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A simple two-loop voltage mode control scheme for the two inductor step-down buck converter is proposed. This is a voltage-mode control scheme in which the external sawtooth generator for the PWM generation is not required. The controller implementation requires only a single error amplifier and gives almost current-mode control performance. The proposed converter gives lower ripple in the input current and reduces the input filtering requirements as compared to the conventional buck topology. To reduce the input current ripple even more, integrated magnetic components with ripple steering phenomena are proposed. For modelling the converter a signal-flow-graph approach is developed to find the converter open, closed-loop small-signal transfer functions and to eliminate the complexity in the mathematical analysis. A unified signal-flow-graph model of the converter, from which the complete behaviour can be predetermined, is developed. Effectiveness of the proposed control scheme and performance improvement is demonstrated through simulations. Experimental results of load voltage regulation against line and load changes are provided to validate the proposed modelling and control scheme.
Date of Publication: 4 Nov. 2005