VARIABLE OUTPUT TYPE CONSTANT CURRENT SOURCE CIRCUIT INCLUDING FIRST SELF-BIASING TYPE CONSTANT CURRENT CIRCUIT, SWITCHING CIRCUIT, AND SECOND CONSTANT CURRENT CIRCUIT

摘要

PURPOSE: A variable output type constant current source circuit is provided to change output current through stages, and prevent complication of circuit and increase in the size of a semiconductor substrate. CONSTITUTION: A variable output type constant current source circuit comprises a first self-biasing type constant current circuit(3a); a switching circuit(5); and a second constant current circuit(4). The first constant current circuit includes a resistor connected in serial; a first transistor(M1); a second transistor(M2) which cooperates with the first transistor to supply a predetermined voltage to both ends of the resistor and generate a reference current; a third transistor(M3) connected in serial to the first transistor; and a fourth transistor(M4) connected in serial to the second transistor, and cooperating with the third transistor to constitute a current mirror circuit. The switching circuit has a fifth transistor(M5) connected in serial to the resistor. The second constant current circuit is connected in parallel to a serial circuit of the second transistor, the resistor, and the fifth transistor. The current passing through the second transistor and the fourth transistor varies in accordance with the state of the fifth transistor, to thereby vary an output current.