Grounding loop of DC-DC converter

    DC-DC converter supplies power for each circuit in the whole system. Although each circuit may perform well on the test bench, the overall performance of the system often does not reach the performance effect of each circuit. Why? There are many potential factors, and the overall grounding system of each circuit in the system is the primary reason. The designer needs to be very clear about how each circuit is grounded and whether there is a grounding loop in the system.

    When there is more than one ground connection between two circuits and/or systems, a ground loop is formed. The repeated grounding channel is equivalent to forming a ring antenna to receive the interface signal (current is converted into voltage through the grounding resistance). The consequence of receiving the induced voltage of the ground loop is that the system reference voltage to the ground is unstable with the superposition of the induced voltage. These induced noise voltages will become part of the overall system response!

    In addition, the grounding loop forms a common line, which causes the grounding current to return to the origin of the grounding electrode of the system through more than one channel. For example, the power supplies of multiple computers are connected to each other through the grounding in the common office wiring configuration, but can also be connected through the data communication wiring. Therefore, computers are often connected to each other through more than one grounding channel. When there are multiple grounding channels between multiple computers, the configuration formed is called "grounding loop". Whenever a ground loop occurs, the ground reference point will receive superimposed signals, forming system interference and noise.

    When some components in the system are powered by different ground wires rather than other components in the system, or the ground potential between two circuits in the system is different, the measurement, communication or video system will generate a ground loop. Generally, the potential difference of the connection to the ground will cause current flow. This will modulate the circuit input and other signals will appear in the normal input. In the example shown in Figure 1, two grounding instruments are grounded through the signal line and the main ground wire is interconnected. In this case, 1A current in the line will form a 0.1V voltage difference between the two instrument grounding points.

    Figure 1 Typical grounding loop

    Because of the voltage difference between the instruments, the signal in the interconnection wire will add this voltage difference to the signal, causing the wire to appear voltage "alternating sound". This is one reason why 60 Hz noise (or horizontal interference of video signal) is heard in the audio signal. Another problem is the current flowing in the ground wire of the signal cable. This current will also flow into cables and equipment. Designers always pay attention to the grounding of the grounding terminal, but often do not optimize the design to eliminate the sensitivity of background noise. Therefore, when designing the internal grounding circuit of the system correctly, it is the most basic requirement to ensure that the grounding loop current will not cause problems in the system.

    As another example, the grounding loop is a common problem when multiple audio-visual system components are connected together. The common noise of audio system is often caused by the problem of ground loop. In addition, audible "alternating sound" is also a typical grounding loop problem (of course, it depends on the AC power supply voltage frequency used in the country). Of course, the most common example of the grounding loop problem is that the system uses the instrument connected to the socket, while the other instrument is connected to the grounding socket at different locations in the room.

    Ideally, each system in a room should be connected to the same grounding point, and the signal/antenna network should eventually be connected to the same grounding point. This is ideal because the grounding of the system and each instrument is connected by the same grounding reference point to point (central grounding star connection mode). In this case, it must be considered that some equipment (and systems) also use shielded wire links. The current flows from one device to another through the ground wire, and then returns to the first device through the shielded wire. This loop will also pick up interference from nearby magnetic fields and RF transmitters (such as mobile phones). As a result, the unwanted signal amplified is heard. By the way, the grounding loop will not cause problems under the following conditions:

    1) The wires in the loop do not transmit current;

    2) The loop is not exposed to external changing magnetic field;

    3) There is no radio frequency interference nearby.

    If there is current flow in the ground wire, noise interference will occur when there is a certain potential difference. In addition, a small voltage difference will also add noise to the signal. This situation will cause audio communication sound, video interference image and computer network transmission error.

    Good analog system design, analog system test and measurement need to carefully design the system grounding channel to avoid grounding loops.