| 摘要 |
PURPOSE:To carry out output control according to the characteristics of load without installing a special circuit by composing a controlling circuit in the way of releasing a control to keep an output voltage of a chopper circuit constant when a duty ratio reaches a prescribed value. CONSTITUTION:A discharge lamp lighting circuit 1 is so called a full bridge circuit and composed of transistors Q1-Q4 as switching devices which are connected in pairs in series, a choke coil L1 and a discharge lamp DL as a HID lamp inserted between connecting points of each circuit of transistors Q1, Q3 and Q2, Q4 in series. Current amount to the discharge lamp lighting circuit 1 is detected by a resistor R3 and ON-OFF control of each transistor Q1-Q4 is carried out by a controlling circuit Co1 according to the current amount. When electric power consumption of the discharge lamp DL reaches Wa, a controlling circuit Co controls not to increase the electric power consumption more. In this way, the controlling circuit is set in a way of setting the duty ratio of a transistor Q to be the maximum in a range of electric power consumption Wl at least a prescribed value. |
