Switching regulator capable of stable operation and improved frequency characteristics in a broad input and output voltage range and method for controlling operation thereof

1. A switching regulator for converting a supply voltage input to an input terminal into a predetermined constant voltage and outputting the predetermined constant voltage as an output voltage from an output terminal, comprising:

a switching element configured to perform switching in accordance with an input control signal;

an inductor charged with the supply voltage by the switching of said switching element;

a rectifying element configured to discharge said inductor when said switching element is switched off and charging of said inductor is stopped; and

a control circuit unit configured to generate an error voltage based on a difference of voltage between a proportional voltage proportionate to the output voltage and a predetermined reference voltage, generate a pulse signal with a duty cycle in accordance with the error voltage, and output the pulse signal to a control electrode of said switching element so as to perform switching control of said switching element, wherein

said control circuit unit is configured to generate a feedback voltage in accordance with the duty cycle of the pulse signal, generate the pulse signal with the duty cycle based on a difference of voltage between the generated feedback voltage and the error voltage, vary the difference of voltage in accordance with the duty cycle of the pulse signal, thereby performing feedback control, integrate the pulse signal and add a slope voltage having a voltage tilt in accordance with the duty cycle of the pulse signal to a signal with ripple obtained by the integration so as to generate the feedback voltage.

2. The switching regulator according to claim 1 , wherein said control circuit unit is configured to compare the error voltage with the feedback voltage and generate the pulse signal with a duty cycle based on a result of the comparison.

3. The switching regulator according to claim 2 , wherein said control circuit unit includes:

an error voltage generating circuit unit configured to generate and output the error voltage based on the difference of voltage between the proportional voltage proportionate to the output voltage and the predetermined reference voltage;

a pulse modulating circuit unit configured to generate the pulse signal with the duty cycle in accordance with the error voltage and output the pulse signal to the control electrode of said switching element so as to perform switching control of said switching element; and

a feedback circuit unit configured to generate and output the feedback voltage in accordance with the duty cycle of the pulse signal, wherein said pulse modulating circuit unit is configured to compare the error voltage with the feedback voltage and generate the pulse signal with a duty cycle based on a result of the comparison of the error voltage and the feedback voltage.

4. The switching regulator according to claim 3 , wherein said feedback circuit unit is configured to generate the feedback voltage by integrating the pulse signal.

5. The switching regulator according to claim 3 , wherein the pulse modulating circuit unit includes:

a comparator, a first input terminal of the comparator being directly connected to the error voltage, and a second input terminal of the comparator being directly connected to the feedback voltage; and

a flip-flop circuit configured to generate the pulse signal based on an output signal from the comparator.

6. The switching regulator according to claim 3 , wherein said error voltage generating circuit unit includes:

an output voltage detecting circuit configured to divide the output voltage and generate and output the proportional voltage;

a reference voltage generating circuit configured to generate and output the reference voltage; and

an error amplifying circuit configured to amplify the difference of voltage between the proportional voltage and the reference voltage and generate and output the error voltage.

7. The switching regulator according to claim 3 , wherein said pulse modulating circuit unit includes:

a voltage comparison circuit configured to compare the error voltage with the feedback voltage and generate and output a binary signal indicating a result of the comparison; and

an RS flip-flop circuit configured to receive a predetermined clock signal at one input terminal and an output signal of said voltage comparison circuit at the other input terminal and generate and output the pulse signal based on each signal level of the output signal and the clock signal.

8. The switching regulator according to claim 4 , wherein said feedback circuit unit includes:

a first switch configured to perform switching in accordance with the pulse signal;

a second switch configured to perform switching opposite to the switching of said first switch in accordance with the pulse signal;

a resistor;

a capacitor supplied with a current to be charged via said resistor in accordance with the switching of said first switch;

a constant current source configured to discharge said capacitor in accordance with the switching of said second switch; and

a slope voltage generating circuit configured to generate the slope voltage and add the generated slope voltage to a voltage of a charging and discharging terminal of said capacitor at a time of charging so as to generate the feedback voltage.

9. The switching regulator according to claim 4 , wherein said feedback circuit unit includes:

a first switch configured to perform switching in accordance with the pulse signal;

a second switch configured to perform switching opposite to the switching of said first switch in accordance with the pulse signal;

a capacitor;

a constant current source configured to perform charging by supplying a predetermined constant current to said capacitor in accordance with the switching of said first switch; and

a resistor configured to form a predetermined time constant when said capacitor is discharged in accordance with the switching of said second switch.

10. The switching regulator according to claim 4 , wherein said feedback circuit unit includes:

a first switch configured to perform switching in accordance with the pulse signal;

a second switch configured to perform switching opposite to the switching of said first switch in accordance with the pulse signal;

a capacitor;

a constant current source configured to perform charging by supplying a predetermined constant current to said capacitor in accordance with the switching of said first switch;

a resistor configured to form a predetermined time constant when said capacitor is discharged in accordance with the switching of said second switch; and

a slope voltage generating circuit configured to generate the slope voltage and add the generated slope voltage to a voltage of a charging and discharging terminal of said capacitor at a time of charging so as to generate the feedback voltage.

11. A method for controlling operation of a switching regulator, said method comprising:

switching by a switching element in accordance with an input control signal;

charging an inductor with an input voltage by the switching of said switching element; and

discharging said inductor when said switching element is switched off and charging of said inductor is stopped;

generating an error voltage based on a difference of voltage between a proportional voltage proportionate to an output voltage output from an output terminal and a predetermined reference voltage;

generating a pulse signal with a duty cycle in accordance with the error voltage and outputting the pulse signal to said switching element so as to perform switching control of said switching element;

converting the input voltage into a predetermined constant voltage and outputting the predetermined constant voltage as the output voltage;

generating a feedback voltage in accordance with the duty cycle of the pulse signal;

generating the pulse signal with the duty cycle based on a difference of voltage between the generated feedback voltage and the error voltage;

varying the difference of voltage in accordance with the duty cycle of the pulse signal, thereby performing feedback control;

integrating the pulse signal; and

adding a slope voltage having a voltage tilt in accordance with the duty cycle of the pulse signal to a signal with ripple obtained by the integration so as to generate the feedback voltage.

12. The method for controlling operation of a switching regulator according to claim 11 , further comprising:

comparing the error voltage with the feedback voltage; and

generating the pulse signal with the duty cycle based on a result of the comparison.

13. The method for controlling operation of a switching regulator according to claim 11 , further comprising generating the feedback voltage by integrating the pulse signal.