Research On Switching Power Supply With Wide Input Voltage Range

Compared with battery energy storage,supercapacitors have the advantages of high power density and long life,so they are widely used in industries such as new energy power generation,new energy vehicles,and emergency power supplies.During the application of supercapacitors,its voltage changes drastically as the stored energy changes.Usually,the ratio of the maximum voltage to the minimum voltage is more than twice,so the converter control power supply matched with it must adapt to a wide input voltage range.For EPS power supplies that use supercapacitors as energy storage media,a high-efficiency control power supply with a wide input voltage range has been developed.According to the characteristics of wide input voltage range,the flyback converter is choosed as the basic topology.In view of the problems of high hard-switching voltage stress and low efficiency of traditional flyback converters,a quasi-resonant flyback converter is designed to achieve valley turn-on and improve efficiency.However,the leakage inductance energy cannot be used in the quasi-resonant converter,and the active clamp flyback converter is proposed to further improve the efficiency.The clamp capacitor is used in active clamp flyback converter to absorb the leakage inductance energy,and at the same time,transformer magnetizing inductance and transformer leakage inductance are used to form a resonant circuit to achieve soft switching of power devices,thereby improving efficiency and reducing EMI.There is a huge difference in the energy storage of the junction capacitance of the main switch under a wide input voltage range.In order to achieve soft switching in a larger load range,the bilateral excitation method is selected,and the soft switching is realized through the excitation inductance.The influence of the input voltage on the discharge of the junction capacitor is analyzed.The higher the input voltage,the longer the discharge time of the junction capacitor and the greater the energy storage required by the inductance.The influence of the clamp capacitor on the realization of ZVS on the primary side and ZCS on the secondary side is analyzed.The wide input voltage will affect the discharge time,so an adaptive dead time control is designed.For different loads,four different working modes are designed to switch between standby mode,light load mode,adjustable frequency hopping mode,and adjustable load mode.In order to further reduce the loss on the rectifier side,the secondary side chooses a synchronous rectifier tube instead of a diode,and analyzes the ZCS turn-off condition of the synchronous rectifier tube to achieve higher efficiency.A switching power supply with input DC 110 V to 310 V and output DC 24V/70 W was designed.The traditional RCD passive clamp flyback switching power supply controller uses the UC3842 chip,the quasi-resonant uses UCC28600 as the main control chip,and the active clamp uses the latest flyback active clamp chip UCC28780.Quasi-resonance can reduce switching losses through valley turn-on.The active clamp converter recovers the leakage inductance energy and monitors the drain voltage of the main switch in real time to achieve ZVS turn-on,which can achieve higher efficiency.By comparing the efficiency of the three power supplies,it is found that the efficiency of the active clamp is nearly 10% higher than that of the traditional passive clamp flyback switching power supply,and it is nearly 5%higher than the quasi-resonant power supply under heavy load.Through experiments,the process of the switch tube to realize the ZVS turn-on is observed,and the phenomenon of losing the soft switch is analyzed,and the soft switch is re-realized by adjusting the dead time.The theory and prototype experiments show that the active clamp flyback converter can be applied under the condition of a wide input voltage range,and can realize a high-efficiency and high-reliability auxiliary power supply.