| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To suppress the power loss of a switching element even if a voltage is increased that is applied to a switching element connected to a semiconductor light source. <P>SOLUTION: A method for suppressing the power loss of a switching element comprises steps of inserting a transistor 14 and a resistor R1 in series in a current supply path 22, connecting an operational amplifier 16 to the gate of the transistor 14, connecting a feedback circuit 18 between the drain-source of the operational amplifier 16, inputting voltages at both ends of the resistor R1 to a negative input of the operational amplifier 16, dividing a voltage between the drain and the source of the transistor 14 by a resistor R8, a thermistor TH and a resistor R7, performing control for making a predetermined current I0 flow into the transistor 14 by the operational amplifier 16 until the voltages at both the ends of the resistor R8 exceed a zener voltage of a zener diode Z1, and performing control for making the operational amplifier 16 derate a forward current of the transistor 14 so as to be smaller than the predetermined current I0 with an increase of a negative input when the voltages at both the ends of the resistor R8 exceed the zener voltage of the zener diode Z1. <P>COPYRIGHT: (C)2006,JPO&NCIPI</p> |
