When designing a circuit, engineers can prevent each circuit from interfering with each other in the normal operation of the circuit, so that it can work effectively in compatibility with each other. According to the nature of the circuit, the "zero potential" - "ground" in the circuit is divided into different categories.
First of all, we come to know a few "grounds": "hot ground" refers to the area directly or indirectly connected to the AC grid; "cold ground" refers to the area that is not connected to the grid; the signal "ground" is also called Reference "ground" is the reference point of zero potential, which is the common end of the circuit signal circuit; the protection "ground" is set in order to protect personnel safety in Class I electrical equipment (devices that cannot be protected only by insulation) A power wiring method in which one end is connected to the outer casing of the electric appliance, and the other end is reliably connected to the earth.
First, the signal "ground"
The signal "ground", also known as the reference "ground", is the reference point of zero potential, and is also the common end of the circuit signal loop, the graphic symbol "⊥".
1) DC ground: DC circuit "ground", zero potential reference point.
2) Exchange place: The neutral line of AC power should be distinguished from the ground line.
3) Power ground: zero current reference point for high current network devices and power amplifier devices.
4) Analog ground: Zero potential reference point for amplifier, sample-and-hold, A/D converter and comparator.
5) Digital ground: also called logic ground, is the zero potential reference point of the digital circuit.
6) "Hot ground": The switching power supply does not need to use a transformer. The "ground" of the switching circuit is related to the mains grid. It is called "hot ground" and it is charged.
7) "Cold ground": Because the high-frequency transformer of the switching power supply isolates the input and output terminals; and because its feedback circuit is commonly used for photoelectric coupling, it can transmit feedback signals and isolate the "ground" of both sides, so the ground of the output terminal is called For "cold land", it is not charged. The graphic symbol is “⊥â€.
Second, the "ground" in the sound
1) Shielded wire grounding: In order to prevent interference, the sound system of the metal case is connected with the signal “groundâ€. This is called shield grounding.
2) Audio dedicated "ground": In order to prevent interference, professional audio must be connected to the audio dedicated "ground" in addition to shielding the "ground". This grounding device should be buried specifically and should be connected to the corresponding grounding of the isolation transformer and the shielded regulated power supply as a dedicated audio grounding point in the sound control room.
Third, distinguish between "hot land" and "cold land"
In the input AC, we generally refer to a "fire" line (phase line) and a "zero" line (center line), which is DC after being assembled by a bridge stack (or diode). Generally, the negative terminal of the filter capacitor is used as a reference potential, that is, "hot ground". At this time, the positive terminal of the filter capacitor is +300V. At this time, if the ground is referred to the "ground" potential, the "hot ground" is measured, and the "hot ground" is actually an alternating current waveform of 220V. Therefore: 1) If you stand on the ground and touch the "hot place", you will be shocked by the voltage difference of 220V AC between "hot" and the earth; 2) If you stand on a wooden chair (to be completely separated from the earth), to get in touch with the "hot place", it doesn't matter, you won't be shocked. You are the same as the "hot" potential. This is exactly the same as the fact that the bird is standing on the wire and will not be shocked. Remember to use an isolation transformer (1:1 transformer) when repairing a "charged" movement.
Comparative explanation: 1) "Cold ground" generally refers to the "ground line" that can be directly touched, and its potential is the same as that of the earth. Because it is not charged, it becomes "cold land". This is a safe "land";
The circuit ground that is completely isolated from 220V mains and grounded (can be grounded or not grounded on the circuit connection) is called “cold groundâ€; cold ground is isolated by capacitors, or stepped down by a step-down transformer. The negative pole is grounded (the ground through the transformer is cold).
2) “Hot place†refers to the “ground line†that is charged, and must not be touched directly, otherwise it will be shocked;
The ground of the circuit connected to the 220V mains and not grounded (ungrounded) is called "hot ground"; the hot ground is the grounding of the mains direct-output output without the isolation of the capacitor (the ground through the rectifier bridge is hot).
Fourth, the processing method of different ground lines
1. The digital ground and analog ground should be separated. In high demand circuits, the digital ground must be separated from the analog ground. Even for the A/D, D/A converter, the two "grounds" on the same chip should be separated, and only the two "grounds" are connected at one point in the system.
2. Floating and grounding. The floating system of the system floats the ground of each part of the system circuit and is not connected to the earth. This connection has a certain anti-interference ability. However, the insulation resistance between the system and the ground should not be less than 50 MΩ. Once the insulation performance is degraded, it will cause interference. The system is usually floating and the chassis is grounded to enhance the anti-interference ability, which is safe and reliable.
3. Ground at one point. In low frequency circuits, there is not much influence between the wiring and the components. Generally, circuits with a frequency less than 1MHz are grounded at one point.
4. Multi-point grounding. In high-frequency circuits, the effects of parasitic capacitance and inductance are large. Generally, circuits with a frequency greater than 10 MHz are grounded at multiple points.
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