LAUSR

This study shows the derivation of the power-stage transfer functions and input and output impedances of a buck–boost pulse width-modulated (PWM) dc–dc converter operating in continuous-conduction mode. The expressions are derived using the small-signal model obtained by the circuit-averaging technique. Using the small-signal dynamic model, both transient and frequency domain characteristics are determined. An example buck–boost converter with the following specifications was considered: supply voltage 12 V, output voltage 5 V, switching frequency 200 kHz, and output power 10 W. The modification of the power-stage transfer function to include the time delay between the MOSFET gate drive and the duty cycle is considered and is modelled by the first-order Pade approximation. The theoretical predictions were verified by experiments and excellent agreement between the results was observed.