Voltage regulator

• US 9,110,487 B2
• Filed: 05/02/2012
• Issued: 08/18/2015
• Est. Priority Date: 05/12/2011
• Status: Active Grant

• Current Assignee: Ablic Inc. (MinebeaMitsumi Inc.)
• Original Assignee: Seiko Instruments Incorporated (Seiko Group)
• Inventors: Sakaguchi, Kaoru, Imura, Takashi
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): LEE III, HENRY E
• Application Number:
  US13/462,440
• Publication Number:
  US 20120286751A1
• Time in Patent Office: 1,203 Days
• Field of Search: 323311-317
• US Class Current: 1/1
• CPC Class Codes: G05F 1/573 with overcurrent detector

Abstract

Provided is a voltage regulator including an overcurrent protection circuit, which does not need a test circuit. The voltage regulator has a configuration in which a reference voltage circuit includes an element that determines a reference voltage and an overcurrent protection circuit includes an element that determines a maximum output current, the element of the reference voltage circuit and the element of the overcurrent protection circuit having the same characteristics. Accordingly, there is a correlation between an output voltage before trimming and the maximum output current for overcurrent protection. Thus, a maximum output current before trimming can be estimated without performing evaluation by a test circuit.

Claims

1. A voltage regulator, comprising:

a reference voltage circuit for outputting a reference voltage;

a differential amplifier circuit for comparing the reference voltage and a voltage which is based on an output voltage, and controlling a gate voltage of an output transistor so that the output voltage becomes constant; and

an overcurrent protection circuit for detecting a flow of an overcurrent to the output transistor, and limiting a current of the output transistor,

wherein the reference voltage circuit includes a first depletion transistor that determines the reference voltage and the overcurrent protection circuit includes a second depletion transistor that determines one of a maximum output current and a short-circuit current of the output transistor, the first depletion transistor of the reference voltage circuit and the second depletion transistor of the overcurrent protection circuit having the same characteristics, wherein the same characteristics comprise an identical threshold voltage of a depletion transistor.

2. A voltage regulator, comprising:

a reference voltage circuit for outputting a reference voltage;

a differential amplifier circuit for comparing the reference voltage and a voltage which is based on an output voltage, and controlling a gate voltage of an output transistor so that the output voltage becomes constant; and

an overcurrent protection circuit for detecting a flow of an overcurrent to the output transistor, and limiting a current of the output transistor,

wherein the reference voltage circuit includes an element that determines the reference voltage and the overcurrent protection circuit includes an element that determines one of a maximum output current and a short-circuit current of the output transistor, the element of the reference voltage circuit and the element of the overcurrent protection circuit having the same characteristics;

wherein;

the reference voltage circuit comprises a first NMOS depletion transistor and a first NMOS transistor;

the overcurrent protection circuit comprises;

a sense transistor for sensing an output current of the output transistor;

a second NMOS depletion transistor including a gate and a drain which are short-circuited, for allowing a current to flow through the sense transistor; and

a second NMOS transistor which is current-mirror-connected to the second NMOS depletion transistor;

the element that determines the reference voltage comprises the first NMOS depletion transistor and the first NMOS transistor; and

the element that determines the one of the maximum output current and the short-circuit current of the overcurrent protection circuit comprises the second NMOS depletion transistor and the second NMOS transistor.