How to Choose LED Drivers and LED Power Supplies
If you’re building an LED fixture, performing maintenance on existing fixtures, or purchasing LED lights, you might need a constant-current LED driver or constant-voltage power supply for proper LED operation. There are numerous factors that should be considered when choosing a driver or power supply. The information below should help you pick the right power source for your needs.
LEDs typically have a power-limiting device (either driver or resistors) in order to prevent LEDs from being overdriven. A constant-current driver is used to regulate the amount of current that is supplied to an LED or LED array to maximize LED lifetime. If current is not regulated, LED brightness can fluctuate and life span can be shortened. The constant-current driver is used for LEDs or light fixtures that require a stable output current and operate within a range of voltages. Most finished LED products already have a constant-current driver or resistors to regulate current. If you’re building an LED fixture or replacing a constant-current driver, it’s important to verify that the output current and voltage of the driver is compatible with the LEDs’ current and voltage. If your LED product already has a constant-current driver or uses resistors in the LED array, you might need a constant-voltage power supply.
Constant-current LED drivers shown installed on an LED can light fixture and LED disc bulb
Constant-Voltage Power Supplies
Constant-voltage power supplies can be used to power LED products that have resistors or constant-current drivers. Products with these current-regulating devices might require a constant-voltage power supply if they need a different operating voltage than what’s supplied by the power source (home, vehicle, etc.). For example, LED light strips are equipped with current-regulating resistors. If the light strip operates within a 9-14.8-volt direct current (DC) range, it can be installed inside a vehicle with a 12-volt DC system without using a constant-voltage power supply. In order for that light strip to be installed in a home with a 120-volt alternating current (AC) wiring system, the voltage would need to be reduced and converted from AC to DC with a power supply. In some cases, constant-current drivers matching the voltage and current requirements of both the product and the power source (home, vehicle, etc.) are available, and a constant-voltage power supply wouldn’t be necessary.
LED strip light powered by a constant-voltage power supply
When choosing a constant-voltage power supply, you must determine how many watts your light consumes. If your project requires more than one light, you need to determine the total watts used. Make sure to have a large enough power supply to handle the wattage of all of your combined lights. You will need to choose a power supply that is rated at least 20 percent above the total wattage of your lighting system to ensure that you don’t overwork the power supply. An easy way to calculate this is to multiply the total wattage of your lighting by 1.2. For example, if you have five LED path lights that consume four watts each, your combined lighting wattage is 20. Simply multiply 20 watts by 1.2 (20 x 1.2 = 24) to determine which power supply you’ll need. A 24-watt (or higher) power supply will do the trick!
If you’re building an LED fixture or replacing a constant-current driver, it’s important to verify that the output current and voltage of the driver is compatible with the LEDs’ current and voltage. If your LED product requires a constant-voltage power supply or constant-current driver, check the product’s specifications for its operating requirements, and make sure that it is compatible with the specifications of the power supply or driver. Also be sure that the power supply or driver’s input voltage matches that of the location it will be installed in. If you have an LED product with 12-volt DC operation that you wish to use in a 120-volt AC home wiring system, you’ll need a power supply that includes 120 volts in its input range and has 12-volt DC output. A 24-volt DC power supply would not be appropriate because its output voltage isn’t compatible with the voltage of the product.
When choosing a constant-current driver for an LED project, ensure that the current and voltage requirements of the LEDs are met. If LEDs are in a parallel configuration, add all current values while keeping the voltage range steady. If LEDs are used in a series, add all voltage values, but keep current the same as an individual LED.
If your LEDs are dimmable and you want to change their brightness, choose a dimmable driver or power supply. The specifications of these power sources will usually list whether or not they’re dimmable. Specification tables will also list compatible dimmer control types for the drivers or power supplies. There are five commonly used dimming control types:
TRIAC Dimming: Triode for alternating current (TRIAC) dimming is used to control high-voltage dimmable power supplies such as Magnitude Dimmable Power Supplies. These dimmable power supplies work by varying the power on the AC input side of the power supply by means of a TRIAC dimmer. This change in power on the AC input side will vary the voltage on the DC output side and control the intensity of the LEDs. TRIAC dimmers are common hardware store and household dimmers, which include brand names such as Lutron and Leviton.
Pulse-Width Modulation Dimming: Pulse-width modulation (PWM) dimming can be used to control dimmable power supplies such as Mean Well HLG Series and Mean Well LPF Series. This type of dimming control adjusts the output current based on the duty cycle. As the duty cycle increases, current will increase and the LEDs will be brighter. Conversely, if the duty cycle decreases, the current will decrease and the LEDs will be dimmer. Pulse-width modulation for these drivers is based on a 10-volt signal level with a frequency between 100Hz-3KHz. The MCBRF-4A or MLD-5A are compatible for this application.
Resistive Dimming: Resistive dimming can be used to control dimmable power supplies such as Mean Well HLG Series. The resistance can be fixed or variable. If a fixed level of dimming is required, a simple resistor is all that is needed to dim the LEDs to a particular level. If a varying dimmable level is desired, a potentiometer can serve this purpose. By changing the resistance value of the potentiometer, the output current of the power supply changes, and the LED intensity changes. Controlling a single power supply will require a 100K ohm potentiometer for 100 percent intensity (100K ohm) to approximately 10 percent intensity (10K ohm) based on where the wiper is positioned.
1-10 Volt Dimming: 1-10 volt dimming can be used to control dimmable power supplies such as 12-Volt Mean Well HLG-40-240 Series or 24-Volt Mean Well HLG-40-240 Series. This type of dimming control is an older style for compatible dimmable power supplies and is being replaced with 0-10 volt dimmer control. The dimming control works by varying voltage from one to 10 volts DC. A 10-volt signal on the dimming wire will allow for maximum current to flow to the LEDs for maximum intensity. A one-volt signal on the dimming wire allows 10 percent of the current to flow from the power supply, which generates approximately 10 percent of the maximum intensity for the LEDs.
0-10 Volt Dimming: 0-10 volt dimming can be used to control dimmable power supplies such as 12-Volt Mean Well HLG-600 Series or 24-Volt Mean Well HLG-600 Series. This type of dimming control is the most popular and newest style for compatible dimmable power supplies. 0-10V dimming control works by varying the voltage from 0 to 10 volts DC. A 10-volt signal on the dimming wire will allow for maximum current to flow to the LEDs for maximum intensity. A 0.6-volt signal on the dimming wire allows 6 percent of the current to flow from the power supply—dimming the LEDs to approximately six percent of full intensity. A selection of 0-10 volt dimmers can be found here.
Temperature and Weather Resistance
Another factor to consider when you’re choosing a power source is the environment that it will be used in. Power supplies and drivers are most efficient if they are used in environments with temperatures that don’t fall outside of their operating temperature range. Each power supply or driver also has an ingress-protection (IP) rating. IP ratings indicate the size of solids and pressure of liquids that a power supply housing can resist. The first number refers to size of solids—ranging from those as large as a hand to those as small as dust particles. The second number refers to liquid pressure from rain to full immersion. As each number increases, so does its level of protection. Your power supply should have an IP rating that indicates protection from its environment.
The efficiency of a power supply or driver indicates the percentage of power that goes toward making your LED product function. An efficiency of 80 percent or higher is recommended for operating LEDs.
When choosing a driver or power supply, the size of an LED product’s housing or area of installation is important. If you wish to put a constant-current LED driver inside of a product, the driver must be small enough to fit in the product’s housing. Similarly, if the driver or power supply is used outside of the product’s housing, it should fit the area of installation. Drivers and power supplies are available in a variety of sizes to suit your needs.
Class II vs. Class 2
A Class 2 driver or power supply is in accordance with limited power levels defined by the National Electric Code (NEC) and fulfills the requirements of Standard UL 1310. Output is limited to 60 volts DC and 100 watts. Because power sources with this rating have limited output, it might not be possible to power as many LEDs or lights as those that don’t have a Class 2 rating. However, these power supplies and drivers provide protection from fire and electric shock.
A Class II rating refers to a double insulation layer between AC input and DC output wires. These drivers and power supplies do not require a ground connection.