LCD driving voltage for low power segment LCDs

LCD Modules – Custom LCD Modules Design Guide

This article, a continuation in Custom LCD Modules Design Guide for engineers, covers the LCD driving voltages for a static-segmented LCD Display module. This article is good for all types of standard and custom low power segment LCD Displays.

Low Power LCDs: from wall plugs to batteries

Society has become more mobile and nowhere can this be better observed than the transformation from power hungry stationary electronic products, which once required their power from a wall outlet, to battery-powered portable handheld devices.

We have seen an increase in the number of battery powered LCD designs. As a result, the design engineer’s number one priority is to maximize battery life. One way to accomplish this is to integrate to a low power LCD module such as a segment LCD Display.

Segment liquid crystal display technology is one of the lowest ‘power hungry’ display options available, a TN (Twisted Nematic) display with no backlight can draw as little as 2uA per square centimeter.

Low LCD driving voltage options

Custom segment LCD displays allow the design engineer to choose the LCD driving voltage with the two most popular options being 3.3V and 5V (3.3V being the most popular for battery-powered devices.)

3.3V segment LCD for battery applications

AA batteries are popular for portable devices each battery can generate between 1.5 volts and 1.65 volts. Two AA’s in series can provide the necessary 3.0V or 3.3V.

A customer’s design may include a charge pump (bump circuit, or booster) to increase the LCD driving voltage levels that are too low and also to provide a constant LCD driving voltage to the display.

The LCD can display poor contrast and in some cases, ghosting, if the product does not provide some type of voltage regulation. The batteries will start out fresh and strong providing a nice dark segment, but fade as the batteries’ potential drops below a threshold.

5V Segment LCD for non-battery applications

5 Volt segment displays are still the first choice for non-battery powered products. One reason for choosing 5V over 3.3V is its improved performance in cold temperatures. As the ambient temperature of a LCD decreases, more power is required to produce the dark segments. The electrical characteristics chart below illustrates the increase in the LCD driving voltage to drive the LCD as the temperature drops.

Low power segment LCDs with a LED backlight

Segment LCD displays operating in a low ambient light environment will require a backlight or side-lit backlight to be readable.

When ordering a segment LCD display with LED backlight it is important to remember that backlights draw a much higher current than a segment display. In fact, a LED backlight may require anywhere from 15mA for small displays to 75mA for larger displays. You may want to add a timer circuit that shuts the backlight off after just a few seconds of use.

When integrating a LED backlight into a customer’s segment LCD, we recommend a backlight that will operate at the same voltage as the LCD.

Is there a new battery-powered product design requiring a LCD in your near future? Focus Display Solutions offers US-based engineer design and support for your segment LCD display. Call us at 480-503-4295 or click here.

© 2013 Focus Display Solutions / Focus Display Solutions is a designer and supplier of segment LCDs.