| 摘要 |
PROBLEM TO BE SOLVED: To prevent fluctuation of the value of current flowing in an FET, due to fluctuation in the voltage and operating temperature of a main power supply and that in the threshold of the FET, using a simple circuit configuration. SOLUTION: A main current Id1, flowing into the FET 1 from a differential amplification section consisting of the FETs 4 and 5 flows to a resistor R1, thus generating a monitoring voltage Vmon in the resistor R1, and determining a gate voltage Vg which is the division voltage value of resistors R2 and R3, based on the monitor voltage Vmon. The gate voltage Vg is inputted to the gate terminal of the FETs 1 to 3 at a constant-current control section, thus controlling the current value of the FETs 1 to 3. For example, if the main current Id1 flowing in the FET 1 is increased, the level of the monitor voltage Vmon drops to a GND side, and the gate voltage Vg is decreased, thus causing the current of the FET 1 to be reduced. In this manner, the FET 1 is subjected to constant-current control, based on the gate voltage Vg, and consequently, can compensate for the current fluctuation in each FET.
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