In contrast to Chapter 1, in which a single-loop, voltage-mode control is employed, this chapter uses current-mode control with an inner, current feedback loop, and it results in a two-loop system. The current feedback may be implemented in two approaches: a magnetic current sensor or a low-value resistive element in series with the primary power switch.
Current-mode pulse-width-modulation (PWM) gains significantly different from voltage-mode PWM is derived. It results in two loops. Once the inner current loop is absorbed, the procedure to identify the error amplifier is similar to the one presented in Chapter 1.