Ins & Outs of LED Drivers
As we discussed our earlier article about how LED lighting works, the needs of this type of illumination are a bit unique when compared to your conventional incandescent lighting, and even fluorescent lighting.
Although LED lighting has many great benefits -- including energy efficiency, long life, and environmental friendliness -- one of its potential disadvantages is that LEDs requires a flow of consistent and constant electrical current at all times, at the exact voltage it requires. Doing this also allows the LEDs to stay a consistent temperature -- if an LED runs too hot, it may begin to malfunction and experience poor performance.
To help keep LEDs running in top form is where an LED driver comes in.
What is an LED Driver?
An LED driver is a device that does exactly what it sounds like -- it drives the power that is being given to an individual LED or string of LEDs.
As we mentioned previously, a good thing about LEDs is that they are energy efficient -- they do not require a large amount of power to get them going. LEDs actually work on DC power at a rather low voltage -- usually between 2V to 4V. Because of that, they require something that will convert AC into DC for them, and also will help keep them protected from any power surges that might occur, causing the LEDs to become overheated and become problematic.
So in essence the LED driver acts not only as an electrical current management system, but also as a protective buffer. It's like Baby Bear in the Goldilocks tale -- everything is just right.
Constant Voltage vs. Constant Current
As you look at the variety of LED driver products out there today, you'll notice there are two distinct types -- constant voltage and constant current. Both are meant to do different things and are for different situations. It's important to read the product specifications of your LED lamp to make sure you are using the correct type, as they are not meant to be used interchangeably.
A constant voltage driver is used for LED products that require a steady and constant DC voltage to keep it performing well. Many times a constant voltage will be used with an LED lap or other product that has a built-in driver for the current already installed, and all it really needs is something to keep the voltage consistent. It is also mainly used in applications where the LEDs are configured in strips and are all parallel connected to the driver, so everybody receives the same amount of voltage from the driver.
Constant voltage drivers many times are used with LEDs for illuminating landscape and accent lighting, back-lighting for advertising signs, and huge high-definition LED displays. Usually they are available in a number of different wattages, and can also come with dimming capabilities.
Rather than regulating the voltage, a constant current LED driver manages the actual current that comes in to the LED's diode that is required to get things jumping in the p-n junction. Additionally, this type of driver helps regulate the amount of forward current that can occur between the LEDs as a result of photons being created when the LED is turned on. Too much of this forward current can potentially overheat the LED, causing it to malfunction.
A constant current driver is primarily used in situations where an LED lamp or product does not already have a current driver built in, so it is needed to keep a consistent current running through a string or series of LEDs. And constant current drivers can be found in a variety of different configurations.
A key piece of understanding how LED drivers work is knowing the different ways that LEDs can be configured. The two most common ways LEDs are configured are series and parallel.
In a series configuration, one LED's anode (aka positively charged electrode) is connected to another's cathode (aka negatively charged electrode). This enables a single, non-stop current to flow through all the LEDs in the series, usually called a string.
Important to note that in order to keep the entire string of LEDs running, you have to make sure you're providing enough voltage for the sum of them all. So, for instance, if each LED needs 2V to illuminate and you have 10 LEDs, you will need 20V to give them the power they need.
Another standard configuration for LEDs is a parallel configuration. Here multiple strings of LEDs are connected in parallel -- or side-by-side -- to a driver. So, for instance, if you had 50 LEDs you could have five strings of 10 LEDs each running parallel, rather than all 50 in one string. A parallel configuration is many times used in situations where you want to limit the voltage needed to operate the strings of LEDs.
Parallel strings of LEDs can also be configured again, this time into what is known as a matrix. This happens when sets of parallel strings of LEDs are connected to each other in a series.
Dimming & Color Sequencing
Depending on their specifications, some LED drivers can also facilitate dimming and/or color sequencing for the LEDs they are connected to.
Depending on the type of LED driver you select, their dimming skill can cover the full range. Dimming is done through the driver by either shortening the amount of leading current going through it, or by a method called pulse width modulation (PWM). Most drivers that offer dimming use PWM, which allows dimming without flickering and with usually very little color change in the LEDs.
It is good to note that dimming does not effect an LED's competence, nor does it have a negative impact on how long it lasts. In fact, dimming can potentially help LEDs last longer as it will reduce the amount of temperature it creates when lit.
With color sequencing or changing, many times an LED string or product may have LEDs of different colors. In fact, many times a "white" colored LED lamp is actually not using "white" colored LEDs, but rather different colors that when shown together produce white light. So with a driver with this capability, you would be able to control the different colors of LEDs in the product to create a full rainbow of different colors depending on which were on and which were turned off.