Switching power supply operable in an intermittent driving mode
A switching power supply includes: a switching output circuit configured to generate an output voltage from an input voltage by charging a capacitor by turning on and off an output transistor; a control circuit configured to halt the driving of the switching output circuit when charging electric charge to the capacitor per switching event is limited to a lower limit value and the output voltage, or a feedback voltage commensurate therewith, is raised from a predetermined reference voltage; and a lower limit value setting circuit configured to variably control the lower limit value during the driven period of the switching output circuit. For example, the lower limit value setting circuit can increase the lower limit value with increase in the number of times of switching.
1. A switching power supply comprising:
a switching output circuit configured to generate an output voltage from an input voltage by charging a capacitor by turning on and off an output transistor;
a lower limit value setting circuit configured to set a lower limit value of charging electric charge supplied to the capacitor per switching event;
a control circuit configured:
to control a duty of the switching output circuit such that the output voltage or a feedback voltage commensurate therewith remains equal to a predetermined reference voltage and
to operate in an intermittent driving mode in which the control circuit repeats ON/OFF driving and halting of the switching output circuit when, as a result of the charging electric charge to the capacitor per switching event being limited to the lower limit value, the output voltage or the feedback voltage deviates, by rising, from the reference voltage; and
the lower limit value setting circuit is configured to variably control the lower limit value during an ON/OFF-driven period of the switching output circuit in the intermittent driving mode.
2. The switching power supply according to claim 1 , wherein the lower limit value setting circuit is configured to increase the lower limit value with increase in a number of times of switching in the ON/OFF-driven period.
3. The switching power supply according to claim 1 , wherein the lower limit value setting circuit is configured to increase the lower limit value with increase in load.
4. The switching power supply according to claim 1 , wherein the lower limit value setting circuit is configured to generate a lower limit value setting signal by comparing a sensed value of an inductor current passing in the switching output circuit with a predetermined reference current value.
5. The switching power supply according to claim 4 , wherein the lower limit value setting circuit is configured to variably control timing of pulse generation in the lower limit value setting signal by varying the reference current value.
6. The switching power supply according to claim 4 , further comprising:
an error amplifier configured to generate an error signal between the output voltage, or the feedback voltage, and the reference voltage;
an oscillator configured to generate an on-signal that is pulse-driven at a predetermined switching frequency; and
a PWM comparator configured to generate an off-signal by comparing the error signal with a ramp signal,
wherein the control circuit is configured to turn on the output transistor at a timing of pulse generation in the on-signal, and to turn off the output transistor at whichever is later of a timing of pulse generation in the off-signal and a timing of pulse generation in the lower limit value setting signal.
7. The switching power supply according to claim 1 , further comprising:
a first comparator configured to generate a first comparison signal by comparing the output voltage, or the feedback voltage, with a predetermined high-side threshold voltage; and
a second comparator configured to generate a second comparison signal by comparing the output voltage, or the feedback voltage, with a predetermined low-side threshold voltage lower than the high-side threshold voltage,
wherein the control circuit is configured to halt ON/OFF driving of the switching output circuit according to the first comparison signal, and to restart ON/OFF driving of the switching output circuit according to the second comparison signal.
8. The switching power supply according to claim 7 , wherein the high-side and low-side threshold voltages each have a voltage value equal to a voltage value of the reference voltage multiplied by a coefficient greater than one.
9. The switching power supply according to claim 1 , wherein the switching output circuit is of a step-down, step-up, step-up/down, or inverting type.
10. A switching power supply comprising:
a switching output circuit configured to generate an output voltage from an input voltage by charging a capacitor by turning on and off an output transistor;
a lower limit value setting circuit configured to set a lower limit value of charging electric charge fed to the capacitor per switching event; and
a control circuit configured
to control a duty of the switching output circuit such that the output voltage or a feedback voltage commensurate therewith remains equal to a predetermined reference voltage and
to operate in an intermittent driving mode in which the control circuit repeats ON/OFF driving and halting of the switching output circuit when, as a result of the charging electric charge to the capacitor per switching event being limited to the lower limit value, the output voltage or the feedback voltage deviates, by rising, from the reference voltage,
wherein the control circuit is configured to control at least one of driving halt timing and driving restart timing of the switching output circuit, thereby to make a ripple frequency of the output voltage in the intermittent driving mode a frequency that does not cause the capacitor to give off audible noise.
11. The switching power supply according to claim 10 , wherein the control circuit is configured to forcibly halt ON/OFF driving of the switching output circuit when, during ON/OFF driving of the switching output circuit, a predetermined upper-limit time has elapsed since a previous driving halt timing.
12. The switching power supply according to claim 11 , wherein the upper-limit time is shorter than a reciprocal of a human audible upper-limit frequency.
13. The switching power supply according to claim 10 , wherein the control circuit is configured to forcibly restart ON/OFF driving of the switching output circuit when, during halting of the switching output circuit, a predetermined upper-limit time has elapsed since a previous driving restart timing.
14. The switching power supply according to claim 10 , wherein the control circuit is configured to perform gradient determination on the output voltage, or the feedback voltage, after halting ON/OFF driving of the switching output circuit, and to determine, according to a result of the determination, whether or not to continue ON/OFF driving of the switching output circuit.
15. The switching power supply according to claim 14 , wherein
the control circuit is configured to forcibly restart ON/OFF driving of the switching output circuit if a gradient of the feedback voltage is steeper than a predetermined value.
16. The switching power supply according to claim 14 , wherein the control circuit is configured to enter a power saving mode in which supply of electric power is cut off except to a circuit needed to restart ON/OFF driving of the switching output circuit if a gradient of the feedback voltage is not steeper than a predetermined value.
17. The switching power supply according to claim 10 , further comprising:
a first comparator configured to generate a first comparison signal by comparing the output voltage, or the feedback voltage, with a predetermined high-side threshold voltage; and
a second comparator configured to generate a second comparison signal by comparing the output voltage, or the feedback voltage, with a predetermined low-side threshold voltage lower than the high-side threshold voltage,
wherein the control circuit is configured to halt ON/OFF driving of the switching output circuit according to the first comparison signal, and to restart ON/OFF driving of the switching output circuit according to the second comparison signal.
18. The switching power supply according to claim 17 , wherein
the high-side and low-side threshold voltages each have a voltage value equal to a voltage value of the reference voltage multiplied by a coefficient greater than one.
19. The switching power supply according to claim 10 , wherein the switching output circuit is of a step-down, step-up, step-up/down, or inverting type.
20. A switching power supply comprising:
a switching output circuit configured to generate an output voltage from an input voltage by charging a capacitor by turning on and off an output transistor;
a lower limit value setting circuit configured to set a lower limit value of charging electric charge fed to the capacitor per switching event; and
a control circuit configured to operate in an intermittent driving mode in which the control circuit repeats driving and halting of the switching output circuit when the output voltage, or a feedback voltage commensurate therewith, is raised from the reference voltage by operation of the lower limit value setting circuit,
wherein
the control circuit is configured to control at least one of driving halt timing and driving restart timing of the switching output circuit, thereby to make a ripple frequency of the output voltage in the intermittent driving mode a frequency that does not cause the capacitor to give off audible noise,
the control circuit is configured to forcibly halt driving of the switching output circuit when, during driving of the switching output circuit, a predetermined upper-limit time has elapsed since a previous driving halt timing, and
the upper-limit time is shorter than a reciprocal of a human audible upper-limit frequency.
21. A switching power supply comprising:
a switching output circuit configured to generate an output voltage from an input voltage by charging a capacitor by turning on and off an output transistor;
a lower limit value setting circuit configured to set a lower limit value of charging electric charge fed to the capacitor per switching event; and
a control circuit configured to operate in an intermittent driving mode in which the control circuit repeats driving and halting of the switching output circuit when the output voltage, or a feedback voltage commensurate therewith, is raised from the reference voltage by operation of the lower limit value setting circuit,
wherein
the control circuit is configured to control at least one of driving halt timing and driving restart timing of the switching output circuit, thereby to make a ripple frequency of the output voltage in the intermittent driving mode a frequency that does not cause the capacitor to give off audible noise,
the switching power supply further comprises:
a first comparator configured to generate a first comparison signal by comparing the output voltage, or the feedback voltage, with a predetermined high-side threshold voltage; and
a second comparator configured to generate a second comparison signal by comparing the output voltage, or the feedback voltage, with a predetermined low-side threshold voltage lower than the high-side threshold voltage, and
the control circuit is configured to halt driving of the switching output circuit according to the first comparison signal, and to restart driving of the switching output circuit according to the second comparison signal.
22. The switching power supply according to claim 21 , wherein
the high-side and low-side threshold voltages each have a voltage value equal to a voltage value of the reference voltage multiplied by a coefficient greater than one.