Voltage regulator

• US 20080012543A1
• Filed: 07/02/2007
• Published: 01/17/2008
• Est. Priority Date: 07/13/2006
• Status: Active Grant

• Current Assignee: RICOH Electronic Devices Co., Ltd. (Nisshinbo Holdings Incorporated)
• Original Assignee: Ricoh Company Limited
• Inventors: Negoro, Takaaki
• Granted Patent: US 7,719,242 B2
• Time in Patent Office: Days
• US Class Current: 323/272
• CPC Class Codes: G05F 1/46 wherein the variable actually regulated by the final control device is dc G05F1/625 takes precedence

Abstract

A voltage regulator is disclosed that includes an output transistor outputting a current according to an input control signal to an output terminal; a control circuit part controlling the operation of the output transistor; a switching circuit part connecting the substrate gate and the gate of the output transistor to one of the input terminal and the output terminal and one of the output of the control circuit part and the output terminal, respectively, in accordance with the relationship in magnitude between a voltage at an input terminal and a voltage at the output terminal; a first rectifier element connected between the input terminal and a power supply end; and a second rectifier element connected between the output terminal and the power supply end.

Claims

1. A voltage regulator converting a voltage input to an input terminal into a predetermined constant voltage and outputting the constant voltage from an output terminal, the voltage regulator comprising:

an output transistor formed of a MOS transistor, the output transistor being configured to output a current according to an input control signal from the input terminal to the output terminal;

a control circuit part configured to control an operation of the output transistor so that a voltage proportional to the voltage output from the output terminal is a predetermined reference voltage;

a switching circuit part configured to connect a substrate gate of the output transistor to one of the input terminal and the output terminal and to connect a gate of the output transistor to one of an output of the control circuit part and the output terminal in accordance with a relationship in magnitude between a voltage at the input terminal and a voltage at the output terminal;

a first rectifier element connected between the input terminal and a power supply end, from which power is supplied to the control circuit part and the switching circuit part, so as to allow current to flow from the input terminal to the control circuit part and the switching circuit part; and

a second rectifier element connected between the output terminal and the power supply end so as to allow current to flow from the output terminal to the control circuit part and the switching circuit part.

2. The voltage regulator as claimed in claim 1, wherein the switching circuit part is configured to connect the substrate gate and the gate of the output transistor to the output terminal in response to the voltage at the output terminal becoming greater than the voltage at the input terminal.

3. The voltage regulator as claimed in claim 1, wherein the switching circuit part is configured to connect the substrate gate of the output transistor to the input terminal and the gate of the output transistor to the output of the control circuit part in response to the voltage at the output terminal becoming less than the voltage at the input terminal.

4. The voltage regulator as claimed in claim 1, wherein the switching circuit part comprises:

a voltage comparator circuit part configured to compare a voltage at the power supply end and the voltage at the output terminal and to generate and output a signal representing a result of the comparison;

a connection switching circuit part configured to connect the substrate gate of the output transistor to one of the input terminal and the output terminal in accordance with the output signal of the voltage comparator circuit part; and

a gate voltage switching circuit part configured to connect the gate of the output transistor to one of the output of the control circuit part and the output terminal in accordance with the output signal of the voltage comparator circuit part.

5. The voltage regulator as claimed in claim 4, wherein the connection switching circuit part comprises:

a first switch configured to connect the substrate gate of the output transistor to the output terminal in accordance with an input first control signal;

a second switch configured to connect the substrate gate of the output transistor to the input terminal in accordance with an input second control signal; and

a switching control circuit configured to control operations of the first switch and the second switch in accordance with the output signal of the voltage comparator circuit part.

6. The voltage regulator as claimed in claim 5, wherein:

each of the output transistor, the first switch, and the second switch comprises a PMOS transistor; and

each of the PMOS transistors of the first switch and the second switch has a substrate gate thereof connected to the substrate gate of the output transistor.

7. The voltage regulator as claimed in claim 5, wherein:

each of the output transistor, the first switch, and the second switch comprises a PMOS transistor; and

each of the PMOS transistors of the first switch and the second switch has a substrate gate thereof connected to the power supply end.

8. The voltage regulator as claimed in claim 1, wherein the switching circuit part comprises:

a voltage comparator circuit part configured to compare a voltage at the power supply end and the voltage at the output terminal and to generate and output a signal representing a result of the comparison;

a connection switching circuit part configured to connect the substrate gate of the output transistor to one of the input terminal and the output terminal in accordance with a voltage difference between the input terminal and the output terminal; and

a gate voltage switching circuit part configured to connect the gate of the output transistor to one of the output of the control circuit part and the output terminal in accordance with the output signal of the voltage comparator circuit part.

9. The voltage regulator as claimed in claim 8, wherein the connection switching circuit part comprises:

a first MOS transistor connected between the input terminal and the substrate gate of the output transistor, and having a gate thereof connected to the output terminal; and

a second MOS transistor connected between the output terminal and the substrate gate of the output transistor, and having a gate thereof connected to the input terminal.

10. The voltage regulator as claimed in claim 9, wherein:

each of the output transistor, the first MOS transistor, and the second MOS transistor comprises a PMOS transistor; and

each of the first MOS transistor and the second MOS transistor has a substrate gate thereof connected to the substrate gate of the output transistor.

11. The voltage regulator as claimed in claim 9, wherein:

each of the output transistor, the first MOS transistor, and the second MOS transistor comprises a PMOS transistor; and

each of the first MOS transistor and the second MOS transistor has a substrate gate thereof connected to the power supply end.

12. The voltage regulator as claimed in claim 1, wherein each of the first rectifier element and the second rectifier element is a diode.

13. The voltage regulator as claimed in claim 1, wherein:

the first rectifier element is a PMOS transistor having a substrate gate thereof connected to a source thereof and having a drain thereof connected to the input terminal, the PMOS transistor being configured to perform switching in accordance with a signal input from the switching circuit part, the signal representing a relationship in magnitude between the voltage at the input terminal and the voltage at the output terminal; and

the second rectifier element is a PMOS transistor having a substrate gate thereof connected to a source thereof and having a drain thereof connected to the output terminal, wherein a control signal output from the control circuit part is input to a gate of the PMOS transistor, the control signal controlling the operation of the output transistor.

14. The voltage regulator as claimed in claim 1, wherein the output transistor, the control circuit part, the first rectifier element, the second rectifier element, and the switching circuit part are integrated into a single IC.