| 摘要 |
PURPOSE:To devise to protect a thyristor even if an instataneous interruption of service is given by detectng the voltage between thyristor termials for checking a gate signal from the thyristor unless the voltage is risen over a certain set point. CONSTITUTION:A resonance circuit is composed of a condenser 7 and a reactor 8. The reactor is used for a heating coil. The voltage between terminals of a thyristor 5 is detected by terminals A and B of a VF detecting circuit 10. For example, when the voltage between the terminals is under the command set by a Zener diode 102, a transistor (Tr) is off and Tr 111 is on. When the voltage between the terminals is risen to the set voltage, Tr 104 is on and Tr 111 is off for starting the charging of a condenser 114 through resistances 112 and 113. When the condenser voltage is risen to the set voltage set by resistances 115 and 116, a gate signal is given from a comparator 117 to the thyristor 5. |
