| 摘要 |
PROBLEM TO BE SOLVED: To lessen the resistance of a lamp current sensing circuit. SOLUTION: A discharge lamp lighting device includes an amplifier circuit 21 which amplifies the sensing voltage of a lamp current detecting circuit (resistor 20), and a control circuit composed of a gradient changeover circuit 22, impedance conversion circuit, adder circuit 24, reference voltage source 25, comparator circuit 26 and error amplifier circuit 27 prepares a control signal on the basis of the output of the amplifier circuit 21 and the output of a lamp voltage sensing circuit (R21 and R22) and supplies it to a pulse width control means 28, and thereby the On width of a PNP transistor Tr20 is controlled, so that the value of sensing resistor of the lamp current sensing circuit can be lessened. |
