The electromagnetic protection technology of the charging pile display kit mainly focuses on electromagnetic compatibility (EMC). The core objective is to ensure that the display screen operates stably in the strong electromagnetic interference environment of the charging pile while not generating excessive electromagnetic radiation to the outside.

The display screen of the charging pile needs to pass strict EMC tests, mainly based on:

Domestically: GB/T 17626 (Immunity tests for electrostatic discharge, electrical fast transient burst, surge, etc.), GB 4824 (Radio frequency interference Test).

International: EN 55032 (Radiated/conducted disturbance), EN 55035 (Immunity: ESD ±8kV contact /±15kV air, EFT ±2kV, surge ±2kV common mode, etc.).

The following are the main technical classifications and specific measures:

I. Shielding Technology

Shielding is the core means to prevent electromagnetic fields from penetrating sensitive electronic components and to stop the leakage of electromagnetic radiation.

1. Structural shielding

Metal casing/shielding cover: Conductive coating or metal stamping casing is adopted. Metal shielding covers are added to sensitive circuits such as LCD backlight drive circuits and main control chips to ensure good connection between the shielding cover and the PCB ground layer.

Gap treatment: Conductive gaskets, conductive adhesives or spring plates are used at the joints of the shell to achieve continuous conduction and prevent electromagnetic leakage.

Ventilation hole design: It adopts a hexagonal honeycomb structure, taking into account both heat dissipation and shielding performance.

2. Special shielding for display screens

FPC flat cable shielding: The display flat cable adopts a double-sided copper-plated shielding layer, and both ends are grounded 360° through conductive foam or spring sheets, which can effectively reduce high-frequency radiation.

ITO conductive film: ITO (indium tin oxide) conductive film is added to the surface of the display screen to discharge static electricity and shield radio frequency interference, and at the same time, it is electrically connected to the ground terminal to eliminate static electricity accumulation.

3. Cable shielding

The signal lines and power lines should be shielded cables. The shielding layer needs to be looped 360° to the shielding shell of the connector and firmly connected to the metal casing of the equipment to avoid "pigtail" grounding.

I I. Filtering Technology

Filtering is used to suppress electromagnetic interference conducted through power lines and signal lines.

1. Power port filtering

π -type /LC filter: An LC π -type filter is used at the power input end. Use a common-mode choke in combination with a Y capacitor to suppress common-mode interference.

Multi-stage filtering: It adopts a two-stage filtering structure, with electrolytic capacitors connected in parallel to high-frequency ceramic capacitors to cover a wide frequency band.

Through-hole capacitors/three-terminal capacitors: Selected at the power supply inlet for specific frequency bands, they provide superior high-frequency filtering performance.

2. Signal line filtering

Connect small capacitors in parallel between high-speed signal pairs such as LVDS to suppress differential mode noise. Series high-impedance magnetic beads reduce high-frequency crosstalk.

Filter capacitors are added to the critical signal lines to absorb ESD pulses, and small resistors are connected in series to limit the ESD current.

3. Interface protection

Add ESD protection devices such as TVS diodes at the input and output interfaces of the display screen to prevent electrostatic discharge interference.

I I I. Grounding Technology

A good grounding design is the foundation of EMC protection.

1. Grounding method selection

Single-point grounding for low-frequency circuits: Low-frequency sensitive circuits such as MCUS and ADCs adopt single-point grounding to avoid ground loop interference.

High-frequency circuit multi-point grounding: High-frequency modules such as RF/WiFi adopt multi-point grounding to provide a low-impedance return path.

2. Ground level design

Complete ground plane: PCB design should use large and complete ground planes as much as possible to ensure the integrity of the ground plane. Adding a ground wire near the high-frequency signal provides a low-impedance return flow.

Ground wire impedance control: A combination of multi-point grounding and single-point grounding is adopted. The metal frame of the display screen and the main unit shell are connected at multiple points through conductive foam to reduce the ground potential difference.

3. Cross-segmentation processing

When the signal line crosses the power supply division, capacitors are placed on both sides for sewing. The digital ground and the analog ground are connected at a single point through a 0Ω resistor or magnetic bead.

Iv. PCB Layout and Routing Optimization

1. Layout principles

Key signal isolation: Arrange the clock signal, high-speed data bus and low-speed signal separately to avoid parallel traces exceeding 50mm. The distance between the sensitive circuit (such as the reset signal line) and the power line should be ≥5mm.

Layered design: It adopts a four-layer board structure, with high-speed signal lines laid in the inner layer and the top/bottom layer laid to reduce radiation coupling.

2. Clock and signal optimization

Spread spectrum technology: The clock of the main control chip is spread spectrum to disperse energy over a wider frequency band and reduce peak radiation.

Backlight drive optimization: The PWM dimming frequency avoids the AM broadcasting band, and a soft-start circuit is added to reduce switching noise.

V. Software Collaborative Protection

Watchdog timer: Prevents abnormal high-frequency signal output caused by program deviation.

Dynamic voltage adjustment: Adjust the supply voltage in real time according to load changes to reduce power supply ripple.

Vi. Materials and Processes

Conductive materials: New shielding materials such as conductive rubber and conductive foam are selected to enhance the shielding effect of the gaps.

Surface treatment: The shell is treated with conductive oxidation.

Graphene heat dissipation: Adding graphene to the rear cover shell enhances heat absorption and dissipation, indirectly reducing the deterioration of electromagnetic performance caused by temperature rise.

The electromagnetic protection of the charging pile display screen kit is a systematic project. It requires the comprehensive application of three core technologies: shielding, filtering, and grounding, along with optimized PCB layout and wiring, software algorithms, and strict testing and verification, to ensure the stable and reliable operation of the display screen in the strong electromagnetic interference environment generated by high-power charging of the charging pile.