What is an LED Driver?

An LED driver is an important electrical component that controls the power supplied to an LED or a series of LEDs. Failure to incorporate this component in an LED circuit can lead to system malfunction.

LED Driver Module

An LED driver module typically consists of an LED driver IC and the necessary external components already integrated on a printed circuit board (PCB). The module can also include additional components, such as connectors, switches, and heat sinks, depending on the application.

Parameters of an LED driver

Integrating an LED driver is highly essential to safeguard your LEDs against damage since the forward voltage (V_f) of a high-power LED tends to vary with temperature. Forward voltage denotes the amount of voltage required for an LED to conduct electricity and emit light. As the temperature rises, the forward voltage of the LED decreases, prompting the LED to draw more current. This, in turn, heats up the LED further, leading to a spike in current until the LED eventually burns out. This phenomenon is referred to as thermal runaway. A constant current LED driver helps avert Thermal Runaway by regulating the power supply to match the electrical properties of the LED. Thus, it compensates for the changes in forward voltage while providing a consistent current to the LED.

Other important parameters of LED drivers include output current, which determines the amount of current the driver can supply to the LED, and output voltage, which is the voltage that the driver supplies to the LED. The maximum output power of the driver, as well as its efficiency and operating temperature range, are also important parameters to consider.

The input voltage of an LED driver module is a critical parameter that must be considered carefully when selecting a driver for a particular application. One simple formula that can be used to determine the appropriate input voltage is:

Here, V_o represents the voltage overhead for the driver, V_f is the forward voltage of the LEDs to power, and LED_n is the number of LEDs to power.

Types of LED Drivers

There are several types of LED drivers available for different applications:

• White LED drivers: These drivers provide power and control for white light-emitting diodes for backlighting applications and have high efficiencies of up to 90% with very low noise.
• LED PWM drivers: These drivers enable programmable control of color, pattern, and intensity, and can be programmed through an I2C compatible interface. They are ideal for applications that require this level of flexibility.
• RGB LED drivers: They are software-controlled via the SPI interface and internal registers, allowing for complete control over all functions of the driver.
• Constant current LED drivers: These drivers provide constant current include internal circuitry that constantly monitors the loop current of each LED. This circuitry automatically adjusts the output DC voltage to the lowest value necessary to produce the highest forward voltage for each LED.
• 7-segment LED drivers: They are designed for 7-segment displays which use a combinational logic circuit that receives a 4-bit BCD input and generates seven output signals. These signals are then utilized to control the individual segments of the display, providing accurate and precise output display control.

Special features of an LED driver

LED drivers are produced to meet industry standards and can also be tailored for specific applications. An example of a specialized product is an LED display driver, which features a pin that enables continuous brightness control by a variable resistor to set a reference current. LED display drivers are generally compatible with TTL and capable of handling up to 15mA current, as well as providing wide power supply operation. These drivers find applications in portable electronic devices such as cell phones, digital cameras, digital clocks, and counters, as well as in DVD and MP3 players.

LED Driver IC

An LED driver IC is a single semiconductor device that performs the LED driver function. It is usually a small integrated circuit that requires some external components to complete the circuit, such as resistors, capacitors, and inductors.

The diagram above depicts a basic LED driver circuit that employs an LM317T voltage regulator integrated circuit. This IC features a 3-terminal positive voltage regulator that can supply a load current of up to 1.5 A while delivering an adjustable output voltage between 1.2 V and 37 V by an external resistor. The LM317T also has built-in features such as internal current limiting, thermal shutdown, and safe area compensation to ensure safe and reliable operation. Its versatile design enables it to regulate both voltage and current, and by adjusting the resistor, this LED driver can easily power any LED within the current range of 1.5 A.

Applications of LED Driver

LED drivers are widely used in commercial, industrial, and residential lighting applications to provide constant current and voltage to the LEDs. They are used in automotive lighting systems, such as headlights, taillights, and interior lighting, to provide high-efficiency and reliable operation. These drivers are also used in LED-based signs and displays, such as billboards, scoreboards, and electronic displays. 

LED drivers are used in various consumer electronic devices, such as smartphones, laptops, and televisions, to provide backlighting and indicator lights. They are used in medical equipment, such as surgical lamps and diagnostic instruments, to provide high-quality and efficient lighting. These drivers also have applications in horticulture lighting systems to provide the necessary light intensity and spectrum for plant growth.