• Category 1 (CAT1): Bandwidth 750kHz, used for alarm and voice transmission, not for data.
• Category 2 (CAT2): Bandwidth 1MHz, for voice and data up to 4Mbit/s, used in older token networks.
• Category 3 (CAT3): Bandwidth 16MHz, up to 10Mbit/s, for voice and 10BASE-T Ethernet, largely obsolete.
• Category 4 (CAT4): Bandwidth 20MHz, up to 16Mbit/s, for token-based LANs and 10/100BASE-T, not widely adopted.
• Category 5 (CAT5): Bandwidth 100MHz, up to 100Mbit/s, for 100BASE-T and 1000BASE-T networks, commonly used with RJ connectors.
• Category 5e (CAT5e): Lower attenuation and crosstalk, higher ACR and SNR, used for Gigabit Ethernet.
• Category 6 (CAT6): Bandwidth 1–250MHz, provides double the bandwidth of CAT5e, suitable for >1Gbit/s applications.
• Category 6A (CAT6A): Bandwidth 500MHz, up to 10Gbit/s, standard diameter 6mm.
• Category 7 (CAT7): Bandwidth 600MHz, up to 10Gbit/s, single-wire diameter 8mm, multi-core 6mm, for future 10 Gigabit Ethernet.

Secondary Heading 4: LED Display Lightning Protection Design

(1) Lightning Protection Measures

LED displays are highly susceptible to lightning damage due to their high-density integrated circuits. Lightning can cause mechanical, electrical, and thermal damage, potentially leading to fires. Lightning protection measures must comply with the Code for Design of Lightning Protection of Buildings (GB 50057—1994):

1. Direct Lightning Protection:
   • For displays not within the protection range of nearby tall buildings, install a lightning rod on or near the display’s steel structure.
2. Induced Lightning Protection:
   • Install Level 1 and 2 power surge protectors in the display’s power system and Level 3 in the equipment room. Phase wire cross-section ≥10mm², ground wire ≥16mm².
   • Install signal surge protectors on signal lines (e.g., network surge protectors for Ethernet, DB9 protectors for serial interfaces).
3. Line Protection:
   • Use shielded cables for power and signal lines, laid underground.
4. Grounding System:
   • Front-end grounding resistance ≤4Ω, equipment room ≤1Ω.
   • Connect the display’s steel structure and casing for equipotential bonding, with grounding resistance <10Ω. Add an artificial grounding grid if necessary.

(2) Power Distribution System Lightning Protection Configuration

1. TN-C System:
   • Configured with Level 1, 2, and 3 surge protectors connected to the main grounding busbar, as shown in Figure 2-13.

LED Display Electrostatic Discharge (ESD) Protection

(1) Electrostatic Discharge (ESD) Definition

ESD is the abbreviation for Electro-Static Discharge, meaning the discharge of static electricity. ESD pulses have a wide bandwidth, short rise time, and high peak energy. In dry weather, when one person touches another, they may feel a shock; when removing a synthetic fiber sweater in the dark, bright sparks may be visible. These are ESD phenomena.

The definition of electrostatic discharge is: the transfer of charge between objects with different electrostatic potentials due to proximity or direct contact. Charges remain stable under the following two conditions: (1) When trapped on conductive but electrically insulated objects, such as a metal screwdriver with a plastic handle. (2) When residing on an insulating surface (e.g., plastic) without flowing.

Interactions between materials (e.g., friction, contact, induction, or conduction) cause materials to gain or lose electrons, disrupting electrical balance and accumulating charges. The accumulation of charges results in static electricity on the material’s surface. When charges accumulate to sufficient strength, they may discharge, breaking down surrounding materials to achieve a new electrical balance. This rapid neutralization of static charges is called electrostatic discharge. Due to its fast rate and typically low discharge resistance, it often causes instantaneous large currents, potentially exceeding 20A. Such discharges, if passing through integrated circuits, can cause significant damage.

ESD is a discipline studying the generation and dissipation of static electricity, electrostatic discharge models, and effects such as thermal (spark) effects and electromagnetic effects (electromagnetic interference, EMI, and electromagnetic compatibility, EMC). Internationally, devices used for electrostatic protection are commonly referred to as “ESD” devices. In China, these are often called ESD circuit protection devices or static suppressors. ESD has multiple models to describe how devices are damaged, such as the Human Body Model (HBM), Charged Device Model (CDM), and Field-Induced Model.

(2) ESD Damage Mechanisms

Component breakdown caused by electrostatic discharge is the most common and severe hazard in the electronics industry, particularly in electronic product manufacturing. Electrostatic discharge can cause hard breakdown or soft breakdown in devices. Hard breakdown results in permanent failure, such as open or short circuits at the device’s output or input. Hard breakdown causes instantaneous thermal damage within the chip, secondary breakdown of metal bonds, melting of dielectrics, or surface breakdown, ultimately leading to complete and permanent failure of the integrated circuit. When the electrostatic discharge energy reaches a certain level, it can cause the integrated circuit to explode, completely burning out the chip and exposing it, potentially causing personal injury or equipment failure. Hard breakdown characteristics are evident and can generally be detected before the assembled component or circuit board is delivered.

Soft breakdown (soft failure) causes performance degradation or reduced parameter metrics without complete failure, creating hidden risks that are difficult to detect during final quality inspections. Circuits damaged by static electricity may exhibit latent damage, leading to parameter changes, quality degradation, and reduced lifespan. Over time, with changes in temperature, time, or voltage, various faults may emerge, preventing normal operation—this is known as soft failure. If the damaged chip is part of critical control systems, such as network control centers, automatic broadcast control systems, production scheduling control centers, electronic warfare command systems, automatic navigation systems, or rocket launch control systems, the consequences can be unpredictable. Latent damage poses a greater risk, causing more severe direct or indirect losses. Soft breakdown is difficult to detect and has hidden characteristics, making it more hazardous. Data indicates that 90% of ESD-induced device damage is latent soft breakdown, while 10% is immediate failure.

Soft breakdown can degrade device performance and lower parameter metrics, creating fault risks. Since soft breakdown may cause intermittent circuit performance (due to reduced metrics), it is hard to detect and causes significant trouble during operation and fault diagnosis. Devices with soft breakdown may still function with issues, showing no fundamental performance changes and potentially passing factory inspections, but they are prone to further failures. Multiple soft breakdowns can lead to hard breakdown, causing abnormal equipment operation.

ESD occurs frequently in electronic equipment, generating potentially destructive voltages, currents, and electromagnetic fields during discharge. Due to the fast discharge rate and low discharge resistance, instantaneous large currents are common, which can burn out related components if passing through integrated circuits.

ESD generates strong peak pulse currents with rich high-frequency components, with frequencies potentially exceeding 1GHz. These high-frequency pulses make PCB traces highly effective receiving antennas, inducing high-level noise.

ESD interferes with circuits in two ways: one is direct damage through conducted currents, and the other is interference from electromagnetic fields coupled through capacitance, inductance, or spatial radiation.

The field generated by ESD currents can penetrate equipment directly or couple through holes, gaps, or input/output cables to sensitive circuits. As ESD currents flow through the system, they excite the paths they traverse, generating radiation waves with wavelengths ranging from a few centimeters to hundreds of meters. This radiated energy produces electromagnetic noise that can damage electronic equipment or interfere with its operation.

If the voltage or current induced by ESD exceeds the circuit’s signal level, it may cause malfunctions or even insulation breakdown, triggering larger currents and ultimately burning out related components. In high-impedance circuits, where currents are small, capacitive coupling dominates, and ESD-induced voltages affect signal levels. In low-impedance circuits, inductive coupling dominates, and ESD currents cause device failure. The two main ESD damage mechanisms are: (1) Thermal failure due to heat generated by ESD currents. (2) Insulation breakdown due to high ESD voltage, triggering larger currents and further thermal failure.

Both types of damage may occur simultaneously in an electronic device. For example, insulation breakdown may trigger large currents, leading to further thermal failure. In addition to causing circuit damage, electrostatic discharge can easily interfere with electronic circuits. ESD interference occurs in two forms: conducted interference and radiated interference.

ESD failure can be permanent or temporary. If the voltage or current generated during contact or conducted discharge is too high, it may cause permanent device damage, such as when touching a circuit in winter, rendering the equipment unusable. In some cases, smaller circuit noise may cause occasional abnormal results without damaging the equipment, known as temporary ESD failure.

Electromagnetic pulses from electrostatic induction and discharge also pose risks, with frequency bands ranging from hundreds of kHz to tens of MHz and levels up to tens of millivolts, capable of damaging static-sensitive devices (SSDs). With increasing integration, smaller sizes, finer photolithographic lines, narrower line spacing, and the use of new materials with low anti-static properties, the electrostatic resistance of integrated circuits has significantly decreased. Some believe that integrated circuits with ESD protection are immune to static damage. However, while protection circuits provide some defense, they can still be significantly damaged when exposed to thousands of volts of static electricity in human or work environments. All integrated circuits are static-sensitive, differing only in their threshold voltage tolerance. Human-perceptible electrostatic discharge occurs above 2500V, so reducing static to imperceptible levels does not eliminate the risk of damage to electronic equipment. Therefore, ESD protection should focus on comprehensive prevention to mitigate risks proactively.

(3) Characteristics of ESD Damage to LED Displays

The characteristics of ESD damage to LED displays are as follows: (1) Concealment: The human body cannot perceive static electricity unless discharge occurs, but even then, there may be no shock sensation, as human-perceptible ESD voltage is 2–3kV, making static electricity concealed. (2) Latency: Some electronic components show no significant performance degradation after ESD damage, but repeated discharges cause internal damage, creating hidden risks, making ESD damage latent. (3) Randomness: From production to failure, a component is constantly at risk from static electricity, which is generated and causes damage randomly. (4) Complexity: Analyzing ESD-damaged components is time-consuming, labor-intensive, and costly due to the fine, delicate, and microscopic structure of electronic products. It often requires high-precision tools like scanning electron microscopes. Even so, distinguishing ESD damage from other failure causes is challenging, often mistaken for early failure or unknown failure. Before fully understanding ESD damage, it is often misattributed, masking the true cause, making ESD damage analysis complex.

(4) ESD Protection Device Selection Considerations

In the lightning protection design of LED display information transmission systems, selecting appropriate ESD protection devices is critical, ensuring compatibility with the system. Key factors for selecting ESD protection devices for LED display information interfaces include:

1. Surge forms that may be induced on the information transmission line (e.g., waveform, time parameters, and maximum peak value).
2. Critical breakdown voltage of the information interface circuit under simulated lightning impact.
3. Data signal level of the information interface under normal operating conditions.
4. Residual voltage parameters of the ESD protection device under simulated lightning impact.
5. Impact resistance of the ESD protection device.
6. Operating frequency of the information transmission system.
7. Interface type of the information interface.
8. Operating voltage of the information interface.

(1) ESD Protection Device Selection for Ordinary Data Lines: Ordinary data lines are highly susceptible to ESD impact, leading to data disruption, making ESD protection devices essential. For example, the typical application circuit for NXP Semiconductor’s PESDxS2UT is shown in Figure 2-17.

(2) Conversion Cable Fabrication: The control card interface (e.g., 08 interface) and unit board interface (e.g., P10 unit board with 12 interface) differ. The control card has R1, R2, R3, R4, etc., corresponding to rows 1, 2, 3, 4 of unit boards, respectively, as shown in Figure 2-24.

Figure 2-27: 220V Power Line and Switch Power Supply Connection Diagram