Development of high efficiency, low stress, low pollution, low output ripple communication switching power supply

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Development of high efficiency, low stress, low pollution, low output ripple communication switching power supply [Copy link]

High-frequency switching communication power supply system is the main power supply equipment in the communication, power, transportation, finance and other industries. It is a high-tech product integrating circuit, magnetic circuit, control and computer technology. At present, many large companies at home and abroad, including Advance in the UK, Huawei, ZTE, Tonglihuan, etc., have a series of products for sale. However, with the development of the communication industry and power electronics technology, power supply technology is also constantly advancing. This paper analyzes several key technologies that affect the performance of switching power supply, and on this basis develops a new type of high-reliability, high-efficiency, low-pollution switching power supply system.

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2 Main technical requirements of the market for new switching power supplies (1) High reliability switching power supply system MTBF (mean time between failures) should be ≥ 150,000 hours. (2) Low electromagnetic pollution mainly includes low input harmonic interference and low high-frequency electromagnetic interference. (3) Low output ripple Large ripple is one of the shortcomings of switching power supplies and is the main cause of digital circuit malfunction and computer crashes.

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3 Composition of the new switching power supply The principle block diagram of the new low-pollution, high-efficiency, low-stress, low output ripple switching power supply is shown in Figure 1, which mainly includes EMI and surge absorption filter circuit, front-stage active soft switching power factor correction circuit, phase-shift resonant soft switching DC/DC conversion circuit and output ripple suppression circuit.

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4 Low-stress and high-reliability power conversion technology The switching stress of power devices (including thermal stress and electrical stress) is the main factor affecting the reliability of power supply. The thermal stress of power devices includes two parts: steady-state temperature rise and dynamic power consumption during the switching process. The steady-state temperature rise is mainly related to the efficiency of the system. Only by reducing the power consumption of each component of the system (mainly including the power consumption of transformers, conversion devices, and absorption circuits) can the system efficiency be improved and the steady-state temperature rise be reduced. Dynamic loss is the UI product during the switching process, which can be reduced by dislocating the voltage and current waveforms during the switching process. The electrical stress of power devices is the rate of change and peak value of voltage and current during the switching process. Soft switching conversion technology is used in new power supply designs to reduce the stress of power devices and improve system reliability. Soft switching conversion technology includes two parts: front-stage power factor correction, soft switching conversion technology, and rear-stage phase shift soft switching conversion technology. The principles of the front-stage power factor correction and soft switching conversion circuit are shown in Figure 2. The control circuit is completed by Unitrode's UC3855. The main and auxiliary tube driving waveforms are shown in Figure 3. V1 is the main switch tube, and V2 is the auxiliary switch tube. V2 is turned on before the main switch V1 is turned on to achieve ZVS turn-on of the main switch tube, thereby significantly reducing the switching loss and switching electrical stress of the power device and improving the reliability and electromagnetic compatibility of the system.

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High-frequency electromagnetic interference is another type of pollution of switching power supplies, which refers to high-frequency conducted interference of 150kHz to 30MHz. It mainly includes two types of interference: normal mode interference, that is, the interference between input lines caused by high-frequency device switching; common mode interference, that is, the interference between input lines and chassis ground caused by leakage current between power devices, transformers and chassis ground. Normal mode and common mode filter networks are used in power supplies to filter out high-frequency interference from power supplies. In addition, the use of farad ground shields between power devices, transformers and chassis ground, the use of soft switching technology for main power conversion, and the optimization of input inductor filter network design can also significantly enhance the power supply's anti-high-frequency interference performance.

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6 Output ripple suppression measures The output ripple of the switching power supply mainly comes from four aspects, namely, input AC power supply noise, high-frequency differential mode noise, common mode noise caused by parasitic parameters, and ultra-high frequency resonant noise generated during the switching process of the power device. The AC power supply noise mainly comes from the input power frequency AC component, which can be eliminated by using the pre-stage pre-stabilization and increasing the closed-loop gain of the DC/DC converter. The high-frequency differential mode noise comes from the high-frequency power switch conversion circuit. Its size is mainly related to the conversion frequency of the switching power supply, the structure and parameters of the output filter. The power conversion frequency should be increased as much as possible in the design to reduce the high-frequency switching noise. The common mode noise mainly comes from the leakage current between the power device, the transformer and the chassis ground. The parasitic capacitance between the power device, the transformer and the chassis ground should be minimized, and the common mode inductor and common mode capacitor should be added on the output side to reduce the output common mode noise. The ultra-high frequency resonant noise mainly comes from the resonance of the diode junction capacitance during the reverse recovery of the high-frequency rectifier diode and the junction capacitance of the power device and the parasitic inductance of the line during the switching of the power device. The frequency is generally 1 to 10MHz. The ultra-high frequency resonant noise can be reduced by selecting soft recovery diodes, switching tubes with small junction capacitance, and reducing the wiring length.