Practical application of valley current mode control in a flyback converter with a large duty cycle

This study proposes the application of valley current mode (VCM) control in a flyback dc–dc converter with a large duty cycle. The use of VCM control eliminates the need of slope compensation in operation under a duty cycle greater than 50%. For operation with duty cycle near the boundary value (50%), a relatively small compensation ramp is required comparing with that of the conventional peak current mode (PCM) control. Moreover, the noise sensitivity issue of PCM control is also addressed by the change of the current sensing position in VCM and hence the immunity against the current spike. The VCM-controlled flyback converter achieves consistent steady-state and transient-response performances as its PCM-controlled counterpart. Stability analyses of inner current loop and overall closed-loop system are presented. Experiments are also conducted to evaluate the effectiveness of VCM control in controlling the flyback dc–dc converter.