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The Principle Of PCB Design

2017-06-19 15:26:52 | 日記

Power supply circuit is an important part of electronic products, power circuit design is good or bad, directly related to product performance is good or bad. Our electronic products are mainly power supply circuit with high-frequency power supply and high-frequency switching power supply. In theory, the linear power supply is how much current the user needs, how much current the input will provide; the switching power supply is how much power the user needs, and how much power is provided at the input.

Linear power supply devices work in a linear state, such as our commonly used regulator chip LM7805, LM317, SPX1117 and so on.

Linear power supply is rectifier, filter, regulator, energy storage and other functional components, at the same time, the general use of linear power supply for the series power supply, the output current is equal to the input current, I1 = I2 + I3, I3 is the reference side, the current is very small , So I1 ≈ i3. Why should we talk about the current, because the PCB design, the width of each line is not casually set, is based on the schematic diagram of the current between the components of the node to determine the size. Current size, current flow to find out, doing the board is just right.

PCB design, the layout of the electronic components to be compact, so that all the connections as short as possible, according to the schematic components of the relationship between the components to the layout and alignment. The power map is the first rectifier, and then filter, filter is the regulator, the regulator is the energy storage capacitor, after the capacitor to the back of the circuit after the electricity. Figure 2 is the schematic diagram of the PCB above, the two maps are similar. Left and right is the line is a bit different, the left side of the power supply after rectification directly to the regulator chip input pin, and then is the regulator capacitor, where the capacitance of the filter effect sent a lot of difference, there are problems on the output. The right figure is a better map. We must not only consider the flow of the power supply problem, but also must consider the return problem, in general, the positive power line and ground return line as much as possible with the same, close to each other. It adds the cr123a battery.

Design of linear power PCB should also pay attention to the linear power supply voltage regulator chip cooling problem, how is the heat, if the regulator chip front voltage is 10V, the output is 5V, the output current of 500mA, that in the regulator chip There is a voltage drop of 5V, the heat generated on the 2.5W; if the input voltage is 15V, the voltage drop is 10V, the heat generated on the 5W, so we cloth is to be based on cooling power to make enough Cooling space or a reasonable heat sink. Linear power supply is generally used in the relatively small pressure, the current is relatively small occasions, otherwise, please switch the switching power supply circuit.

High frequency switching power supply
Switching power supply is through the circuit control switch for high-speed conduction and cut-off, resulting in PWM waveform, through the inductor and freewheeling diode, the use of electromagnetic conversion method of voltage regulator. Switching power supply power, high efficiency, heat is small, we generally use the circuit are: LM2575, MC34063, SP6659 and so on. Switching power supply is theoretically equal to the power at both ends of the circuit, the voltage is inversely proportional to the current inversely proportional.

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