| 摘要 |
PURPOSE:To reduce the cost and number of used parts and, at the same time, to eliminate the necessity of pulse control from an electric secondary side, by respectively connecting one ends of 1st and 2nd resistances, whose other ends are connected to the gate electrode of a triode AC switch, with the connecting point of a positive- characteristic thermistor and demagnetizing coil and an electrode provided on the AC input source side. CONSTITUTION:When a switch 2 is turned on, an electric current is made to flow to resistances 6 and 7 through a positive-characteristic thermistor 3 and a trigger voltage is applied to the gate electrode of a triode AC switch 5. As a result, the switch 5 is turned on and a gradually decreasing electric current is made to flow to a demagnetizing coil 4 as a demagnetizing current. On the other hand, the trigger voltage applied to the gate electrode of the triode AC switch 5 also becomes a gradually dropping AC voltage by the action of the thermistor 3 and, after a fixed time, further drops to a level which is lower than a prescribed level required for turning on the switch 5 and the triode AC switch 5 is turned off because an AC voltage of the opposite polarity is applied to the main electrodes of the switch. Therefore, the pulse generating circuit which is required for controlling the turning on and turning off of the switch 5 as a switching element becomes unnecessary.
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