US 7,248,030 B2Granted

Circuit and method for controlling step-up/step-down DC-DC converter

AssigneeFujitsu Limited

InventorTakahiro Yoshino

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Abstract

A step-up/step-down DC-DC converter for reducing loss caused by activation and inactivation of transistors. An error amplifier included in a control circuit generates an error signal in accordance with voltage difference between an output voltage and a reference voltage. A PWM comparator compares a triangular wave signal and the error signal to generate a control pulse signal having a pulse width that is in accordance with the voltage difference between the output voltage and the reference voltage. A pulse detector monitors the control pulse signal and generates a mode switch signal for switching the operation mode of the DC-DC converter in accordance with a monitoring state of the control pulse signal. A switch provides the PWM comparator with the triangular wave signal or an offset signal, which is generated by adding an offset voltage to the triangular wave signal, in response to the mode switch signal.

Claims20

Dependent claims

A step-up/step-down DC-DC converter for generating an output voltage from an input voltage, the step-up/step-down DC-DC converter comprising:

a choke coil;
a pair of step-down transistors and a pair of step-up transistors connected to the choke coil;
and
a control circuit for controlling the pair of step-down transistors and the pair of step-up transistors based on the output voltage of the DC-DC converter, the control circuit including:
an error amplifier for comparing the output voltage with a reference voltage and generating an error signal that is in accordance with voltage difference between the output voltage and the reference voltage;
a pulse width modulation comparator, connected to the error amplifier, for comparing the error signal with a triangular wave signal and generating a control pulse signal having a pulse width that is in accordance with the voltage difference between the output voltage and the reference voltage;
a pulse detector, connected to the pulse width modulation comparator, for receiving the control pulse signal and generating a mode switch signal for switching an operation mode of the DC-DC converter in accordance with the state of the control pulse signal;
and
an offset voltage adding unit, connected to the pulse detector, for adding an offset voltage to the triangular wave signal or to the error signal in response to the mode switch signal.

6 more elements

A control circuit for a step-up/step-down DC-DC converter including a choke coil, a pair of step-down transistors connected to the choke coil, and a pair of step-up transistors connected to the choke coil, wherein the control circuit controls the pair of step-down transistors and the pair of step-up transistors based on an output voltage of the DC-DC converter, the control circuit comprising:

an error amplifier for comparing the output voltage with a reference voltage and generating an error signal that is in accordance with voltage difference between the output voltage and the reference voltage;
a pulse width modulation comparator, connected to the error amplifier, for comparing the error signal with a triangular wave signal and generating a control pulse signal having a pulse width that is in accordance with the voltage difference between the output voltage and the reference voltage;
a pulse detector, connected to the pulse width modulation comparator, for receiving the control pulse signal and generating a mode switch signal for switching an operation mode of the DC-DC converter in accordance with the state of the control pulse signal;
and
an offset voltage adding unit, connected to the pulse detector, for adding an offset voltage to the triangular wave signal or the error signal in response to the mode switch signal.

2 more elements

A method for controlling a step-up/step-down DC-DC converter including a choke coil, a pair of step-down transistors connected to the choke coil, and a pair of step-up transistors connected to the choke coil, the method comprising:

comparing an output voltage of the DC/DC converter with a reference voltage and generating an error signal that is in accordance with voltage difference between the output voltage and the reference voltage;
comparing the error signal with a triangular wave signal and generating a control pulse signal having a pulse width that is in accordance with the voltage difference between the output voltage and the reference voltage;
controlling the pair of step-down transistors and the pair of step-up transistors based on the control pulse signal;
generating a mode switch signal for switching an operation mode of the DC-DC converter in accordance with the state of the control pulse signal;
and
adding an offset voltage to the triangular wave signal or the error signal in accordance with the mode switch signal.

3 more elements

Dependencies are inferred from the claim text.