In electronics, a display driver is a semiconductor integrated circuit that provides an interface function between a microprocessor, microcontroller, general-purpose peripheral interface, and a particular type of display device, such as LED. A display driver typically accepts commands and data using an industry-standard general-purpose serial or parallel interface. Then, it generates signals with suitable voltage, current, timing, and demultiplexing to make the display show the desired text or image. LED drivers control the amount of current and voltage supplied to the light-emitting diodes (LEDs). These drivers are designed and manufactured to meet most industry specifications. Even some specialized LED display driver products are commonly available.

An LED driver IC is an integrated circuit (IC) that provides brightness and backlighting color control. They are usually found in an LED driver circuit, which can test an LED to maintain brightness and increase LED life. Some LED drivers are used in portable devices like cellphones, digital cameras, digital clocks, and counters in terms of applications. Other LED drivers are used in DVD and MP3 players.

Types of LED Display Drivers

  • White LED drivers – These provide white light for backlighting and offers very low noise. Typical efficiencies are as high as 90%.
  • LED PWM drivers –  These can be programmed through an I2C compatible interface. LED PWM drivers are used for applications that require color, pattern, and intensity programmability control.
  • RGB LED drivers – All functions are controlled by software through internal registers and the SPI interface.
  • Constant current LED drivers – These feature internal circuitry that monitors each LED’s loop current and automatically adjusts the generated output DC voltage to the minimum value required to produce the highest forward voltage.
  • 7-segment LED drivers – These are LED display drivers that use a combinational logic circuit that accepts a 4-bit BCD input and generates seven output signals to control seven individual display segments.

Light-emitting diodes (LEDs) are semiconductor devices that emit light when an electrical current passes through semiconductor materials. For LEDs to perform at their best, they need LED drivers’ assistance to provide better efficiency, reliability, and longevity. LED drivers are electrical or electronic devices that prevent damage to LEDs by regulating its forward voltage that changes with temperature, avoiding thermal runaway while delivering a constant current to the LED.

Some Common Practices/Uses

  • Automotive lighting – Every automotive lighting solution includes a distinctive LED driver. They are used for visibility or energy-saving solutions. These drivers will dissipate heat at different levels, depending on the environment and placement. LED lighting can improve drivers’ and pedestrians’ safety by enhancing the range of visibility when the headlights are turned ON, OFF, or dimmed to perform at any stage of the journey efficiently.
  • 16 × 16 displays – These are becoming more common because they are great for outdoor use like storage signs, billboards, public transport signs, and many more. It is possible to create signs in multiple languages that require more LEDs with a 16 × 16 display.
  • Smartphone backlighting – The amount of LEDs changes depending on the size of the smartphone display. Bigger displays require more LEDs for backlighting applications. LED drivers can offer significant power reduction through different backlight architectures: direct and edge backlight. Two major dimming modes are used for LED backlight applications: global dimming (all LED strings are dimmed together) and local dimming (LED strings are dimmed independently).

How Does It Work

An LED driver is needed to run LEDs properly. Unlike most electronic devices, LEDs are current driven devices, not voltage driven. Even a minuscule change in voltage can lead to a huge change in current. Hence, it is important that the drive current is regulated and not the voltage. LED drivers are usually switching mode devices that convert the input voltage into a voltage at which the current drawn by the LEDs is equal to its drive current. The drive current is regulated for optimum brightness, LED service life, and battery life. A drive current lower than the maximum drive current of an LED can greatly prolong service and battery life.

An LED driver is somewhat like cruise control in a car. It helps to control the current that goes to the LED. Without the LED driver, the LEDs would become too hot and unstable, leading to thermal runaways, resulting in bad performance or failure. This means that in an LED light, the driver does all the heavy lifting. Your LED itself might be the best, but it won’t stay that way if you don’t have a good LED driver. This is because most LED lights run on low voltage with DC. Essentially, an LED driver helps to rectify the high voltage with AC from the mains power supply to low voltage with DC for the LED lights. LEDs actually work on DC power at a rather low voltage—usually between 2V to 4V.

LED Display Driver (8-Digit) – MAX7219CNG

MAX7219 LED Display Driver (2)

The MAX7219CNG is a compact, serial input/output common-cathode display driver that can interface microprocessors to 7-segment numeric LED displays of up to 8 digits, bar-graph displays, or 64 individual LEDs. Only one external resistor is required to set the segment current for all LEDs. This device comes in a 24-pin DIP package.

MAX7219-IC-Pinout

Uses

  • When you want to convert serial data to parallel data
  • Used to reduce I/O pin usage of controller or processor
  • Used to control 64 LEDs using only 3 PINS
  • Preferred for 7-Segment Displays
  • Used to control more display segments by connecting more chips in serial

How to Use LED Display Drivers

The IC is utilized like any shift register. First, we will send serial data to the chip bit by bit, and once all data is sent, we will tell the chip to shift this serial data to the output by enabling the CS pin. Now, connect the DIN, CS, and CLK pins. These three pins are important to control the chip. Then, select the resistor/s for the ISET pin. To drive the display without error, we will choose the appropriate resistor.

There are two ways to use this chip. One is to follow the instructions given in the datasheet to send the data bit by bit. The second way is to use libraries previously written for this chip. Using the libraries is the easiest way to get the required result. With libraries, you can just enter the required data to send without worrying about anything. We will send data to the chip through a DIN pin. The data is sent bit by bit by setting the clock of the chip for each bit. The chip stores the serial data in its registers until all data is received. After completing data sending, we will set the CS pin for the chip to shift all data stored in its register to the output. Once the chip’s data is put out, it will light up the corresponding LEDs to display the result. Some of its applications include digital electronics, servers, memory units, networking, and digital systems.

Sample Schematic Diagram Using LED Display Driver

MAX7219 SCHEMATIC