The paper introduces the principle of driving circuit of switching power in peak current control mode. When duty-cycle is

D

>

50%

the reasons for instability and oscillation in the system are analyzed

the relationship of the inductor current slope

duty-cycle and system stability is discussed. The way of slope compensation is applied to realizing stability of driving circuit in peak current control mode and the principle of slope compensation and design step and compensation circuit is given.Finally

the paper gives a practical slope compensation circuit of fly-back converter controlled by UC3842.The result of simulation and expe-riment shows that slope compensation circuit can realize switch power stability in peak current control mode when duty-cycle is

D

>

50%

and can ensure stability of system and ability of anti-interference.