POWER SUPPLY APPARATUS HAVING SWITCHABLE SWITCHING REGULATOR AND LINEAR REGULATOR

• US 20090072626A1
• Filed: 05/25/2006
• Published: 03/19/2009
• Est. Priority Date: 05/26/2005
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Watanabe, Hiroyuki, Yamamoto, Isao
• Granted Patent: US 7,812,580 B2
• Time in Patent Office: Days
• US Class Current: 307/85
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 1/0045 Converters combining the concepts of switch-mode regulation and linear regulation, e.g. linear pre-regulator to switching converter, linear and switching converter in parallel, same converter or same transistor operating either in linear or switching mode
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A control circuit is provided in which two power sources can be efficiently switched, for a power supply apparatus provided with a step down switching regulator and a linear regulator. A PWM controller generates a pulse width modulation signal with which a duty ratio is controlled so that output voltage of the switching regulator approaches a predetermined reference voltage. A compulsory OFF circuit monitors a switching voltage, and when a first threshold voltage is exceeded, switches a synchronous rectifier transistor OFF. A minimum ON time setting circuit limits the duty ratio of the pulse width modulation signal, so that ON time of the switching transistor is longer than a predetermined minimum value. A selector circuit monitors an error voltage, and when a predetermined state continues for a predetermined first period, puts the linear regulator in an operating state, and the step down switching regulator in a halt state.

Claims

1. A control circuit of a power supply apparatus in which a step down switching regulator and a linear regulator can be switched, the control circuit comprising:

an output stage, including a switching transistor and a synchronous rectifier transistor connected in series between an input terminal and grounding, which outputs a voltage at a connection point of the two transistors, as a switching voltage, to a switching regulator output circuit;

a pulse width modulator, which generates a pulse width modulation signal with which a duty ratio is controlled so that output voltage of the switching regulator output circuit approaches a predetermined reference voltage;

a compulsory OFF circuit, which monitors the switching voltage, and switches OFF the synchronous rectifier transistor when the switching voltage exceeds a first threshold voltage;

a minimum ON time setting circuit, which receives the pulse width modulation signal, limits the duty ratio of the pulse width modulation signal so that ON time of the switching transistor is longer than a predetermined minimum value;

a driver circuit, which generates a first and a second gate voltage to be applied to a gate terminal of the switching transistor and the synchronous rectifier transistor, based on an output signal of the minimum ON time setting circuit; and

a selector circuit, which monitors an error voltage between the output voltage and the reference voltage, and when a predetermined state continues for a predetermined determination period, puts the linear regulator in an operating state, and puts the step down switching regulator in a halt state.

2. A control circuit according to claim 1, wherein, after a predetermined light-load transition period has elapsed, after putting the linear regulator in an operating state, the selector circuit puts the step down switching regulator in a halt state.

3. A control circuit according to claim 1, wherein the predetermined state is a state in which the error voltage is larger than a predetermined second threshold voltage.

4. A control circuit according to claim 3, wherein the selector circuit comprises:

a comparator, which compares the error voltage and the second threshold voltage; and

a time measurement circuit, which measures time at which an output signal of the comparator has a predetermined level;

and when the time measured by the time measurement circuit reaches the determination period, the linear regulator is put in an operating state, and the step down switching regulator is put in a halt state.

5. A control circuit according to claim 4, wherein the time measurement circuit comprises a digital filter in which the determination period is set as a time constant.

6. A control circuit according to claim 1, wherein the selector circuit further comprises a current monitoring circuit, which monitors output current of the linear regulator, and when the output current exceeds a predetermined threshold current, puts the step down switching regulator in an operating state, and puts the linear regulator in a halt state.

7. A control circuit according to claim 6, wherein, after a predetermined heavy-load transition period has elapsed, after putting the step down switching regulator in an operating state, the current monitoring circuit puts the linear regulator in a halt state.

8. A control circuit according to claim 6, wherein the linear regulator comprises:

an output transistor, one end of which is connected to the input terminal, and another end of which is connected to an end of the inductor; and

an error amplifier, to which the output voltage and the reference voltage are inputted, and whose output is connected to a control terminal of the output transistor; and

the current monitoring circuit comprises;

a sensing transistor connected commonly with the control terminal to the output transistor;

a sensing resistor arranged on an electrical current path of the sensing transistor; and

a comparator, which compares a voltage drop across the sensing resistor and a predetermined third threshold voltage corresponding to the threshold current.

9. A control circuit according to claim 1, wherein the control circuit is integrated on a single semiconductor substrate.

10. A power supply apparatus comprising:

a switching regulator output circuit including an output capacitor and an inductor, one end of the output capacitor being grounded, and one end of the inductor being connected to the other end of the output capacitor; and

the control circuit according to claim 1, which supplies a switching voltage to the switching regulator output circuit;

wherein

output voltage of the switching regulator output circuit and output voltage of the linear regulator are switched and outputted.

11. An electronic device comprising:

a battery, which outputs a battery voltage;

a microcomputer; and

the power supply apparatus according to claim 10, which steps down the battery voltage and supplies the microcomputer.