Simulation of Flyback Converter with Current Mode Control

It was mentioned previously that, owing to its simplicity, the flyback converter has been the favorite choice in low-power switching converters. Taking advantage of modern control concepts, that merit is further augmented by the current-mode control scheme delineated in Chapter 13. Therefore, to give one more example of the power of computer simulation and to prove the unique advantage of current-mode control, this chapter again presents the mathematical procedures leading to a fairly complete simulation in its entirety. The schematic shown in Fig. 14-1 gives the actual circuit diagram that consists of an isolated inductor, output rectifier and filter, load, feedback network, error amplifier, current-mode PWM chip SG1846 by Silicon General, solid-state switch, and current sensing resistor. At first glance, and by comparing with Fig. 13-1 of the forward converter, the flyback topology is truly lower in component count. The corresponding analytic description of the circuit operation is therefore expected to be less lengthy and straightforward. Again, the following will first present the descriptive equations in differential form, then the discrete form, and simulation results follow.