Patent ID: 7612542

Claim:
A power unit which includes a DC power source and a switching converter that includes a switching element for turning on and off an input primary voltage from the DC power source and a reactor to be charged and discharged according to turning on and off of the switching element, and can adjust an output voltage by charging and discharging the reactor, comprising: a detection means which detects the output voltage value, a duty setting means which decides a duty ratio so as to converge a difference between the output voltage value and a reference voltage value at a predetermined allowable value, a switching means which drives the switching element according to the duty ratio set by the duty setting means; and current value estimating means which estimates a current value flowing in the switching element by using the input primary voltage value, a duty ratio of the switching element, and an inductance of the reactor, wherein the switching means drives the switching element based on the estimated current value so as to prevent the estimated current value from becoming equal to or more than a predetermined allowable current value.