“In life, you may have been exposed to various Electronic products, then you may not know some of its components, such as the switching power supply that it may contain, then let the editor lead everyone to learn the switching power supply layout and Some principles of printed board wiring.
In life, you may have been exposed to various electronic products, then you may not know some of its components, such as the switching power supply that it may contain, then let the editor lead everyone to learn the switching power supply layout and Some principles of printed board wiring.
The input switch tube is connected to the transformer, and the output transformer is connected to the rectifier tube. The pulse voltage connection should be as short as possible. The pulse current loop is as small as possible. For example, the input filter capacitor is positive for the transformer of the switch tube, and the return capacitor is negative. The X capacitor from the output part of the transformer to the output of the rectifier to the output capacitance of the output Inductor and back to the transformer circuit should be as close as possible to the input end of the switching power supply and the input line should be avoided in parallel with other circuits. The Y capacitor should be placed on the ground terminal or FG connection end of the chassis. Keep a certain distance between the common contact inductor and the transformer to avoid magnetic coupling. If it is not easy to handle, you can add a shielding layer between the common-mode inductor and the transformer. The above items have a greater impact on the EMC performance of the switching power supply.
Generally, two output capacitors can be used, one close to the rectifier and the other close to the output terminal, which will affect the output ripple index of the power supply. The parallel effect of two small-capacity capacitors should be better than that of large-capacity capacitors. The heating device must keep a certain distance from the electrolytic capacitor to extend the service life of the entire machine. Electrolytic capacitors are the key to the life of switching power supplies. For example, transformers, power tubes and high-power resistors must be far away from electrolysis, and there must be a space for heat dissipation between electrolysis. If possible, it can be placed in the air inlet.
Pay attention to the control part: the connection of the high impedance weak signal circuit should be as short as possible, such as the sampling feedback loop. When handling, please try to avoid interference. Current sampling signal circuits, especially current control circuits, are not easy to handle.
Line spacing: With the continuous improvement and perfection of the printed circuit board manufacturing process, the line spacing of general processing plants is equal to or less than 0.1mm without any problem, which can fully meet the requirements of most applications. Taking into account the components and production processes used in the switching power supply, usually the minimum line spacing of the double panel is set to 0.3mm, the minimum line spacing of the single panel is set to 0.5mm, and the minimum spacing between the pads, pads and The through-hole or through-hole is set to 0.5mm to avoid “bridging” during the soldering operation. In this way, most board factories can easily meet the production requirements, can control the yield rate very high, and can also achieve a reasonable wiring density and have a more economical cost. The minimum line spacing is only applicable to signal control circuits and low-voltage circuits with a voltage lower than 63V. When the line-to-line voltage is greater than this value, the line spacing can usually be selected according to the empirical value of 500V/1mm.
In view of the fact that some relevant standards have clear regulations on the line spacing, it must be strictly implemented in accordance with the relevant standards, such as the connection between the AC input terminal and the fuse terminal. Some power supplies have high requirements for volume, such as modular power supplies. Usually, the line spacing on the input side of the transformer is 1mm, which has proved feasible in practice. For power products with AC input and (isolated) DC output, the stricter rule is that the safety distance must be greater than or equal to 6mm. Of course, this depends on the relevant standards and implementation methods. Generally, the safety distance can be represented by the distance on both sides of the feedback optical coupler, and the principle is that it is greater than or equal to this distance. Slots can also be made on the printed circuit board under the optocoupler to increase the creepage distance to meet the insulation requirements. Generally, the distance between the AC input side wiring or board assembly of the switching power supply and the non-insulated housing and radiator should be greater than 5mm, and the distance between the output side wiring or assembly and the housing or radiator should be greater than 5mm. Than 2mm, or strictly abide by safety regulations.
Common method: The above slotting method is suitable for occasions with insufficient spacing. By the way, this method is usually also used to protect the discharge gap, which is very common in the AC input and power supply of the TV picture tube tail board. This method has been widely used in modular power supplies, and good results can be obtained under potting conditions.
Method 2: Use insulating paper. Insulating materials such as blue-shell paper, polyester film, PTFE oriented film, etc. can be used. Generally, green shell paper or polyester film is used as a general power source to fill between the circuit board and the metal shell. The material has high mechanical strength and certain moisture resistance. PTFE oriented film is widely used in module power supply due to its high temperature resistance. An insulating film can also be placed between the component and the surrounding conductors to improve the insulation resistance.