LED DRIVER - PRINCIPLE & TYPES

A LED driver is an electrical device that regulates power to a LED or a string of LEDs. A LED driver is a self-contained power supply which regulates the power required for the LED or array of LEDs. The power level required changes throughout the LED’s temperature increases and decreases. Without the correct LED light driver the LEDs would become too hot and unstable resulting in failure and bad performance. To ensure the LEDs function perfectly, the self-contained LED driver is required to supply a maintained constant amount of power to the LED. It is a crucial piece to an LED circuit and to operate without one will result in system failure.

Characteristics of an LED

LEDs are semiconductors where the junctions produce light when powered by a DC voltage. Like all semiconductors, they only conduct electricity in one direction and, consequently, the connecting wires indicate the polarity. Light comes from the LED when electrical current flows through it from the anode (+) to the cathode (-).

The amount of light produced is proportional to the applied voltage and current. If too much voltage is applied or too much current flows, the LED emitter will be permanently damaged. When the LED is conducting and producing light, the current flow is termed the forward current, and the applied voltage, the forward voltage.

One of the principal non-linear characteristics of an LED is that relatively small changes in forward voltage can result in more significant changes in the forward current, as shown in Figure 

More forward current emits more light from the LED's junction. The forward current produces a heating effect in the LED, which, in turn, can result in more current flow. This unwanted attribute of an LED emitter creates a thermal runaway condition, driving more current and further increasing the temperature. If this is not stopped, it causes the LED junction to fail.

The LED driver is a self-contained power supply which has outputs that are matched to the electrical characteristics of the LED(s). This helps avoid thermal runaway as the constant current LED driver compensates for the changes in the forward voltage while delivering a constant current to the LED.

The LED driver provides low voltage and protection for the LEDs.

Individual LED bulbs operate at voltages ranging from about 1.5 to 3.5 volts and currents of up to a maximum of 30mA. The domestic bulbs may consist of several bulbs, in series and parallel combinations and which requires a total voltage of between 12 and 24 V DC. The LED driver rectifies the AC and lowers the level to suit the requirements. This means converting the high AC mains voltage which ranges from 120 Volts to 277Volts, to the required low DC voltage.

The LED drivers provide protection to the LED bulbs against current and voltage fluctuations. The drivers ensure that the voltage and current to the LED bulbs remains within the operating range of the LEDs regardless of fluctuations in the mains supply. The protection avoids providing too much voltage and current that would degrade the LEDs or too low current that would reduce the light output.

LED drivers, used to power LED-based lighting installations, are available in two different types: constant voltage and constant current.

Constant voltage LED driver

A constant voltage LED driver delivers a tightly regulated output voltage across all load conditions to the LED light(s). Typically, these units are mains-powered AC-DC power supplies specifically designed for LED lighting applications.

Constant voltage LED drivers will continue to supply the output voltage up to a maximum current limit, above which the overcurrent protection (OCP) will turn off the DC supply.

The available range of output voltages depends on the type of application but typically includes the popular nominal output voltages of 12 VDC and 24 VDC for small single LED installations. However, for large scale LED installations, the trend to gather multiple LEDs into multiple series-connected strings pushes the drive voltage requirement into the hundreds of volts.

Constant current LED driver

As the name suggests, a constant current LED driver supplies a carefully controlled current flow across a given range of output voltages. Such LED driver power supplies quote the nominal continuous current output in mA or A, and the voltage range over which it operates. The driver varies the output voltage to maintain the current at the prescribed value.

Constant current LED drivers are particularly well suited for high power lighting applications. They maintain optimal and consistent light output, particularly for strings of LEDs, while preventing thermal runaway conditions from occurring.

Constant power LED drivers

A recent innovation in LED drivers is the constant power LED driver that controls the output voltage and current to deliver constant power to the LED. Combining the ability to control the voltage and the current allows driving the LED for the optimum amount of light output and junction temperature so that it operates at its peak capability.

Above all, constant power LED drivers provide lighting engineers with a more flexible and easily configurable LED drive capability to suit a diverse range of applications. Rather than having to specify either a constant current or a constant voltage driver, the lighting systems designer has a more versatile driver capability that can help simplify lighting implementations.

Selection of LED driver

The selection of an LED driver involves several vital criteria, of which LED voltage, current, and the type of application are the primary considerations.

For simple, small LED lighting applications, a constant voltage LED driver is probably all that is required. However, as the number of or the output power of the LEDs increases - mainly where long strings are involved - the need to more carefully manage the drive current warrants the use of a constant current LED driver.

From a practical design perspective, the constant power driver offers the most flexibility.

LED lighting spans many different indoor and outdoor use cases from product display cabinets to motorway lighting and everything in between. LED-based lighting provides an energy efficient, controllable, and reliable means of lighting any environment. Powering the LED requires a well-designed driver that can operate continuously, is dimmable and does not cause flicker. With this in mind, our power specialists can help you find the right solution for your designs.


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