JP4739901B2 - Switching power supply device and control circuit thereof, and electronic device using the same - Google Patents

Description

  The present invention relates to a step-up switching power supply device that outputs a plurality of voltages.

  Small information terminals such as mobile phones and PDAs (Personal Digital Assistance) in recent years require a voltage higher than the output voltage of a battery, such as an LED (Light Emitting Diode) used for a liquid crystal backlight. Device exists. For example, in these small information terminals, a Li-ion battery is often used, and its output voltage is usually about 3.5 V, and is about 4.2 V even when fully charged, but the LED has a battery voltage as its driving voltage. Requires a higher voltage. As described above, when a voltage higher than the battery voltage is required, the battery voltage is boosted using a booster circuit such as a switching regulator to obtain a voltage necessary for driving a load circuit such as an LED. Yes.

Patent Document 1 describes a technique for providing a switching power supply device capable of generating a plurality of output voltages at low cost and in a space-saving manner. In this technique, a switching regulator for outputting a plurality of DC voltages shares the inductor and the main switch with a plurality of output voltages, thereby reducing the number of components.
JP 2003-289666 A

According to the technique described in the above document, a plurality of boosted DC voltages can be obtained with a simple circuit configuration, but there is room for further improvement when looking at the power consumption, that is, the efficiency of the power supply device. .
The present invention has been made in view of such a situation, and an object thereof is to provide a booster circuit that simultaneously outputs a plurality of output voltages, similar to the technique described in the above-mentioned document, and further, power consumption. Is to provide a switching power supply device and a control circuit thereof.

  One embodiment of the present invention relates to a control circuit for a switching power supply apparatus that boosts an input voltage and outputs first and second output voltages. The control circuit outputs a voltage corresponding to the first output voltage, a first error amplifier for amplifying an error of a predetermined first reference voltage, and a first error voltage output from the first error amplifier from the oscillator. A first pulse width modulation comparator that outputs a first pulse width modulation signal, a voltage according to the second output voltage, and a second error amplifier that amplifies an error of a predetermined second reference voltage. A second error voltage output from the second error amplifier is compared with a periodic voltage output from the oscillator, and a second pulse width modulation comparator that outputs a second pulse width modulation signal; a first pulse width modulation signal; and Based on the second pulse width modulation signal, a logic circuit that turns on and off the main switch and the two synchronous rectification switches in a time-division manner is compared with a voltage corresponding to the first output voltage with the first reference voltage. Comprising a first comparator, a voltage corresponding to the second output voltage, a second comparator which compares a second reference voltage. The control circuit operates the oscillator and the first and second pulse width modulation comparators when the first output voltage is higher than the first reference voltage and the second output voltage is higher than the second reference voltage at light load. Stop.

  According to this aspect, in the light load where the load current decreases, when the first and second output voltages are higher than the first and second reference voltages, respectively, the oscillator, which is an unnecessary circuit block, the first and second By stopping the operation of the pulse width modulation comparator, power consumption can be reduced.

  The first and second error amplifiers may be configured integrally by sharing the first and second comparators and the operational amplifier, respectively. A voltage according to the output voltage may be input to the first input terminal of the operational amplifier, and a feedback capacitor and a feedback switch connected in series between the output terminal and the second input terminal of the operational amplifier may be provided. The feedback switch may be turned on during normal load, while the feedback switch may be turned off during light load.

  In this case, the operational amplifier can function as an error amplifier by turning on the feedback switch at normal load, and the operational amplifier can function as a comparator by turning off the feedback switch at light load. be able to. As a result, the error amplifier and the comparator can be configured integrally, so that the circuit area can be reduced.

  The control circuit further includes a maximum duty ratio setting comparator that compares a predetermined set voltage with a periodic voltage output from the oscillator and outputs a duty ratio fixed signal with a fixed duty ratio, and includes first and second pulse widths. The upper limit of the duty ratio of the modulation signal may be limited to the duty ratio of the duty ratio fixed signal.

  In this case, by setting an upper limit on the duty ratio of the first and second pulse width modulation signals at a light load, the duty ratio becomes 100% to prevent the switching operation from stopping. it can.

  The control circuit may further include a control terminal, and may switch between a light load time and a normal load based on a control signal input from the outside to the control terminal.

  The control circuit may be integrated on a single semiconductor substrate. “Integrated integration” includes the case where all of the circuit components are formed on a semiconductor substrate and the case where the main components of the circuit are integrated. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate. By integrating the control circuit as one LSI, the circuit area can be reduced.

  Another aspect of the present invention is a switching power supply device that boosts an input voltage and outputs first and second output voltages. This switching power supply device includes an input terminal to which an input voltage is applied, first and second output terminals for outputting first and second output voltages, and an inductor connected in series between the input terminal and a fixed potential terminal. And the main switch, the connection point of the inductor and the main switch, and the first and second synchronous rectification switches provided between the first and second output terminals, respectively, and the first and second synchronous rectification switches. Control for controlling on / off of the first and second diodes, the first and second output capacitors provided between the first and second output terminals and the fixed potential terminal, the main switch, and the first and second synchronous rectification switches A circuit. The control circuit alternately turns on and off the main switch and the first and second switches during normal operation, and turns on and off only the main switch during light loads.

  According to this aspect, the current consumption of the circuit is reduced by stopping the operation of an unnecessary block such as an oscillator at the time of a light load in which the frequency of turning on and off the main switch and the first and second synchronous rectification switches decreases. Efficiency can be improved.

  Yet another embodiment of the present invention is also a switching power supply apparatus that boosts an input voltage and outputs first and second output voltages. The switching power supply device includes an input terminal to which an input voltage is applied, first and second output terminals for outputting first and second output voltages, and a first output terminal provided between the first output terminal and the fixed potential terminal. A first output capacitor, a second output capacitor provided between the second output terminal and the fixed potential terminal, an inductor and a first switch connected in series between the input terminal and the fixed potential terminal, and an inductor and a first switch A connection point, a second switch provided between the first output terminals, a connection point between the inductor and the first switch, a third switch and a fourth switch provided in series between the second output terminals, and a second switch In parallel with the first diode, the cathode terminal is provided on the second output terminal side, and in parallel with the fourth switch, the cathode terminal is provided on the second output terminal side. 2 Dio Comprising de and a control circuit for controlling on and off of the fourth switch from the first, a. In the normal operation, the control circuit turns on the first switch and the second switch in order, the first switch and the third switch in turn on, and the fourth switch in the period in which the third switch is on. The second period during which the first switch is turned on is alternately repeated, while at the time of light load, the third period during which the first switch is turned on and the fourth period during which the first switch and the third switch are turned on in turn are alternately performed. repeat.

  According to this aspect, at a light load in which the frequency of turning on and off the first switch to the fourth switch decreases, the operation of unnecessary blocks such as an oscillator is stopped, thereby reducing the current consumption of the circuit and improving the efficiency. be able to.

  Yet another embodiment of the present invention is an electronic device. The electronic device includes a battery, the above-described switching power supply device that boosts the voltage of the battery, and a plurality of loads that are driven by first and second output voltages output from the switching power supply device.

  According to this aspect, when the current flowing through the load is reduced, the current consumption inside the switching power supply device can be reduced, so that the battery life can be extended.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the switching power supply device according to the present invention, power consumption at light load can be reduced.

  FIG. 1 shows an overall configuration of a switching power supply apparatus 100 according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of an electronic device in which the switching power supply device 100 of FIG. 1 is mounted.

2 is a mobile phone terminal, for example, and includes a battery 310, a power supply device 320, an analog circuit 330, a digital circuit 340, a liquid crystal panel (hereinafter referred to as an LCD panel) 350, and an LED 360.
The battery 310 is a lithium ion battery, for example, and outputs about 3 to 4 V as the battery voltage Vbat. The analog circuit 330 includes high-frequency circuits such as a power amplifier, an antenna switch, an LNA (Low Noise Amplifier), a mixer, and a PLL (Phase Locked Loop), and includes a circuit block that stably operates at a power supply voltage Vcc = 3.4V. . The digital circuit 340 includes various DSPs (Digital Signal Processors) and the like, and includes a circuit block that stably operates at a power supply voltage Vdd = 3.4V.

  The LCD panel 350 displays character information and image information to the user, and a voltage higher than the battery voltage Vbat is required for driving. The LED 360 includes RGB three-color LEDs (Light Emitting Diodes), and is used as a backlight or illumination for the LCD panel 350. A drive voltage of 4 V or more is required for driving the LED 360.

The power supply device 320 is a multi-channel switching power supply, and includes a switching regulator for stepping down or stepping up the battery voltage Vbat as necessary for each channel. The power supply device 320 includes an analog circuit 330, a digital circuit 340, an LCD panel 350, and an LED 360. Provide an appropriate power supply voltage.
The switching power supply apparatus 100 according to the present embodiment can be used for the purpose of supplying the power supply voltage to a plurality of loads that operate at a voltage higher than the battery voltage Vbat, such as the LCD panel 350 and the LED 360. Hereinafter, the configuration of the switching power supply apparatus 100 according to the present embodiment will be described in detail.

  Returning to FIG. The switching power supply device 100 includes an input terminal 102, a first output terminal 104, and a second output terminal 106. The switching power supply device 100 boosts the input voltage Vin applied to the input terminal 102 to generate a first output voltage Vout1 and a second output voltage Vout2. Are output from the first output terminal 104 and the second output terminal 106, respectively.

  The switching power supply device 100 includes an inductor L, a first output capacitor Co1, a second output capacitor Co2, a first switch SW1 to a fourth switch SW4, a first diode D1, a second diode D2, and a control unit 10.

  In addition to the inductor L and the first switch SW1, the second switch SW2, the first diode D1, and the first output capacitor Co1 constitute a first boost circuit that boosts the input voltage Vin.

One end of the inductor L is connected to the input terminal 102. The first switch SW1 is connected between the inductor L and a ground terminal having a fixed potential, and functions as a main switch of the step-up switching regulator.
The second switch SW <b> 2 is connected between the connection point of the inductor L and the first switch SW <b> 1 and the first output terminal 104. The first diode D1 is connected in parallel with the second switch SW2. The first diode D1 has a cathode terminal connected to the first output terminal 104 side and an anode terminal connected to the inductor L side so that a current flows from the inductor L toward the first output terminal 104.

  On / off of the first switch SW1 and the second switch SW2 is controlled by the control unit 10. When the first switch SW1 is on and the second switch SW2 is off, an inductor current flows from the input terminal 102 to the ground terminal via the inductor L and the first switch SW1, and at this time, the inductor L Energy proportional to the square of is stored.

  Next, when the first switch SW1 is turned off and the second switch SW2 is turned on, the inductor current flowing to the ground terminal via the first switch SW1 flows to the second switch SW2 side. At this time, the energy stored in the inductor L is transferred to the first output capacitor Co1. Since the back electromotive force is generated in the inductor L in the direction of preventing the current, the first output capacitor Co1 is charged by the voltage obtained by boosting the input voltage Vin. The boosted voltage is smoothed by the first output capacitor Co1 and output as the first output voltage Vout1.

  The ratio between the first output voltage Vout1 and the input voltage Vin, that is, the step-up rate is determined according to the ratio of the ON time of the first switch SW1 and the second switch SW2. While detecting the first output voltage Vout1, the control unit 10 controls the ON period of the first switch SW1 and the second switch SW2 by a pulse width modulation (PWM) method so that a desired boost rate is obtained.

  Similarly, the second booster circuit includes a third switch SW3, a fourth switch SW4, a second diode D2, and a second output capacitor Co2 in addition to the inductor L and the first switch SW1.

  When the second booster circuit is compared with the first booster circuit, the configuration is the same except that a third switch SW3 is added. In the second booster circuit, the first switch SW1 is turned on to pass current through the inductor L to store energy. Next, by turning on the third switch SW3 and the fourth switch SW4, the energy is transferred to the second output capacitor Co2, and the smoothed second output voltage Vout2 is output from the second output terminal 106.

  In the present embodiment, it is assumed that the boosting rate of the first boosting circuit is set higher than the boosting rate of the second boosting circuit, and the first output voltage Vout1 and the second output voltage Vout2 include Vout1> Assume that Vout2 holds.

  The switching power supply device 100 can be switched in operation mode between normal operation and light load. Each operation mode is hereinafter referred to as a normal operation mode and a light load mode. The switching power supply apparatus 100 includes a control terminal 108, and a control signal Vcont for instructing normal operation and light load is input. The control signal Vcont is input to the control unit 10 and switches the switching sequence of the first switch SW1 to the fourth switch SW4 between the normal operation mode and the light load mode. In the present embodiment, it is assumed that the control signal Vcont operates in the normal mode when the control signal Vcont is at the high level and operates in the light load mode when the control signal Vcont is at the low level.

  FIG. 3 is a circuit diagram showing the switching power supply device 100 according to the present embodiment in more detail. In the figure, a region surrounded by a broken line represents the switching power supply control circuit 200 and is integrated. An inductor L, a first output capacitor Co1, a second output capacitor Co2, a first diode D1, and a second diode D2 are externally attached to the switching power supply control circuit 200, and the switching power supply device 100 is configured.

In the switching power supply control circuit 200, the first switch SW1 to the fourth switch SW4 are configured by a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).
The first switch SW1 is an N-type MOS transistor, and its back gate terminal is grounded.
The second switch SW2 and the third switch SW3 are P-type MOS transistors, and their back gate terminals are connected to the first output terminal 104.
The fourth switch SW4 is also a P-type MOS transistor, and its back gate terminal is connected to the second output terminal 106.

  The gate terminals of the first switch SW1 to the fourth switch SW4 are connected to the control unit 10, and the gate-source voltage is controlled by the switching signal to switch the on / off state.

  FIG. 4 is a circuit diagram showing a configuration of the control unit 10 of FIG. The controller 10 includes resistors R11, R12, R21, R22, a first operational amplifier 12, a first PWM comparator 14, a first AND gate 16, a first feedback capacitor Cfb1, a first feedback switch SWfb1, a second operational amplifier 22, and a second PWM. It includes a comparator 24, a second AND gate 26, a second feedback capacitor Cfb 2, a second feedback switch SWfb 2, an oscillator 30, a maximum duty ratio setting comparator 32, a comparator 34, and a logic circuit 40.

The first output voltage Vout1 is fed back to the first feedback terminal 110. The resistors R11 and R12 divide the first output voltage Vout1 and output the first feedback voltage Vout1 ′ = R12 / (R11 + R12).
The first operational amplifier 12 functions as a comparator that compares the first reference voltage Vref1 and the first feedback voltage Vout1 ′ when the load is light, and during normal operation, the first operational amplifier 12 compares the first reference voltage Vref1 and the first feedback voltage Vout1 ′. It functions as an error amplifier that amplifies the voltage error. A first feedback capacitor Cfb1 and a first feedback switch SWfb1 are provided in series between the output terminal and the inverting input terminal of the first operational amplifier 12, and the first operational amplifier 12 has the first feedback switch SWfb1 turned on. Sometimes it functions as an error amplifier, and when it is off, it functions as a comparator. On / off of the first feedback switch SWfb1 is controlled based on the control signal Vcont.

  The first error voltage Verr1 output from the first operational amplifier 12 is input to the inverting input terminal of the first PWM comparator 14. The non-inverting input terminal of the first PWM comparator 14 receives the triangular voltage or sawtooth-shaped periodic voltage Vosc output from the oscillator 30. The first PWM comparator 14 compares the first error voltage Verr1 and the periodic voltage Vosc, and is a first pulse width modulation signal (hereinafter referred to as a first PWM signal Vpwm1) that is at a high level when Vosc> Verr1 and at a low level when Vosc <Verr1. ) Is output.

  Similarly, the resistors R21, R22, the second operational amplifier 22, the second feedback capacitor Cfb2, the second feedback switch SWfb2, and the second PWM comparator 24 generate the second PWM signal Vpwm2.

  The periodic voltage Vosc output from the oscillator 30 is input to the non-inverting input terminal of the maximum duty ratio setting comparator 32, and a predetermined maximum duty ratio setting voltage Vmax is input to the inverting input terminal. From the maximum duty ratio setting comparator 32, for example, a duty ratio fixed signal Vfix having a duty ratio fixed to about 80% is output.

  The first AND gate 16 outputs the logical product of the first PWM signal Vpwm1 and the fixed duty ratio signal Vfix as the first signal Sig1 to the subsequent logic circuit 40. The second AND gate 26 outputs the logical product of the second PWM signal Vpwm2 and the duty ratio fixed signal Vfix to the logic circuit 40 as the second signal Sig2. The duty ratios of the first signal Sig1 and the second signal Sig2 change according to the first output voltage Vout1 and the second output voltage Vout2, respectively, and the maximum value of the duty ratio is limited by the duty ratio fixed signal Vfix.

  The logic circuit 40 controls on / off of the first switch SW1 to the fourth switch SW4 based on the first signal Sig1 and the second signal Sig2.

  The comparator 34 compares the first error voltage Verr1 and the second error voltage Verr2 with the threshold voltage Vth, and generates an enable signal EN. The enable signal EN is at a high level when Verr1 <Vth and Verr2 <Vth at a light load, that is, when both the first error voltage Verr1 and the second error voltage Verr2 are at a low level, and otherwise at a low level. It becomes. The oscillator 30, the first PWM comparator 14, the second PWM comparator 24, and the maximum duty ratio setting comparator 32 are stopped when the enable signal EN is at a high level, and the current consumption of the circuit is reduced.

  The operation of the switching power supply apparatus 100 configured as described above will be described with reference to FIGS. FIGS. 5A and 5B are time charts showing the on / off states of the switches in the switching power supply apparatus 100. FIG. 5A and 5B show time charts in the normal operation mode and the light load mode, respectively. In this time chart, the high level and the low level respectively correspond to the on / off state of the switch.

  First, the operation in the normal operation mode of the switching power supply apparatus 100 will be described. The switching power supply device 100 operates in the normal mode when a high level is input as the control signal Vcont to the control terminal 108.

  In the normal mode, as shown in FIG. 5A, the input voltage Vin is boosted by alternately repeating the first period T1 and the second period T2, respectively, from the first output terminal 104 and the second output terminal 106, respectively. The first output voltage Vout1 and the second output voltage Vout2 are output.

  In the first period T1, the first switch SW1 and the second switch SW2 are sequentially turned on. By turning on the first switch SW1, a current flows through the inductor L from between the input terminals 102 toward the ground terminal. Inductor L stores energy proportional to the square of the current.

  Next, when the first switch SW1 is turned off and the second switch SW2 is turned on, the current flowing through the inductor L flows into the first output capacitor Co1 connected to the first output terminal 104, and the stored energy. Is transferred to the first output capacitor Co1. As a result, back electromotive force is generated in the inductor L, and a voltage obtained by boosting the input voltage Vin is output to the first output terminal 104.

Next, in the second period T2, the first switch SW1 and the third switch SW3 are sequentially turned on. When the first switch SW1 is turned on, current flows again from the input terminal 102 to the ground terminal in the inductor L, and energy is stored.
Next, the first switch is turned off, and the third switch SW3 and the fourth switch SW4 are turned on. The current flowing through the inductor L flows into the second output capacitor Co2 connected to the second output terminal 106, and the stored energy is transferred. As a result, back electromotive force is generated in the inductor L, and a voltage obtained by boosting the input voltage Vin is output to the second output terminal 106.
The on period Ton3 of the third switch SW3 is fixed longer than the maximum value of the on period Ton4 of the fourth switch SW4, and is boosted by the ratio of the on period Ton1 of the first switch SW1 and the on period Ton4 of the fourth switch SW4. The rate is adjusted.

  In this way, the first period T1 in which the energy stored in the inductor L is transferred to the first output capacitor Co1 and the second period T2 in which the energy stored in the inductor L is transferred to the second output capacitor Co2 are alternately repeated. As a result, the first output voltage Vout1 and the second output voltage Vout2 are output.

  Next, the operation in the light load mode of the switching power supply apparatus 100 will be described. The switching power supply device 100 is switched to the light load mode when a low level is input to the control terminal 108 as the control signal Vcont.

  In the light load mode, as shown in FIG. 5B, the input voltage Vin is boosted by alternately repeating the third period T3 and the fourth period T4, and from the first output terminal 104 and the second output terminal 106 The first output voltage Vout1 and the second output voltage Vout2 are output, respectively.

  In the third period T3, only the first switch SW1 is turned on. By turning on the first switch SW1, a current flows through the inductor L from between the input terminals 102 toward the ground terminal. Inductor L stores energy proportional to the square of the current.

  Next, the first switch SW1 is turned off, but the second switch SW2 is not turned on in the light load mode. As a result, the current flowing in the inductor L flows to the first output capacitor Co1 connected to the first output terminal 104 via the first diode D1, and the energy stored in the inductor L is the first output capacitor Co1. Forwarded to Since back electromotive force is generated in the inductor L, a voltage obtained by boosting the input voltage Vin is output to the first output terminal 104.

In the fourth period T4, the first switch SW1 and the third switch SW3 are sequentially turned on. When the first switch SW1 is turned on, current flows again from the input terminal 102 to the ground terminal in the inductor L, and energy is stored.
Next, only the third switch SW3 is turned on, and the fourth switch SW4 remains off. As a result, the current flowing through the inductor L flows into the second output capacitor Co2 via the third switch and the second diode D2, and the stored energy is transferred to the second output capacitor Co2.

  In order to change the gate voltage of the MOS transistor constituting the switch, it is necessary to charge and discharge the gate capacitance, so that current is generated in the control unit 10 when the switch is turned on / off. Therefore, by stopping the on / off switching of the second switch SW2 and the fourth switch SW4 at light load, the current consumption is reduced and the efficiency at light load is improved.

Further, the following effect can be obtained by providing the third switch SW3 in series with the fourth switch SW4. In the present embodiment, the first switch SW1 to the fourth switch SW4 are controlled so that the first output voltage Vout1 and the second output voltage Vout2 satisfy Vout1> Vout2. If the third switch SW3 is not provided, there is a possibility that a voltage higher than the forward voltage Vf is applied to the second diode D2 and it is turned on. When the second diode D2 is turned on, the energy stored in the inductor L should be transferred to the first output capacitor Co1 in the first period T1 in the normal operation mode or the third period T3 in the light load mode. Nevertheless, there arises a problem that current flows into the second output capacitor Co2 via the second diode D2.
Therefore, by providing the third switch SW3 and turning it off in the first period T1 and the third period T3, a normal boosting operation can be performed even when Vout1> Vout2.

  Further, connecting the back gate of the third switch SW3 to the first output terminal 104 has the following effects. In order to normally switch the third switch SW3 on and off, the back gate terminal needs to be fixed at a high potential. However, since the voltage at the connection point of the third switch SW3 and the fourth switch SW4 is unstable when the switching power supply device 100 is activated, if the back gate terminal is connected to this connection point, the second output voltage Vout2 may not rise normally. On the other hand, the first output terminal 104 outputs a voltage that has dropped from the input voltage Vin by the forward voltage Vf of the first diode D1 even immediately after startup, and is stable. Therefore, the stability of the switching power supply device 100 can be improved by connecting the back gate terminal of the third switch SW3 to the first output terminal 104.

  Switching power supply device 100 according to the present embodiment further reduces power consumption by the following operation. FIG. 6 is a time chart showing the operating state of the switching power supply apparatus 100 according to the present embodiment. In the light load mode, the control signal Vcont becomes low level, and the first feedback switch SWfb1 and the second feedback switch SWfb2 in FIG. 4 are turned off. As a result, the first operational amplifier 12 and the second operational amplifier 22 operate as comparators.

  When the load is light, the first output capacitor Co1 and the second output capacitor Co2 are intermittently charged, and the intermittent operation is repeated in which the charged charge is discharged by supplying current to the load thereafter. Accordingly, the first feedback voltage Vout1 ′ (that is, the first output voltage Vout1) and the second feedback voltage Vout2 ′ (that is, the second output voltage Vout2) are increased by a single switching operation as shown in FIG. When the voltage drops slowly to the reference voltage again due to the current, it rises again due to the switching operation.

  The first error voltage Verr1 output from the first operational amplifier 12 is at a low level when the first feedback voltage Vout1 'is higher than the first reference voltage Vref1. The second error voltage Verr2 output from the second operational amplifier 22 is at a low level when the second feedback voltage Vout2 'is higher than the second reference voltage Vref2. The comparator 34 sets the enable signal EN to a high level when both the first error voltage Verr1 and the second error voltage Verr2 are at a low level. When the enable signal EN is at a high level, the oscillator 30, the first PWM comparator 14, the second PWM comparator 24, and the maximum duty ratio setting comparator 32 stop their operations. As shown in FIG. 6, when the oscillator 30 stops, the periodic voltage Vosc becomes a constant value.

  Conversely, when the first feedback voltage Vout1 ′ is lower than the first reference voltage Vref1 or the second feedback voltage Vout2 ′ is lower than the second reference voltage Vref2 at the time of light load, that is, the first error voltage Verr1 and the second error. When at least one of the voltages Verr2 is at a high level, the first output voltage Vout1 or the second output voltage Vout2 is lowered. Therefore, it is necessary to operate the oscillator 30 and the like in preparation for the next switching operation. Therefore, in this case, the enable signal EN is set to the low level to operate the oscillator 30 and the like.

  As described above, according to the switching power supply device 100 according to the present embodiment, the voltage corresponding to the first output voltage Vout1 and the second output voltage Vout2 is monitored at light load, and both of them are associated with each other. When the voltage is higher than the first reference voltage Vref1 and the second reference voltage Vref2 specified in the above, it is possible to appropriately reduce power consumption by stopping unnecessary circuit blocks such as the oscillator 30.

  In addition, a switch is provided in the feedback path of the first operational amplifier 12 and the second operational amplifier 22 that function as an error amplifier during normal operation, and the feedback path is cut off at light loads, thereby using each as a comparator. . As a result, it is not necessary to provide a separate comparator from the error amplifier for generating the PWM signal, so that the circuit area can be reduced.

  Further, when the first operational amplifier 12 and the second operational amplifier 22 are operated as comparators at a light load, the duty ratio of the first PWM signal Vpwm1 and the second PWM signal Vpwm2 may become 100%. Operation stops. Therefore, the switching operation can be prevented from stopping by providing the maximum duty ratio setting comparator 32 and setting the upper limit to the duty ratio of the first PWM signal Vpwm1 and the second PWM signal Vpwm2.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  If the parasitic diode of the MOS transistor constituting the second switch SW2 is formed with a sufficient size, the first diode D1 may be substituted with the parasitic diode. Similarly, the second diode D2 may be replaced with a parasitic diode of the fourth switch SW4.

  In the embodiment, an element formed of a MOSFET can be replaced with another transistor such as a bipolar transistor. These selections may be determined according to the semiconductor manufacturing process, cost, and use required for the circuit.

  The enable signal EN may be generated not by the comparator 34 but by a logical operation. For example, in the present embodiment, the enable signal EN can be generated by taking the logical product of the inverted signal of the first error voltage Verr1 and the inverted signal of the second error voltage Verr2.

  In the embodiment, the case where the switching power supply control circuit 200 is integrated is described. However, all elements constituting the switching power supply apparatus 100 may be integrated or separated into another integrated circuit. It may be configured, and a part thereof may be configured by discrete parts. Which part is integrated may be determined according to cost, occupied area, application, and the like.

It is a figure which shows the structure of the switching power supply device which concerns on embodiment. It is a block diagram which shows the structure of the electronic device carrying the switching power supply device of FIG. It is a circuit diagram which shows the switching power supply device of FIG. 1 in detail. It is a circuit diagram which shows the structure of the control part of FIG. FIGS. 5A and 5B are time charts showing the on / off states of the switches in the switching power supply apparatus of FIG. It is a time chart which shows the operation state at the time of the light load of the switching power supply device of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Control part, 12 1st operational amplifier, 14 1st PWM comparator, 16 1st AND gate, 22 2nd operational amplifier, 24 2nd PWM comparator, 26 2nd AND gate, 30 Oscillator, 32 Maximum duty ratio setting comparator, 34 Comparator, 40 Logic circuit, 100 switching power supply device, 102 input terminal, 104 first output terminal, 106 second output terminal, 108 control terminal, 110 first feedback terminal, 112 second feedback terminal, 200 switching power supply control circuit, Co1 first output Capacitor, Co2 second output capacitor, D1 first diode, D2 second diode, SW1 first switch, SW2 second switch, SW3 third switch, SW4 fourth switch, Vout First output voltage, Vout2 second output voltage.

Claims (7)

A switching power supply control circuit for boosting an input voltage and outputting first and second output voltages,
A voltage corresponding to the first output voltage and a first error amplifier for amplifying an error of a predetermined first reference voltage;
A first pulse width modulation comparator that compares a first error voltage output from the first error amplifier with a periodic voltage output from an oscillator and outputs a first pulse width modulation signal;
A voltage corresponding to the second output voltage and a second error amplifier for amplifying an error between a predetermined second reference voltage;
A second pulse width modulation comparator that compares a second error voltage output from the second error amplifier with the periodic voltage output from the oscillator and outputs a second pulse width modulation signal;
A logic circuit for time-dividing and turning on and off the main switch and the two synchronous rectification switches based on the first pulse width modulation signal and the second pulse width modulation signal;
A first comparator for comparing a voltage according to the first output voltage with the first reference voltage;
A second comparator for comparing a voltage according to the second output voltage with the second reference voltage;
With
When the first output voltage is higher than the first reference voltage and the second output voltage is higher than the second reference voltage at light load, the oscillator and the first and second pulse width modulation comparators operate. the stop,
The first and second error amplifiers are configured integrally by sharing the first and second comparators and the operational amplifier, respectively.
A voltage corresponding to the output voltage is input to the first input terminal of the operational amplifier,
A feedback capacitor and a feedback switch connected in series between the output terminal and the second input terminal of the operational amplifier;
A control circuit which turns on the feedback switch during a normal load and turns off the feedback switch during a light load . A maximum duty ratio setting comparator that compares a predetermined set voltage with a periodic voltage output from the oscillator and outputs a duty ratio fixed signal with a fixed duty ratio; the control circuit of claim 1 in which the upper limit of the duty ratio, characterized in that to limit the duty ratio of the duty ratio fixing signal.   The control circuit according to claim 1, further comprising a control terminal, wherein the control circuit switches between a light load time and a normal load time based on a control signal input from the outside to the control terminal. Control circuit according to any one of claims 1 to 3, characterized in that it is integrated on a single semiconductor substrate. A switching power supply device that boosts an input voltage and outputs first and second output voltages,
An input terminal to which the input voltage is applied;
First and second output terminals for outputting the first and second output voltages, respectively;
An inductor and a main switch connected in series between the input terminal and the fixed potential terminal;
First and second synchronous rectification switches respectively provided between a connection point of the inductor and the main switch and the first and second output terminals;
First and second diodes provided in parallel to the first and second synchronous rectifier switches;
First and second output capacitors provided between the first and second output terminals and a fixed potential terminal;
The control circuit according to any one of claims 1 to 4, which controls on / off of the main switch and the first and second synchronous rectification switches;
The control circuit alternately turns on and off the main switch and the first and second switches during normal operation, and turns on and off only the main switch during light loads. Switching power supply. A switching power supply device that boosts an input voltage and outputs first and second output voltages,
An input terminal to which the input voltage is applied;
First and second output terminals for outputting the first and second output voltages, respectively;
A first output capacitor provided between the first output terminal and a fixed potential terminal;
A second output capacitor provided between the second output terminal and a fixed potential terminal;
An inductor and a first switch connected in series between the input terminal and a fixed potential terminal;
A connection point between the inductor and the first switch; a second switch provided between the first output terminals;
A connection point between the inductor and the first switch, and third and fourth switches provided in series between the second output terminals;
A first diode provided in parallel with the second switch so that a cathode terminal is on the second output terminal side;
A second diode provided in parallel with the fourth switch so that a cathode terminal is on the second output terminal side;
The control circuit according to any one of claims 1 to 4, which controls on / off of the first to fourth switches;
And the control circuit, during normal operation,
A first period for sequentially turning on the first switch and the second switch; and a second period for sequentially turning on the first switch and the third switch and turning on the fourth switch while the third switch is on. And alternately, while at light load,
A switching power supply device characterized by alternately repeating a third period for turning on the first switch and a fourth period for sequentially turning on the first switch and the third switch. Battery,
The switching power supply device according to claim 5 or 6 , which boosts the voltage of the battery;
A plurality of loads driven by the first and second output voltages output from the switching power supply device;
An electronic device comprising:

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