| 摘要 |
PURPOSE:To simplify a circuit constitution and facilitate the production of the circuit by using a protective fuse, a primary-side current detecting circuit, and first and second gate circuits as principal circuit elements to constitute a circuit which detects rate short generated in a high voltage coil and protects it. CONSTITUTION:When rate short-circuit is generated in a high voltage coil 26, a primary-side current IB is increased. In accordance with this increase, a primary-side current capacity, namely, a detection voltage e1 detected by a detecting resistor 33 is increased. When this detection voltage e1 exceeds the turning-on operation voltage of a PNP transistor TR 34, the TR 34 is turned on to open the gate, and the operating current is applied to the second gate circuit from the collector side. When the TR 34 is turned on over a section of time delay due to the time constant, the gate of a thyristor 41 is opened. Then, the circuit between the anode of an input power source and the earth is shorted and a large current is made flow to a protective fuse 32 to fuse the protective fuse 32. Consequently, smoking and firing from a flyback transformer are prevented. |
