Abstract: The backrest of a chair comprises an inner low rigidity flexible back-receiving portion and an outer high-rigidity side frame spaced from the back-receiving portion via a slit. The backrest is integrally molded by synthetic resin, thereby shortening manufacturing process and reducing its cost. Comfort of a sitting person is also attained.

Abstract: In a power conversion apparatus, a first switch is connected in series with a dc capacitor between P and N terminals of a dc circuit. The first switch is formed of a switched valve device and a diode connected in reverse parallel with each other. The switched valve device of the first switch and switched valve devices used in individual arms of a second power converter are voltage-driven switched valve devices. An on-gate voltage of the switched valve device of the first switch is made lower than an on-gate voltage of the switched valve devices of the second power converter.

Abstract: In a gate control device for four self-arc extinction elements connected in series and two self-arc extinction elements connected in reverse parallel between the respective terminals of clamp diodes, individually, there is provided a PWM circuit that generates conduction control commands, and a gate control circuit including a delay circuit group that generates gate signals with respect to the respective self-arc extinction elements on the basis of respective conduction control commands. A pair of the self-arc extinction elements are rendered conductive at the same time, and another pair of the self-arc extinction elements are rendered conductive at the same time.

Abstract: In a gate control device for self-arc extinction elements (T1) to (T4) and self-arc extinction elements (T5) and (T6) connected in reverse parallel between the respective both terminals of clamp diodes (D5) and (D6), individually, there are provided a PWM circuit (2) that generates conduction control commands (SP) and (SN), and a gate control circuit (3) including a delay circuit group that generates gate signals (ST1) to (ST6) with respect to the respective self-arc extinction elements on the basis of the respective conduction control commands. The self-arc extinction elements (T3) and (T5) are rendered conductive at the same time under control, and the self-arc extinction elements (T2) and (T6) are rendered conductive at the same time under control.

Abstract: The backrest of a chair comprises an inner low rigidity flexible back-receiving portion and an outer high-rigidity side frame spaced from the back-receiving portion via a slit. The backrest is integrally molded by synthetic resin, thereby shortening manufacturing process and reducing its cost. Comfort of a sitting person is also attained.

Abstract: A chair comprises a back cushion material, a back plate and a back frame. The chair is used for looking at a display of a personal computer at suitable posture when it is reclined. The back plate comprises upper and lower shell which are connected by a flexible bent portion to each other. The back plate is mounted to the back frame at the upper end and a lower portion. When the chair is reclined, the upper shell is moved forwards and the lower shell is moved rearwards, so that an angle between the upper and lower shells may become smaller. Thus, the operator can take suitable posture for looking at the display any time.