Pulse width modulation circuit and illuminating device incorporating same

摘要

In a pulse width modulation circuit, which generates an output whose pulse width is modulated by controlling a duty ratio of an oscillation circuit adapted to generate an oscillation at a frequency determined by a resistor (RT) and a capacitor (CT) to be electrically charged via the resistor (RT), there is provided a resistance value varying means to vary a value of the resistor (RT). The value of the resistor is varied by shorting the both ends of the resistor (RT) with a transistor (TRZ), whereby the capacitor (CT) is charged in a reduced amount of time realizing a high-speed pulse width modulation circuit. <IMAGE>