CONSTANT CURRENT SOURCE CIRCUIT

PURPOSE:To supply a current of large value to a load circuit without increasing the gate width of an FET by using an FET and a resistance connected between the drain and the gate of the FET. CONSTITUTION:A resistance 3 is formed between the drain and the source of an FET 2, and the FET 2 and the resistance 3 form a constant current circuit. This current circuit supplies a constant current to a load circuit connected in series to a drain-source circuit of the FET 2. In such a constitution, the voltage VA is applied to the drain together with the voltage VB lower than the VA applied to the source. Thus the voltage decided by the resistance ratio set between a diode and the resistance 3 is applied between the gate and the source of the FET 2. Thus a slight current flows between the gate and the source of the FET 2. As a result, the positive voltage is generated between the gate and the source of the FET 2. Thus the value of the current supplied to the circuit 4 can be changed by selecting the ratio between the resistance 3 and the gate-source resistance value of the FET 2. Then a current of large value can be supplied to the circuit 4.