Dropper-type DC stabilized power supply circuit provided with difference amplifiers for supplying a stable output voltage

#The present invention relates to a dropper-type DC stabilized power supply circuit in which a power transistor is provided in series with a power supply line connecting a DC power source and a DC load so that an output voltage is stabilized by controlling a base current of the power transistor, and especially pertains to an improvement of the responsiveness of the output voltage when stabilizing the voltage.

#FIG. 8 is a block diagram illustrating an electric structure of a typical dropper-type DC stabilized power supply circuit 1 of conventional art. This DC stabilized power supply circuit 1 is generally arranged such that an output capacitor c is externally attached to a circuit chip 2 of a semiconductor, and a power transistor q is provided in series with a power source line 3 between an input terminal p1 connected to a DC power source so as to receive an input voltage Vin and an output terminal p2 connected to a DC load so as to output an output voltage Vo. The base current of the power transistor q is controlled by a base drive circuit composed of a control transistor tr, etc.

#The output voltage Vo is divided by voltage dividing resistors r1 and r2 so that a divided voltage value Vadj is generated, and the divided voltage value Vadj and an external reference voltage Vref, the latter complying with a band gap voltage, are supplied to a difference amplifier a. The voltages Vadj and Vref are compared with each other by the difference amplifier a, and the difference between the voltages is amplified so as to be sent to the base of the control transistor tr. Also, the control transistor tr controls the base current of the power transistor q and hence the output voltage Vo is kept at a constant value. Between the base and the emitter of the power transistor q, a bias resistor r3 is provided, whereas to the emitter of the control transistor tr, a current restraining resistor r4 is connected. These resistors r3 and r4 constitute the above-identified base drive circuit.

#FIG. 1 is a block diagram illustrating an electrical arrangement of a DC stabilized power supply circuit in accordance with an embodiment of the present invention.

#FIG. 2 is an electric circuit diagram illustrating a first difference amplifier of the DC stabilized power supply circuit in FIG. 1.

#FIG. 3 is an electric circuit diagram illustrating a second difference amplifier of the DC stabilized power supply circuit in FIG. 1.

#Referring to FIGS. 1 to 7, an embodiment of the present invention will be described as follows.

#FIG. 1 is a block diagram illustrating an electrical arrangement of a DC stabilized power supply circuit 11 in accordance with the present embodiment. This DC stabilized power supply circuit 11 is generally arranged such that an output capacitor C is externally attached to a circuit chip 12 of a semiconductor, and a power transistor Q is connected in series with a power source line 13 provided between (i) an input terminal P1 connected to a DC power source so as to receive an input voltage Vin and (ii) an output terminal P2 connected to a DC load so as to output an output voltage Vo. The base current Id of the power transistor Q is controlled by a base drive circuit composed of a control transistor TR1, etc.

#The output voltage Vo is divided by voltage dividing resistors R1 and R2 so that a divided voltage value Vadj is generated, and the divided voltage value Vadj and an external reference voltage Vref, the latter being produced with reference to a band gap voltage, are supplied to a difference amplifier A1. The voltages Vadj and Vref are compared with each other by the difference amplifier A1, and the difference between the voltages is amplified so as to be sent to the base of the control transistor TR1. Also, the control transistor TR1 controls the base current of the power transistor Q and hence the output voltage Vo is kept at a constant value. Between the base and emitter of the power transistor Q, a bypass transistor TR2 which is described later is provided, whereas to the emitter of the control transistor TR1, a current restraining resistor R3 is connected. The bypass transistor TR2 and the resistor R3 constitute the above-identified base drive circuit.