| 摘要 |
PROBLEM TO BE SOLVED: To provide a power unit preventing application of great stresses to the switching elements of an inverter circuit during startup. SOLUTION: The input of power is detected by a voltage detector circuit 12. A capacitor C14 is charged gradually, the collector-emitter current of a transistor Q11 is decreased, and the collector-emitter current of a transistor Q12 is smoothly decreased for turning off. Since the apparent resistance values of a resistance R14 and the emitter and collector of the transistor Q12 increase gradually, the apparent impedance of the parallel circuit of resistances R1, R14 increases smoothly and a control circuit 4 is finally controlled by the resistance value of only the resistance R1. Since a current flowing in the resistance R1 increases even if currents flowing in the drain and source of a field effect transistor Q1 are of the same value, the output of a step-up chopper circuit 3 is reduced to eliminate overshoot during the input of power so as to prevent application of great stresses to field effect transistors Q2, Q3. |
