The inputs of the slope calculation module are the sampling result Vo and the output mode_F of the voltage monitoring module, when the output is the LTH mode, the rising slope Kup of Vo is calculated, and the voltage changes of N1 LTH mode switch periods are used for equivalency replacement, i.e., Kup=Vo(n)?Vo(n?N1), wherein Vo(n) is the sampling result of the current period, Vo(n?N1) is the sampling result before N1 periods, and Kup is the size of Kslope outputted; when the output mode of the voltage monitoring module is the HTL mode, the descending slope Kdown of Vo is calculated, the voltage changes of N2 HTL mode switch periods are used for equivalency replacement, i.e., Kdown=Vo(n?N2)?Vo(n), wherein Kdown is the size of Kslope outputted; and when the output mode of the voltage monitoring module is the normal working mode, the module does not work, and the output result Kslope keeps unchanged through latching. The output result Kslope of the module is inputted to the mode control module.

The input of the error calculation module is the output Vo of the sampling circuit, and the difference of subtracting the output voltage Vo from the reference voltage Vref is the current sampling error, which is donated as e1, and inputted to the PID module.