| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a lighting circuit capable of suppressing variation in brightness even if there is variation in the resistance value of each lamp and extending service life of a lamp by setting a current value supplied to each lamp to a minimum value of a rated current and lighting the lamp. SOLUTION: A lighting circuit L1 of a lamp PL1 comprises the lamp PL1, a transistor Tr1 for current control, a resistor R1, and similarly L2 and L3. A resistor R0 and a Zener diode ZD comprise a bias voltage circuit of Tr1 to Tr3 and comes into contact with a power source Vcc together with the lighting circuits PL1 to PL3. The lamps PL1 to PL3 are driven by the same setting current I and is set to a rated current of a dark lamp with its least current in the lamps PL1 to PL3. Thereby, when the rated or more current is let flow in the dark lamp, a voltage between lamp terminals is prevented from exceeding a rated voltage, thereby making it possible to extend service life.</p> |
