Bi-frequency PWM technique for switching dc-dc converters

To improve the electromagnetic interference (EMI) performance of PWM controlled switching dc-dc converters, bi-frequency pulse width modulation (BF-PWM) technique is presented in this paper. The principle of BF-PWM modulation is illustrated and the characteristics of BF-PWM controlled buck converter operating in discontinuous conduction mode (DCM) are studied. For BF-PWM technique, two high frequency switching control pulses with the same turn-on time but different frequencies are modulated by a low-frequency PWM signal. The spectrum of the switching signal is thus spread and the spectral power level is reduced. Experimental results show that BF-PWM controlled buck converter benefits better EMI performance compared with voltage-mode PWM controlled buck converter.