Abstract: A power inverter for use in the system interconnection of a direct-current supply with a commercial alternating-current supply includes an inverter circuit and a filter circuit. Feedback signals affecting the frequency of an output to be produced by the inverter circuit are taken from the filter circuit having frequency response characteristics such that the phase angle is reduced to 0.degree. at three frequencies consisting of a higher frequency, lower frequency and commercial frequency, the last of which lies halfway between the first and second. Under the normal condition, the frequency of the output produced by the inverter circuit is equal to the commercial frequency. In the event of a power failure or power cut in the commercial alternating-current supply system, deviation from the commercial frequency is caused by the characteristics of the filter circuit.

Abstract: A safety device for an automobile vehicle includes a first integration circuit for integrating an output value generated from a G sensor and a decision circuit for comparing the integrated value with a predetermined decision level to determine whether the safety device should be activated. In the first integration circuit, a previously integrated value is incrementally reduced to provide a current integrated value.

Abstract: A power source apparatus for microwave oven includes a half-bridge converter including a series connection of switching elements, a series connection of resonance capacitors, and a high frequency transformer having a primary winding and a secondary winding, and the half-bridge converter is driven by an output of a diode bridge which receives a commercial power source of 200 V. A current transformer detects a current of the primary winding. A control circuit compares a voltage equal to an average value of the current detected by the current transformer and a voltage set by a microcomputer, and controls the switching elements at a frequency in proportion to a magnitude of a difference of the both voltages, whereby a high frequency high voltage is induced on the secondary winding and applied to a voltage doubler rectifying circuit, and then a direct current high voltage is applied to a magnetron.