Frequency Stabilization and EMI Noise Reduction of COT Method Ripple-Controlled Switching Converters with Output Voltage Ripple Cancellation

Abstract

This paper proposes a new EMI reduction and automatic ripple cancellation technique about the ripple-controlled converter with the ripple injection and Constant-On Time (COT) method. The ripple-controlled converters have no stable clock and it is difficult to reduce the EMI noise by shaking the operating frequency. The new method of EMI reduction is that the COT pulse width is modulated by the triangular signal so that the operating frequency is modulated and the spectrum peak level of the clock frequency is greatly reduced. But the output voltage ripple is much increased because of the change of the duty ratio of the operating frequency. The increaced ripple is canceled by adding the modulation signal to the ripple injection circuit. Moreover stabiliztion of the operating frequency on Discontinuous Conduction Mode (DCM) is reported. The operating frequency falls down on DCM mode in the COT converters. To stabilize the operating frequency, cheking the operating period is fedback to control the COT pulse width