US 3,939,399 AGranted

Power circuit with shunt transistor

AssigneesHitachi, Ltd., Nippon Electric Co., Ltd.

InventorsMichiro Funatsu, Eiichi Matsumura

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Abstract

A power circuit is comprised of a control transistor connected in series between one terminal of a power source and one terminal of a load, an error detecting amplifier circuit for detecting and amplifying changes of the load voltage, a drive transistor for driving the control transistor in response to the output current from the error detecting amplifier circuit, an input-output voltage difference detecting transistor which conducts when the difference between the input and the output voltages of the control transistor decreases to below a predetermined value, and a shunt transistor for shunting the current supplied to the drive transistor when it is activated by the output current of the input-output voltage difference detecting transistor. The power circuit operates as a constant voltage circuit when the input voltage is not lower than the predetermined value, while it operates as a ripple filter with a wide operable range when the input voltage decreases to below the predetermined value.

Claims7

Dependent claims

A power circuit comprising:

a control transistor having a control terminal, an input terminal and an output terminal, said input terminal being connected with one terminal of the power source while said output terminal being connected with one terminal of a load;
an error detecting amplifier circuit connected across the load, for detecting and amplifying changes of the load voltage;
a drive transistor having a control terminal being connected with the output terminal of said error detecting amplifier circuit, a common terminal being connected with the other terminals of the power source and of the load, and an output terminal, which is for amplifying the output current of said error detecting amplifier circuit and supplying it to said control transistor;
a transistor for detecting the difference between the input voltage to and the output voltage from said control transistor, which conducts to produce at an output terminal an output current in accordance with said voltage difference when said voltage difference decreases to below a predetermined value of voltage;
and
a shunt transistor having an input terminal connecting with the control terminal of said drive transistor, an output terminal connected with the other terminals of the power source and the load, and a control terminal connected with the output terminal of said difference detecting transistor to shunt the current supplied from said error detecting amplifier circuit to said drive transistor in accordance with the output current from said difference detecting transistor.

3 more elements

A power circuit comprising:

a control transistor whose emitter is connected to one terminal of the power source circuit, and whose collector is connected to one terminal of a load;
an error detecting amplifier circuit connected across the load for detecting the change of the load voltage and amplifying it;
a drive transistor whose base is connected to the output terminal of said error detecting amplifier circuit, whose emitter is connected to the other terminals of the power source circuit and the load, and whose collector is connected to the base of said control transistor for supplying the output current of said error detecting amplifier circuit to the base of said control transistor;
a series-connected circuit consisting of a resistor and a constant current source being connected across the power source circuit;
a detecting transistor whose emitter is connected to the collector of said control transistor whose base is connected to the connecting point of said resistor and said constant current source, which produces the output current at its collector in accordance with the emitter-collector voltage of said control transistor, when the emitter-collector voltage thereof reduces to below a predetermined value;
and
a shunt transistor whose collector is connected to the base of said drive transistor, whose emitter electrode is connected to the other terminal of the power source circuit, and whose base is connected to the collector of said detecting transistor, which is for shunting the output current from said error detecting amplifier in accordance with the output current of said transistor.

4 more elements

Dependencies are inferred from the claim text.