First, let's start with the design and production process of the switching power supply. Let's talk about the design of the printed board. Switching power supplies operate at high frequencies and high pulse states and are a special type of analog circuit. The layout of the high frequency circuit must be followed when laying the board.

1. Layout: The pulse voltage connection is as short as possible. The input switch is connected to the transformer and the output transformer is connected to the rectifier. The pulse current loop is as small as possible as the input filter capacitor is positive to the return capacitance of the transformer to the switch. Output part of the transformer output to the rectifier to the output inductor to the output capacitor return transformer circuit X capacitor should be as close as possible to the input end of the switching power supply, the input line should avoid parallel with other circuits, should be avoided. The Y capacitor should be placed at the chassis ground terminal or FG connector. The total inductance is kept at a certain distance from the transformer to avoid magnetic coupling. If it is not handled well, a shield can be added between the common inductor and the transformer. The above items have a great influence on the EMC performance of the switching power supply.

The output capacitor can generally be used with two ones close to the rectifier and the other should be close to the output terminal, which can affect the output ripple index of the power supply. The parallel effect of two small-capacity capacitors should be better than using a large-capacity capacitor. The heating device should be kept at a certain distance from the electrolytic capacitor to extend the life of the whole machine. The electrolytic capacitor is the bottle strength of the switching power supply life. For example, the transformer, the power tube, the high-power resistor should be kept away from the electrolysis, and the heat dissipation space must be left between the electrolysis. , conditions allow it to be placed at the air inlet.

The control part should pay attention to: the high-impedance weak signal circuit connection should be as short as possible, such as the sampling feedback loop. In the processing, try to avoid the interference, current sampling signal circuit, especially the current control type circuit, the processing is not easy, some unexpected The accident, there are some tricks, now take the example of 3843 circuit (1) Figure 1 is better than Figure 2, Figure 2 is full of oscilloscope to observe the current waveform on the superimposed spikes, due to the interference limit point than the design value Low, Figure 1 does not have this phenomenon, there is a switch tube drive signal circuit, the switch tube drive resistance should be close to the switch tube, which can improve the operational reliability of the switch tube, which is related to the high DC impedance voltage drive characteristics of the power MOSFET.

Line spacing: With the continuous improvement and improvement of the printed circuit board manufacturing process, there is no problem in the general processing factory to make the line spacing equal to or less than 0.1mm, which can fully satisfy most applications. Considering the components and production process used in the switching power supply, the minimum line spacing of the dual-panel is set to 0.3mm, the minimum line spacing of the single-panel is set to 0.5mm, and the pads and pads, pads and vias or vias are used. Holes with a minimum spacing of 0.5mm avoid "bridging" during soldering operations. Therefore, most of the board manufacturers can easily meet the production requirements, and can control the yield very high, and can achieve reasonable wiring density and a more economical cost.

The minimum line spacing is only suitable for the signal control circuit and the low voltage circuit with a voltage lower than 63V. When the line voltage is greater than this value, the line spacing can generally be taken according to the empirical value of 500V/1mm.

In view of the fact that there are some related standards that have clear provisions on the line spacing, it must be strictly in accordance with the standard, such as the AC inlet end to the fuse end connection. Some power supplies are very demanding, such as module power. The general transformer input side line spacing of 1mm has proven to be feasible. For AC input, (isolated) DC output power products, the stricter rule is that the safety spacing should be greater than or equal to 6mm, which is determined by the relevant standards and implementation methods. The general safety spacing can be taken as the reference by the distance between the two sides of the feedback optocoupler. The principle is greater than or equal to this distance. It is also possible to slot the printed circuit board under the optocoupler to increase the creepage distance to meet the insulation requirements. Generally, the spacing of the AC input side of the switching power supply or the components on the board is not more than 5mm from the non-insulated housing, and the distance between the output side wiring or the device from the housing or the heat sink is greater than 2mm, or strictly in accordance with safety regulations.

Common methods: The above mentioned method of slotting the circuit board is suitable for some occasions where the spacing is not enough. By the way, this method is also commonly used as a protection discharge gap, which is common in the TV picture tube tail plate and the power AC input. . This method has been widely used in module power supply and can achieve good results under potting conditions.

Method 2: pad insulation paper, which can be insulated materials such as green paper, polyester film, and PTFE oriented film. Generally, the general-purpose power supply uses a green paper or a polyester film pad between the circuit board and the metal casing. This material has high mechanical strength and has a certain resistance to moisture. PTFE oriented film is widely used in module power supplies due to its high temperature resistance. An insulating film may also be interposed between the component and the surrounding conductor to improve the insulation resistance.

Note: Some device insulation covers cannot be used as an insulating medium to reduce the safety spacing, such as the outer skin of electrolytic capacitors, which may be subject to heat shrinkage under high temperature conditions. Space should be left at the front end of the large electrolytic explosion-proof tank to ensure that the electrolytic capacitor can be unimpeded in the extreme case.

Printed copper sheet wiring precautions

Trace current density: Most electronic circuits are now made of insulating plates. The copper thickness of the common circuit board is 35μm, and the current density value can be taken according to the empirical value of 1A/mm. For the specific calculation, please refer to the textbook. In order to ensure the mechanical strength of the routing, the line width should be greater than or equal to 0.3mm (other non-power circuit boards may have a smaller minimum line width). The copper thickness is 70μm. The circuit board is also commonly used in switching power supplies, so the current density can be higher.

In addition, the commonly used circuit board design tool software generally has design specifications, such as line width, line spacing, dry disk via size and other parameters can be set. When designing a circuit board, the design software can be automatically executed according to specifications, saving a lot of time, reducing part of the workload and reducing the error rate.

Generally, a double panel is used for a line or wiring line having a relatively high reliability requirement. It is characterized by moderate cost and high reliability, which can satisfy most applications.

Some products in the module power supply line also use multi-layer boards, which are mainly convenient for integrating power devices such as transformer inductors, optimizing wiring and power tube heat dissipation. The utility model has the advantages of good process consistency and good heat dissipation of the transformer, but the disadvantage is that the cost is high and the flexibility is poor, and it is only suitable for industrial large-scale production.

Single-panel, market-distributed general-purpose switching power supplies almost all use single-sided circuit boards, which have the advantage of low cost, and some measures in design and production process can also ensure their performance.

Today, I talk about some experience of single-sided printed board design. Because of the low cost and easy manufacturing, single-panel is widely used in switching power supply lines. Because it only has one side of copper, the electrical connection of the device and the mechanical fixing must be Rely on that layer of copper, you must be careful when handling.

In order to ensure good soldering mechanical structure performance, the single-panel pad should be slightly larger to ensure good bonding force between the copper foil and the substrate, without being peeled off or broken when subjected to vibration. Generally, the width of the soldering ring should be greater than 0.3mm. The diameter of the pad hole should be slightly larger than the diameter of the device pin, but it should not be too large. The distance between the pin and the pad is the shortest. The size of the hole does not hinder the normal inspection. The diameter of the pad hole is generally larger than the diameter of the pin by 0.1-0.2mm. The multi-pin device can also be larger to ensure smooth inspection.

The electrical connection should be as wide as possible. The width of the principle should be larger than the diameter of the pad. In special cases, the line must be widened at the intersection with the pad (commonly known as teardrop formation) to avoid breakage in certain condition lines and pads. The principle minimum line width should be greater than 0.5mm.

The components on the single panel should be close to the circuit board. For devices that require overhead heat dissipation, it is necessary to add a sleeve to the pin between the device and the circuit board to support the device and increase the insulation. To minimize or avoid external force impact on the pad and pin connection. The effect is enhanced to enhance the firmness of the weld. The heavier components on the board can increase the support connection point and strengthen the connection strength with the circuit board, such as transformers, power device heat sinks.

The single-panel soldering surface pin can be left longer without affecting the distance between the outer casing and the outer casing. The advantage is that the strength of the welded part can be increased, the welding area can be increased, and the phenomenon of virtual welding can be found immediately. When the pin is cut long, the welded part is less stressed. In Taiwan and Japan, the process of bending the device pins on the soldering surface at a 45-degree angle to the board and then soldering is the same as above. Today, I will talk about some of the issues in the dual-panel design. In some application environments where the requirements are relatively high, or the density of the traces is relatively large, the performance of the double-sided printed board is much better than that of the single panel.

The double-pad pad has a higher metallization strength than the hole, and the solder ring can be smaller than the single-layer. The hole diameter of the pad hole is slightly larger than the diameter of the pin, because the solder solution penetrates into the top layer through the solder hole during the soldering process. Pads to increase soldering reliability. However, there is a drawback. If the hole is too large, some devices may float under the impact of the jet tin during wave soldering, causing some defects.

For the processing of large current traces, the line width can be processed according to the previous post. If the width is not enough, it can generally be solved by adding tin to the trace on the trace to solve the problem.

1. Set the trace to the pad property so that the trace is not covered by the solder resist when the board is manufactured, and the hot air is plated with tin.

2. Place the pad at the wiring and set the pad to the shape that requires the trace. Be careful to set the pad hole to zero.

3, placing the wire in the solder mask, this method is the most flexible, but not all circuit board manufacturers will understand your intention, you need to use text description. No solder resist is applied to the place where the solder mask is placed.

Several methods of tinning the line are as above. It should be noted that if the wide traces are all plated with tin, after soldering, a large amount of solder will be bonded, and the distribution is uneven, which affects the appearance. Generally, the width of tin plating can be 1~1.5mm, the length can be determined according to the line, and the tin plating part is 0.5~1mm. The double-sided circuit board provides great selectivity for layout and routing, which can make wiring more. It tends to be reasonable. Regarding the grounding, the power ground and the signal ground must be separated, and the two grounds can be merged at the filter capacitor to avoid the occurrence of unstable accidental factors caused by the large pulse current passing through the signal ground. The signal control loop uses a grounding method as much as possible. There is a trick to place ungrounded traces on the same wiring layer and finally on the other layer. The output line generally passes through the filter capacitor and then to the load. The input line must also pass through the capacitor and then to the transformer. The theoretical basis is to let the ripple current pass through the travel filter capacitor.

Voltage feedback sampling, in order to avoid the influence of large current through the trace, the sampling point of the feedback voltage must be placed at the end of the power output to improve the load effect of the whole machine.

The change of the trace from one wiring layer to the other is generally via vias, which should not be achieved through the device pin pads, because it is possible to break the connection when the device is inserted, and when every 1A current is passed. There should be at least 2 vias, the via hole principle should be greater than 0.5mm, and generally 0.8mm to ensure processing reliability.

The device dissipates heat. In some low-power power supplies, the circuit board traces can also function as a heat sink. The feature is that the traces are as wide as possible to increase the heat dissipation area, and no solder resist is applied. The vias can be uniformly placed to enhance the thermal conductivity. .

Fuel Oil Control Panel

Due to electrical equipment installed in heating control switchboard the distribution of electrical energy maybe controlled automatically. Sensors installed in the facility, give information about ambient temperature, temperature of the object and temperature of the inner medium of the object.

Then, depending on the information received and set working modes, automatic Control Cabinet will switch on or switch off the heating, increase or decrease necessary temperature. Thus, the use of heating switchboard ensures proper and economical energy management, as well as rapid response and prevention of emergency situations.

Performed main tasks are following:
switching of high-power power supply and heating sections for the roof and gutter systems, water pipes and large diameter tanks, parts of the object in the open air, electrical systems, floor heating in the buildings or in the open areas;
Protection against electrocution;
Protection against short-circuit.

Functionality of the heating systems control cabinet
Functions of heating control system may differ depending on the requirements and specifications of the customer. Main functions are:

the possibility to switch control modes (manual or automatic);
maintain the set temperature of the heated object;
operating mode control;
Heating equipment protection from overheating, over current(overload), short circuit protection;
a complete and safe shutdown of heating equipment from the power supply in case of accidents.

Thermal Oil Control Panel,Thermal Oil Control Box, Fuel Oil Control Panel, Marine Fuel Oil Control Console

Nantong Double Star Automation Equipment Co., Ltd. , https://www.nt-doublestar.com