Ripple injection circuit and electronic device equipped with this circuit
A ripple injection circuit equipped with: a capacitor that passes a frequency component of an input voltage or a frequency component of an output voltage and that generates a first ripple voltage having a first ripple component; and an integration circuit that integrates a comparison result signal and that generates a second ripple voltage having a second ripple component. The first ripple component and the second ripple component are added to a feedback voltage.
1. A ripple voltage injection circuit comprising:
a first integration circuit configured to integrate a switching voltage generated by turning on and off a switching device to generate a first ripple voltage including a first ripple component; and
a second integration circuit configured to integrate a comparison result signal, which is a result of comparing a feedback voltage with a reference voltage, to generate a second ripple voltage including a second ripple component, wherein:
the first and second ripple components are added to the feedback voltage,
the first integration circuit includes a first resistor to which the switching voltage is fed and a first capacitor, the first resistor having a first resistance,
the second integration circuit includes a second resistor to which the comparison result signal is fed and a second capacitor, the second resistor having a second resistance,
the first resistance of the first resistor and the second resistance of the second resistor are set such that a first value is higher than a second value, wherein:
the first value is obtained by dividing a high level of the comparison result signal by the second resistance of the second resistor,
the second value is obtained by dividing an output voltage by the first resistance of the first resistor, and
the output voltage is obtained by smoothing the switching voltage.
2. The ripple voltage injection circuit according to claim 1 , wherein the first and second capacitors have the same capacitance.
3. The ripple voltage injection circuit according to claim 1 , wherein
the feedback voltage is generated by a feedback voltage generation circuit including a first voltage division resistor to which the output voltage is applied and a second voltage division resistor connected in series between the first voltage division resistor and a ground voltage, the second voltage division resistor having a resistance, and
the first resistance of the first resistor is set such that the first resistance of the first resistor is higher than the resistance of the second voltage division resistor, and the first resistance of the first resistor is higher than the second resistance of the second resistor.
4. The ripple voltage injection circuit according to claim 1 , wherein
the feedback voltage is generated by a feedback voltage generation circuit including a first voltage division resistor to which the output voltage is applied and a second voltage division resistor connected in series between the first voltage division resistor and a ground voltage, the first voltage division resistor having a resistance, and
when the resistance of the first voltage division resistor is represented by R and a minimum frequency of a frequency component included in the reference voltage is represented by f, a capacity C of the capacitor or of the first capacitor is set to fulfill R>(½ πfC).
5. A step-up switching power supply circuit comprising:
the ripple voltage injection circuit according to claim 1 ;
a voltage generation circuit configured to smooth, with a capacitor, a voltage generated in an inductor by turning on and off the switching device connected to one end of the inductor to generate the output voltage higher than an input voltage fed to another end of the inductor;
a feedback voltage generation circuit configured to divide the output voltage to generate the feedback voltage; and
a comparison circuit configured to output the comparison result signal;
wherein the switching device is turned on and off based on the comparison result signal.
6. The step-up switching power supply circuit according to claim 5 , wherein a signal which varies with time and of which a minimum value is greater than zero is used as the reference voltage.
7. The step-up switching power supply circuit according to claim 5 , wherein an output terminal of the comparison circuit is directly connected to a control terminal of the switching device.
8. The step-up switching power supply circuit according to claim 7 , wherein when an input capacity of the switching device is represented by C ISS , a switching frequency of the switching device is represented by f sw , a maximum output current of the comparison circuit is represented by I GmAx , and a high level of the comparison result signal is represented by V GH , the input capacity C ISS of the switching device is set so as to fulfill 2C ISS V GH /I GMAX <1/f SW .
9. An electronic device comprising:
the step-up switching power supply circuit according to claim 5 ; and
a load circuit to which an output of the step-up switching power supply circuit is connected.