Switching regulator and electronic device therewith

• US 7,576,531 B2
• Filed: 03/14/2006
• Issued: 08/18/2009
• Est. Priority Date: 03/28/2005
• Status: Expired due to Fees

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Nakabayashi, Hirotaka
• Primary Examiner(s): Laxton; Gary L
• Application Number:
  US11/908,314
• Publication Number:
  US 20090066304A1
• Time in Patent Office: 1,253 Days
• Field of Search: 323/265, 323/282, 323/284, 323/285, 323/299, 323/315, 323/351, 323/908, 361/87, 361/93.9, 363/50
• US Class Current: 323/285
• CPC Class Codes: H02H 1/0046 Commutating the detecting means in dependance of the fault, e.g. for reducing their number
• CPC Class Codes: H02H 7/1227 responsive to abnormalities in the output circuit, e.g. short circuit
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A switching regulator according to the invention includes: an output switching element; an output feedback circuit generating an error voltage (Verr) according to an error between an output voltage (Vout) and a target voltage; a switching control circuit turning on and off the output switching element based on the error voltage (Verr); a short-circuit current protection circuit that includes a first comparator (CMP1) comparing a reference voltage (Vs) commensurate with an output current (iout) with a first threshold voltage (Vth1) and that instructs, based on this comparison result, whether to drive the switching control circuit; and a drive current generating circuit that includes a second comparator (CMP2) comparing the error voltage (Verr) with a second threshold voltage (Vth2) and that determines, based on this comparison result, whether to supply a drive current (i1) to the first comparator (CMP1). With this configuration, it is possible to reduce the waste of electric power without spoiling the reliability of short-circuit current protection.

Claims

1. A switching regulator comprising:

an output switching element connected between an input terminal to which an input voltage is applied and an output terminal from which an output voltage is derived to be fed to a load;

an output feedback circuit generating an error voltage varying according to an error between an actual value of and a target value of the output voltage;

a switching control circuit turning on and off the output switching element based on the error voltage so that the error of the output voltage is reduced;

a short-circuit current protection circuit including;

a first comparator comparing with a predetermined first threshold voltage an output current reference voltage varying according to an output current to the load,

the short-circuit current protection circuit generating, based on a comparison output signal from the first comparator, a short-circuit current protection signal instructing whether to drive the switching control circuit; and

a drive current generating circuit including;

a second comparator operating with a drive current lower than a drive current for the first comparator and comparing the error voltage with a predetermined second threshold voltage,

the drive current generating circuit determining, based on a comparison output signal from the second comparator, whether to supply the drive current to the first comparator.

2. The switching regulator of claim 1,

wherein the drive current generating circuit prohibits supply of the drive current to the first comparator until the output current reaches a second threshold current determined by the second threshold voltage, and the drive current generating circuit allows supply of the drive current to the first comparator when the output current reaches the second threshold current, and,

the short-circuit current protection circuit allows driving of the switching control circuit after supply of the drive current to the short-circuit current protection circuit is allowed until the output current reaches a first threshold current that is determined by the first threshold voltage and that is higher than the second threshold current, and the short-circuit current protection circuit prohibits driving of the switching control circuit when the output current reaches the first threshold current.

3. The switching regulator of claim 2,

wherein the drive current generating circuit comprises:

a constant current source generating a constant current lower than the drive current for the first comparator;

a mirror amplifier circuit mirror-amplifying the constant current to generate the drive current for the first comparator; and

a switching element connected between an output terminal of the constant current source and ground and turned on and off based on the comparison output signal from the second comparator such that,

the switching element remains on until the output current reaches the second threshold current, and

the switching element is turned off when the output current reaches the second threshold current.

4. An electronic device comprising:

a battery serving as a power source for the electronic device; and

means for converting an output of the battery,

wherein used as the means is the switching regulator of any one of claims 1 to 3.