| 摘要 |
PROBLEM TO BE SOLVED: To provide a stabilized direct current power supply unit for preventing thermal destruction of an output transistor even when the output transistor is provided externally. SOLUTION: A conventional external indication means for a state of a device using only a small LED as a light emitting element had a problem that an operator of the device can misjudge or overlook a state of the device because the light emitting portion of the LED was small, and it is an obstacle for downsizing the device because an LED attachment portion had to be provided in the device even though the LED is small. The stabilized direct current power supply unit comprises a current detection circuit (a current detection resistor R1 and an operation amplifier 6) for detecting an output current of an external output transistor 1; an operation amplifier 9 for detecting a voltage between an input and an output of the output transistor 1; a multiplication circuit 10 for multiplying an output of the current detection circuit and an output of the operation amplifier 9; and a protection circuit (operation amplifier 7, a constant current source 8 and an external resistor R2) for controlling a gain of an operation amplifier 4 for driving the output transistor 1 based on an output of the multiplication circuit 10 so that a wattage of the output transistor 1 does not exceeds a certain value. COPYRIGHT: (C)2004,JPO
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