By Energy Hamd - December 12, 2021




        1. Constant current versus constant voltage

    Finding the right LED driver is harder than it looks. There are many factors to consider when choosing. The first choice is to choose between a constant current LED driver or a constant voltage LED driver.

    Usually 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 options?

        2. Constant current LED drivers versus constant voltage LED drivers

    Constant current and constant voltage drivers are two viable options for a power supply for LED light sources, what differs is how they handle power. The drivers distribute the energy needed by the LED.

    Role of a driver:

  • Regulate the intensity necessary for the correct operation of the LED
  • Preserve the lifespan of the LED

            3. What is a constant current LED driver?

    The constant current LED drivers are designed for a designated range of output voltages and a fixed output current (mA). LEDs that are designed to operate on a constant current driver require a designated supply of current typically specified in milliamps (mA) or amps (A). These drivers vary the voltage along an electronic circuit, which allows the current to remain constant throughout the LED system. Higher ratings make the LED brighter, but if left unregulated, the LED will draw more current than expected.

    In addition, too much current will shorten the life of the LED. A constant current driver is the best way to drive high power LEDs because it maintains constant brightness across all LEDs positioned in series.

        4. What is a constant voltage LED driver?

    Constant voltage drivers are designed for a single direct current (DC) output voltage. The most common constant voltage drivers (or power supplies) are 12VDC or 24VDC. An LED light that is rated for constant voltage typically specifies the amount of input voltage it needs to function properly.

    A constant voltage power supply receives a standard voltage (120-277VAC). This is the energy that is produced by your wall outlets. Constant voltage drivers switch this alternating voltage (VAC) to a low direct voltage (VDC). The driver will always maintain a constant voltage regardless of the type of current load applied to it. An example of a constant voltage power supply (see above).

    This driver will maintain a constant 12VDC if the current remains below the maximum of 5 amps indicated in the table. Most often, constant voltage drivers are implemented in the lamps under the cabinet and LED strip.

        5. So how do I know what kind of LED driver I need?

5.1. The case of constant current conductors:

    If you look at high power LEDs, a unique feature is the exponential relationship between the forward voltage applied to the LED and the current flowing through it. You can see this clearly from the electrical characteristics in the graph below. When the LED is on, even the smallest voltage change of 5% (2.74V to 2.87V) can create a 100% increase in the led current as you can see by the current of the red marks, and passes from 350mA to 700mA.

    Now higher current makes the LED brighter, but it will eventually damage the LED as well. In figure 2, the maximum forward current and the derating curves under different ambient temperature conditions. In the example above, the driver will power the LED at 700mA, however, if you did not have a current limiter, the LED would draw more current as its electrical characteristics changed due to the increase in temperature. . This would end up pushing the current curve over the limit ... especially in warmer environments. The excess direct current will cause additional heat, shorten the life of the LEDs. We call it thermal runaway. This is the reason why the preferred method of powering high power LEDs is with a constant current LED driver. With a constant current source, even when the voltage changes with temperature, the driver keeps the current constant without over-driving the LED and preventing thermal runaway.

5.2. When should I use a constant voltage LED driver?

    The most common LED strips are designed with a group of LEDs (SMD) laid in series. Manufacturers ensure that the conductive quality of the copper network of the ribbon and LED components are of the correct value and in the correct position so that the LEDs on the ribbon are less prone to variation from the voltage source (which causes uncomfortable blinking of the light). As the current is already regulated, a constant voltage is sufficient to power the group of LEDs.

    When LEDs or a set of LEDs are constructed in this way, they usually indicate a voltage at which to operate. So if you see that your ribbon is showing 12VDC, all you will need is a constant voltage source of 12VDC because the current is already regulated by integrated circuits in the ribbon.

5.3. Advantage of using a CONSTANT VOLTAGE LED driver

    You use a constant voltage LED driver only when you are using an LED or matrix that has been specified to take a certain voltage. This is useful because:

  • Constant voltage is a more popular technology and therefore more familiar to many users.
  • The cost of constant voltage driver is also lower.

5.4. Advantage of using a CONSTANT CURRENT LED driver

    So when you are building your own luminaire or working with high power LEDs, it is in your best interest to use constant current drivers:

  • They avoid exceeding the maximum current allowable by the LEDs, thus preventing deterioration and thermal runaway.
  • They make it easier for designers to control applications and help create light with more consistent brightness.


    On LED-DA, you will find an offer for each of the products offered in this blog and we can advise and support you on your projects. Do not hesitate to contact us on 09 72 62 70 68 or by clicking here to fill out the form describing your project.



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