A Comparative Study of Analog Voltage-mode Control Methods for Ultra-Fast Tracking Power Supplies

This paper presents a theoretical and experimental comparison of the standard PWM/PID voltage-mode control method for single-phase buck converters with two high-performance self-oscillating (a.k.a. sliding mode) control methods. The application considered is ultra-fast tracking power supplies (UFTPSs) for RF power amplifiers, where the switching converter needs to track a varying reference voltage precisely and quickly while maintaining low output impedance. The small-signal analyses performed on the different controllers show that the hysteretic-type controller can achieve the highest loop gain, leading to superior output impedance performance in the UFTPS application; this is explained using a recently proposed small-signal model for the hysteretic comparator. The analytical findings are verified experimentally as well as by simulation. Experimentally, the use of hysteretic self-oscillating control is shown to reduce the worst-case UFTPS output impedance by a factor of 10.