Design of Various Protection Circuits for Internal Components of DC Switching Power Supply
With the development of science and technology, the relationship between power electronic equipment and people's work and life is becoming increasingly close, and electronic equipment cannot do without a reliable power supply. Therefore, DC switching power supplies have begun to play an increasingly important role and have entered various Various electronic and electrical equipment fields, program-controlled switches, communications, electronic testing equipment power supply, control equipment power supply, etc. have widely used DC switching power supply [1-3]. At the same time, with the development of many high-tech technologies, including high-frequency switching technology, soft switching technology, power factor correction technology, synchronous rectification technology, intelligent technology, surface mount technology and other technologies, switching power supply technology is constantly innovating, which is the foundation for DC switching. The power supply provides a wide range of development space. However, due to the complex control circuit in the switching power supply, the ability of transistors and integrated devices to withstand electrical and thermal shocks is poor, which brings great inconvenience to users during use. In order to protect the safety of the switching power supply itself and the load, according to the principle and characteristics of the DC switching power supply, the overheat protection, overcurrent protection, overvoltage protection and soft start protection circuits are designed.
working principle
DC switching power supply is composed of input part, power conversion part, output part and control part. The power conversion part is the core of the switching power supply, which performs high-frequency chopping on the unsteady DC and completes the conversion function required for the output. It is mainly composed of switching transistors and high frequency transformers. Figure 1 shows the schematic diagram and equivalent functional block diagram of a DC switching power supply, which is composed of a full-wave rectifier, a switching tube V, an excitation signal, a freewheeling diode Vp, an energy storage inductor and a filter capacitor C. In fact, the core part of a DC switching power supply is a DC transformer.
features
In order to meet the needs of users, major switching power supply manufacturers at home and abroad are committed to synchronously developing new high-intelligence components, especially by improving the loss of the secondary rectification device, and on the power ferrite (Mn-Zn) material Increase scientific and technological innovation to improve the high magnetic performance obtained at high frequency and large magnetic flux density. At the same time, the application of SMT technology has made great progress in switching power supplies. Components are arranged on both sides of the circuit board to ensure the switching power supply. Light, small and thin. Therefore, the development trend of DC switching power supply is high frequency, high reliability, low consumption, low noise, anti-interference and modularization.
The disadvantage of DC switching power supply is that there is relatively serious switching interference, and the ability to adapt to harsh environments and sudden failures is weak. Due to the gap between domestic microelectronics technology, production technology of resistive capacitor devices and magnetic material technology and some technologically advanced countries, the production technology of DC switching power supply is difficult, maintenance troublesome and costly.
Protection of DC switching power supply
Based on the characteristics of the DC switching power supply and the actual electrical conditions, in order to make the DC switching power supply work safely and reliably in harsh environments and sudden failures, this paper designs a variety of protection circuits according to different situations.
Overcurrent protection circuit
In the DC switching power supply circuit, in order to protect the regulator tube from being burned when the circuit is short-circuited and the current increases. The basic method is that when the output current exceeds a certain value, the adjustment tube is in a reverse bias state, so that it is cut off and the circuit current is automatically cut off. The overcurrent protection circuit is composed of triode BG2 and voltage divider resistors R4 and R5. When the circuit works normally, the base potential of BG2 is higher than the emitter potential through the voltage action of R4 and R5, and the emitter junction bears the reverse voltage. So BG2 is in a cut-off state (equivalent to an open circuit), which has no effect on the voltage regulator circuit. When the circuit is short-circuited, the output voltage is zero, and the emitter of BG2 is equivalent to grounding, then BG2 is in a saturated conduction state (equivalent to short-circuit), so that the base and emitter of the adjustment tube BG1 are close to short-circuit, and are in a cut-off state. Cut off the circuit current to achieve the purpose of protection.
