| 摘要 |
PURPOSE:To carry out ON/OFF of a lamp certainly according to an external signal by composing a light modulation controlling apparatus used for a liquid crystal display device of an OA appliance, etc., with a PWM circuit which generates a pulse with a duty ratio responding to a modulation signal, an auto matic monolithic inverter, a main transistor, and a switching transistor. CONSTITUTION:In a common light modulation controlling circuit for cold cath ode ray-tube modulation lighting in 2-3W level for use of back light, even when a transistor 7 is turned OFF by sending of a lamp OF signal to a base of the transistor 7, the oscillation of an inverter sometime does not stop and a lamp 9 is not alway turned OFF. The transistor 7 is removed from common circuit, a starting resistor 6 is connected directly to a direct current electric power source VCC, and a PNP transistor 11 for reversing a lamp ON/OFF signal and applying it to a base of a transistor 5 is additionally installed. By this way, at the time of an input of a lamp OFF signal, it is applied to the base of the transistor 11 so as to turn the transistor 5 ON, short-circuit a main transistor 1, and stop the oscillation of an inverter. |
