REGULATOR

Provided is a regulator configured to output a stable voltage even when a power supply voltage fluctuates suddenly. The regulator includes: a reference voltage circuit; a differential amplifier; a depletion type NMOS transistor; and a bleeder circuit, in which a power supply terminal of the differential amplifier is connected to an output terminal of the regulator. Further, a power supply terminal of the reference voltage circuit is connected to the output terminal of the regulator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a circuit diagram of a regulator according to an embodiment of the present invention. The regulator according to the embodiment of the present invention includes a reference voltage circuit1, a differential amplifier2, a depletion type NMOS transistor3, and a voltage dividing circuit4.

The reference voltage circuit1has a positive electrode connected to a power supply terminal and a negative electrode connected to a ground terminal. The differential amplifier2has a non-inverting input terminal connected to an output terminal of the reference voltage circuit1, an inverting input terminal connected to an output terminal of the voltage dividing circuit4, a positive electrode connected to an output terminal of the regulator, and a negative electrode connected to the ground terminal. The depletion type NMOS transistor3has a drain connected to the power supply terminal, a source connected to the output terminal of the regulator, and a gate connected to an output terminal of the differential amplifier2. The voltage dividing circuit4is connected between the output terminal of the regulator and the ground terminal.

An output voltage Vout of the regulator according to the embodiment of the present invention is determined as expressed in Expression 1.

where Vref represents a reference voltage, and R1 and R2 represent resistance values of resistors constituting the voltage dividing circuit.

In the regulator according to the embodiment of the present invention, the positive electrode of the differential amplifier2is connected to the output terminal of the regulator. In other words, the differential amplifier2operates by using the output voltage Vout of the regulator as power supply. Therefore, even when a power supply voltage Vin fluctuates suddenly, an output voltage Vg of the differential amplifier2does not fluctuate.

As described above, in the regulator according to the embodiment of the present invention, even when the power supply voltage Vin fluctuates suddenly, the stable output voltage Vout is output.

FIG. 2is a circuit diagram of another example of the regulator according to the embodiment of the present invention.

The regulator ofFIG. 2has a configuration in which the positive electrode of the reference voltage circuit1is also connected to the output terminal of the regulator.

The reference voltage circuit is designed to output a fixed voltage as the reference voltage Vref regardless of the power supply voltage. In the configuration as illustrated inFIG. 2, the reference voltage circuit is even less likely to be affected by the fluctuation of the power supply voltage. Therefore, the regulator ofFIG. 2outputs the stable output voltage Vout even when the power supply voltage Vin fluctuates suddenly.