VOLTAGE REGULATOR

• US 20110062921A1
• Filed: 09/15/2009
• Published: 03/17/2011
• Est. Priority Date: 09/15/2009
• Status: Active Grant

• Current Assignee: Ablic Inc. (Minebea Mitsumi, Inc.)
• Original Assignee: Seiko Instruments Incorporated (Seiko Group)
• Inventors: Sudou, Minoru
• Granted Patent: US 8,198,875 B2
• Time in Patent Office: Days
• US Class Current: 323/273
• CPC Class Codes: G05F 1/56 using semiconductor devices in series with the load as final control devices G05F1/461 takes precedence

Abstract

Provided is a voltage regulator capable of securely preventing a reverse current from an output terminal (122) with lower current consumption, irrespective of magnitude of a voltage of a VDD terminal (121). Such a configuration is adopted that the voltage of the VDD terminal (121) and a voltage of the output terminal (122) of the voltage regulator are compared with each other with the use of a voltage generated between a transistor and a constant current circuit, to thereby reduce current consumption of a backup battery. Besides, such a configuration is also adopted that a gate of an output transistor is connected with the output terminal (122) based on an output of a comparator circuit, to thereby prevent the reverse current securely.

Claims

1. A voltage regulator, comprising:

an output transistor that is provided between a power supply terminal and an output terminal;

an error amplifier for controlling a gate voltage of the output transistor so that a voltage of the output terminal becomes constant;

a second transistor for connecting a substrate of the output transistor with the power supply terminal;

a third transistor for connecting the substrate of the output transistor with the output terminal; and

a comparator circuit for comparing a voltage of the power supply terminal with the voltage of the output terminal, and performing control of switching the second transistor and the third transistor based on a result of the comparing, wherein;

the comparator circuit comprises;

a fourth transistor having a source connected with the power supply terminal, a gate connected with a drain, and the drain connected with a first constant current circuit; and

a fifth transistor having a source connected with the output terminal, a gate connected with the gate of the fourth transistor, and a drain connected with a second constant current circuit; and

the comparator circuit outputs the result of the comparing based on a voltage of a connection point between the fifth transistor and the second constant current circuit.

2. A voltage regulator according to claim 1, wherein the comparator circuit is configured to:

turn ON the second transistor when the voltage of the power supply terminal is higher than the voltage of the output terminal; and

turn ON the third transistor when the voltage of the power supply terminal is lower than the voltage of the output terminal.

3. A voltage regulator according to claim 2, wherein the comparator circuit has a hysteresis function.

4. A voltage regulator according to claim 3, wherein:

the comparator circuit further comprises;

a sixth transistor that is connected in series with the fifth transistor; and

a seventh transistor that is connected in parallel with the fifth transistor; and

the hysteresis function is realized by controlling the seventh transistor based on the output of the comparator circuit.

5. A voltage regulator according to claim 3, wherein:

the comparator circuit further comprises;

an eighth transistor that is connected in series with the fourth transistor; and

a ninth transistor that is connected in parallel with the fourth transistor; and

the hysteresis function is realized by controlling the ninth transistor based on the output of the comparator circuit.