Dual modulation using the half bridge with complementary control

A dual modulation control scheme is employed to generate two tightly controlled output voltages in an asymmetrical half-bridge PWM converter. The main output is controlled via duty ratio modulation while the second output via frequency modulation. Such a combination provides a cost-effective circuit with an optimal balance between operating frequency (thus size of magnetic components) and efficiency. In this paper, the circuit operation of the converter is described and its small signal behavior analyzed. Design constraints due to frequency-dependent nature of the power stage and some practical design considerations are also discussed.