| 摘要 |
PURPOSE:To prevent an overcurrent and prevent the exothermic of a transistor at the time of part failure by providing an overcurrent detecting circuit in an inverter lighting circuit. CONSTITUTION:At the time of normal lighting, a transistor 6 is turned on and off at a duty corresponding to the input level of a comparator 7 to supply an electric power of a certain ratio to an inverter part. When a capacitor 3 is short circuited or the emitter or base of transistors 4, 5 is opened to stop oscillation, a current I rapidly increases. If this state is continued, a transistor 6 and the transistor having no failure of the transistors 4, 5 will be exothermic. According to this circuit, when the both end voltages of a resistance 8 is increased to VBE enough to turn on a transistor 9 by the overcurrent, the current is sent to the transistor 9 and also to the gate of a thyristor 10, and the transistor 6 is turned off regardless of the level of light control signal to prevent the exothermic of the transistors 4, 5, 6. |
