&#;What type of LED driver do I need?&#; Searching for LED drivers can be more difficult than you think with the variety of options out there. There are plenty of factors to look at when choosing the one that works best for you, we have a thorough run-through of this in our guide on LED drivers here. One important choice is that of choosing a constant current LED driver versus a constant voltage LED driver. Now, it&#;s known that LED drivers are considered constant current devices, so why do manufacturers offer constant voltage drivers for LEDs as well? How can we tell the difference between these two?
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Constant current and Constant voltage drivers are both viable options for a power supply for LED light sources, what differs is the way in which they deliver the power. LED drivers are the driving force that provides and regulates the necessary power to make sure the LEDs operate in a safe and consistent manner. Understanding the difference between the two types can:
Constant current LED drivers are designed for a designated range of output voltages and a fixed output current (mA). LEDs that are rated to operate on a constant current driver require a designated supply of current usually specified in milliamps (mA) or amps (A). These drivers vary the voltage along an electronic circuit which allows current to remain constant throughout the LED system. Mean Well&#;s AP Constant Current Driver is a good example shown below:
Higher current ratings do make the LED brighter, but if not regulated, the LED will draw more current than it is rated for. Thermal Runaway refers to excess current beyond the LEDs maximum drive current which results in drastically lower LED life-spans and premature burn outs due to increased temperature. A constant current driver is the best way to drive high power LEDs as it maintains a consistent brightness across all LEDs in-series.
Constant voltage drivers are designed for a single direct current (DC) output voltage. Most common constant voltage drivers (or Power Supplies) are 12VDC or 24VDC. An LED light that is rated for constant voltage usually specifies the amount of input voltage it needs to operate correctly.
A constant voltage power supply receives standard line voltage (120-277VAC). This is the type of power that is typically output from your wall outlets around the home. Constant Voltage Drivers switch this alternating current voltage (VAC) to a low direct current voltage (VDC). The driver will always maintain a constant voltage no matter what kind of current load is put on it. An example of a constant voltage power supply is below in the Mean Well LPV-60-12.
The LPV-60-12 will maintain a constant 12VDC if the current stays below the 5-amp maximum shown in the table. Most often, constant voltage drivers are implemented in under-cabinet lights and other LED flex strip applications but it is not limited to those categories.
If you take a look at high powered LEDs, one unique characteristic is the exponential relationship between the applied forward voltage to the LED and the current flowing through it. You can see this clearly from the electrical characteristics of the Cree XP-G2 below in Figure 1. When the LED is turned on, even the smallest 5% change in voltage (2.74V to 2.87V) can create a 100% increase in current driven to the XP-G2 as you can see at the red marks current went from 350mA to 700mA.
Now higher current does make the LED brighter, but it also will eventually over-drive the LED. See Figure 2 for Cree&#;s specifications of the maximum forward current and the de-rating curves in different ambient temperature conditions. In the example above we would still be alright driving the XP-G2 LED at 700mA, however, if you didn&#;t have a current limiting device, the LED would draw more current as it&#;s electrical characteristics changed due to temperature increase. This would eventually push the current way above the limit&#;especially in hotter environments. The excess forward current would result in extra heat within the system, cut down on the LEDs lifespan, and eventually ruin the LED. We call this thermal runaway which is explained in more detail here. This is the reason the preferred method of powering high powered LEDs is with a constant current LED driver. With a constant current source, even as the voltage changes with temperature the driver keeps the current steady while not over driving the LED and preventing thermal runaway.
The above example is with high powered LEDs and on a smaller scale as we only talked of using one LED. With lighting in the real world, it isn&#;t convenient or economical to build everything by hand from a single diode, LEDs are usually used together in series and/or parallel circuits to create the desired outcome. Fortunately for lighting designers, manufacturers have introduced many LED products to the market that have multiple LEDs already assembled together like LED rope light, LED strips, LED bars, etc.
The most common LED strips are designed with a group of LEDs in series with a current-limiting resistor in line with them. The manufacturers make sure the resistors are of the right value and in the right position so that the LEDs on the strips will be less prone to the variation of the voltage source as we talked of with the XP-G2. Since their current is already being regulated, all they need is a constant voltage to power the LED(s).
When LEDs or an array of LEDs are constructed like this they will typically state a voltage to be run at. So if you see that your strip takes 12VDC, don&#;t worry about a constant current driver, all you will need is a 12VDC constant voltage source as the current is already being regulated by on board circuitry that the manufacturer has built in.
So when you&#;re building your own fixture or working with our high powered LEDs, it is of your best interest to use constant current drivers because:
You use a constant voltage LED driver only when using an LED or array that has been specified to take a certain voltage. This is helpful as:
Feel free to take a look over at our guide to LED strips that has a lot of devices that can be run from constant voltage. Also, if you need help selecting a constant current LED driver, head over to our helpful post on how to choose the right one.
With so many available options, choosing a suitable LED driver can be overwhelming sometimes. But you don&#;t have to worry from now because here in this article, we will discuss every perceptive of LED drivers that you need to consider before making a choice. We will discuss Constant Current (CC) and Constant Voltage (CV) LED drivers, why and when you need them, and some pros and cons.
Before moving towards our main topic, you should know that an LED driver is a device that regulates the flow of current through your LEDs. All the drivers are either constant voltage (CV) or constant current (CC) or both. The question arises, which one of the drivers do you need? The simple answer is that it will mainly depend upon the LED light fitting, your potential application, and others that we will discuss later.
Constant Voltage LED driverLEDs are the most eminent source of light nowadays. The LEDs are semiconductors diodes formed by bringing together two slightly different materials to create a PN junction. They are P-type holes with an excess positive charge and N-type electrons with an extra negative charge. It is typically known as PN junction, and it produces light when DC is applied.
Like all the other semiconductors, LEDs will allow current to pass forward but block the current flow in the reverse order. LED produces light when electric current flows through it from an anode (+) to cathode (-).
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Like traditional PN junction diodes, LEDs are also dependent upon the current with its forward voltage. We can put it like small changes in forwarding voltage will result in significant changes in forwarding current. Usually, LEDs has a forward voltage (Vf) of 2-3.5 V with a 10-200mA forwarding current. We can see that a slight voltage change will result in a big forward current change.
LED V-I characteristicUntil now, there are still many people who think that once the LED voltage is fixed, then the current is fixed, so the use of constant voltage or constant current is the same. In fact, the volt-ampere(V-I) characteristics of LEDs are not fixed, but change with temperature. So the voltage is fixed, the current will not be fixed, but changes with temperature. This is because the LED is a diode, and its volt-ampere characteristic has a negative temperature coefficient.
Temperature coefficient, usually -2mV/degree (-1.5&#;2.5mV/°C), that is, as the temperature rises, its volt-ampere characteristic shifts to the left.
LED temperature coefficientThere are 3 curves in the image above, they represent different characters of LED at different temperatures. At the same 3.3V voltage, the currents are 8mA, 20mA and 37mA at different temperatures.
So the two characteristics above will have an impact on how we choose LED drivers for the LEDs, keep reading and you will find the answer.
A constant current LED driver changes the voltage throughout the electric circuit to maintain the continuous flow of current. To make it easier, you can say that a constant current LED driver will have a fixed output current and variable voltage output. LEDs designed to work on constant current drivers need a designated amount of current for proper working.
Constant Current LED driverThese types of drivers keep the current constant throughout the LED installation by fluctuating the voltage value. The LED light will be brighter with the higher current flow, but if the current flow is not regulated, it will cause the burnout of the LED. This thermal runaway will reduce the LED life span and its quality. For this reason, constant current drivers are so crucial for an LED.
Luminous vs LED forward currentFrom the LED temperature coefficient value we learned that it&#;s better to use a fixed current LED driver to overcome the temperature rise issue.
Constant current drivers are primarily used with LED light fittings manufactured by the &#;direct drive&#; driving method. Direct Drive means where &#;the current output of an LED driver directly powers the LED circuit.&#;
This method has high efficiency and low complexity.
Constant current LED drivers are the finest choice for you if you build your fixture or work dramatically with high-powered LEDs. These drivers can be used with a single bulb or in a chain of LEDs in a series.
For more information, please visit High Efficiency Constant Current LED Strips.
Further in the article, you will see a detailed table on CC and CV driver usage.
The choice of your LED driver dramatically depends on the purpose you are going to use it.
Constant voltage LED drivers are the power supplies. The most common power supplies are 12 VDC or 24 VDC. These drivers are designed for a single direct current output voltage. An LED light manufactured with the concept of constant voltage requires a specific amount of voltage to work effectively.
Constant Voltage 24V LED driverFor these LEDs devices with a current limiter or regulator built-in, the voltage is fixed while the current provided by the constant voltage driver can vary since the LED lights are permanently be wired parallel. For example, two lights will require twice as much current as one light and so on.
No, you can not do that. As the temperature increases, its volt-ampere characteristic shifts to the left. If the applied voltage is constant, the current will obviously increase. The efficiency of the LED itself is very low, and the temperature rise is very high. After the power is turned on, if the heat dissipation is not good, its temperature can easily rise to over eight or ninety degrees.
Assuming that a 3.3V constant voltage source is used to work at 20mA at room temperature, and when the temperature rises to 85 degrees, the current will increase to 35-37mA, and its brightness will not increase. The increase in current will only make its temperature rise higher, which will increase the light attenuation and reduce the lifespan.
And if you use a constant voltage source instead of a constant current source, when working at 20mA at room temperature, when it reaches -40 degrees, the current will be reduced to 8-10mA, and the brightness will be reduced.
For 1W high-power LED chips, the situation is the same, and because of the high power, heat dissipation is more difficult, and the temperature rise problem is more serious. It can be said that in addition to the heat dissipation problem, the use of a constant voltage power supply is the main cause of light decay. Therefore, in principle, the use of a constant voltage power supply for LED is prohibited.
Add current limiting resistors in the circuit. Because when the LED setup has a constant source of current, the CC driver will keep the current flow steady in the system even if the temperature rises with the increase in voltage value. This driver will prevent the LED from overdriving and thermal runaway, thus increasing the life span of the LED.
You can use constant voltage LED drivers to run several LEDs wired parallel such as LED strips. Constant voltage drivers are the best installation option where you need the best efficiency and longevity in your LED.
To get the desired results, LEDs are usually used together in parallel circuits and series. The lighting designers and manufacturers have introduced many LED products in the market, which are already assembled in LED rope, LED bar, LED strips. To ensure the constant voltage, the manufacturers have confirmed that the current limiting resistor is in line with each strip so that the LED strips are less prone to the variation in LED voltage.
The above picture is a circuit of LED strips. We can see that there is a current limiting resistor in the circuit. This type of design is suitable for CV LED drivers. Because if we cut some parts of LED strips, it will still work because the voltage on each string does not change.
So here comes the answer to the above question: if we use CC LED driver for LED strip. Let&#;s say we use a 700mA LED driver, and then each string will get 100mA. And if we cut off one rope, there will be six strips left in the circuit, and the current flow in each strip will rise to 116mA. This high amount of current will cause damage to the LED lights, so it is better to use a constant voltage LED driver in LED strips/strings.
So, when LED strip/strings are built, typically, they will need a static voltage to run on. So, if you know that your LED strip runs on 12VDC, don&#;t worry because the built-in circuitry already regulates the current. You will only need a CV LED driver of 12VDC value.
To move forward and summarize this long discussion, here is a little comparison of CC and CV drivers.
Constant Current Driver Constant Voltage DriverCurrentThe current value is Fixed.The current value is Variable.VoltageThe voltage value Variable.The voltage value is Fixed.Constant Current vs. Constant VoltageWant to read it later?
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Pros:
Cons:
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To select the best-LED driver of your need, you need to consider the following criteria.
For example, for a small LED application, constant voltage LED drivers are enough. But when the number of LED strings increases, used to manage the current flow best results. At this point, you will need constant current LED drivers.
We also have a more detailed article to show you how to choose LED drivers, you can take look if you have an interest.
We all know that LEDs are constant-current driven devices. But we can NOT decide that an LED will ALWAYS require a constant current driver since in some cases, a constant voltage supply will be the best option as we have discussed above. For your easiness, we have compared constant current LED drivers with constant voltage LED drivers to make the best choice for yourself.
Making a good choice for these drivers is crucial for your LED system because they provide and regulate the necessary power to the LED. They also make sure that the system is working safely and consistently.
uPowerTek is also providing global certified, well-experimented, and high-quality constant voltage and constant current LED drivers. In February , uPowerTek has announced their New W Constant Current, and 800W Constant Voltage LED driver series. These products are manufactured, keeping in mind the consumer&#;s safety, national security, and product quality management.
The question arises here, why uPowerTek? As the members of the Digital Illumination Interface Alliance (DiiA), uPowerTek always keeps quality and reliability as their priority and also keeps creating extra values for customers by continuously rolling out new products like NFC programmable drivers and high power grow light drivers.
If you want to learn more, please visit our website Custom LED Light Strip.