Adaptive minimum duty cycle design to extend operational voltage range for DCDC converters

A controller for a switched mode power supply (SMPS), comprising:

• an error amplifier configured to compare a sampled output voltage of the SMPS with a first reference voltage to generate an error voltage signal;
• an oscillator circuit configured to provide a clock signal, wherein the oscillator circuit comprises:
• a capacitor;
• a first constant current source;
• a current mirror coupled to the first constant current source to provide a first current for charging the capacitor;
• a comparator for comparing a voltage on the capacitor with a second reference voltage for discharging the capacitor;
• and
• an inverter coupled to an output of the comparator to provide the clock signal;
• an adaptive minimum duty-cycle circuit configured to receive the error voltage signal and to generate a current signal to vary an oscillating frequency of the clock signal in response to the error voltage signal;
• and
• a PWM switching control circuit configured to receive the error voltage signal and the clock signal and to provide a PWM switching control signal for controlling a first power switch and a second power switch of the SMPS.

A method for a switched mode power supply (SMPS), comprising:

• providing an error voltage signal based on a difference between a sampled output voltage of the SMPS and a target voltage;
• generating a clock signal characterized by an oscillating frequency, wherein generating the clock signal comprises:
• using a first current from a first constant current source to charge a capacitor;
• and
• using a comparator for comparing a voltage on the capacitor with a second reference voltage to determine a condition for discharging the capacitor;
• generating a switching control signal based on the error voltage signal and the clock signal using pulse-width modulation (PWM);
• varying the oscillating frequency of the clock signal according to the error voltage signal;
• and
• applying the switching control signal to control a first power switch and a second power switch of the SMPS.