| 摘要 |
PURPOSE:To eliminate a danger of electric shock and to control the phase in a wide range by controlling the firing angle of a switching element with the output signal of a tertiary coil of a tripod transformer coupled electromagnetically with a firing angle control part. CONSTITUTION:When a switch 17 is opened, transistors TRs Q2 and Q1 are not operated, and a voltage is not generated in a tertiary coil 8 at all. But when the switch 17 is closed, a capacitor 20 is charged, and TRs Q2 and Q1 are made conductive when the capacitor 20 reaches a prescribed voltage value. In this case, since TRs Q1 and Q2 are made conductive while showing a negative resistance, the electric charge of the capacitor 20 is discharged, and a pulse is generated synchronously with a power source frequency, and a TR21 is made cnductive to short-circuit a secondary coil 7. Then, a voltage is induced in the tertiary coil (360 deg. or less behind the power source frequency), and a switching element 14 is fired in accordance with short-circuit of the coil 7, and a voltage is applied to a load. The value of a variable resistance 19 is changed to control the phase in the range of 0-180 deg.. |
