| 摘要 |
PURPOSE:To stabilize the control current of a switching element, to reduce the electric power loss of a circuit, and to minimize the capacity of a power source by controlling a control signal supplied to a switching element according to temperature variation and load variation. CONSTITUTION:An FET 6 is connected to the constant voltage source 1 of the driving device through a shunt resistance 2 and a diode 5a and the base of a power transistor TR 4 as the switching element is connected to the FET 6. Further, the anode electrode of the FET 7 is connected between the TR 4 and FET 6 through a diode 5b and the output terminal 7c of an inverting amplifier 7 is connected through a diode 5c to the connection point between the diode 5b and a resistance 13 connected to the ground potential. A voltage set by resistances 8a and 8b and a variable resistance 10 is applied to the negative input terminal 7a of this amplifier 7 and a control signal from a control input terminal 12 which is superposed upon a voltage divided by resistances 9a and 9b is applied to the positive terminal 7b. Then, the output voltage of the amplifier 7 is controlled by a voltage drop across the resistance 2 to make the control current of the TR 4 nearly constant at any time.
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