are designed for low voltage applications, are more compact and operate at lower temperatures.
Isolation Transformers – They separate one circuit from another and are used in situations where sensitive equipment needs be isolated from potentially dangerous high voltage.
3. LED DRIVERS
An LED driver or power supply provides a similar function as a ballast does for a fluorescent or HID lighting system or a transformer used in a low voltage bulb. The driver regulates the power and provides the LED lighting system with the right amount of electricity to perform optimally. If an LED stops operating before the end of its rated lifetime, they can usually be saved by replacing the driver.
LED drivers convert incoming AC power to the proper DC voltage and regulate the current flowing through the LED during operation, protecting the LEDs from line-voltage fluctuations. LED drivers are different to conventional power supplies in that they supply constant power to the LED, even as the electrical properties or temperature changes. The right driver maintains stability and efficiency and prevents the LED from overheating.
Types of LED Drivers include:
Constant Current drivers – They fix the current of the system and vary the voltage to the LED depending on the load. Low voltage DC constant current drivers are recommended for most applications since they are safe, efficient and reliable and have more dimming and output options.
Constant-Voltage drivers – They require a fixed voltage and add the LED loads until the maximum output currents are reached. Applications for constant voltage drivers include: under cabinet lighting, rope-lighting, backlit ad signs, traffic information signs and large screen LED displays.
Internal Drivers vs External Drivers
Internal drivers are more often used in household application since it makes it easier to replace old incandescent or CFL bulbs. LEDs requiring an external driver include cove lights, downlights, tape lights, panels and lights rated for outdoors. These are typically used for commercial, outdoor or streetlights. The driver is separate since it’s often easier and cheaper to replace the driver than the LEDS. Manufacturers typically specify whether the LED requires a separate driver and what kind it should be.
Questions to ask before choosing an LED driver:
- Do you need a constant current or constant voltage LED driver?
- How many and what type of LEDs are being used?
- What voltage range will you use?
- Are there space or power limitations?
- Environmental standards – e.g. for outdoor applications, is lightning an issue?
- Are there any special requirements, such as dimming or high ambient temperature?
- Are there other considerations such as cost or efficiency and performance compliance?
- What is the lifetime required of the driver?
Stay tuned for our next post which will cover the essentials of light colour temperature.
IIf you have any questions about drivers or would like a consultation on your project, we'd be happy to help. Simply click on the link below.