Delta-sigma modulated Class D series resonant converter

This paper proposes to apply the 1-bit delta-sigma modulator to a series resonant converter. The 1-bit delta-sigma modulator, which is an analog to digital (A/D) converter, outputs a 1-bit (1/0) signal based on the analog input signal. This technology has been applied to digital audio amplifiers in the markets. These days, the delta-sigma modulation is also applied to switching power converters instead of the pulse width modulation (PWM). Applying the 1-bit signal to the driving signal for a switching converter, the output can be well controlled almost continuously with low sub-harmonics. In this study, one of the characteristics of the delta-sigma modulation that is ldquoperiodicityrdquo of the 1-bit output signal is focused. In voltage-source series resonant converters, zero-current switching (ZCS) is maintained when the switching frequency is equal to the resonant frequency. Therefore, the periodical 1-bit output signal of the delta-sigma modulator is a perfect method to regulate the output power/voltage of series resonant converters. In this paper, it is proposed to apply a 1-bit delta sigma modulator PCM4202 to the Class D series resonant converter for the output voltage regulation. The theoretical approach, simulation results, and experimental results with a low-voltage prototype circuit are introduced. The ZCS of the switching devices is confirmed in the simulation and the circuit experiments. In circuit experiments, the output power from 0.094 W at 0.97 V to 5.56 W at 7.43 V is obtained from the input voltage 20.0 V with the load resistance 9.92 Omega at 198.7 kHz, where the measured power conversion efficiencies are 54.7% at 0.97 V and 71.4% at 7.43 V The output voltage can be smoothly and continuously changed within the range. No specific sub-harmonies are observed in time domain and in frequency domain.