开关电源设计及其英文翻译.doc

Switching Power Supply Design
Switching power supply work in high frequency, high pulse state, are analog circuits in a rather special kind. Cloth boards to follow the principle of high-frequency circuit wiring.

1, layout:
Pulse voltage connection as short as possible including input switch connected to the transformer, output transformer to the rectifier tube cable. Pulse current loop as small as possible such as the input filter capacitor is returned to the transformer to the switch capacitor negative. Some out-ended output transformers are the output rectifier to the output capacitor back to transformer circuit X capacitor as close as possible to the input switching power supply, input lines should be avoided in parallel with other circuits, should be avoided. Y capacitor should be placed in the chassis ground terminal or FG connectors. A total of touch induction and transformer to maintain a certain distance in order to avoid magnetic coupling. Such as poor handling of feeling in between inductor and transformer plus a shield, over a number of EMC performance for power supply to the greater impact.
General the output capacitor can be used the other two a close rectifier output terminal should be close to, can affect the power supply output ripple index, two small capacitor in parallel results should be better than using a large capacitor. Heating devices to maintain a certain distance, and electrolytic capacitors to extend machine life, electrolytic capacitors is the switching power supply bottleneck life, such as transformers, power control, high power resistors and electrolytic to maintain the distance required between the electrolyte leaving space for heat dissipation , conditions permitting, may be placed in the inlet.
Control part to pay attention to: Weak signal high impedance circuit connected to sample the feedback loop as short as in the processing as far as possible avoid interference, the current sampling signal circuits, in particular the current control circuit, easy to deal with some unexpected bad The accident, which had some skill, now to 3843 the circuit example shown in Figure (1) Figure 1 better than Yu Figure 2, Figure 2 Zai full time by observing the current waveform oscilloscope Mingxian superimposed spikes, Youyuganrao limited flow ratio design Zhi Dian low, Figure 1 there is no such phenomenon, there are switch drive signal circuit, switch resistance should be close to the switch driver can switch the work to improve the reliability of this and the high DC impedance voltage power MOSFET driver characteristics.
Second, routing
Alignment of current density: now the majority of electronic circuit board using insulated copper constitute tied. Common PCB copper thickness of 35μm, the alignment value can be obtained in accordance with 1A/mm experience the value of current density, the specific calculations can be found in textbooks. To ensure the alignment principles of mechanical strength should be greater than or equal to the width of 0.3mm (other non-power supply circuit board may be smaller minimum line width). PCB copper thickness of 70μm is also common in switching power supply, then the current density can be higher.
Add that, now Changyong circuit board design tool design software generally items such as line width, line spacing, hole size and so dry plate Guo Jin Xing parameters can be set. In the design of circuit boards, design software automatically in accordance with the specifications, can save time, reduce some of the workload and reduce the error rate.
Generally higher on the reliability of lines or line density wiring can be used double panel. Characterized by moderate cost, high reliability, to meet most applications.
The ranks of some of the power module products are also used plywood, mainly to facilitate integration of power devices such as transformer inductance to optimize wiring, cooling and other power tube. Good consistency with the craft beautiful, transformer cooling good advantage, but its disadvantage is high cost, poor flexibility, only suitable for industrial mass production.

Single-sided, the market circulation of almost universal switching power supply using single-sided circuit board, which has the advantage of lower costs in the design and production technology are also taken some measures to ensure its performance.
Single PCB design today to talk about some experience, as a single panel with low cost, easy-to-manufacture features, the switching power supply circuit has been widely used, because of its side tied only copper, the device's electrical connections, mechanical fixation should rely on the copper layer, the processing must be careful.
To ensure good performance of the mechanical structure welding, single-sided pad should be slightly larger to ensure that the copper and substrate tied good focus, and thus will not be shocked when the copper strip, broken off. General welding ring width should be greater than 0.3mm. Pad diameter should be slightly larger than the diameter of the device pins, but not too large, to ensure pin and pad by the solder connection between the shortest distance, plate hole size should not hinder the normal conditions for the degree of investigation, the pad diameter is generally greater than pin diameter 0.1-0.2mm. Multi-pin device to ensure a smooth investigation documents can also be larger.
Electrical connection should be as wide as possible, in principle, should be larger than the width of pad diameter, special circumstances should be connected in line with the need to widen the intersection pad (commonly known as Generation tears), to avoid breaking certain conditions, line and pad. Principle of minimum line width should be greater than 0.5mm.
Single-board components to be close to the circuit board. Need overhead cooling device to device and circuit board between the pins plus casing, can play a supporting device and increase the dual role of insulation to minimize or avoid external shocks on the pad and the pin junction impact and enhance the firmness of welding. Circuit board supporting the weight of large parts can increase the connection point, can enhance joint strength between the circuit board, such as transformers, power device heat sink.
Single-sided welding pins without affecting the surface and the shell spacing of the prior conditions, it can be to stay longer, the advantage of increased strength of welded parts, increase weld area and immediately found a Weld phenomenon. Shear pin long legs, the welding force smaller parts. In Taiwan, the Japanese often use the device pins in the welding area and the circuit board was bent 45 degrees, and then welding process, its reasoning Ibid. Double panel today to talk about the design of some of the issues, in relatively high number of requests, or take the line density of the larger application environments using double-sided PCB, its performance and various indicators of a lot better than a single panel.
Two-panel pad as holes have been high intensity metal processing welding ring smaller than a single panel, the pad hole diameter slightly larger in diameter than pins, as in the welding process solder solution conducive to penetrate through the top hole solder pad to increase the welding reliability. But there is a disadvantage if the hole is too large, wave soldering tin when the jet impact in the lower part of the device may go up, have some flaws.
High current handling of alignment, line width in accordance with pre-quote processing, such as the width is not enough to go online in general can be used to increase the thickness of tin plating solution, the method has a good variety of
1. Will take the line set to pad property, so that when the circuit board manufacturing solder alignment will not be covered, the whole hot air normally be tin plated.
2. In the wiring by placing pads, the pad is set to take in line shape, pay attention to the pad holes set to zero.
3. In the solder layer placed on line, this method is the most flexible, but not all PCB manufacturers will understand your intentions, needed captions. Place the line in the solder layer of the site will not coated solder tinning line several methods as above, to note that, if the alignment of a very wide all plated with tin in solder after the solder will bond a lot and distribution is very uneven, affecting appearance. Article tin can be used generally slender width in the 1 ~ 1.5mm, length can be determined according to lines, tin part of the interval 0.5 ~ 1mm
Double-sided circuit board for the layout, the alignment provides a very selective, make wiring more reasonable. On the ground, the power ground and signal ground must be separated, the two to converge in filter capacitors, in order to avoid a large pulsed current through the signal ground connection instability caused by unexpected factors, the signal control circuit grounding point as far as possible, a skill, as far as possible the alignment of the non-grounded wiring layer in the same place, the last shop in another layer of earth. Output line through the filter capacitors, the general first, and then to the load, input line must also pass capacitor, to the transformer, the theoretical basis is to ripple through trip filter capacitor.
Voltage feedback sampling, in order to avoid high current through the alignment of the feedback voltage on the sampling point must be the most peripheral power output to increase the load effect of target machine.
Alignment change from a wiring layer to another wiring layer generally used hole connected, not through the pin pad device to achieve, because the plug in the device may be damaged when the relationship between this connection, there is current in every passage of 1A, at least two through-hole, through hole diameter is greater than the principle of 0.5mm, 0.8mm generally processed ensure reliability.
Cooling devices, in some small power supply, the circuit board traces can be and cooling, characterized by the alignment as generous as possible to increase the cooling area is not coated solder, conditions can even be placed over holes, enhanced thermal conductivity .
Today to talk about the aluminum plate in the switching power supply application and multilayer printed circuit in the switching power supply applications.
Aluminum plate by its own structure, has the following characteristics: very good thermal conductivity, single Mianfu copper, the device can only be placed in tied copper surface, can not open electrical connection hole so as not to place jumper in accordance with a single panel.
Aluminum plate is generally placed patch device, switch, the output rectifier heat conduction through the substrate to go out, very low thermal resistance, high reliability can be achieved. Transformer with planar chip structure, but also through substrate cooling, the temperature is lower than the conventional, the same size transformer with a large aluminum plate structure available output power. Aluminum plate jumper bridge approach can be used. Aluminum plate power are generally composed by the two PCB, another one to place the control circuit board, through the physical connection between the two boards is integrated.
As the excellent thermal conductivity of aluminum plate, in a small amount of manual welding more difficult, solder cooling too fast and prone to problems of a simple and practical way of existing, an ironing ordinary iron (preferably temperature regulation function), over and iron for the last, fixed, and temperature to 150 ℃ and above the aluminum plate on the iron, heating time, and then affix the components according to conventional methods and welding, soldering iron temperature is appropriate to the device easy to , is too high when the device may be damaged, or even copper strip aluminum plate, the temperature is too low welding effect is not good, to be flexible.
Recent years, with the multi-layer circuit board applications in switching power supply circuit, printed circuit transformer makes it possible, due to multilayer, smaller spacing also can take advantage of Bianya Qi window section, the main circuit board can be re- Add 1-2 formed by the multilayer printed coil to use the window, the purpose of reducing circuit current density, due to adopt printed coil, reducing manual intervention, transformers consistency, surface structure, low leakage inductance, coupling good . Open-type magnetic core, good heat dissipation. Because of its many advantages, is conducive to mass production, it is widely used. But the research and development of large initial investment, not suitable for small-scale health.
Switching power supply is divided into, two forms of isolation and non-isolated, isolated here mainly to talk about switching power supply topologies form below, non-specified, are to isolate the power. Isolated power supply in accordance with the structure of different forms, can be divided into two categories: a forward and flyback. Flyback transformer primary side means that when the Vice-edge conduction cut-off, transformer storage. Close of the primary, secondary side conduction, the energy released to the load of work status, general conventional flyback power multiplex, twin-tube is not common. Forward refers to the primary conduction in transformer secondary side while the corresponding output voltage is induced into the load, the direct transfer of energy through the transformer. According to specifications can be divided into conventional forward, including the single-transistor forward, Double Forward. Half-bridge, bridge circuits are all forward circuit.
Forward and flyback circuits have their own characteristics in the process of circuit design to achieve optimal cost-effective, can be applied flexibly. Usually in the low-power flyback can be adopted. Slightly larger forward circuit can use a single tube, medium-power can use Double Forward circuit or half-bridge circuit, low-voltage push-pull circuit, and the half-bridge work in the same state. High power output, generally used bridge circuit, low voltage can be applied push-pull circuit.
Flyback power supply because of its simple structure, and to cut the size of a similar size and transformer inductance, the power supply in the medium has been widely applied. Presentation referred to in some flyback power supply can do dozens of watts, output power exceeding 100 watts would be no advantage to them difficult. Under normal circumstances, I think so, but it can not be generalized, PI's TOP chips can do 300 watts, an article describes the flyback power supply can be on the KW, but not seen in kind. Power output and the output voltage level.