July 20, 2023
It’s probably safe to say that LEDs (light emitting diodes) have become the standard source for all lighting needs. This is because they are our most efficient lighting option, but did you know they can be made even more efficient?
Firstly, it's important to note that all LED fixtures use direct current, or DC power, rather than alternating current (AC) power. Secondly, the drivers used for LED lighting can provide DC power that either has a constant voltage or constant current. This article will compare the benefits and disadvantages of using either constant voltage or current drivers with LED lighting. To do so, first this article will delve into the relationship between current and voltage with respect to the formula for power, and then what this means for the difference between constant current and constant voltage drivers.
Current and voltage characteristics of diodes have an interdependent relationship; if voltage increases, the current increases exponentially, like in the image below. Conversely, if current increases, voltage only increases incrementally (not nearly as dramatically).
Have a look at the formula for power below to get a better understanding of the general relationship between voltage, current, and power.
To differentiate between the two types of drivers, constant voltage drivers maintain a consistent voltage, where the current can fluctuate depending on the required power. On the other hand, constant current drivers provide a consistent current, and the voltage fluctuates depending on the power required. Aside from LED drivers being either constant current, or constant voltage, they can also be integrated or external. External LED drivers are usually constant voltage (typically 12V, 24V, or 48V), and are located separately from the fixture (or remotely). One benefit to this is that heat dissipated from the driver will not affect the LED fixture. Integrated LED drivers, on the other hand, are connected to the light fixture (or bulb), and are usually constant current. Being integrated drivers, they exist in very close proximity to the actual light fixture, so any heat dissipated from them could negatively affect the performance and lifetime of the actual LED's. Damage is especially likely if the drivers are inefficient, and therefore emit more wasted energy in the form of heat.
For more information on LEDs, you can read our blog post: How DC Lighting Is Taking Over The Lighting Industry
Although external LED drivers, in theory, cause less wear to LED fixtures (because the heat that they emit won't affect the LED's), they are usually constant voltage, and this can be harmful to the LED's, without the proper protection in place. To explain this further, using constant voltage drivers with LED fixtures means that a single, unchanging voltage is sent to the fixture. If the full power sent to the LED fixture needs to change (to dim or brighten a light, for example), the current will be what changes to affect the total power sent to the fixture. But, even if just the slightest adjustment to the voltage is made, current can increase or decrease exponentially. This means that using a constant voltage driver with an LED light can easily supply way too much current to an LED, which can significantly shorten the lifespan of an LED fixture. Fixtures with constant voltage LED drivers typically have lower efficiency and efficacy (lumens per watt), because extra components are required to protect the LED's from accidentally consuming too much current. Overcurrent protection (OCP) devices for LED fixtures with remote drivers are typically resistors. If you have an LED strip lying around, you can actually see the resistors in-between the LED's on the strip that are used to protect them from burning out.
These maintain current at a relatively safe level for LED lighting to operate without burning out prematurely. OCP typically makes use of resistors to self-regulate current when it exceeds the limit of the LED, so that LEDs can use constant voltage drivers. unfortunately, when the resistor limits the current to protect the LED, it burns off the extra current as heat, ultimately wasting power to protect the LED's. Despite the lower efficiency being a disadvantage, constant voltage drivers are less costly than constant current drivers, so they are often used in many applications, like LED strip lights, because the manufacturer would not typically spring for more expensive drivers in these cases.
Constant current drivers provide LED lights with the correct current in a controlled fashion. This type of driver maintains a constant current by fluctuating the voltage sent to the LED fixture. As mentioned before, when considering the voltage-current characteristics of a diode, current changes dramatically for small changes in voltage. For this reason, voltage levels are easier to control with precision, and can thus be adjusted more accurately because they don’t change as dramatically as current would in a constant voltage driver. This precision is what makes constant current drivers a better option for LED lighting applications.
Because LEDs do not receive extra current when a constant current driver is used, using these drivers in LED lighting applications reduces wear on LED light fixtures, thus increasing their lifespan. This is why constant current drivers are primarily used in applications where efficiency and power need to be optimized, such as in high power lighting applications (outdoor, industrial, and commercial). These drivers are also very reliable when it comes to maintaining a constant brightness because they can more easily maintain a consistent light output. As a result of all these benefits, thermal runaway is also minimized. One major disadvantage to constant current drivers is that they can be much more costly. However, they are still much more efficient to use with LED lighting than constant voltage drivers, because a constant current LED fixture doesn't need resistors to protect the diodes from overcurrent faults. So springing for constant current drivers for LED lighting applications usually pays for itself.
Based on what we’ve now learned about both constant current and constant voltage drivers, it is safe to say that constant current is the better option for LED lights. Constant current drivers can provide consistent brightness levels, whereas constant voltage drivers can typically cause flickering because of where they lack when it comes to controlling current fluctuations with precision. This lack also significantly shortens the lifetime of LED lighting that uses constant voltage drivers. LED lighting systems that use constant voltage drivers are also typically more inefficient because of the need for current regulation. On the other hand, constant current drivers don’t need any additional components, making their systems more efficient in LED lighting applications. Although, constant current drivers are typically more expensive than constant voltage drivers, their increased efficiency more than makes up for the extra cost.
Here’s a recap on some of the main differences between constant voltage and constant current drivers in LED lighting applications: