Useful information sharing | Come and get the various "grounds" in the switching power supply

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Useful information sharing | Come and get the various "grounds" in the switching power supply [Copy link]

The classic definition of " ground " is "an equipotential point or plane that serves as a reference for an electrical circuit or system."

Ideally, the ground wire should be a physical entity with zero potential and zero impedance. However, in actual wiring, the ground wire on the PCB has its own impedance component, as well as reactance components composed of distributed capacitance and inductance.

In addition, the ground source (power supply, signal source) forms a loop, and the electric field of this loop will induce the RF current of the external electromagnetic field, which is often called "noise", thus causing EMI problems.

Considerations about "ground" in the actual wiring process of the switching power supply: According to the actual application, first distinguish the types of wires, and then choose different grounding methods. Regardless of the grounding method, the principle of "low impedance, low noise" must be followed.

Classification of "ground" in switching power supply:

1. DC ground : The "ground" of a DC circuit, the zero potential reference point.

2. AC ground : The neutral line of AC power. This ground usually generates noise and should be distinguished from the earth.

3. Analog ground : The zero potential of various analog signals.

4. Digital ground . Also called logic ground, it is the zero potential of various switching (digital) signals in digital circuits.

5. Hot ground . The switching power supply does not need to use an industrial frequency transformer. The "ground" of its switching circuit is related to the mains power grid, the so-called "hot ground", which is electrified.

6. Cold ground . Since the high-frequency transformer of the switching power supply isolates the input and output ends, and since its feedback circuit often uses a photocoupler, which can both transmit feedback signals and isolate the "ground" of both sides, the ground at the output end is called "cold ground" and it is not electrified.

7. Power ground : The zero potential reference point for high current network devices, power electronics and magnetic devices.

8. Signal ground . Generally refers to the ground wire for sensing changing signals.

9. Safety : Providing a grounding loop can prevent the risk of electric shock.

10. Shielded ground : Provide 0V reference or electromagnetic shielding for interconnected cables and main racks to prevent electrostatic induction and magnetic field induction.

11. System ground : The common reference point for analog and digital signals of the entire system.

12. Floating ground : A branch in the circuit is used as a 0V reference without being grounded.

There are several ways to connect to the ground:

1. Single-point grounding . It means that the ground wires of all circuits are connected to the same point of the common ground wire to reduce mutual interference between ground loops. It can prevent the currents and RF currents in different subsystems from passing through the same return path, thereby avoiding the common-mode noise coupling between them. According to the characteristics of different systems, you can choose between series single-point grounding and parallel single-point grounding.

2. Multi-point grounding : It means that each circuit in the system is grounded nearby.

3. Mixed grounding . It is a comprehensive application of single-point grounding and multi-point grounding. Generally, it is based on single-point grounding and then multi-point grounding through some inductors or capacitors. It uses the characteristics of different impedances of inductors and capacitors at different frequencies to make the ground system have different grounding structures at different frequencies. It is mainly suitable for circuit systems working at mixed frequencies.

It is important to distinguish the ground of analog circuits from the ground of digital circuits, as well as their best common connection points. In low-frequency circuits, the operating frequency of the signal is less than 1MHz, and the inductance between its wiring and devices has little effect, while the loop formed by the grounding circuit has a greater impact on interference, so single-point grounding should be used. When the signal operating frequency is greater than 10MHz, the ground line impedance becomes very large. At this time, the ground line impedance should be reduced as much as possible, and multi-point grounding should be used nearby. When the operating frequency is between 1 and 10MHz, if single-point grounding is used, the ground line length must not exceed 1/20 of the wavelength, otherwise multi-point grounding should be used.