POWER SUPPLY DEVICE AND ELECTRICAL DEVICE EQUIPPED WITH THE SAME

Abstract

A power supply device includes a first transistor connected in series between an input terminal to which an input voltage is applied and an output terminal from which an output voltage is led out; a second transistor connected between the input terminal and the output terminal in parallel with the first transistor, and which is arranged to supply a portion of the output current to a load as a detection current; a control voltage production unit arranged to produce a control voltage of the first and second transistors so that the output voltage is maintained at a specified target value; a first constant current source arranged to produce a first constant current; a variable current source arranged to produce a variable current in accordance with the output voltage; a first resistor arranged to produce a reference voltage in accordance with a combined current of the first constant current and the variable current; a second constant current source arranged to produce a second constant current; a second resistor arranged to produce a detection voltage in accordance with a combined current of the second constant current and the detection current; and an offset circuit arranged to apply an offset to the control voltage in accordance with the reference voltage and the detection voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a preferred embodiment of the electrical device of the present invention.

FIG. 2 is a circuit diagram showing one example of the construction of the power supply device 20.

FIG. 3 is a circuit diagram showing one example of the construction of the offset circuit OFS.

FIG. 4 is a circuit diagram showing one example of the construction of the variable current source Iv.

FIG. 5 is a correlation graph of io-Vo in a preferred embodiment of the present invention.

FIGS. 6( a) and 6(b) show conventional io-Vo correlation graphs.

Claims

1. A power supply device comprising: a first transistor connected in series between an input terminal to which an input voltage is applied and an output terminal from which an output voltage is led out;a second transistor connected between said input terminal and said output terminal in parallel with the first transistor, and which is arranged to supply a portion of the output current to a load as a detection current;a control voltage production unit arranged to produce a control voltage of the first and second transistors so that said output voltage is maintained at a specified target value;a first constant current source arranged to produce a first constant current;a variable current source arranged to produce a variable current in accordance with said output voltage;a first resistor arranged to produce a reference voltage in accordance with a combined current of the first constant current and said variable current;a second constant current source arranged to produce a second constant current;a second resistor arranged to produce a detection voltage in accordance with a combined current of the second constant current and said detection current; andan offset circuit arranged to apply an offset to said control voltage in accordance with said reference voltage and said detection voltage.

2. The power supply device according to claim 1, wherein said variable current source is arranged to reduce said variable current in accordance with a drop in said output voltage, said reference voltage and said detection voltage exhibit an increase in voltage value in accordance with a decrease in currents respectively flowing through the first and second resistors, and said offset circuit does not apply any offset to said control voltage when said detection voltage is higher than said reference voltage, and conversely said offset circuit applies an offset to said control voltage so that the first and second transistors are closed in accordance with the increase in the differential voltage when said detection voltage is lower than said reference voltage.

3. The power supply device according to claim 1, wherein said variable current source comprises: a constant current source arranged to produce a specified constant current;a PNP bipolar transistor whose emitter is connected to the output terminal of said constant current source, whose collector is connected to the ground terminal, and whose base is connected to the application terminal of said output voltage or a divided voltage thereof; andan NPN bipolar transistor whose base is connected to the emitter of said PNP bipolar transistor, whose emitter is connected to the ground terminal via a resistor, and whose collector is connected to the output terminal of said variable current.

4. The power supply device according to claim 1, wherein the first and second transistors are field effect transistors.

5. The power supply device according to claim 1, wherein said first and second transistors are P-channel field effect transistors.

6. The power supply device according to claim 1, wherein the offset circuit includes NPN bipolar transistors, PNP bipolar transistors, a resistor, and a constant current source.

7. The power supply device according to claim 1, wherein the variable current source includes a PNP bipolar transistor, an NPN bipolar transistor, a resistor, and a constant current source.

8. The power supply device according to claim 1, wherein the offset circuit includes a differential amplifier to which said reference voltage and said detection voltage and such that driving control of one of said first and second transistors is performed in accordance with differentially amplified output produced by the offset circuit.

9. An electrical device comprising a power supply device according to claim 1.