Power supply circuit

Abstract

To provide a power supply circuit capable of generating power supply voltage of a desired electrical potential without bringing increase of current consumption and increase of a layout area.SOLUTION: A power supply circuit provided with a voltage regulator and a charge pump circuit boosting output voltage of the voltage regulator has a switching circuit selecting either DC voltage inputted to a voltage input terminal or output voltage of the charge pump circuit and supplying the voltage to an amplifier of the voltage regulator as operation voltage, and a monitoring circuit monitoring the output voltage of the charge pump circuit and outputting a predetermined signal when detecting that the output voltage reaches a predetermined electrical potential. The switching circuit supplies the input DC voltage of the voltage input terminal to the amplifier as the operation voltage while the output voltage of the charge pump circuit is lower than the predetermined electrical potential according to the signal outputted from the monitoring circuit, and supplies the output voltage of the charge pump circuit to the amplifier as the operation voltage when the output voltage of the charge pump circuit becomes higher than the predetermined electrical potential.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power supply circuit including a charge pump circuit, and is related to a technology effective for use in a power supply circuit that supplies an appropriate power supply voltage to a load such as a circuit block in an IC (integrated circuit) or another IC, or a single power supply circuit IC (power supply device).

Background Art

[0002] A power supply circuit is used to supply an appropriate power supply voltage to a load such as an IC or a circuit block in an IC. Various types of power supply circuits are known, such as linear regulators and switching regulators, and there are also power supply circuits incorporating a charge pump circuit. As an invention related to a power supply circuit incorporating a charge pump circuit, there is, for example, one described in Patent Document 1. Also, as an invention related to a charge pump circuit, there is, for example, one described in Patent Document 2.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a system that uses an N-channel MOS transistor as a transistor that supplies a current flowing to a load in order to drive a load such as a motor, as shown in FIG. 3, it is necessary to supply voltages (VCP, VRG) that appropriately operate a pre-driver (drive circuits 110 and 120) that drives the gate terminal of the MOS transistor that supplies current to the motor. Therefore, the inventor considered using a power supply circuit including a regulator REG as shown in FIG. 4 and a charge pump circuit CPC that boosts the voltage thereof as a circuit that generates the power supply voltage of the drive circuit.

[0005] As a result, since the regulator REG of the power supply circuit shown in FIG. 4 uses an N-channel MOS transistor, it is necessary to operate an amplifier AMP that drives and controls this in the saturation region. And, in order to operate this amplifier AMP in the saturation region, a potential of VDD + VRG that is higher than the input voltage VDD by the output voltage VRG of the regulator REG is required as its operating voltage VBIAS. Therefore, a circuit that generates such a potential VBIAS separately from the input voltage VDD must be added. As a result, it became clear that there are problems in that the current consumption increases by the amount of the circuit to be added and the layout area of the circuit increases.

[0006] The present invention has been made paying attention to the above problems, and an object thereof is to provide a power supply circuit that can generate a power supply voltage of a desired potential without providing a circuit that generates an operating voltage higher than the input voltage separately therefrom, that is, without causing an increase in current consumption and an increase in layout area.

Means for Solving the Problems

[0007] To achieve the above object, the present invention provides a voltage regulator having a transistor connected to a voltage input terminal and an amplifier that controls the transistor, and converting a DC voltage input to the voltage input terminal into a predetermined DC voltage and outputting the converted voltage; and a charge pump circuit that outputs a DC voltage obtained by boosting the output voltage of the voltage regulator. In a power supply circuit including A switching circuit that selects either the DC voltage input to the voltage input terminal or the output voltage of the charge pump circuit and supplies it as an operating voltage to the amplifier, and a monitoring circuit that monitors the output voltage of the charge pump circuit and outputs a predetermined signal when it detects that a predetermined potential has been reached. The switching circuit, according to the signal output from the monitoring circuit, supplies the input DC voltage of the voltage input terminal as the operating voltage to the amplifier while the output voltage of the charge pump circuit is lower than the predetermined potential, and is configured to supply the output voltage of the charge pump circuit as the operating voltage to the amplifier when the output voltage of the charge pump circuit becomes higher than the predetermined potential.

[0008] According to the power supply circuit having the above configuration, there is no need to separately provide a circuit for generating an operating voltage higher than the input voltage. As a result, it is possible to generate a power supply voltage of a desired potential without causing an increase in current consumption and an increase in layout area due to the addition of a circuit.

Advantages of the Invention

[0009] According to the power supply circuit of the present invention, there is an effect that it is possible to generate a power supply voltage of a desired potential without causing an increase in current consumption and an increase in layout area.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a circuit configuration diagram of an embodiment of a power supply circuit according to the present invention, and FIG. 2 shows its operation timing. As shown in FIG. 1, the power supply circuit of this embodiment is composed of a series regulator (hereinafter referred to as a regulator) 10 and a charge pump circuit 20.

[0012] The above regulator 10 includes an N-channel MOS transistor M0 having a drain terminal connected to a voltage input terminal IN to which a DC voltage VDD supplied from a battery or the like is input, an error amplifier 11 for generating a gate control voltage of the transistor M0, a voltage dividing circuit 12 composed of series resistors R1 and R2 connected between the source terminal of the transistor M0 and the ground point GND, and a multiplexer 13.

[0013] The voltage divided by the above voltage dividing circuit 12 is fed back to the non-inverting input terminal of the error amplifier 11. A reference voltage VBG generated by a circuit such as a BGR (bandgap reference) circuit is input to the inverting input terminal of the error amplifier 11, and a voltage corresponding to the potential difference between the reference voltage VBG and the feedback voltage VFB is applied to the gate terminal of the transistor M0. Thereby, the error amplifier 11 controls the transistor M0 so that the feedback voltage VFB coincides with the reference voltage VBG. Then, the generated voltage VRG is output from the output terminal OUT1 and supplied to the charge pump circuit 20.

[0014] The multiplexer 13 selects either the DC voltage VDD input to the voltage input terminal IN or the voltage VCP supplied from the charge pump circuit 20 as the operating voltage VBIAS and supplies it to the error amplifier 11 to operate the amplifier. Also, the switching control signal RDY of the multiplexer 13 is supplied from the charge pump circuit 20 as will be described later. The multiplexer 13 at the start of operation of the circuit is set to select the DC voltage VDD and supply it to the error amplifier 11. Note that instead of the multiplexer 13, a switching circuit composed of switch elements may be used.

[0015] The charge pump circuit 20 includes switch elements SW1 and SW2 connected in series between the source terminal (node N0) of the transistor M0 and the ground point GND of the circuit, switch elements SW3 and SW4 connected in series between the voltage input terminal IN and the voltage output terminal OUT2, and a comparator 21 that compares the voltage VCP at the voltage output terminal OUT2 with a predetermined reference voltage Vref. Also, a capacitor C1 is connected between the connection node N1 of the switch elements SW1 and SW2 and the connection node N2 of the switch elements SW3 and SW4, and a capacitor C2 is connected between the voltage input terminal IN and the voltage output terminal OUT2. It is preferable to use a comparator 21 having a hysteresis characteristic.

[0016] Of the switch elements SW1 to SW4, SW1 and SW4 are controlled to be turned on and off by a clock signal (pulse) φ1 of a predetermined frequency, and SW2 and SW3 are controlled to be turned on and off by a clock signal φ2 having a phase opposite to that of the clock signal φ1 by 180 degrees. Note that the clock signal φ2 can be generated by inverting φ1 with an inverter. Also, the clock signals φ1 and φ2 are alternately turned on and off with a dead time in between. The clock signals φ1 and φ2 may be supplied from outside the power supply circuit, or may be supplied from a clock generator composed of an oscillation circuit and a waveform shaping circuit provided in the power supply circuit.

[0017] As described above, since the clock signals φ1 and φ2 are pulse signals with a 180-degree phase difference, during the period when the switch elements SW1 and SW4 are turned off by the clock signal φ1, SW2 and SW3 are turned on by the clock signal φ2, and thus the capacitor C1 is charged with a charge corresponding to the input voltage VDD. During the period when SW2 and SW3 are turned off, SW1 and SW4 are turned on, and the charge stored in the capacitor C1 is transferred to the capacitor C2.

[0018] By repeating the above operation, as shown in Fig. 2(A), the voltage VCP at the output terminal OUT2 increases step by step. When the output voltage VCP exceeds the reference voltage Vref which is the threshold value, as shown in Fig. 2(C), the output RDY of the comparator 21 changes from the low level to the high level (timing t1). Then, since the output RDY of the comparator 21 is supplied as a switching control signal to the multiplexer 13, the output voltage VCP is supplied as the operating voltage VBIAS to the error amplifier 11 instead of the input voltage VDD.

[0019] As a result, the error amplifier 11 operates in the saturation region, and it is prevented that the level of the voltage VRG generated by the regulator 10 decreases. Also, in a system provided with an amplifier (drive circuit) that operates receiving the voltage VRG generated by the regulator 10 as the power supply voltage, the amplifier can be made to operate in the saturation region. In Fig. 2, a waveform is shown in which the output voltage VCP reaches the target voltage with a three-step change. However, for example, when a capacitor with a relatively small capacitance value is used to reduce the size of the IC, the output voltage VCP will reach the target voltage through more stepwise changes.

[0020] Next, with reference to Fig. 3, a case where the power supply circuit of the present invention is applied to a power supply circuit incorporated in a drive IC constituting a motor drive system as an example will be described. The motor drive system shown in Fig. 3 has a function of converting the DC voltage VDD supplied from a DC power supply into an AC voltage to be supplied to a motor 200 as a load, and includes a high-side transistor M1, a low-side transistor M2, and a driving IC 100 for driving these transistors M1 and M2. The load 200 is not limited to a motor.

[0021] The driving IC 100 is a pre-driver for driving the externally attached transistors M1 and M2 to the IC. Although not particularly limited, N-channel field effect transistors (FETs) are used here for the transistors M1 and M2. Also, the driving IC 100 incorporates a power supply circuit 101 for generating a voltage for operating the drive circuit, and the power supply circuit of the above-described embodiment (Fig. 1) is used as the power supply circuit 101.

[0022] The driving IC 100 in Fig. 3 drives the transistors M1 and M2 according to signals (clock CLK, high-side command signal HIN, and low-side command signal LIN) supplied from a controller (not shown), thereby switching (turning on or off) the transistors M1 and M2. The high-side command signal HIN and the low-side command signal LIN change in synchronization with the clock CLK. The driving IC 100 alternately turns on the transistors M1 and M2 with a dead time for turning off the transistors M1 and M2 according to the high-side command signal HIN and the low-side command signal LIN.

[0023] Also, the driving IC 100 includes a control circuit 130, a high-side source current source 111, a high-side sink current source 112, a low-side source current source 121, and a low-side sink current source 122. The driving IC 100 also includes a high-side driving terminal GH, an intermediate terminal SH, a low-side driving terminal GL, and a ground terminal PGND.

[0024] The control circuit 130 controls a source current source 111 that turns on the transistor M1 and a sink current source 112 that turns off the transistor M1. Also, the control circuit 130 controls a source current source 121 that turns on the transistor M2 and a sink current source 122 that turns off the transistor M2. To realize such functions, the control circuit 130 includes a logic circuit 131, a high-side control circuit 132, and a low-side control circuit 133.

[0025] Based on the high-side command signal HIN and the low-side command signal LIN, the logic circuit 131 generates a drive command HHIN for source control and a drive command HLIN for sink control. Also, based on the high-side command signal HIN and the low-side command signal LIN, the logic circuit 131 generates a drive command LHIN for source control and a drive command LLIN for sink control. Note that the logic circuit 131 may be outside the control circuit 130 and even outside the driving IC 100.

[0026] According to the drive command HHIN for source control, the high-side control circuit 132 controls the source current generated by the high-side source current source 111. Also, according to the drive command HLIN for sink control, the high-side control circuit 132 controls the sink current generated by the high-side sink current source 112. Further, according to the drive commands HHIN and HLIN, the high-side control circuit 132 alternately turns on the output transistors of the current sources 111 and 112 with a dead time that turns off the output transistors of the current sources 111 and 112 in between.

[0027] The low-side control circuit 133 controls the source current generated by the low-side source current source 121 in accordance with the drive command LHIN for source control. Further, the low-side control circuit 133 controls the sink current generated by the low-side sink current source 122 in accordance with the drive command LLIN for sink control. Furthermore, the low-side control circuit 133 alternately turns on the output transistors of the current sources 121 and 122 with a dead time for turning off the output transistors of the current sources 121 and 122 in accordance with the drive command LHIN and the drive command LLIN.

[0028] The source current source 111 includes an output transistor formed of a P-channel MOSFET, and generates a source current flowing into the gate of the transistor M1. The source current source 111 is connected between a drive terminal GH connected to the gate of the transistor M1 and a power supply node of the high-side power supply voltage VCP. The power supply voltage VCP is equal to the sum of the DC voltage VDD and the low-side power supply voltage (regulator voltage VRG). The power supply voltage VCP is generated, for example, by the aforementioned charge pump 20 in the power supply circuit 101 using the DC voltage VDD and the regulator voltage VRG.

[0029] The driving IC 100 charges the gate of the transistor M1 by flowing a source current from the PMOS output transistor of the source current source 111 into the drive terminal GH, and turns on the transistor M1. Further, the driving IC 100 discharges the gate of the transistor M1 by drawing a sink current from the drive terminal GH into the NMOS output transistor of the sink current source 112, and turns off the transistor M1. Similarly, the driving IC 100 charges the gate of the transistor M2 by flowing a source current from the PMOS output transistor of the source current source 121 into the drive terminal GL, and turns on the transistor M2. Further, the driving IC 100 discharges the gate of the transistor M2 by drawing a sink current from the drive terminal GL into the NMOS output transistor of the sink current source 122, and turns off the transistor M2.

[0030] Furthermore, the driving IC 100 includes a high-side source current source 111 as a first driving source 110 that uses the boosted voltage (power supply voltage VCP) generated by the charge pump in the power supply circuit 101. The driving IC 100 includes a low-side source current source 121 as a second driving source 120 that uses the regulator voltage VRG generated by the regulator in the power supply circuit 101. Also, the output signal RDY of the comparator 21 provided in the charge pump circuit 20 of the power supply circuit of the above-described embodiment (FIG. 1) may be supplied to the logic circuit 131, or a signal delayed by a predetermined number of seconds may be generated by a counter and supplied. The comparator 21 functions as a voltage monitoring circuit that monitors the voltage VCP generated by the charge pump circuit 20.

[0031] When the output signal RDY of the voltage monitoring circuit (comparator 21) is asserted because the voltage VCP generated by the charge pump circuit 20 becomes higher than a predetermined potential, the logic circuit 131 permits the operations of the high-side source current source 111 and the low-side source current source 121. Thereby, the logic circuit 131 starts generating a driving command HHIN for source control and a driving command HLIN for sink control based on the high-side command signal HIN and the low-side command signal LIN.

[0032] Also, the logic circuit 131 starts generating a driving command LHIN for source control and a driving command LLIN for sink control based on the high-side command signal HIN and the low-side command signal LIN. Thus, when the output signal RDY of the voltage monitoring circuit (comparator 21) is asserted, the first driving source 110 and the second driving source 120 can be prevented from driving the transistors M1 and M2 in a state where the power supply voltage VCP generated by the boosting operation of the charge pump has not risen sufficiently.

[0033] As described above, the present invention has been described based on the embodiments, but the present invention is not limited to the above embodiments. For example, in the above embodiments, the power supply circuit used to supply the power supply voltage to the drive circuit in the IC built in the IC has been described. However, instead of being built in the IC together with other circuits, the power supply circuit of FIG. 1 may be configured as one IC (power supply device). And a terminal OUT1 for outputting the voltage VRG generated by the regulator 10 and a terminal P1 for outputting the output signal RDY of the comparator 21 to other circuits may be provided. Further, the capacitors C1 and C2 constituting the charge pump circuit 20 may be connected as externally attached elements of the IC.

[0034] In the above embodiment, the power supply circuit configured to generate the voltage VCP obtained by boosting the voltage VRG generated by the regulator 10 by a single-stage charge pump has been described. However, it is also possible to increase the number of stages of the charge pump in the charge pump circuit 20 to generate an even higher voltage. Furthermore, in the above application system (FIG. 3), what is used as the power supply circuit in the IC for driving the motor has been described. However, the present invention can also be used for a power supply circuit provided in a high-side switch IC or the like.

Description of Reference Numerals

[0035] 10... Regulator, 11... Error amplifier, 12... Voltage dividing circuit, 13... Multiplexer, 20... Charge pump, 21... Comparator (monitoring circuit), 100... Driving IC, 101... Power supply circuit, 110... First driving source, 120... Second driving source, 130... Control circuit, 131... Logic circuit, 200... Load (motor)

Claims

1. A power supply circuit comprising: a voltage regulator having a transistor connected to a voltage input terminal and an amplifier for controlling the transistor, the voltage regulator converting a DC voltage input to the voltage input terminal into a predetermined DC voltage and outputting it; and a charge pump circuit for outputting a DC voltage obtained by boosting the output voltage of the voltage regulator, a switching circuit for selecting either the DC voltage input to the voltage input terminal or the output voltage of the charge pump circuit and supplying it as an operating voltage to the amplifier, a monitoring circuit for monitoring the output voltage of the charge pump circuit and outputting a predetermined signal when it detects that a predetermined potential has been reached, wherein the switching circuit, in response to the signal output from the monitoring circuit, supplies the input DC voltage of the voltage input terminal to the amplifier as an operating voltage while the output voltage of the charge pump circuit is lower than the predetermined potential, and is configured to supply the output voltage of the charge pump circuit to the amplifier as an operating voltage when the output voltage of the charge pump circuit becomes higher than the predetermined potential. A power supply circuit characterized by this.

2. A first output terminal for externally outputting the output voltage of the voltage regulator, A second output terminal for externally outputting the output voltage of the charge pump circuit. The power supply circuit according to claim 1, characterized by comprising this.

3. A third output terminal for externally outputting the output signal of the monitoring circuit. The power supply circuit according to claim 1 or 2, characterized by comprising this.

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