| Switching power supply is the energy source of most power electronic systems.With the development of power electronic technology,switching power supply with low output voltage and high output current has become a very popular trend nowadays.For example,in some large-scale integrated circuits and complex single-board design,power supply needs a lot of current,so how to improve the efficiency of switching power supply with high current output has become an important problem to be solved urgently.In traditional DC-DC switching power supply,the rectifier part of the secondary side usually uses Schottky diode or fast recovery diode,which makes use of the characteristic that the diode can only conduct electricity unilaterally.But the diode has a relatively large on-off voltage drop.When the output current is high,it will produce very large on-off loss,which will seriously affects the transmission efficiency of switching power supply.Therefore,synchronous rectification technology is proposed.The core of synchronous rectification technology is to use MOSFET instead of diode to rectify,and to achieve the same function as diode by controlling the switch of MOSFET synchronize with the switches on the primary side.Because the on-resistance of MOSFET is very small,only a few mΩ,so the on-loss of MOSFET is much less than that of diode when the output current is very large.In addition,the switching time of MOSFET is relatively short,so it is suitable for working at high frequency.This paper analyzes the basic characteristics and main losses of MOSFET,as well as the operation characteristics and main losses of diodes,and then compares the advantages of using synchronous rectification technology of MOSFET.By analyzing the driving mode of synchronous rectifier MOSFET,a driving mode combining self-driving and external driving is proposed,that is,sampling voltage in the circuit itself,and then providing driving waveform externally.The advantage of this method is that it can not only avoid the misleading of MOSFET caused by poor driving signal when self-driving,but also avoid the difficulty of synchronizing the driving signal and the switching of power MOSFET when external driving.The synchronous rectifier unit is also designed and implemented in this paper,and the circuit is well operated after testing.This paper also designs a half-bridge DC-DC switching power supply test prototype,including the traditional diode rectifier circuit and synchronous rectifier circuit,to detect the designed synchronous rectifier unit.On the basis of the design work mentioned above,this paper also designs and implements the power inversion part,control driver part,output filter part and feedback compensation part of half-bridge power supply,and builds a test platform to test and compare the two power supply prototypes.Finally,the experimental data are analyzed and it is concluded that the synchronous rectification technology can improve the efficiency and performance of switching power supply,which is of great significance for the development of switching power supply. |
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