LED drivers can be a confusing part of LED technology. There are so many different types and variations that it can seem a little overwhelming at times. That’s why I wanted to write a quick post explaining the varieties, what makes them different, and things you should look for when choosing the LED driver(s) for your lighting application.

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What is an LED driver you might ask? An LED driver is an electrical device that regulates power to an LED or a string of LEDs. It is a crucial piece to an LED circuit and to operate without one will result in system failure.

One of the critical functions of an LED driver is preventing damage to your LEDs due to changes in forward voltage (Vf). The forward voltage is the amount of volts the light emitting diode requires to conduct electricity and light up. As the temperature rises, the forward voltage of the LED decreases, leading the LED to draw more current. This continuous cycle, known as Thermal Runaway, can ultimately destroy the LED. The LED driver plays a vital role by compensating for changes in forward voltage and consistently delivering the required current to the LED to avoid thermal runaway.

Things to Consider Before Selecting an LED Driver

• What type of LEDs are being used and how many?
  • Find out forward voltage, recommended driving current, etc.
• Do I need a constant current LED driver or a constant voltage LED driver?
  • We go over constant current vs. constant voltage here.
• What type of power will be used? (DC, AC, batteries, etc.)
  • Running from AC? See how an AC driver will benefit you!
• What are the space limitations?
  • Working in a tight area? Not a lot of voltage to work with?
• What are the main goals of the application?
  • Size, cost, efficiency, performance, etc.
• Any special features needed?
  • Dimming, pulsing, microprocessor control, etc.

Main Types of LED Drivers

Firstly, you should know there are two main types of drivers: low voltage DC input drivers (generally 5-36VDC) and high voltage AC input drivers (generally 90-277VAC). AC LED drivers are also known as Off-Line drivers. Although low voltage DC input drivers are usually recommended for most applications due to their efficiency and reliability, AC drivers can be more beneficial for large-scale residential and commercial lighting.

Understanding Drive Current

Next, it's essential to understand the drive current needed for your LEDs. Higher drive currents result in brighter LEDs but also increase power consumption. It is vital to balance the recommended drive current and heat sink requirements to prevent overheating and burning out the LEDs.

A Little Bit About Dimming

DC Dimming

Low voltage DC powered drivers offer several dimming options. The simplest way is by using a potentiometer to enable a full range of 0-100% dimming.

Another option is using a 0-10V wall dimmer, such as our A019 Low Voltage Dimming Control, particularly beneficial when working with multiple units.

AC Dimming

For AC power drivers, 0-10V dimming is also an option. Additionally, many AC drivers are compatible with popular residential dimming systems like Lutron and Leviton.

How Many LEDs Can You Run with a Driver?

The number of LEDs you can run from a single driver depends on dividing the maximum output voltage of the driver by the forward voltage of your LEDs. For instance, with the Wired 1000mA BuckPuck driver and a 24V input, you can achieve a maximum output voltage of 22 volts.

What Do I Need for Power?

To determine the input voltage needed for your LEDs, you can use the formula:

Vo + (Vf x LEDn) = Vin

Where:

Vo = Voltage overhead for drivers (e.g., 2 volts for DC LuxDrive drivers)

Vf = Forward voltage of LEDs

LEDn = Number of LEDs

Vin = Input voltage to the driver

For instance, for 6 Cree XPG2 LEDs, the calculation would be:

2 + (3.0 x 6) = 20

This means a minimum input voltage of 20VDC is needed. You can utilize a higher voltage up to the maximum input rating of the driver for optimal performance.

To calculate the appropriate power supply wattage, use the formula:

Vf x Drive Current (in Amps)

For 6 XPG2 LEDs:

3.0 V x 1A = 3 Watts per LED

Adding a 20% cushion, the total requirement would be:

18 watts x 1.2 = 21.6 watts

Hence, a 25 Watt power supply with a 24 Volt output would be ideal.

What if I Don't Have Enough Voltage? Using an LED Boost Driver (FlexBlock)

FlexBlock LED drivers are boost drivers capable of outputting higher voltages than supplied. This is particularly useful when input voltage is limited, and you need to power more LEDs in series. The maximum number of LEDs you can power is determined by the formula:

48VDC – Vin

For instance, using a 12VDC power supply, a FlexBlock in Boost-Only Mode can power up to 16 LEDs.

Checking Wattage for High Power AC Input Drivers

For AC input drivers, the required wattage can be calculated by:

[Vf x Current (in Amps)] x LEDn = Wattage

For 6 Cree XPG2 LEDs at 700mA:

[2.9 x .7] x 6 = 12.18

Hence, an AC driver like the Phihong 15 Watt LED driver would be suitable.

Tools for Understanding and Finding the Right LED Driver

Hopefully, this has given you a comprehensive understanding of LED drivers and how to select the right one for your application. If you have more questions, feel free to contact us at (802) 728-6031 or sales@LEDsupply.com. We also offer a Driver Selector tool to help you calculate the best driver for your circuit specs.

If your application requires a custom size and output, please contact LEDdynamics. Their LUXdrive division can quickly design and manufacture custom LED drivers in the United States.

Thanks for reading, and I hope this post clarifies LED drivers for you.

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