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Switch Power Supply PCB Design Analysis
May 22, 2018 1:51:54 Reply
Switch power supply PCB design analysis
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 voltage wiring density is low, the signal line spacing can be increased due to the high- and low-level between the signal cable should be as short and spacing, in general, would take the line spacing is set to pads of the printed circuit board hole edge to 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, which have the advantage of pad not easy peeling, but the cables and pads are not easy to disconnect.
has proved that even if the circuit schematic design is correct, inappropriate design of printed circuit boards, electronic devices that 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 current loop:
(1) the power switch AC circuit
(2) the output of the rectified AC circuit
(3) the input source current loop
(4) the output load current loop input circuit through a near-dc current to the input capacitance 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 and Transition time is usually about 50ns. both circuit most susceptible to electromagnetic interference, and must therefore be in the power supply, other printed wiring prior to the AC circuit, each of the three main elements filter capacitors, the power switch or rectifier, the inductor or transformer should be placed next to each other and to adjust the position of the element to their current path can be short.
The establishment of a switching power supply, the best way to layout and electrical design is similar, the best design process as placed transformers, design the power switch current loop, design output rectifier current loop, connected to an AC power circuit of the control circuit, design input current source circuit and the input filter design the output load circuit and the output filter circuit on the basis of functional units.
All of the components of the circuit when it is necessary to conform to the following principles:
(1) The first thing 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 rectangle, the aspect ratio of 3:2 or 4:3, located on the edge of the circuit board components, away from the circuit board edge is generally not less than
(2) on the device, taking into account the subsequent soldering is not too intense;
(3) to each of the functional circuit of the core components 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 device
(4) 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-volume production.
(5) In accordance with the circuit process for each of the functional circuit unit so that the layout for the signal, and the signal as much as possible to the uniform direction.
(6) the layout of the overriding principle is to ensure that the cabling of the pass rate, mobile devices with a cable connection, the connection between the devices.
(7) As far as possible, to minimize loop area to contain the power of the radiation interference.
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