Anti-interference of switch power supply in microcomputer and monitoring system

Switching power supplies have advantages such as high efficiency and are widely used in electronic equipment. Although some switching power supplies use electrostatic shielding to suppress common-mode interference, the internal components of the switching power supply are arranged relatively closely, the distance between the power supply and the output line wire is relatively close, and the grounding wire is relatively long, so the ability to prevent external interference is poor, especially at high frequencies. Usually, a power filter is added at the power inlet to prevent the intrusion of power interference. The grounding point of the filter should be reliably grounded at the shortest distance. All power lines must pass through the filter before entering the equipment, that is, the filter is installed at the power line inlet of the chassis.

Microcomputer protection and monitoring devices require multiple independent power supplies. It is best to use independent functional block power supplies on each plug-in board to further control mutual interference.

Isolation measures. Isolation measures to prevent interference from endangering the protection device mainly include the following aspects: AC signals such as AC voltage, current, and power can be converted into DC quantities through a transmitter and sent to the microcomputer to prevent interference from AC signals. The AC quantities are isolated by small intermediate voltage transformers and current transformers to isolate the AC "ground" from the DC "ground" and increase the system's anti-interference ability. All analog quantities are isolated by the photoelectric isolation unit before being sent to the host, so that the power ground wires of the internal and external systems of the microcomputer are completely isolated electrically, improving the system's anti-interference ability.

All switch input and output (including trip output, signals to be monitored, etc.) contacts and digital output (such as printer interface) during substation operation should be photoelectrically isolated.

Shielding. The casing is made of iron material to achieve shielding of electric and magnetic fields. Double-layer shielding measures should be adopted when necessary. In situations where the electric field is very strong, you can also consider installing a copper mesh lining in the iron casing.

Channel interference processing. In order to control the interference between channels and reduce the magnetic field coupling interference generated in the secondary circuit of the current transformer and the electric field interference from the secondary line of the voltage transformer, it is absolutely not allowed to bundle them with the weak current signal line output by the transmitter when installing the transmitter panel. The two must be routed separately and as far away as possible to avoid parallelism. The DC voltage signal output by each transmitter plug-in has a wire that is grounded together with the microcomputer power supply. In order to avoid the signal ground wire forming a loop and causing magnetic field interference, a single-point grounding method must be used.

Reasonable distribution and layout of plug-ins. Grounding, shielding and isolation measures cannot completely block the intrusion of interference signals. In order to prevent the adverse consequences caused by residual surges, the protection and control circuits can be reasonably divided into several plug-ins, and the parts that are most afraid of interference can be concentrated on one or several plug-ins, placed in the inner shielding box, and kept as far away from the interference source and the parts related to the interference source as possible.