Industry Article

LCD Displays for Electric Vehicle Chargers

February 06, 2023 by Qiang Dong, Topway

This article discusses the challenges of designing electric vehicle charger displays and how to specify an effective LCD solution.

With the steady increase in electric vehicle (EV) use, there comes a demand for effective LCD screen solutions for EV chargers. Several issues can arise when choosing a screen, such as weather conditions, water and dust exposure, power efficiency, readability, and EMC performance.

Figure 1. Displays for EV charging stations need highly reliable, easy-to-read, weather-resistant displays. Image used courtesy of Topway

Among the screen options available, many engineers have settled on thin-film-transistor liquid-crystal displays (TFT LCDs), which work well when correctly specified. This article will discuss challenges associated with designing EV charger displays, why TFT LCDs work well in EV applications, and how to specify an effective TFT LCD solution.


EV Charger Display Challenges

EV charging stations provide some unique challenges when creating user displays. First, since the display will be used outdoors, it’s important to consider its weather resistance, including resistance to UV exposure, immersion, water, and dust. 

Outdoor EV charger displays may also be exposed to a wide range of temperatures, which can impact the performance of critical components and affect the screen's readability. These temperatures will, at some point, fall into the extreme category. 

There is also the challenge of a screen that can be read in bright sunlight and dark conditions. The displays need brighter screens even in the sunlight than the standard LCD solution illustrated in Figure 2.


Figure 2. While an LCD may be easy to read indoors, sunshine makes it more difficult to see. Image used courtesy of Topway


There are always issues with electromagnetic compatibility (EMC), electromagnetic interference (EMI), and associated national and international standards. Furthermore, low power consumption is a must, especially related to sustainable, environmentally friendly designs such as EVs.


TFT LCDs for EV Chargers

One of the most effective solutions for EV charger displays is TFT LCDs, which are flat-panel display screens that respond to touch but are not triggered by water droplets. They have a reputation for being sharper and brighter than a typical LCD when a partially reflective mirror layer is included between the backlight and the LCD, which turns part of the reflected ambient light into a portion of the light source for the LCD. There are TFT LCDs on the market that meet the requirements for EV chargers, including resistance to common weather issues (e.g., temperature, exposure to water and dust), excellent power efficiency, readability in all lighting conditions, and good EMC performance.


Figure 3. Typical block diagram for a TFT LCD for EV charger use. Image used courtesy of Topway


A simple block diagram for a TFT LCD with a 5-inch screen size is shown in Figure 3. Notice the backlight circuit, which includes pulse width modulation (PWM) to support adjustable brightness.

PWM is used to adjust brightness by pulsing (rapidly turning on and off) LED lights for periods that cause the brightness to appear steady. Adjustments are made to brightness by modifying the percentage of time the LED lights remain on.


Specifying TFT LCD Display Solutions

Since EV chargers are outdoors, they will be exposed to many outside elements most other technology can avoid. Engineers should look for TFT LCDs with enclosures qualified for UL-F1 and suitable for outdoor use, including UV light, water exposure, and immersion per UL 746C. UL 746C applies to materials for outdoor use, where they will be subject to UV light exposure and water immersion. 

To be rated UL-F1, several tests must be done. UV exposure is tested using either a twin-enclosed carbon weatherometer for 720 hours or a xenon-arc weatherometer for 1000 hours. Water immersion is tested by immersing the specimen for seven days in water that is 70°C. 

In addition, a UL-F1 rating also requires before and after testing related to mechanical strength, mechanical impact, and flammability. If the specimen does not suffer any significant degradation after these tests have been performed, it is rated UL-F1 and suitable for outdoor use. 

The front panel enclosure for the TFT LCD must also be qualified for IP65 and IK08 ratings, making them highly resistant to water and dust ingress and impact protection. IP stands for ingress protection, and to receive an IP65 designation, an enclosure design must successfully resist 12.5 liters/min of water projected by a 6.3 mm nozzle (from any direction) at a pressure of 30 kPa over 15 minutes without suffering any harmful effects.

 An IK rating deals with impact, and an enclosure with an IK08 rating can withstand dropping a 1.7 kg mass from a height of 300 mm onto the surface of the enclosure. It is also vital for engineers to verify that potential TFT LCD solutions provide reliable performance over a wide range of temperatures (e.g., -20°C to 70°C). This depends on both the enclosure used and the operating temperature range of the TFT LCD and its related circuitry.

Brightness levels are critical and should be at least 700 cd per square meter to provide a minimum brightness level for reading in darkness. And the brightness should be adjustable to reduce average power consumption, with the best approach involving a PWM module, as discussed earlier, combined with a photosensitive circuit to make automatic adjustments of the pulse-width signal pulsing time depending on the outdoor brightness. This ensures that the user of the EV Charger can read it both in extreme darkness and bright daytime light.

Anytime electrical charging is involved, there will be complex EMC/EMI issues. If applicable EMC/EMI standards are not met, the EV charger display and nearby circuitry can behave in unexpected and potentially dangerous ways. In particular, DC-DC and AC-DC conversions will create problematic electrical noise. The high electric current in EV chargers results in strong magnetic fields that create a path for EMI. Engineers should seek out TFT LCD solutions that have to meet strict EMC/EMI testing standards, such as the following:

  • Electrostatic discharge immunity, which evaluates how durable an electronic device is when electrostatic discharge occurs when touched by a person
  • IEC 61000-4-4, an EFT ( electrical fast transient)/burst immunity test to ensure circuits are immune to EFT and burst events related to inductive loads
  • EN 61000-4-3,  a radiated, radio-frequency, electromagnetic field immunity test to assess how well equipment can operate as intended when subject to RF by applying amplitude-modulated signal (1 kHz – 80%) to the enclosure, power, and signal ports of the equipment
  • GB/T 17626 standard, a Chinese standard that addresses EMC, testing and measurement techniques, and surge immunity 
  • GB 4824 radio-frequency disturbance test, which looks at the disturbance characteristics, limits, and methods of measurement for equipment

Finally, TFT LCDs exhibit lower power consumption than other equivalent solutions, which can be hard to do when dealing with high-brightness displays. The TFT LCD solution chosen by an engineer must also be low maintenance and have a backlight lifespan of at least 50,000 hours. This reduces the M&O costs and downtime for chargers (which can be especially critical when chargers are located in more rural areas).


Case Study: Outdoor Charging Stations for China

Topway supplied TFT LCDs for China’s State Grid charging stations, shown in Figure 4, and after 65 years, these displays still provide reliable performance, even in extremely harsh weather conditions. 


Figure 4. LCD TFT solutions from Topway have proven highly effective for the EV charger needs of China’s State Grid. Image used courtesy of Topway


It was critical that the EV display achieve the correct brightness level for readability in all outdoor conditions. This is not a feature inherent to TFT LCDs; however, Topway solved this problem by automatically adjusting the backlight with a PWM and photosensitive circuit.

Also of concern was the ruggedness of the EV charger display. China’s State Grid was looking for a display rated for outdoor use and could handle a wide range of temperatures during exposure to the sun. In China, the temperatures can easily range from -20°C to 70°C between winter and summer. Topway meets these requirements using high-quality material and components for the enclosure and the TFT LCD, as well as an anti-UV film to provide added UV protection.

EMC/EMI requirements are critical to a display's safe, reliable operation for an EV charger. Because EV charging applications involve significant electromagnetic emissions and TFT LCD screens can be highly susceptible to them, China’s State Grid required a display solution that was highly resistant to EMC and EMI. Topway addressed this issue by including defense measures that would eliminate EMI, shortening cables used for the power supply and data, utilizing low voltage differential signaling, and using EMI shields on important components.


Current Topway Solutions for EV Chargers

Topway has continued improving TFT LCD designs for EV charger applications with their 5" Color TFT LCD Module LVDS 800x480 (Figure 5) and 7" Color TFT LCD Display LVDS 800x480. These TFT LCD solutions meet all the outlined requirements from previous sections. For example, they are UL-F1 rated for outdoor use, both  IP65 and IK08 rated, and designed for use over an operating temperature range of  -20°C to 70°C. They also include a UV-resistant film to support a long useful life despite intense UV exposure. 

The 5” screen has a 700 cd per meter squared brightness, while the 7” screen is brighter at 900 cd per meter squared, and the brightness is automatically adjusted through a combination of PWM and a photosensitive circuit.

Topway’s EV charger solutions have passed all applicable EMC/EMI testing requirements and have a lifespan of at least 50,000 hours. Both have a 5 V input and an LVDS interface to support fast response times.


Figure 5. Topway 5" Color TFT LCD Module LVDS 800x480 and 7" Color TFT LCD Display LVDS 800x480 are excellent options for EV chargers. Image used courtesy of Topway


The 5” display has 800x480, an active area of 108.0mm x 64.8mm, and an outline of 200.0mm x 105.0mm x 22.0mm. The 7” display has a resolution of 800x480 but with a larger active area of 154.08mm x 85.92mm, and an outline of 340.0mm x 400.0mm x 36.0mm.

When correctly specified, TFT LCDs work well for EV chargers. Contact Topway to find out how TFT LCDs can change how you design EV chargers.