Patent ID: 8129975
Filing Date: 2012-03-06
Classification: H02M,Y02B

Abstract:
1. A synchronous rectifying DC-DC converter increasing or decreasing an input voltage to an output voltage, comprising: a switching transistor being turned on and off at a duty cycle according to a ratio between the input voltage and the output voltage to stop and start a supply of the input voltage to convert the input voltage into a pulsed voltage; a commutating transistor being tuned off in synchronization with turning on of the switching transistor; a ramp generator outputting a ramp synchronizing to a switching period of the switching transistor; an error amplifier into which a feedback signal of the output voltage and a reference voltage for the output voltage are input; a holding circuit for temporarily holding a peak voltage of the ramp output from the ramp generator; a variable amplifier amplifying the peak voltage held in the holding circuit in accordance with a first value stored in a nonvolatile memory; a first comparator comparing the voltage of the ramp with an output voltage of the error amplifier and, when the voltage of the ramp is lower than the output voltage of the error amplifier, outputting a logic signal for turning on the switching transistor and, when the voltage of the ramp exceeds the output voltage of the error amplifier, outputting a logic signal for turning off the switching transistor; a second comparator comparing an output voltage of the variable amplifier with the output voltage of the error amplifier and, when the output voltage of the variable amplifier exceeds the output voltage of the error amplifier, outputting a logic signal for turning on the commutating transistor and, when the output voltage of the variable amplifier is lower than the output voltage of the error amplifier, outputting a logic signal for turning off the commutating transistor; a third comparator comparing the output voltage of the variable amplifier with the voltage of the ramp and, when the output voltage of the variable amplifier exceeds the voltage of the ramp, outputting a logic signal for turning on the commutating transistor and, when the output voltage of the variable amplifier is lower than the voltage of the ramp, outputting a logic signal for turning off the commutating transistor; a delay circuit inserting a delay time in a logic signal output from the first comparator; and an AND circuit performing an AND operation on logic signals output from the delay circuit, the second comparator, and the third comparator; wherein the switching transistor is turned on or off on the basis of a logic signal output from the first comparator, and the commutating transistor is turned on or off on the basis of a logic signal output from the AND circuit.