| 摘要 |
PURPOSE:To always maintain a current value of a circuit current flowing from a current source for a circuit by continuously detecting a current value of a current flowing from a current source for a light emitting element by current control means, and sending a control signal in such a manner that a current value of a difference between a maximum current value and a detected current value flows by a current source for control. CONSTITUTION:Since an emitter current of a transistor Q1, i.e., a bias power source IB of a light emitting element becomes '0' when the Q1 is OFF, a voltage across a resistor R3 is '0'. RD is so decided as to become VBE(Q2)+VBE(Q1)+VBE (Q4)+ID.RD=Vc. When a maximum current flows to the Q1, if R3 is so decided as to become VBE(Q2)+VBE(Q3)+VBE(Q4)+R1.RB=Vc, no voltage is generated at the RD, and hence the ID becomes '0'. If the IB flows from a '0' state, a voltage is generated across the resistor R3, but since the VBE of the Q2, Q3, Q4 are constant, a voltage across the RD is reduced so that the entire voltage becomes the Vc. If the IB is increased, the ID compensates it so that the current IT for a circuit always becomes constant. |
