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Pcb Design Techniques For Switching Power Supply

April 21, 2018 10:49:27 Reply

In any switch power supply design, the physical design of the PCB boards are the last link in the chain, if the design approach, the PCB may be excessive radiation of electromagnetic interference caused by power is unstable, the following steps for each of the required attention for analysis.

1. From the schematic to PCB design process to

build element Parameters -> Network -> Input of the table design Preferences -> Manual Layout -> -> Verify manually cabling design - > Review ->CAM output.

2. Preferences

adjacent wire spacing must meet the electrical safety requirements, and in order to facilitate the operation and production and spacing should be as wide as possible. At least the minimum distance to be suitable for the


wiring density is low, the signal line spacing can be increased appropriately, for high- and low-level between the signal cable should be as short and spacing, in general, would take the line spacing is set to the 8mil. The hole in the edge of the pad to the printed circuit board edge distance is larger than 1mm, so that you can avoid the processing is the pad deficiency. When used in conjunction with a pad attached to the smaller, to the pad and the connection between the cable design into water droplets, such benefits are not easy to solder pad peeling, but the cables and pads are not easy to disconnect.

3. The component layout

has proved that even if the


schematic design, printed circuit board design, the


devices have a negative impact on reliability. For example, if the printed circuit board two thin parallel lines that are closer together, it is a signal waveform, the delay in the transmission line terminal form a reflective noise; as a result of power, and the thoughtful consideration of interference, will make the product's performance, therefore, in the design of printed circuit boards, it should be noted in the correct way. Each switch power supply has four



/ Power Switch AC circuit

/ output rectifier AC circuit

/ input source current loop

/ output load current loop input circuit

through a near-dc current to the input


charging, the filter capacitance mainly serve as a high-speed storage; similarly, the output filter capacitors are used to store the output from the rectifier of high-frequency energy and, at the same time the output load circuit of DC power. Therefore, the input and output filter capacitor terminals, the input and output current loop should be only from the Filter Capacitor terminal is connected to the power supply; if the input/output circuit and Power Switch/rectifier circuit with the connection between the capacitance of the terminal directly connected to AC power will be determined by the input or output filter capacitor and radiation into the environment.

The power switch AC circuit and the rectifier of AC circuit contains a high amplitude ladder current to flow in the harmonic content is high, its frequency is much larger than the Switch Base Frequency, peak amplitude up to continuous input/output dc current range of 5 times, the transition time is approximately 50ns. The two loop most susceptible to electromagnetic interference, and must therefore be in the power supply, other printed wiring cloth before the AC circuit, each of the three main elements filter capacitors, the power switch or rectifier,



should be placed next to each other and to adjust the position of the element to their current path as short as possible.

The establishment of a switching power supply, the best way to layout and electrical design is similar, the best design process is as follows:

1. Place the transformer

2. Design the power switch current loop

3. Design output rectifier current loop

4. Connect to AC power circuit of the control circuit

design input current source circuit and the input


design the output load circuit and the output filter in accordance with the circuit of a functional unit, all of the components of the circuit when it is necessary to conform to the following principles:

- first to consider PCB size. Pcb size is too large, the printed lines long, the impedance increases, the resistance to noise reduced capacity, the cost is too small; and the heat is not very good, and the adjacent lines are vulnerable to interference. The best shape is rectangular, the aspect ratio of 3:2 or 4:3, located on the edge of the circuit board components, away from the edge of the Board is usually not less than 2mm

-- on the device, taking into account the subsequent soldering is not too dense

-- to each circuit element is the core of the Center, built around it to make the layout. Components should be uniform, neat, compact arrangement on the PCB to minimize and reduce the components of the connection between the lead and the decoupling capacitor as close as possible to the VCC

in the work of the high frequency circuits, it is necessary to consider the components of the distribution between parameters. General circuit should, as far as possible, so that components are arranged in parallel. This is not only beautiful, but the solder easily, easy-to-batch production

-- the process in accordance with the Circuit arrangements for each of the functional circuit unit so that the layout for the signal flow and enable signal as much as possible to the uniform direction

-- the layout of the first principle is to ensure that the cabling of the pass rate, mobile devices with a cable connection, the connection between the devices together

-- as far as possible, to minimize loop area to contain the power of the radiation interference

4. Routing

Switch Power Supply contains high-frequency signals, PCB

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