A more complex method, although still valid in AC-DC conversion, is to use a capacitor between the power rail and the AC side of the system. The typical place to do this in the PCB layout is close to the transformer. You can do this easily in your schematics: just locate the component you need for your capacitor, and then bridge the ground nets with a direct connection. Y-rated capacitors are a good choice here for higher voltage/current designs. Tying Grounds with a Capacitor Maintains DC Isolationįortunately, there is a simple solution: tie together the planes with capacitors. This is done with a capacitor across the two GND regions. We need to maintain this isolation while also providing some way to divert high frequency noise back to the input side and eventually earth. The reason we have two grounds that might include a potential difference is to create a secondary reference that does not expose the user to the input side, which might be a source of high current. In this drawing, a signal sourced over the left ground region (GND1) might be measured incorrectly over the right ground region (GND2) if the two ground regions have a potential difference between them. When I write “voltage a component measures”, it means a 5 V signal defined over one ground region in a system may not be measured at 5V when measured over some other ground region in a system. The reason ground is so important is that it defines the voltage that a component measures when it operates in a system. This is true of switching power supplies, particularly more complex supplies like LLC resonant converters. These ground systems are not always over a single ground plane for a variety of reasons. The reason for this is simple: unless you’re only operating at low voltage and low current, you typically want isolation in the design to protect users from safety hazards. Power supplies built with transformer coupling, such as AC-DC converters, DC-DC switching converters, or combinations of these two systems, will be built with a transformer bridging these gaps in the PCB layout. A signal ground generally refers to anything that is not earth or chassis. Signal ground: This is sometimes incorrectly delineated as analog ground and digital ground (don’t split your grounds like this).Chassis ground: This applies in an enclosure with metal elements, where metal in the enclosure is used to create a ground connection.Earth ground: This is a literal electrical connection back to earth, which is present as the safety line (PE) on 3-wire AC lines.If you think about the practical construction of this system, there are three different possible choices to use for ground: Suppose you’re designing a system that needs to perform power conversion (AC to DC), regulation, and delivery to your circuits in your design. Ground Construction in an Isolated Power Supply Because bad ground connections can create noise problems, or even a safety hazard, let’s look at the best practices for creating ground connections in your power regulation section when converting AC to DC on your board. These rules even apply in a PCB for an isolated DC charger or a DC power adapter as the design may need to be connected back to earth, depending on the application and safety concerns. If you’re integrating an isolated power supply onto a board with the rest of your major circuitry, you’ll still need to connect grounds in your system. One important aspect of integrating a power supply into your system is setting up and connecting grounds correctly, even for isolated power supplies. Unfortunately, real systems with integrated power sections, or even just power regulator modules you want to integrate into a larger system, aren’t so simple and need some custom design to ensure they operate correctly. Everything needed to provide stable power at a specific DC or AC level, and with relatively low noise is built into the unit, and you as the designer don’t really have to do anything except connect some leads to the board. Most designers that work with a bench-top power supply are likely using an isolated regulated (switching) PSU that plugs into the wall.
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