Floating ground and ground are two commonly used grounding methods in electronic circuit design, and they differ in application scenarios and advantages and disadvantages.
Floating ground
Floating ground refers to a circuit or device that is not directly connected to the earth by a conductor; that is, its ground wire is not connected to the earth. The advantages of floating ground include:
Reduce interference: Floating ground can isolate circuits or equipment from the common ground wire, reducing interference caused by ground loop currents and common conductors.
Safety: Floating ground can prevent micro-electric shocks, especially in medical devices such as pacemakers and electrocardiographs.
High isolation resistance: Floating ground can provide a large isolation resistance between power ground and signal ground, preventing electromagnetic interference caused by common ground impedance circuit coupling.
However, floating ground also has some drawbacks:
Static electricity accumulation: Because floating circuits have no conductive connection to the ground, static electricity is easily accumulated and electrostatic discharge can occur, which may lead to equipment damage or electric shock to personnel.
Parasitic capacitance effects: Floating ground circuits are susceptible to parasitic capacitance, which can cause ground potential fluctuations and increase induced interference to analog circuits.
Grounding
Grounding connects the metallic parts of a circuit or device to the earth to provide a safe path for current to escape in the event of a fault or overvoltage. The advantages of grounding include:
Reduce interference: Grounding brings the metal casing or conductor of electrical equipment into contact with the ground, allowing the charge to be released through the ground, thereby reducing interference between wiring and components.
Safety: Grounding helps prevent electric shock, especially when equipment insulation is damaged or leakage current occurs. Grounding can limit line inrush current or high voltage caused by high voltage intrusion into low-voltage lines and equipment.
Noise suppression: Grounding can effectively shield external electromagnetic interference, reduce radiation and conduction interference, thereby protecting equipment performance and data security.
I. The concepts and differences between floating ground and grounded ground
1. Floating ground
Floating ground refers to a situation where there is no reliable conductive connection between the neutral point of an electrical device and the ground, but an electrical connection exists between the device and the ground through the effect of capacitance.
2. Grounding
Grounding refers to the establishment of a reliable conductive connection between the neutral point of electrical equipment and the ground through a conductor or other methods.
II. Advantages and disadvantages of floating ground and grounded ground
1. Advantages of floating terrain
Floating ground can reduce current backflow between electrical equipment and ground, reducing the risk of electric shock, while also improving the equipment's anti-interference capability and reducing the impact of interference signals.
2. Disadvantages of floating terrain
Floating ground may cause problems such as equipment drift, difficulty in detecting electrical faults, and insufficient resistance to electric shock. It is also not suitable for some occasions with high requirements for electrical interference resistance.
3. Advantages of grounding
Grounding can ensure the safe and reliable operation of electrical equipment, effectively avoid the risk of electric shock, and improve the anti-interference ability of electrical equipment.
4. Disadvantages of grounding
Grounding makes equipment more complex, increases failure and maintenance costs, and is not suitable for some situations with high requirements for electrical interference immunity.
III. Applicable Scenarios for Floating Ground and Grounded Ground
1. Floating Ground Application Scenarios
Floating ground is suitable for applications where electrical equipment requires high interference immunity, such as electronic equipment and instrumentation equipment.
2. Grounding application occasions
Grounding is suitable for applications requiring high electrical safety and stability, such as power transmission, lighting power supplies, and motor drives.
【Summarize】
This article introduces the concepts and differences between floating ground and grounding, and discusses in detail their advantages, disadvantages, and applicable scenarios. The appropriate electrical grounding method should be selected based on the actual situation to ensure the safe operation and interference resistance of equipment.
"Ground" is a very important concept in electronics. Because there are many classifications and functions of "ground", it is easy to be confused. Therefore, we will summarize the concept of "ground".
"Grounding" has two meanings: signal grounding inside equipment and equipment grounding to the earth. These two concepts are different and have different purposes. The classic definition of "ground" is "an equipotential point or plane that serves as a reference for a circuit or system".
01
Signal ground, also known as reference ground, is the reference point with zero potential and is also the common terminal that constitutes the signal loop of the circuit.
DC ground: The "ground" of a DC circuit, the zero-potential reference point.
Alternating current neutral wire: The neutral wire for alternating current. It should be distinguished from the ground wire.
Power ground: The zero-potential reference point for high-current network devices and power amplifier devices.
Analog ground: The zero-potential reference point for amplifiers, sample-and-hold circuits, A/D converters, and comparators.
Digital ground, also called logic ground, is the zero-potential reference point of digital circuits.
"Hot ground": Switching power supplies do not require the use of power frequency transformers. The "ground" of their switching circuits is related to the mains power grid, which is called "hot ground" and is energized.
"Cold ground": Because the high-frequency transformer of the switching power supply isolates the input and output terminals; and because its feedback circuit often uses an optocoupler, which can both transmit feedback signals and isolate the "ground" of both sides; therefore, the ground at the output terminal is called "cold ground", which is not energized.
02
Signal grounding in signal grounding equipment may use a single point or a piece of metal within the equipment as the grounding reference point for the signal, providing a common reference potential for all signals within the equipment. Types include single-point grounding, multi-point grounding, floating ground, and hybrid grounding.
Single-point grounding refers to a circuit system where only one physical point is defined as the grounding reference point, and all other points requiring grounding are directly connected to this point. In low-frequency circuits, there is little impact between wiring and components. Circuits with frequencies below 1MHz typically use single-point grounding.
Multi-point grounding refers to the practice of directly connecting each grounding point in an electronic device to the nearest grounding plane (i.e., the device's metal base plate). In high-frequency circuits, parasitic capacitance and inductance have a significant impact. Circuits with frequencies higher than 10MHz typically employ multi-point grounding.
Floating ground means that the circuit's ground is not connected to the earth by any conductor. Virtual ground: a point that is not grounded but is at the same potential as the earth. Its advantage is that the circuit is not affected by the electrical properties of the earth. Floating ground allows for a large isolation resistance between power ground (high voltage ground) and signal ground (low voltage ground), thus preventing electromagnetic interference caused by common-impedance circuit coupling.
Its disadvantage is that the circuit is susceptible to parasitic capacitance, which causes fluctuations in the circuit's ground potential and increases induced interference to analog circuits. A compromise is to connect a large-value bleeder resistor between the floating ground and the common ground to release the accumulated charge. Care must be taken to control the impedance of the bleeder resistor; too low a resistance will affect the acceptable leakage current of the equipment.
03
Separating AC power ground from DC power ground: Generally, the neutral wire of an AC power supply is grounded. However, due to grounding resistance and the current flowing through it, the neutral wire potential is not exactly zero potential from the earth. Furthermore, there is often a lot of interference on the AC power neutral wire. If the AC power ground and DC power ground are not separated, it will affect the normal operation of the DC power supply and subsequent DC circuits. Therefore, using floating ground technology, which separates the AC power ground from the DC power ground, can isolate interference from the AC power ground wire.
Floating ground technology for amplifiers: For amplifiers, especially those with small input signals and high gain, even a tiny interference signal at the input can cause malfunctions. Therefore, employing floating ground technology can block interference signals from entering and improve the amplifier's electromagnetic compatibility.
Precautions for floating technology:
Maximize the ground insulation resistance of the floating ground system to help reduce the common-mode interference current entering the floating ground system.
Note the parasitic capacitance of the floating ground system to the ground; high-frequency interference signals may still couple into the floating ground system through this parasitic capacitance.
Floating ground technology must be combined with electromagnetic compatibility technologies such as shielding and isolation to achieve better results.
When using floating ground technology, attention should be paid to the hazards of static electricity and voltage backlash to equipment and personnel.
Hybrid grounding: Hybrid grounding allows the grounding system to exhibit different characteristics at low and high frequencies, which is necessary in broadband sensitive circuits. Capacitors have high impedance to low frequencies and DC, thus preventing ground loops between modules. When separating DC ground and RF ground, connect the DC ground of each subsystem to the RF ground through a 10–100 nF capacitor. These two grounds should be connected at a low impedance point, chosen where the highest switching speed (di/dt) signal is present.
04
In engineering practice, in addition to carefully considering the internal signal grounding of equipment, the equipment's signal ground, chassis, and earth are usually connected together, with earth serving as the equipment's grounding reference point. The purpose of connecting the equipment to earth is:
Protective grounding: Protective grounding is a reliable electrical connection between the metal casing (or frame) of equipment, which is not energized during normal operation, and the grounding device. It is a wiring method set up to protect personnel safety. One end of the protective ground wire is connected to the casing of the appliance, and the other end is reliably connected to the earth.
Anti-static grounding: Discharges the charge accumulated on the chassis to prevent the chassis potential from rising due to charge accumulation, which could cause instability in circuit operation.
Shielding ground: To prevent the potential of the equipment relative to the ground from changing under the influence of the external electromagnetic environment, which could cause instability in the operation of the equipment.
In addition, there are lightning protection grounding and dedicated audio grounding in audio equipment, etc.
