| 摘要 |
PROBLEM TO BE SOLVED: To suppress harmonic current, harmonic voltage, and voltage fluctuation flicker, and prevent deterioration and malfunction of a device, by increasing a current continuously or by steps to a steady state when a lamp is turned on and decreasing the current continuously or by steps when the lamp is turned off. SOLUTION: When an on-signal is inputted into a control-signal input terminal 14 to turn on a tungsten halogen lamp, an output voltage of a reference-voltage generating circuit 10 begins to gradually rise. A voltage comparator 12 compares it with a voltage of a triangular-wave oscillating circuit 11, and outputs a signal to a driver 13 for turning on an IGBT 8 during a period in which the output voltage of the reference-voltage generating circuit 10 is greater than the output voltage of the triangular-wave oscillating circuit 11 and turning off the IGBT 8 during a period in which the output voltage of the reference-voltage generating circuit 10 is smaller than the output voltage of the triangular-wave oscillating circuit 11. Also when the lamp is turned off, the PWA control is performed under which turning on and off of the IGBT 8 are repeated. Changes in voltage and current are suppressed by a choke coil 4, therefore their peaks are reduced and their changes become gradual, and harmonics of the fundamental frequency of the PWM control are less liable to occur.
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