Minimum Output Ripple and Fixed Operating Frequency Based on Modulation Injection for COT Ripple Control Converter This paper proposes a minimum output ripple and fixed operating frequency technique based on the modulation injection for a constant ontime (COT) ripple control converter. Basically, the modulation injection approach aims to add a modulation signal to the output inductor to fix the operating frequency on the discontinuous conduction mode (DCM) and does not affect the inductor current ripple injection. Moreover, the spread spectrum of pulse width modulation (PWM) method is also applied to reduce the electromagnetic interference (EMI) noise. The illustrative simulation results indicate that the proposed converter operates stably at a fixed switching frequency (1.6MHz), and the output ripple is kept very small (5mVpp). EMI noise levels are also kept below 50mV, which is compared to 5V desired voltage.

Output Voltage Ripple Reduction with Nosie Spread Spectrum for DualPhase LLC Resonant Converter In recent years, the restriction of Electro Magnetic Interference (EMI) due to switching noise of a switching power supply becomes more severe, and there are many regulations worldwide. In this paper, we propose a method to spread the noise spectrum by modulating the switching frequency to reduce the EMI noise in the LLC resonant converter. The LLC resonant converter is used to adjust the output voltage by controlling the switching frequency. However, its EMI noise reduction by the frequency modulation increases the output voltage ripple. Then we propose a dualphase LLC resonant converter, where the output voltage ripple increase is suppressed by the frequency modulation so as to cancel the ripples with each other.