A switched mode power supply includes a power circuit and a control circuit coupled to the power circuit for regulating its output voltage. The control circuit is configured to generate a control signal for at least one power switch of the power circuit using a reference voltage, determine if a duty cycle of the control signal is within a defined range, sense one or more output parameters of the power circuit including the output voltage of the power circuit, and in response to determining the duty cycle of the control signal is outside the defined range, adjust the reference voltage to adjust the duty cycle of the control signal. The reference voltage is adjustable over time to thereby linearly adjust the output voltage of the power circuit. Other example switched mode power supplies, control circuits, and methods for regulating output voltages of switched mode power supplies are also disclosed.