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What is a LED driver? Which one do I need?

What is a LED driver? Which one do I need?

Choosing the right LED Drivers can be a daunting task! There are so many different types and variations that it can seem a little bit confusing. This post will explain the varieties, what makes them different, and things you should look for when choosing a hobby LED driver(s) for your projects or applications.




What is an LED driver you might ask? 


A LED driver is a device that regulates electric current to illuminate a LED(light emitting diode).  It is an important component in a LED lighting circuit.  Failure to use one will more than likely end up with a failing LED(s). Using a LED driver will prevent damage to your LEDs as the forward voltage (Vf) of a LED changes with temperature. Forward Voltage is the amount of volts the light emitting diode requires to conduct electricity and light up. As temperature increases, the forward voltage of the LED decreases, causing the LED to draw more current. The LED will continue to get hotter and draw more current until the LED burns itself out, this is known in the electronics world as Thermal Runaway. Basically, the LED driver is a self-contained power supply which has outputs that are matched to the electrical characteristics of the LED(s). This helps avoid thermal runaway as the constant current LED driver compensates for the changes in the forward voltage while delivering current to the LED.




Things to consider when buying LED drivers.


 What type of LEDs are being used and how many?

What is the forward voltage, recommended driving current?

Do I need a constant current LED driver or a constant voltage LED driver?

Will you use AC or DC power?

What are the space limitations- do you want to utilize the driver within the model or outside of it?

Do you need any special features?

Do you need dimming capability, microprocessor-controlled drivers, etc.



First off, there are a couple of things you should know about LED drivers. There are two main types, those that use low voltage DC input power (generally 5-36VDC) and those that use high voltage AC input power (generally 90-277VAC). LED drivers that use high-voltage AC power are called Off-Line drivers, or AC LED drivers. In most applications using a low voltage DC input LED driver is recommended. Even if your input is high voltage AC, using an additional switching power supply will make it possible to use a DC input driver in which case you will have two power supplies. Low voltage DC drivers are recommended as they are extremely efficient and reliable. 

Also know, you need to know the drive current that you want to put to the LED. Higher drive currents will result in more light from the LED, and will also require more wattage to run the light and thus will be less efficient. It is important to know your LED’s specs so you know the recommended drive currents and heat sink requirements, so you don’t burn the LED out with too much current or excess heat.

 


Do you need Dimming?


The way by which LEDs are Dimmed varies with what kind of power you are going to use.

DC Dimming is best handled by a low voltage simple solution. The simplest dimming solution for these low voltage DC drives is using a potentiometer. This gives a full range of 0-100% dimming.  Another option is a PWM controlled dimming circuit.

Dimming AC drivers will require something like a low voltage wall dimmer. For high voltage AC power drivers there are a couple DIY circuit options, but you should probably go for a AC driver with built-in dimming.


How many LEDs can you run with a driver?


It depends on how you are configuring your LEDs in the circuit.  Normally you have the option to wire your LEDs in parallel or series. The maximum number of LEDs you can run from a single driver is determined by dividing the maximum output voltage of the driver by the forward voltage of your LED(s). 


How do you calculate the power requirements for your LED(s)?


Input voltage equals your maximum output voltage for the driver of your choosing after you take into account the driver circuit overhead voltage. Make sure you know the minimum and maximum input voltages for your LED driver supply. For an example if you are using one of our 6-Watt LEDC1236HCPWPB6W which can take input voltages from 1.2-6VDC and boosts output to 7-12V@1400mA Max., this paired with four (4) of our CREE (XP/XT) LEDs offered here on the site which have a 2.85Vf, you can find what your input voltage should be for an application by using this simple formula.

Vo + (Vf x LEDn) = Vin

Vo = Voltage overhead for drivers 

In this case we will forgo the Vo as the design of our drivers use very little in overhead. Simplified this is:

(Vf x LEDn) = Vin  (Series)

(Vf x LEDn)/LEDn = Vin  (Parallel)

Where:

Vf = Forward voltage of LEDs you wish to power

LEDn = The number of LEDs you want to power

Vin = Input voltage to the driver

For example, if you need to power 4 CREE (XP/XT) from a DC power source, then Vin would need to be at least 12VDC based on the following calculation.

(2.85 x 4) = 11.4 for running in series.  (Up to 4 CREEs (XP/XT) with this driver)

This determines the minimum input voltage you need to provide. Next you need to find the right power supply that can provide the wattage of the whole LED circuit. The calculation for LED wattage is:

Vf x Drive Current (in Amps)  

Using the 4 CREE (XP/XT) LEDs from above we can find our watts.

2.85 V x 350mA = .99 or 1 Watt per LED

Total Wattage for the circuit = 4 x 1 = 4 Watts

It is good practice to allow a 20% ‘cushion’ to your wattage calculation. Adding this 20% cushion will prevent the power supply from being over-worked. Overworking the power supply can cause the LEDs to flicker or cause premature failure of the power supply. Just calculate the cushion by multiplying the total wattage by 1.2. So, for our above example we would want at least 4.8 Watts (4 x 1.2 = 4.8). 


Still not sure how to find the right LED driver?


You should now have a good basic understanding on what am LED driver is and what you need to look for in selecting a driver along with a power supply and LEDs that is sufficient enough to work for your project. If you are still unsure or have questions, we are here to help.  Contact us by phone or email us at sales@craftLEDs.com.

Thank you and pleasant shopping!

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