A Unified PWM Switch Model for Current- and Voltage-Mode Control with Automatic Transition between DCM and CCM

A PWM switch model for simulating and analyzing fixed frequency operated dc-dc converters, which covers at the same time current- and voltage-mode control, and can auto-transition between discontinuous and continuous conduction mode, is proposed. It is based on the classic PWM switch model for voltage-mode operation, with an additionally integrated duty cycle modulator. In this form, the model always has the same four terminals, and the different operating modes are set up by just changing parameters. Therefore, the same simulation model can be used for different control and operating modes. The proposed model is suitable for dc, small-signal ac, and large-signal transient simulations in programs such as SPICE. Besides model derivation, its verification is provided by comparing transient and small-signal simulations against other average and switching circuit models.