Switching Power Supply Component Layout and Printed Circuit Board Wiring
The radiated nuisance of a switching power supply is proportional to the product of the current size in the current path, the loop area of the path, and the square of the current frequency, i.e., the radiated nuisance E ∝ I-A-f2. The prerequisite for the application of this relationship is that the size of the path is much smaller than the wavelength of the frequency.
The above equation shows that reducing the pathway area is the key to reducing the radiated nuisance, which means that the components of the switching power supply should be closely arranged with each other. In the primary circuit, the input capacitor, transistor and transformer are required to be close to each other, and the wiring is compact; in the secondary circuit, the diode, transformer and output capacitor are required to be close to this.
On the printed circuit board, the positive load current conductors on both sides of the printed circuit board, and try to make the two current-carrying conductors parallel to each other, because parallel close to the positive load current conductors generated by the external magnetic field tends to cancel each other out.
Electromagnetic coupling between the wiring is carried out through the electric and magnetic fields, so in the wiring, attention should be paid to the electric field and magnetic field coupling suppression. The suppression of electric field methods are
1) try to increase the distance between the lines, so that the capacitive coupling is * small;.
2) use electrostatic shielding, shielding layer to be grounded; and
3) reduce the input impedance of the sensitive line.
The magnetic field suppression methods are
1) Reduce the source of nuisance and sensitive circuit loop area; 2) Increase the inter-wire area; 3) Reduce the input impedance of sensitive circuits.
2) Increase the distance between the lines, so that the coupling nuisance sources and sensitive circuits between the mutual inductance as small as possible.
3) It is best to make the source of nuisance and sensitive circuits at right angles to the wiring, in order to greatly reduce the coupling between the lines.
