Design input current source circuit and input filter design output load circuit and output filter according to the functional unit of the circuit, layout of all components of the circuit should conform to the following principles:
(1) the PCB size should be considered first.
When the PCB size is too large, the length of the printed line increases, the impedance increases, the anti-noise capability decreases, and the cost increases.Too small is not good heat dissipation, and adjacent lines are vulnerable to interference.The optimum rectangular shape of the circuit board, with a length/width ratio of 3:2 or 4:3, is the component on the edge of the circuit board, which is not less than 2mm from the edge of the circuit board.
(2) when placing devices, consider welding in the future, not too dense.
(3) center on the core elements of each functional circuit and arrange around it.The components should be uniformly, neatly and compactly arranged on the PCB, and the leads and connections between the components should be minimized and shortened. The decoupling capacitors should be as close to the VCC of the components as possible.
(4) the distribution parameters between components should be considered for the circuit operating at high frequency.General circuits should be as close to parallel as possible.In this way, not only beautiful, and easy to install welding, easy to mass production.
(5) arrange the position of each functional circuit unit according to the circuit process, make the layout convenient for signal flow, and keep the signal as consistent as possible.
(6) the first principle of layout is to guarantee the routing rate of the wiring, pay attention to the connection of flight wires when moving devices, and put the connected devices together.
(7) reduce the loop area as much as possible to inhibit the radiation interference of the switching power supply.
High frequency signals are included in the wiring switch power supply. Any printed line on the PCB can act as an antenna. The length and width of printed line will affect its impedance and inductance, thus affecting the frequency response.Even the printed wires passing through the dc signal are coupled from the adjacent printed wires to the radio frequency signal and cause circuit problems (or even radiate out the interfering signals again).Therefore, all printed wires passing through the ac current should be designed as short and wide as possible, which means that all components connected to the printed wires and connected to other power cords must be placed close together.The length of the printed line is directly proportional to the inductance and impedance, while the width is inversely proportional to the inductance and impedance of the printed line.The length reflects the wavelength of the printed line response. The longer the length, the lower the frequency of the printed line to transmit and receive electromagnetic waves, the more radio-frequency energy it radiates.According to the size of printed circuit board current, increase the power line width and reduce the loop resistance.At the same time, make the direction of the power cord and ground wire and the direction of the current consistent, which helps to enhance the anti-noise ability.Ground is the bottom branch of the four current circuits of switching power supply. As the common reference point of the circuit, it plays an important role.