Switching power supply PCB layout technology rules and applications
Today, proper power supply PCB layout techniques are very important as switching power supplies generate electromagnetic waves that can affect the proper functioning of their electronics.
In many cases, a power supply that is perfectly designed on paper may not work properly when it is first commissioned due to a number of problems with the PCB layout of the power supply. For example, for a consumer electronic device on the step-down switching power supply schematic, the designer should be able to distinguish between the power circuit components and control signal circuit components on this circuit diagram, but if the designer will be all the components of this power supply as if they were digital circuits, the same components, then the problem will be quite serious. Switching power supply PCB layout and digital circuit PCB layout is completely different. In the digital circuit layout, many digital chips can be automatically arranged through the PCB software and the connection line between the chip can be automatically connected through the PCB software. With the automatic layout of the layout of the switching power supply can not work properly. Therefore, designers need to master and understand the correct PCB layout technology rules of switching power supply.
Switching power supply PCB layout technology rules
Bypass ceramic capacitor capacity can not be too large, and its parasitic series inductance should be minimized. Multiple capacitors in parallel
Coupling can improve the high frequency impedance characteristics of capacitors
When a capacitor operating frequency in the fo below, capacitance impedance Zc with the rise of frequency and reduce; when the capacitor operating frequency in the fo above, capacitance impedance Zc will become like the inductive impedance with the rise of frequency and increase; when the capacitor operating frequency is close to fo, capacitance impedance is equal to its equivalent series resistance (RESR).
Electrolytic capacitors generally have a large capacitance and a large equivalent series inductance. Because of its low resonant frequency, it can only be used for low frequency filtering. Tantalum capacitors generally have a large capacitance and a small equivalent series inductance, so their resonant frequency will be higher than that of electrolytic capacitors, and they can be used in medium and high frequency filtering. Porcelain chip capacitor capacitance and equivalent series inductance are generally very small, so its resonant frequency is much higher than electrolytic capacitors and tantalum capacitors, so it can be used in high-frequency filtering and bypass circuits. As the resonant frequency of small capacitance ceramic capacitors will be higher than the resonant frequency of large capacitance ceramic capacitors, so in the
Selection of bypass capacitors can not just choose the capacitance value is too high ceramic capacitors. In order to improve the high-frequency characteristics of capacitors, several capacitors with different characteristics can be connected in parallel. Is a number of different characteristics of the capacitor in parallel to improve the impedance effect. By analyzing it is not difficult to understand the importance of this layout rule.) Shows the different ways of aligning the input power (VIN) to the load (RL) on a PCB. In order to reduce the ESL of the filter capacitor (C), the lead length of the capacitor pins should be kept as short as possible: the alignment of VIN positive to RL and VIN negative to RL should be as close as possible.
