In switching power supply design pcb hqew physical design is the last link, if the design method is undeserved, PCB may be too much radiation, electromagnetic interference caused by unstable power supply work, aiming at the matters needed attention in the steps below are analyzed:
A PCB design process, from schematic diagram to build - > element parameters input principle of network design parameters table - > Settings - > manual layout - > the manual wiring - design - > > validation review - > CAM output.
Second, the parameter is set spacing between adjacent wires must be able to meet the requirements of electrical safety, and to facilitate the operation and production, also should try to wide spacing. Minimum spacing can be suitable to withstand voltage, at least in wiring density is lower, the line spacing can be appropriately increased, the high and low level disparity of signal lines should be as much as possible short and increasing spacing, line spacing will generally take set to 8 mil.
Welding disc hole edge to the distance from the edge of the PCB is greater than 1 mm, so that you can avoid solder defects due to process. When connected to the welding plate is fine, get the line to connect between the pads and go line design into water droplets, such are the benefits of bonding pad is not easy to peel, but go line and welding plate is not easy to disconnect.
Three, components layout practice has proved that even if the principle diagram of the circuit design is correct, improper printed circuit board design, also can produce adverse effect on the reliability of electronic equipment. If, for example, two parallel lines in close proximity, PCB will form the signal delay, reflection noise in transmission line terminal formation; Due to power supply, the ground wire is not considerate, can make the product performance degradation, therefore, in the design of printed circuit board, should pay attention to the right way. Each switch power supply with four current loop:
(1). The power switch (2) communication circuit, the output rectifier ac circuit (3). The input signal source current loop
(4). The output load current loop input circuit through an approximation of the dc current of input capacitance charging, filter capacitance is mainly a broadband energy storage effect; Similarly, the output filter capacitor is used to store from high frequency energy output of the rectifier, eliminate the load circuit of the dc power output at the same time. So, the input and output filter capacitor terminal is very important, input and output current loop should be only from the terminal filter capacitor is connected to the power supply; If the input/output circuit and the connection between the power switch/rectifier circuit cannot be attached directly to the terminal of capacitor, energy will be composed of input or output filter capacitor and radiation to the environment. Power switch ac circuits and the communication of the rectifier circuit contains high of trapezoidal current, the current in the harmonic components is very high, its frequency is greater than the switch base frequency, the peak amplitude of up to 5 times for the amplitude of the input/output dc current, transition time is usually about 50 ns. The two circuits are most likely to produce electromagnetic interference, so must the other printed wiring in power source to cloth before these ac circuits, each circuit of three main components of the filter capacitor, power switch rectifier, inductor or transformer shall be placed adjacent to each other, adjust the current path between the component location makes them short.
To be continued