Lamp control circuit having a V-I converter with slopes of different magnitudes and a second resistor connected in series with a first such that the second senses the output current of the V-I converter

摘要

A lamp current i.sub.L flows through a first resistor. Electric current I, which is the output current of a voltage-current converter which converts a lamp voltage V.sub.L to a lamp current I, flows through a second resistor. Feedback control is executed to make V. sub.-, which is the voltage of one terminal of the second resistor, equal a reference voltage V.sub.ref. The power applied to the lamp during start- up is controlled to be the same as the power applied to the lamp during its stable lighting for a predetermined lamp voltage range. Using the following two linear equations, the electric current I is set as I=aV.sub. L +b (where a and b are positive constants) when the lamp voltage V.sub. L is lower than a first predetermined voltage V.sub.a which is less than the lamp voltage during the normal stable lighting period of the lamp, and as I=cV.sub.L +d (where c and d are positive constants with c a and d b), when the lamp voltage V.sub.L is greater than or equal to the first predetermined value V.sub.a.