| 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 Q3 and Q4 are not operated, and a signal voltage is not generated in a tertiary coil 8 at all. But when the switch 17 is closed, a capacitor 20 is charged to make TRs Q3 and Q4 conductive. In this case, since TRs Q3 and Q4 are made conductive while showing a negative resistance, the electric charge of the capacitor 20 is discharged, and a pulse signal synchronized with a power source frequency is generated. A secondary coil 7 is short-circuited by this pulse signal, and a voltage corresponding to this short-circuit is induced in the tertiary coil 8 (360 deg. or less behind the power source frequency) to fire a switching element 14, and a load current is flowed to a load 13. The value of a variable resistance 19 is changed to control the phase in the range of 0-180 deg.. |
