JP2008048547A - Power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply unit by which reduction of a self-consumed current under a light load is attained, and conversion efficiency of electric power is improved as a whole, for a smaller chip size. <P>SOLUTION: The power supply unit is constituted by adding an error amplifier 9 which is not so large in area, and a switch 5 to a switching regulator which converts an input voltage supplied from DC power supply 8 into a predetermined output voltage, by which such a circuit is attained as easily selects the switching regulator and a series regulator only by switching the switch 5, while suppressing an increase in chip area. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply apparatus that consumes less current at light load and has high power efficiency as a whole.

Conventionally, a DC / DC converter or the like is known as a power supply device. The DC / DC converter converts an input voltage into a predetermined output voltage, and includes a charge pump system that uses charging / discharging of a capacitor and a switching regulator that switches an input voltage and uses an inductor.
A switching regulator that efficiently converts an input voltage into a predetermined output voltage has high self-consumption current because it switches power transistors at high speed, but is suitable for heavy loads because of high power conversion efficiency. However, there is a problem in that the power conversion efficiency as a whole decreases due to the magnitude of the self-consumption current at the time of light load.
On the other hand, the series regulator is characterized by low power conversion efficiency, although its own current consumption is small. The low efficiency of power conversion is not a problem at light loads. Considering the low self-consumption current of the series regulator, combining the series regulator with a switching regulator allows both heavy and light loads. As a whole, the power conversion efficiency can be improved.

Patent Document 1 discloses a power supply device of the prior art. This power supply device is a device in which a DC / DC converter and a series regulator are connected with their output ends connected in parallel, and selectively operate based on a mode command signal in consideration of a load current.
JP 2005-198484 A

A power supply device combining a conventional switching regulator with a series regulator such as LDO (Low Dropout Regulator) has the effect of improving the overall power conversion efficiency when used at both heavy and light loads. Is recognized. However, since the switching regulator and the series regulator are provided separately, there is a problem that the chip size is increased.
In view of the above points, the present invention provides a power supply device that reduces the current consumption at the time of light load, improves the power conversion efficiency as a whole, and reduces the chip size.

  According to one aspect of the power supply device of the present invention, a switching unit that outputs an input voltage by switching the first transistor and the second transistor, and an output by smoothing a voltage supplied by switching of the switching unit. A smoothing unit that generates a voltage; a voltage dividing unit that divides the output voltage; and a first error amplifier and a second error that amplify a difference signal between the divided voltage generated from the voltage dividing unit and a reference voltage. A control unit including an amplifier and a comparator that compares the difference signal amplified by the first error amplifier with a reference voltage signal and outputs a signal for controlling on / off of the first transistor and the second transistor; And a switch unit that selectively supplies signals from the second error amplifier and the comparator to the switching unit. When the signal from the second error amplifier is supplied to the first transistor of the switching unit, the signal from the comparator operates as the first regulator of the switching unit. When supplied to the transistor and the second transistor, the transistor operates as a switching regulator.

  When the load is large, it may be operated as the switching regulator, and when the load is small, it may be operated as the series regulator. The first transistor may be a PMOS transistor, and the second transistor may be an NMOS transistor.

  The present invention can easily realize a switching regulator / series regulator switching circuit simply by adding an error amplifier and an analog switch to the switching regulator. The added error amplifier is not so large, and a PMOS transistor with a large area can be used both when using a switching regulator and when using a series regulator, so the chip size is larger than that of a power supply device combining a conventional switching regulator and series regulator. It becomes possible to make it smaller.

The present invention provides a power supply device that reduces the current consumption at the time of a light load, improves the power conversion efficiency as a whole, and reduces the chip size. A power supply device that can switch between a switching regulator and a series regulator can be realized simply by adding an error amplifier and analog switch to the switching regulator.
Hereinafter, embodiments of the invention will be described with reference to examples.

Embodiment 1 will be described with reference to FIG.
FIG. 1 is a circuit diagram of the power supply device of this embodiment. The power supply device of this embodiment smoothes the voltage supplied by switching of the switching unit 1 that outputs the input voltage by switching the first transistor Q1 and the second transistor Q2, and the switching of the switching unit 1. The smoothing unit 3 that generates the output voltage by the voltage, the voltage dividing unit 4 that divides the output voltage, the control unit 2 that adjusts the divided voltage generated from the voltage dividing unit 4 based on a reference voltage, and the control A switch unit 5 (SW1, SW2, SW3) that selectively supplies a signal from the unit 2 to the switching unit 1 is provided.

  The control unit 2 compares the divided voltage generated from the voltage dividing unit 4 with a reference voltage, an error amplifier 21 and an error amplifier 9 that amplify the difference signal, and the difference signal amplified by the error amplifier 21 is converted into a direct current. A comparator 22 that outputs a signal for controlling on / off of the first transistor Q1 and the second transistor Q2 by comparing with a monitor signal of a current supplied from the power source 8 to the switching unit 1 and a reference voltage signal such as an arbitrary triangular wave. And.

  The error amplifier 21 has a non-inverting input terminal for inputting a reference voltage (VREF) and an inverting input terminal for inputting a divided voltage from the voltage dividing unit 4, and a difference signal between the divided voltage and the reference voltage (VREF). And the amplified signal is supplied to the comparator 22. The comparator 22 has an inverting input terminal for inputting the output signal of the error amplifier 21 and a non-inverting input terminal for inputting a reference voltage signal such as a monitor signal for the current supplied to the switching unit 1 and an arbitrary triangular wave. The output signal of the amplifier 21 is compared with the reference voltage signal, and a signal for controlling on / off of the first transistor Q1 and the second transistor Q2 is output. The smoothing unit 3 includes an inductor L1 and a capacitor C1, and generates an output voltage by smoothing a switching voltage supplied by switching of the switching unit 1. The voltage dividing unit 4 includes voltage dividing resistors R 1 and R 2, divides the output voltage, and inputs the divided voltage to the error amplifier 21.

  The first transistor Q1 and the second transistor Q2 are respectively composed of a PMOS transistor and an NMOS transistor, and are ON / OFF controlled according to a signal supplied from the comparator 22. The source of the first transistor Q1 is connected to the DC power supply 8, the gate is connected to the output terminal of the comparator 22 via the switch SW2, and the drain is connected to the drain of the second transistor Q2. The gate of the second transistor Q2 is connected to the output terminal of the comparator 22 via the switch SW3, and the source is grounded (GND).

  One end of the inductor L1 of the smoothing unit 3 is connected to the drain of the first transistor Q1 and the drain of the second transistor Q2, the other end is connected to one end of the capacitor C1, and the other end of the capacitor C1 is grounded. ing. One end of the voltage dividing resistor R1 of the voltage dividing unit 4 is connected to the other end of the inductor L1, the other end is connected to one end of the voltage dividing resistor R2, and the other end of the voltage dividing resistor R2 is grounded (GND). .

  The power supply device according to this embodiment can be operated not only as a switching regulator but also as a series regulator only by adding an error amplifier 9 and an analog switch that do not require a large area to the switching regulator. When operating as a series regulator (LDO), the first transistor Q1 used for the switching transistor of the switching regulator is shared as the output voltage control transistor of the series regulator.

  Further, in the switching regulator, a voltage dividing unit 4 including a resistor R1 and a resistor R2 (voltage dividing resistor) connected between the output terminal 6 and the ground (GND) is also shared by the series regulator. The error amplifier 9 compares the divided voltage obtained by dividing the output voltage with the resistors R1 and R2 with the reference voltage (VREF), applies the output voltage according to the comparison to the gate of the first transistor Q1, By performing this control, a predetermined output voltage can be obtained. A switch SW1 is inserted between the output terminal of the error amplifier 9 and the gate of the first transistor Q1.

  The power supply device is configured to operate as a switching regulator when the load is large, and to operate as a series regulator when the load is small. In order to switch this operation, the switch unit 5 is used. The switch unit 5 includes switches SW1, SW2, and SW3, and is provided between the control unit 2 and the switching unit 1. When operating as a switching regulator, the switch SW1 is turned off to disconnect the output terminal of the error amplifier 9 from the gate of the first transistor Q1, and the switches SW2 and SW3 are turned on to turn on the first transistor Q1 and the second transistor Q2. Each gate of the transistor Q2 and the output terminal of the comparator 22 are connected. When operating as a series regulator, the switch SW1 is turned on to connect the output terminal of the error amplifier 9 and the gate of the first transistor Q1, and the switches SW2 and SW3 are turned off to turn on the first transistor Q1 and the second transistor Q2. Each gate of the transistor Q2 is disconnected from the output terminal of the comparator 22.

The switch unit 5 monitors the load by, for example, a load monitor circuit (not shown) and is controlled based on the monitor signal.
As described above, in this embodiment, the error amplifier 9 and the switch unit 5 that do not require a large area are added to the switching regulator, and the first transistor having a large area can be used both when the switching regulator and the series regulator are used. Since it can be used, the area of the semiconductor chip can be made sufficiently small compared to the conventional one.

The present invention is a power supply device that reduces the current consumption at the time of light load, improves the power conversion efficiency as a whole, and reduces the chip size.
By adding the error amplifier 9 and the analog switch 5, a switching circuit between a switching regulator and a series regulator having a smaller area than the conventional one is realized (see FIG. 1). In the first embodiment, the switch is operated so as to operate as a series regulator when the load is light, and as a switching regulator when the load is large, and the switching is performed based on the load monitor circuit. By switching the switch with an external control signal, it is possible to arbitrarily switch the operation of the switching regulator and the series regulator.

The first transistor Q1 is a PMOS transistor in the first embodiment, but a pnp bipolar transistor can be used in this embodiment.
As described above, also in this embodiment, the error amplifier 9 and the switch unit 5 that do not require a large area are added to the switching regulator, and the first transistor Q1 having a large area can be used either when the switching regulator is used or when the series regulator is used. Therefore, the area of the semiconductor chip can be made sufficiently smaller than that of the conventional one.

The circuit diagram of the power supply device which is one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Switching part 2 ... Control part 3 ... Smoothing part 4 ... Voltage dividing part 5 ... Switch part 6 ... Output terminal 8 ... DC power supply 9 ... Error amplifier 21 ... Error amplifier 22 ... Comparator

Claims (3)

A switching unit that outputs an input voltage by switching the first transistor and the second transistor, a smoothing unit that generates an output voltage by smoothing a voltage supplied by switching of the switching unit, and the output A voltage dividing unit that divides the voltage, and a first error amplifier and a second error amplifier that amplify a difference signal between the divided voltage generated from the voltage dividing unit and a reference voltage, and the first error amplifier. A control unit including a comparator that compares the difference signal thus generated with a reference voltage signal and outputs a signal for controlling on / off of the first transistor and the second transistor; and the second error amplifier and the comparator A switching unit that selectively supplies a signal from the switching unit to the switching unit, and by switching the switching unit When the signal from the second error amplifier is supplied to the first transistor of the switching unit, it operates as a series regulator, and the signal from the comparator receives the first transistor and the second transistor of the switching unit. The power supply device operates as a switching regulator when supplied to the transistor. The power supply device according to claim 1, wherein when the load is large, the power supply device operates as the switching regulator, and when the load is small, the power supply device operates as the series regulator. The power supply device according to claim 1, wherein the first transistor is a PMOS transistor, and the second transistor is an NMOS transistor.

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