The main components of indoor LED screens and outdoor LED displays are LEDs and driver chips, which belong to a collection of microelectronic products. The operating voltage of LEDs is about 5V, and the general operating current is below 20 mA. Its working characteristics determine that it is very vulnerable to static electricity and abnormal voltage or current shocks. Therefore, LED display manufacturers need to take measures to protect the LED display during production and use. The power grounding is the most commonly used protection method for various LED displays.
Why should the power supply be grounded? This is related to the working mode of the switching power supply. Our LED display switching power supply is a device that converts AC 220V mains into a stable output of DC 5V DC power through a series of means such as filtering-rectification-pulse modulation-output rectification-filtering .
In order to ensure the stability of the AC/DC conversion of the power supply, the power supply manufacturer connects an EMI filter circuit from the live wire to the ground wire in the circuit design of the AC 220V input terminal according to the national 3C mandatory standard. In order to ensure the stability of the AC 220V input, all power supplies will have filter leakage during operation, and the leakage current of a single power supply is about 3.5mA. The leakage voltage is about 110V.
When the LED display screen is not grounded, the leakage current may not only cause chip damage or lamp burnout. If more than 20 power supplies are used, the accumulated leakage current reaches more than 70mA. It is enough to cause the leakage protector to act and cut off the power supply. This is also the reason why our display screen cannot use leakage protector.
If the leakage protector is not connected and the LED display screen is not grounded, the leakage current superimposed by the power supply will exceed the safe current of the human body, and the voltage of 110V is enough to cause death! After grounding, the power supply shell voltage is close to 0 to the human body. It shows that there is no potential difference between the power supply and the human body, and the leakage current is led to the ground. Therefore, the LED display must be grounded.
So, what should the standard grounding look like? There are 3 terminals at the power input end, which are the live wire terminal, the neutral wire terminal and the ground terminal. The correct grounding method is to use a special yellow-green bi-color wire for grounding to connect all power ground terminals in series and lock them, and then lead them out to the ground terminal.
When we are grounded, the grounding resistance must be less than 4 ohms to ensure the timely discharge of leakage current. It should be noted that when the lightning protection grounding terminal discharges the lightning strike current, it takes a certain time due to the diffusion of the ground current, and the ground potential will rise in a short time. If the grounding of the LED display screen is connected to the lightning protection grounding terminal, then the ground potential Higher than the display screen, the lightning current will be transmitted to the screen body along the ground wire, causing equipment damage. Therefore, the protective grounding of the LED display shall not be connected to the lightning protection grounding terminal, and the protective grounding terminal must be more than 20 meters away from the lightning protection grounding terminal. Prevent ground potential counterattack.
Summary of LED grounding considerations:
1. Each power supply must be grounded from the ground terminal and locked.
2. The grounding resistance shall not be greater than 4Ω.
3. The ground wire should be an exclusive wire, and it is strictly forbidden to connect with the neutral wire.
4. No air circuit breaker or fuse shall be installed on the ground wire.
5. The ground wire and the ground terminal should be more than 20 away from the lightning protection ground terminal.
It is strictly forbidden for some equipment to use protective grounding instead of protective zero, resulting in mixed connection of protective grounding and protective zero. When the insulation of a protective grounding device is damaged and the phase line touches the shell, the neutral line will have a voltage to the ground, so that a dangerous voltage will be generated on the shell of the protective grounding device.
Therefore, in the line powered by the same bus, the protective grounding and the protective zero connection cannot be mixed, that is, one part of the electrical equipment cannot be connected to zero and another part of the electrical equipment is grounded. Generally, the mains is connected to zero protection, so the electrical equipment using mains should be connected to zero protection.
Post time: Jul-11-2022