| 摘要 |
PURPOSE:To stop the oscillation operation of a switching circuit immediately when it comes to an emitterless condition by providing a triple-terminal control element to stop a current to drive a transistor flowing from a driving circuit of the switching circuit by the current flowing in to a control terminal. CONSTITUTION:When a fluorescent lamp 7 becomes to an emitterless condition, the lamp 7 is discharged with difficulty to increase the impedance, a large current flows through a positive property of thermistor 21, and when the temperature exceeds the Curie temperature, the resistance value increases suddenly. As a result, the potential at the contact of the thermistor 21 and a capacitor rises, and a current flows into the control terminal of a transistor 23 which is a tripleterminal control element through a Zener diode 22 which is a voltage response switching element. And, by this current, the triple-terminal control element is operated to stop the current to drive the transistor 6 of a circuit 11 from the driving circuit of a switching circuit 11. Consequently, the oscillation operation of the circuit 11 is stopped immediately. |
