Patent ID: 7773398

Claim:
A DC power source device comprising: a pair of main switching elements connected in series to a DC power supply; a transformer which comprises a primary winding connected in parallel to at least one of the main switching elements, a first secondary winding and a second secondary winding connected in series to the first secondary winding; a pair of rectification switching elements connected in series to opposite ends of the first and second secondary windings with the adverse polarity; a polarity detecting means for detecting each polarity of the rectification switching elements; and a timer means connected to the polarity detecting means for synchronously driving the rectification switching elements with the switching operation of the main switching elements to produce the DC output between a junction of the first and second secondary windings of the transformer and a junction of the rectification switching elements; wherein the polarity detecting means comprises conduction detectors for producing a conduction detecting signal when electric current flows through the rectification switching element; the timer means comprises: counters for counting up or down during the conductive period of one of the rectification switching elements and counting down or up during the conductive period of the other of the rectification switching elements, and a drive signal generator for turning the one of the rectification switching elements on by making use of the conduction detecting signal from one of the conduction detectors, and turning the one of the rectification switching elements off upon counting up or down to a predetermined counted number by one of the counters and at the same time resetting the one of the counters; and the timer means counts output time of the conduction detecting signal from the polarity detecting means until electric current through the one of the rectification switching elements comes to zero, and turns the other of the rectification switching elements off at the time of, around or immediately before termination of the counted time.