| 摘要 |
PURPOSE:To adjust light intensity smoothly by providing a light intensity adjustment control signal generation circuit, a control voltage generator, and a voltage control oscillator, and using the output of the voltage control oscillator as a clock of the light intensity adjustment control signal generation circuit. CONSTITUTION:A voltage control oscillator VCO90, which is provided for using its frequency-modulated pulse as a clock of a light intensity adjustment control signal generation circuit 30, outputs a output pulse sequence Vf, having a frequency in proportion to an input voltage, to a down counter CO1 for PWM cycle generation of the circuit 30. That is, the output pulse sequence Vf is used as the clock of the counter CO1. On the other hand a zero cross signal Zi is used as a clock of a down counter CO2. A PWM cycle signal Vca, which is output to an inverter 30e, becomes a borrow signal of the counter CO2. Thereby frequency modulation can be set so as a higher frequency at low brightness time and as a lower frequency at high brightness time, and it is possible to M digital style change of brightness unapparent so as light intensity to be adjusted smoothly. |
