| 摘要 |
PURPOSE:To prevent an electric shock and reduce the cost of a device by providing a firing angle control part on the side of a tertiary coil of a tripod transformer and switching AC electric power stepwise. CONSTITUTION:When a switch 13 is closed, a voltage is induced across the tertiary coil 8 and the electric current is converted to direct current by a full- wave rectifier 14. A capacitor 21 is charged, and when its voltage rises above the voltage of the gate G of an NPN and PNP transistor (TR) coupling circuit 22, TRs Q2 and Q1 turn on. The TRs Q1 and Q2 enter a positive feedback state speedily to turn on showing negative resistivity, so the capacitor 21 is discharged speedily, and thus charged and discharged repeatedly in a half cycle by the resistance value switching of a switch 17 to generate a pulse signal synchronizing with the power source frequency, thereby applying a plus voltage to the terminal T1 of a triac 25 and a minus voltage to the gate G. Therefore, the triac 25 turns on corresponding to the phase angle of the pulse signal and the voltage brought under the stepwise phase control of the switch 17 is applied to a load, thereby controlling the AC electric power stepwise. |
