Switching power supply device

1. A switching power supply device, comprising:

an output stage circuit including an output transistor installed between an application end of an input voltage and an application end of an output voltage, and configured to generate the output voltage from the input voltage through a switching operation including an operation of switching the output transistor; and

a main control circuit configured to execute PWM control for causing the output stage circuit to perform the switching operation at a predetermined PWM frequency based on a feedback voltage according to the output voltage,

wherein the main control circuit includes:

a comparison voltage generator configured to generate a comparison voltage on a specific wiring according to the feedback voltage;

a phase compensation circuit connected to the specific wiring and configured to compensate a phase of the comparison voltage;

a ramp voltage generation circuit configured to generate a ramp voltage whose voltage value is changed periodically in a PWM cycle; and

a PWM comparator configured to compare the comparison voltage with the ramp voltage to output a signal indicating a comparison result,

wherein the main control circuit is configured to control the output stage circuit based on an output signal of the PWM comparator,

wherein the phase compensation circuit includes a phase compensation resistor installed between the specific wiring and a predetermined node, and a phase compensation capacitor installed between the predetermined node and a reference conductive portion having a predetermined potential, and

wherein the main control circuit further includes a clamp circuit configured to perform a clamping operation for generating a clamp voltage and clamping a voltage at the predetermined node with the clamp voltage.

2. The switching power supply device of claim 1 , wherein the main control circuit is configured to:

execute the PWM control or off-skip control for keeping the output transistor in an on-state for more than one cycle of the PWM cycle corresponding to a reciprocal of the PWM frequency;

execute the PWM control for causing the output stage circuit to perform the switching operation based on switching of a high-low relationship between the comparison voltage and the ramp voltage in a state in which the comparison voltage is maintained within a fluctuation range of the ramp voltage;

execute the off-skip control in a state in which the switching of the high-low relationship between the comparison voltage and the ramp voltage does not occur for one cycle or more of the PWM cycle; and

execute the clamping operation in conjunction with the execution of the off-skip control.

3. The switching power supply device of claim 2 , wherein upon detecting that the switching of the high-low relationship between the comparison voltage and the ramp voltage does not occur for one cycle of the PWM cycle or more after a start of the PWM control, the main control circuit shifts execution control from the PWM control to the off-skip control and starts the clamping operation, and then upon detecting the switching of the high-low relationship between the comparison voltage and the ramp voltage, the main control circuit returns the execution control to the PWM control and terminates the clamping operation.

4. The switching power supply device of claim 1 , wherein the clamp circuit sets the clamp voltage according to the output voltage.

5. The switching power supply device of claim 4 , wherein the ramp voltage generation circuit sets an amplitude of the ramp voltage according to the input voltage.

6. The switching power supply device of claim 5 , wherein the clamp voltage is proportional to the output voltage, and the amplitude of the ramp voltage is proportional to the input voltage.

7. The switching power supply device of claim 1 , wherein the clamp voltage is a predetermined fixed voltage.

8. The switching power supply device of claim 1 , wherein the comparison voltage generator includes an amplifier configured to input and output a current from and to the specific wiring based on a signal generated according to the feedback voltage or based on the feedback voltage.

9. The switching power supply device of claim 1 , wherein the output stage circuit includes the output transistor and a synchronous rectification transistor directly connected to the output transistor,

wherein the synchronous rectification transistor is installed between the application end of the output voltage and the reference conductive portion, and

wherein the main control circuit is configured to:

in the PWM control, alternately turn on and off the output transistor and the synchronous rectification transistor based on the output signal of the PWM comparator; and

in off-skip control, repeatedly execute a series of unit operations for turning on the output transistor and turning off the synchronous rectification transistor for a time exceeding one cycle of the PWM cycle, and then turning off the output transistor and turning on the synchronous rectification transistor for a time shorter than one cycle of the PWM cycle, or in the off-skip control, maintain the output transistor in an on-state and maintain the synchronous rectification transistor in an off-state.

10. The switching power supply device of claim 1 , wherein a coil is installed between the output transistor and the application end of the output voltage, and when the output transistor is turned on, a current based on the input voltage is allowed to flow toward the application end of the output voltage through the output transistor and the coil.