Abstract:

Firstly,aiming at the full-bridge synchronous rectifier circuit its voltage and current double closed-loop model under digital control is established.Then,the product of sampling switch,zero order holder and digital duty cycle update link in the digital control system are equivalently approximated by the mathematical method,and the transfer function of the internal and external loop of the system is obtained.According to the established model and combined with an example,using bode diagram and control theory,the design idea and method of the inner and outer loop of full-bridge synchronous rectifier circuit under the digital control are established:the inner loop current controller adopts the form of two complex zeros plus one zero pole plus one high frequency pole,the outer loop voltage controller adopts the form of one zero pole plus one high frequency pole plus one zero.Finally,the correctness of the design idea is verified by experiments.

Key words: full bridge synchronous rectifier, digital control, dual closed-loop, transfer function