CONSTANT-CURRENT SOURCE CIRCUIT

PURPOSE:To obtain exactly a fixed ratio of an output current to a reference current, by combining suitably the first-the eighth transistors and the first-the fourth diodes so that they are operated by low voltage. CONSTITUTION:A titled circuit is provided with a transistor Q7 for constituting a constant-current circuit formed by coupling a diode D3 and a mirror, and also is provided with a constant-current circuit constituted of transistors Q8-Q10 which uses a collector current of the transistor Q7 as a reference current. The constant-current circuit is constituted of only transistors Q3, Q4, therefore, even if the reference transistor Q3 is connected with a diode, influence due to a base current of the transistor Q4 is small. Accordingly, collector currents of the transistors Q7, Q4 and Q3 are equal and are decided exactly by a resistance R2. An output current to the reference current being the collector current of the transistor Q7, that is to say, a ratio of a collector current of a transistor group 10 becomes ''1''.