外文文献：
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.
First, 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
