Understanding LED Drivers and How To Choose the Right One – FVTLED

Understanding LED Drivers and How To Choose the Right One

May 21 2019

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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.

What is an LED driver, you may ask? An LED driver is an electronic device used to adjust the power supply of an LED or a series of leds. It is a key part of the LED circuit and can cause system failure without operation.

It is important to use one to prevent LED damage because the high power LED's forward voltage (V f) varies with temperature. The forward voltage is the voltage required for the led to conduct and light up. As the temperature increases, the positive voltage of the LED decreases, causing the LED to absorb more current. The leds will continue to heat up and absorb more current until the leds burn out, also known as thermal runaway. The LED driver is a separate power supply whose output matches the electrical characteristics of the LED. This helps to avoid thermal runaway because the constant-current LED driver compensates for the change in forward voltage while providing a constant current to the LED.

Considerations before selecting an LED driver
What types of leds are used and how many are used?
Find out the forward voltage, recommended driving current, etc.
Do I need constant current LED driver or constant voltage LED driver?
We are talking here about constant current and constant voltage.
What type of power supply will be used? (DC, AC, battery, etc.)
Running from AC? Learn how AC drives will benefit you!
What are the space constraints?
Working in a cramped space? Not a lot of voltage to use?
What are the main goals of the application?
Size, cost, efficiency, performance, etc
What special functions are required?
Dimming, pulse, microprocessor control, etc
First of all, you should know that...
There are two main types of drives, those that use a low-voltage dc input (usually 5-36vdc) and high-voltage ac input (usually 90-277vac). An LED driver using a high voltage ac power supply is called an offline driver or an ac LED driver. In most applications, it is recommended to use a low voltage dc input LED driver. Even if your input is a high voltage AC, you can use a dc input driver with an additional switching power supply. Low voltage dc drives are recommended as they are very efficient and reliable. For smaller applications, more dimming and output options are available than for high-voltage ac drives, so you can use more functionality in your applications. However, if you have a large general lighting project for residential or commercial lighting, you should see how AC drives are better suited for such work.

The second thing you should know
Second, you need to know the drive current to put in the LED. A higher drive current will result in more light coming from the LED, and more wattage is needed to run the light. It is important to understand your LED specifications in order to understand the recommended drive current and radiator requirements so that you do not burn out the LED in the event of excessive current or overheating. Finally, it's nice to know what you need from your lighting application. For example, if you want dimming, you need to select a dimming driver.

A little bit about dimming
Dimming LED varies with the power you use; Therefore, I will introduce the DC and AC dimming options so that we can better understand how to dim all applications, whether DC or AC.

Dc dimming
Low-voltage dc drives can be dimmed easily in several different ways. The simplest dimming solution is to use a potentiometer. This can achieve 0- 100% full range of dimming.

20K ohm potentiometer
20K ohm potentiometer
When you are only a drive circuit but if there are multiple drive from a potentiometer that move light, are usually advised to do so, the value of the potentiometer can Ω from K/N - K is the value of the potentiometer, N is the number of driver you are using. We have a wired BuckPucks with a 5K rotary knob potentiometer for dimmer, but we also have this 20K potentiometer that easily works with our BuckBlock and FlexBlock drivers. Simply connect the dimming ground wire to the center pin and connect the dimming light to one side or the other (select one side just to determine how to dim the knob).

LED drive controller -0-10V dimmer
Your second dimming option is to use a 0-10v wall dimmer, such as our A019 low-voltage dimmer controller. This is better if you have more than one cell, because the 0-10v dimmer can be used with more than one drive at a time. Just connect the dimming light to the input end of the drive.

Communication that move light
For high voltage ac power drives, there are several dimming options depending on your drive. Many ac drives use 0-10v dimming, as we did above. We also provide Mean Well and Phihong LED drivers that provide TRIAC dimming, so they can be used with many front and back dimmers. This is useful because it allows leds to be used in conjunction with very popular residential dimming systems such as lutron and levitan.

How many leds can you run with the driver?
LED drive - wired buckpuck- kma
By dividing the maximum output voltage of the driver by the forward voltage of the LED, the maximum number of leds that a single driver can run can be determined. With the LuxDrive driver, you can determine the maximum output voltage by subtracting 2 volts from the input voltage. This is necessary because the driver requires 2 volts of overhead to power the internal circuit. For example, using a wired 1000mA BuckPuck driver with 24 volts of input, you will get a maximum output voltage of 22 volts.

What does Power need?
This allows us to find the input voltage required by the LED. After all, after accounting for the overhead voltage of the driver circuit, the input voltage is equal to the maximum output voltage of our driver. Make sure you know the minimum and maximum input voltage of the LED driver. For example, we will stick to the 1000mA BuckPuck cable, which can input an input voltage of 7-32vdc. You can use this simple formula when finding the input voltage for your application.

V o + (V f x LED n) = V in

Where:

V o = voltage overhead of the drive - 2 if DC LuxDrive is used; If an AC LuxDrive is used, it is 4

V f = positive voltage of the LED you want to supply

LED n = the number of leds to power

V in = the input voltage of the driver

The forward voltage of Cree xp-g2
Cree XPG2 product page product specifications
For example, if you need to power 6 Cree XPG2 leds from a dc source and you are using the wired BuckPuck above, the following calculation shows that the V in needs to be at least 20VDC.

2 plus 3.0 x 6 is 20

This determines the minimum input voltage you need to provide. There is no harm in using a higher voltage at the driver's maximum input voltage rating, so since we do not carry a 20VDC power supply, you may insist on using a 24VDC power supply to run these leds.

Now this helps us to make sure the voltage works, but in order to find the right power source, we also need to find the power of the entire LED circuit. The wattage of LED is calculated as follows:

V f x drive current (in amperes)

Using the 6 XPG2 leds above, we can find our watts.

Each LED 3.0v x 1A = 3 watts

Total circuit power = 6 x 3 = 18 watts

When calculating the appropriate power for your project, it is important to allow your wattage to be calculated as a 20% "buffer." Adding this 20% cushion prevents the power from overworking. Excessive power supply may cause LED flashing or premature power failure. Just multiply the total wattage by 1.2 to calculate the buffer. Therefore, for our example above, we want at least 21.6 watts (18 x 1.2 = 21.6). The closest universal power supply size is 25 watts, so it is in your best interest to get a 25 watt power supply with 24 volts of output.

What if I don't have enough voltage? Use LED boost driver (FlexBlock)
The FlexBlock LED drivers are booster drivers, which means they can output a higher voltage than the one supplied to them. This allows you to power more series leds using a single LED driver. This is useful for applications where the input voltage is limited and needs to be obtained

LuxDrive constant current LED driver
FlexBlock
Leds are more powerful. Like the BuckPuck driver, the maximum amount of power a single driver can supply to an LED in series is determined by dividing the maximum output voltage of the driver by the forward voltage of the LED. FlexBlock can be connected in two different configurations with different input voltages. In the step-up (standard) mode, FlexBlock can handle LED loads above, below or equal to the power supply voltage. You can use the following formula to find the maximum output voltage of the driver in this mode:

In 48 VDC - V

Therefore, when using 12VDC power and the XPG2 LED above, how many can we run using 700mA FlexBlock? Your maximum output voltage is 36VDC (48-12), and the forward voltage of the XPG2 is 700mA, so by dividing the 36VDC, we can see that the driver can power 12 leds. In boost only mode, FlexBlock can output up to 48VDC from as low as 10VDC. So if you're in Boost mode alone, you can power 16 leds (48/2.9). Here, we continue to use the FlexBlock enhancement driver to provide deep power to your LED.

Check the power of the high power ac input driver
Now that you have AC input drivers, they emit a certain amount of power to run, so you need to find the power of the LED. You can do this using the following formula:

[Vf x current (in amperes)] x LEDn = power

So if we try to power the same 6 Cree XPG2 leds at 700mA, your power will be...

X 6 = 12.18

This means you need to find an ac drive that can run up to 13 watts, like our Phihong 15 watts LED drive.

Note: when designing applications, it is important to consider the minimum output voltage of the offline driver. For example, the minimum output of the drive above is 15 volts. Since the minimum output voltage is greater than our single XPG2 LED (2.9v), you need to connect at least six in series to work with this particular driver.

Tools for understanding and finding the right LED driver
Therefore, you should now have a good idea of what an LED driver is and what to watch out for when selecting a power driver that is adequate for your application. I know there are still problems and you can contact us at (802)728-6031 or sales@LEDsupply.com.

We also have the driver selector tool, which helps calculate the best driver by entering circuit specifications.

Thank you for your attention and I hope this article will help anyone who wants to know what an LED driver is.

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