| 摘要 |
PROBLEM TO BE SOLVED: To provide a power unit which can reduce the power loss with a current detecting resistor, and also can remove the influence of the through current of a switching element. SOLUTION: When pulses are outputted from an oscillating circuit OSC, a flip flop circuit FF is set, and a switching element Q1 is turned on, and the current to a detecting resistor R1 increases with the lapse of time. Then, when this current value and the power value calculated from the input voltage value of a lamp drive circuit LD come to the set values, reset pulses are outputted from the calculation result output terminal of a constant power arithmetic circuit M, and the flip flop circuit FF is reset, the switching element Q1 is turned off. On the other hand, in the case that the through current flows on of the switching element Q1, the output of the oscillating circuit OSC is high and the output of an invetor IN is low at this time, so that reset pulses form the constant power arithmetic circuit M are drawn in via a diode D2, therefore the flip flop circuit FF is not reset. COPYRIGHT: (C)2004,JPO |
