LED Driver. Constant voltage or constant current

Drivers are the technological and efficient equivalent of the old ballasts used in fluorescent lamps and convert alternating current from the mains into direct current suitable for the lighting fixtures. In this way, the LED is protected from fluctuations in mains voltage and other power supply variations that could damage the luminaire.

The driver is key to LED operation.
The driver is key to the operation of LEDs.

On previous occasions we have already commented more extensively on the importance of the driver in LED lighting and differentiated between external and integrated driver. In this case we are going to establish two types of driver depending on how the LED is powered. Thus, we will distinguish between constant current driver and constant voltage driver.

Constant current drivers

A characteristic of LEDs is that there is an exponential relationship between the direct voltage and the current through the LED. Depending on the model, a voltage variation of just 5% can double the circulating current.

Current/intensity ratio of the CREE LED model Xp-E2 Torch
Relationship between current and intensity in the CREE LED Xp-E2 Torch model

Although higher current increases the brightness of the LED, it also tends to overload it. So, we are in a situation where any small fluctuation in the input voltage can raise the current out of control. This results in more heat in the LED, which drastically reduces its lifetime. The maximum current an LED can withstand is determined by the thermal resistance between the junction points of the LED and the environment. This is crucial for the design of the final product where the aim is to minimize the thermal resistance, optimizing its lifetime and optical characteristics. For this reason, using a constant current driver is the best option for powering a high power LED.

When the current increases, the LED emits more light.
When the current increases, the LED emits more light.

Constant voltage drivers

If powering an LED at a constant current level is the best option, why do you need constant voltage drivers? Well, because in real applications systems that integrate several LEDs are used and it is not feasible to power each of them independently.

For the design of luminaires arrays or arrays of LEDs that include the necessary electronics to balance the current levels between its elements are used. In this way, it is only necessary to provide the voltage level required for the circuit to work perfectly.


The constant intensity driver excels at ensuring the integrity of the LED and providing a more consistent light intensity.

In turn, using a constant voltage driver is very useful for the design and installation of lighting solutions and is more economical in large-scale applications.