The LED backlight for Segment Displays

This tech bulletin introduces the LED backlight for a segmented LCD display module and is valid for all types of standard and custom segment LCD displays. Segment LCDs continue to be a popular LCD technology for new designs that require low power consumption and low cost where a color display, such as a TFT or OLED, are not required. Welcome to Focus Display Solutions® LCD Design Guide for engineers.

Segment displays, also called static or direct drive LCDs, are one of the lowest cost LCDs available and remain popular for new product designs thanks to their ability to draw very low power and to be fully customizable.

Customized segment displays are designed and manufactured to the size requested by the customer and contain any number of segments and icons. The NRE (Non-recurring engineering) cost is low and includes US based design assistance with prototype samples.

Segment LCD modules with LED backlights

A LED backlight is required to read the LCD characters when operating in low or no-light ambient conditions. The backlight can be ‘turned ON’ or ‘turned OFF’ independent of the LCD to reduce power usage.

LED (Light Emitting Diode) backlights are preferred for segment LCDs since they are DC (Direct Current) driven, produce no EM interference and offer a long half-life .

The majority of the designs have the backlight attached to the LCD as one unit or module, but they can be built and shipped separately.

LED backlights require more power than the LCD

Segment LCD Displays without a backlight, can operate for as little as 2uA per square centimeter. With the addition of a LED backlight, the current draw will increase to 15mA and possibility as high as 75mA or higher. Therefore the majority of the custom LCD designs from Focus Displays include a transflective polarizer to allow the display to be readable with or without the LED backlight.

LED backlight connections:

LED backlights are DC and require a positive A (LED+) and a negative K (LED-) connection that is independent of the LCD logic voltage. There are several methods to supply power to the LED with three options listed below.

LED backlight with tabs:

The photo below shows a LED backlight with A and K tabs that allow the backlight to be ‘plugged’ into the customer’s PCB. The tabs can then be soldered to hold the backlight in place.

LED backlight with discrete wires:

A LED backlight with two discrete wires, also called a pigtail, allows the customer to draw the backlight power from a different location. The cable can be built to the required length and contains some type of termination (connector).

LED backlight with attached PCB:

The LED backlight, attached to the segment LCD, can be powered through the same type of pins as the LCD. A small PCB is utilized to attach the LED backlight to the back of the LCD polarizer. The pins for both the LCD and the backlight can then be inserted into a dip socket.

Your custom display design is unique and Focus LCDs can help you design the segment LCD with a backlight that will meet your requirements. Focus Display Solutions offers US based engineer design and support for your LCD display.

We’re ready to help you with your custom segment LCD design. Call us at 480-503-4295 or click here.