Switching Power Supply

Abstract

To provide a switching power supply with improved load transient response in discontinuous mode.SOLUTION: An error detection part 16 outputs an error signal VERR according to an error between an output voltage and a target voltage. A PWM control part 20 controls an output part 11 by alternately turns on a low-side transistor Q1 and a high-side transistor Q2 with a duty cycle according to a comparison signal VCOM which is comparison between the error signal VERR and a reference signal VS. A DC bias change part 21 changes a DC bias signal component so that a DC bias signal component in discontinuous mode (DCM) becomes lower than the DC bias signal component in forced PWM control mode (FCM).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a switching power supply device. [Background technology]

[0002] Switching power supplies are known that generate a desired output voltage from an input voltage by turning a transistor on and off. A widely known switching power supply employs a current-mode control method that performs output feedback control by detecting both the output voltage and the coil current (see Patent Document 1). Current-mode control switching power supplies also include those that can switch between a discontinuous mode, which prevents reverse current from flowing through the coil, and a forced PWM mode, which allows reverse current to flow through the coil. However, a problem with this method is that load transient response deteriorates in the discontinuous mode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-171214 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a switching power supply device with improved load transient response in discontinuous mode. [Means for solving the problem]

[0005] In order to achieve the above-mentioned object, the switching power supply device according to the present invention comprises the following features [1] to [ 6 ] is a feature of the product. [1] A switching power supply device that controls an output unit that outputs an output voltage obtained by converting an input voltage, a low-side transistor and a high-side transistor connected in series with each other; an error detection unit that outputs an error signal corresponding to the error between the output voltage and a target voltage; a reference signal generating unit that generates a reference signal including a DC bias signal component and a current signal component corresponding to a coil current flowing through a coil included in the output unit; a PWM comparator that outputs a comparison signal obtained by comparing the reference signal with the error signal; a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor at a duty cycle corresponding to the comparison signal; The DC bias signal component included in the reference signal is variably set. R, the control unit is provided to be switchable between a discontinuous mode in which the low-side transistor is turned off when a reverse current flows through the coil, and a forced PWM control mode in which the low-side transistor and the high-side transistor are alternately kept on even when the reverse current flows through the coil; a DC bias changing unit that changes the DC bias signal component so that the DC bias signal component in the discontinuous mode is lower than the DC bias signal component in the forced PWM control mode; It must be a switching power supply. [2] A switching power supply device that controls an output unit that outputs an output voltage obtained by converting an input voltage, a low-side transistor and a high-side transistor connected in series with each other; an error detection unit that outputs an error signal corresponding to the error between the output voltage and a target voltage; a reference signal generating unit that generates a reference signal including a DC bias signal component and a current signal component corresponding to a coil current flowing through a coil included in the output unit; a PWM comparator that outputs a comparison signal obtained by comparing the reference signal with the error signal; a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor at a duty cycle corresponding to the comparison signal; the DC bias signal component included in the reference signal is variably set; A DC bias change unit changes the DC bias signal component so that the DC bias signal component increases as the ripple current of the coil current increases. It must be a switching power supply. [3] [1] or [2] In the switching power supply device according to the reference signal generating unit includes a DC bias signal generating unit that generates a DC bias signal, a current signal generating unit that generates a current signal, and an adding unit that adds the DC bias signal and the current signal to generate the reference signal; The DC bias signal generating unit is provided so that the DC bias signal is variable. It must be a switching power supply. [4] A switching power supply device that controls an output unit that outputs an output voltage obtained by converting an input voltage, a low-side transistor and a high-side transistor connected in series with each other; an error detection unit that outputs an error signal corresponding to the error between the output voltage and a target voltage; a reference signal generating unit that generates a reference signal including a DC bias signal component and a current signal component corresponding to a coil current flowing through a coil included in the output unit; a PWM comparator that outputs a comparison signal obtained by comparing the reference signal with the error signal; a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor at a duty cycle corresponding to the comparison signal; the DC bias signal component included in the reference signal is variably set; the reference signal generating unit includes a DC bias signal generating unit that generates a DC bias signal, a current signal generating unit that generates a current signal, and an adding unit that adds the DC bias signal and the current signal to generate the reference signal; the adder unit includes a first voltage / current conversion circuit having a first resistor through which a current corresponding to the DC bias signal flows, a second voltage / current conversion circuit having a second resistor through which a current corresponding to the current signal flows, a first current mirror circuit that reflects the current flowing through the first resistor and supplies it to a third resistor, and a second current mirror circuit that reflects the current flowing through the second resistor and supplies it to the third resistor; The resistance value of the first resistor is set to be variable. It must be a switching power supply. [5] A switching power supply device that controls an output unit that outputs an output voltage obtained by converting an input voltage, a low-side transistor and a high-side transistor connected in series with each other; an error detection unit that outputs an error signal corresponding to the error between the output voltage and a target voltage; a reference signal generating unit that generates a reference signal including a DC bias signal component and a current signal component corresponding to a coil current flowing through a coil included in the output unit; a PWM comparator that outputs a comparison signal obtained by comparing the reference signal with the error signal; a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor at a duty cycle corresponding to the comparison signal; the DC bias signal component included in the reference signal is variably set; the reference signal generating unit includes a DC bias signal generating unit that generates a DC bias signal, a current signal generating unit that generates a current signal, and an adding unit that adds the DC bias signal and the current signal to generate the reference signal; the adder unit includes a first voltage / current conversion circuit having a first resistor through which a current corresponding to the DC bias signal flows, a second voltage / current conversion circuit having a second resistor through which a current corresponding to the current signal flows, a first current mirror circuit that reflects the current flowing through the first resistor and supplies it to a third resistor, and a second current mirror circuit that reflects the current flowing through the second resistor and supplies it to the third resistor; the first current mirror circuit is provided so that a current that is folded back to the third resistor is variable; It must be a switching power supply. [6] A switching power supply device that controls an output unit that outputs an output voltage obtained by converting an input voltage, a low-side transistor and a high-side transistor connected in series with each other; an error detection unit that outputs an error signal corresponding to the error between the output voltage and a target voltage; a reference signal generating unit that generates a reference signal including a DC bias signal component and a current signal component corresponding to a coil current flowing through a coil included in the output unit; a PWM comparator that outputs a comparison signal obtained by comparing the reference signal with the error signal; a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor at a duty cycle corresponding to the comparison signal; the DC bias signal component included in the reference signal is variably set; the reference signal generating unit includes a DC bias signal generating unit that generates a DC bias signal, a current signal generating unit that generates a current signal, and an adding unit that adds the DC bias signal and the current signal to generate the reference signal; The current signal generating unit has an instrumentation amplifier that amplifies a voltage value corresponding to the current flowing through the coil, and a reference voltage supplied to the instrumentation amplifier is variably set. It must be a switching power supply. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a switching power supply device with improved load transient response in discontinuous mode.

[0007] The present invention has been briefly described above. The details of the present invention will become clearer by reading the following detailed description of the invention (hereinafter referred to as "embodiments") with reference to the accompanying drawings. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a circuit diagram showing a DC / DC converter incorporating a switching power supply device of the present invention. [Figure 2] Figure 2 is a time chart of the on / off of the high-side transistor, the on / off of the low-side transistor, the potential of the switch terminal, the coil current, the current signal, the slope compensation signal, the DC bias signal, and the reference signal. [Figure 3] FIG. 3 is a time chart of the switch terminal potential, coil current, and reference signal in the FCM. [Figure 4] FIG. 4 is a time chart of the switch terminal potential, coil current, and reference signal in a DCM. [Figure 5] FIG. 5 is a time chart of the load current, switch terminal potential, coil current, error signal, reference signal, and output voltage of a conventional DC / DC converter. [Figure 6] FIG. 6 is a time chart of the load current, switch terminal potential, coil current, error signal, reference signal, and output voltage of the DC / DC converter of this embodiment shown in FIG. [Figure 7] FIG. 7 is a circuit diagram showing details of the DC bias signal generating unit and the adding unit shown in FIG. [Figure 8] FIG. 8 is a circuit diagram showing details of the current signal generating unit shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] (First embodiment) A first embodiment of the present invention will be described below with reference to the drawings.

[0010] A DC / DC converter 1 of this embodiment steps down an input voltage VIN and supplies an output voltage VOUT to a load 2. The input voltage VIN is supplied from a DC power supply 3. The DC / DC converter 1 includes an output unit 11 that steps down the input voltage VIN and outputs it as an output voltage VOUT, a switching power supply device 12 that supplies a pulsed input voltage VIN to the output unit 11 and controls the output unit 11, and a bootstrap capacitor CB.

[0011] The output unit 11 includes a coil L1 and an output capacitor C1. The coil L1 is connected between a switch terminal TSW of the switching power supply device 12 and a load 2. One end of the load 2 is connected to the coil L1 via a resistor R3, and the other end is connected to ground. One end of the output capacitor C1 is connected to the load 2, and the other end is connected to ground.

[0012] The switching power supply device 12 is configured from an IC chip and includes a low-side transistor Q1 (hereinafter sometimes abbreviated as "transistor Q1"), a high-side transistor Q2 (hereinafter sometimes abbreviated as "transistor Q2"), driver units (represented as "DRV" in FIG. 1) 131 and 132, a bootstrap unit 14, a voltage detection unit 15, an error detection unit 16, a PWM comparator 17, a reference signal generation unit 18, an overcurrent detection unit 19, a PWM control unit 20 as a control unit, and a DC bias change unit 21.

[0013] The transistors Q1 and Q2 are configured by Nch power MOSFETs (metal-oxide semiconductor field-effect transistors). The source of the low-side transistor Q1 is connected to ground, and the drain is connected to the switch terminal TSW. The source of the high-side transistor Q2 is connected to the switch terminal TSW and the drain of the transistor Q1, and the drain is connected to the input terminal TIN. The input terminal TIN receives the input voltage VIN supplied from the DC power supply 3.

[0014] As shown in Figure 2, when transistor Q2 is on and transistor Q1 is off, the input voltage VIN is output from switch terminal TSW. In contrast, when transistor Q2 is off and transistor Q1 is on, the ground potential 0V is output from switch terminal TSW. By alternately controlling the on-state of transistors Q1 and Q2, a pulse signal (= pulsed input voltage VIN) with an H level representing the input voltage VIN and an L level representing 0V is output from switch terminal TSW. By inputting this pulse signal to output section 11 and smoothing it with coil L1 and output capacitor C1, an output voltage VOUT corresponding to the duty cycle of the pulse signal can be supplied to load 2.

[0015] When the transistors Q1 and Q2 are switched on and off, a dead time DT is provided during which both transistors Q1 and Q2 are turned off to prevent a short circuit in the DC power supply 3. During the dead time DT, the potential of the switch terminal TSW is −0.7 V, that is, a potential that is lower than the ground potential of 0 V by 0.7 V, the forward voltage of the parasitic diode of the transistor Q1.

[0016] 1, the driver unit 131 is a circuit connected to the gate of the transistor Q1 and drives the transistor Q1 to turn on and off. The driver unit 131 operates by receiving a gate drive voltage VG from a gate drive power supply (denoted as "LDO" in FIG. 1) 141.

[0017] The driver unit 132 is connected to the gate of the transistor Q2 and is a circuit that drives the transistor Q2 to turn on and off. When the transistor Q2 is turned on, the source potential becomes equal to the input voltage VIN. Therefore, even if the gate drive voltage VG is supplied to the gate of the transistor Q2, as with the transistor Q1, the transistor Q2 cannot be kept on. Therefore, the driver unit 132 operates by receiving power from the bootstrap unit 14, which will be described later.

[0018] The bootstrap unit 14 is a circuit that uses a bootstrap capacitor CB to generate a boot voltage VB by adding the voltage across the bootstrap capacitor CB to the potential of the switch terminal TSW (i.e., the source potential of the transistor Q2). The voltage across the bootstrap capacitor CB is approximately equal to the gate drive voltage VG.

[0019] The bootstrap unit 14 has a gate drive power supply 141 and a diode D1. The gate drive power supply 141 generates and outputs a gate drive voltage VG from an input voltage VIN. The diode D1 has an anode connected to the gate drive power supply 141 and a cathode connected to one end of a bootstrap capacitor CB via a boot terminal TB. The other end of the bootstrap capacitor CB is connected to a switch terminal TSW.

[0020] The voltage detection unit 15 outputs a detection voltage VR corresponding to the output voltage VOUT to the error detection unit 16, which will be described later. The voltage detection unit 15 has resistors R1 and R2. One end of the resistor R1 is connected to ground, and the other end is connected to one end of the resistor R2. The other end of the resistor R2 is connected to the output of the output unit 11 via the feedback terminal TFB. A detection voltage VR, which is the output voltage VOUT divided by the resistors R1 and R2, is output to the connection point of the resistors R1 and R2.

[0021] The error detection unit 16 amplifies the error (difference) between the detection voltage VR and the reference voltage VREF and outputs the error signal VERR to the PWM comparator 17. The reference voltage VREF is set so as to be equal to the detection voltage VR output from the voltage detection unit 15 when the output voltage VOUT reaches the target voltage.

[0022] The PWM comparator 17 compares the error signal VERR with the reference signal VS, and outputs a comparison signal VCOM indicating the comparison result.

[0023] The reference signal generating unit 18 generates a reference signal V S that includes a slope compensation signal component, a current signal component, and a DC bias signal component. The reference signal generating unit 18 includes a slope compensation signal generating unit 181 that generates a slope compensation signal, a current signal generating unit 182 that generates a current signal, a DC bias signal generating unit 183 that generates a DC bias signal, and an adding unit 184 that outputs a reference signal V S that is obtained by adding the slope compensation signal, the current detection signal, and the DC bias signal.

[0024] As shown in FIG. 2, the slope compensation signal generating unit 181 outputs a sawtooth waveform slope compensation signal that rises from 0V over one cycle of the pulse signal and returns to 0V when one cycle ends.

[0025] The current signal generating unit 182 generates a current signal corresponding to the coil current IL flowing through the coil L1. The current signal generating unit 182 outputs the voltage across a resistor R3 connected between the coil L1 and the load 2 as a current signal. More specifically, the current signal generating unit 182 is connected to a current detection terminal TSNS1 connected to one end of the resistor R3 and a current detection terminal TSNS2 connected to the other end of the resistor R3. The current signal generating unit 182 amplifies the voltage generated between the current detection terminals TSNS1 and TSNS2 and outputs the amplified voltage as a current signal.

[0026] As shown in Figure 2, the coil current IL increases while the pulse signal output from the switch terminal TSW is at H level (=input voltage VIN), and decreases while the pulse signal output from the switch terminal TSW is at L level (=0V). Similarly, the current signal obtained by IV-converting the coil current IL increases while the pulse signal output from the switch terminal TSW is at H level (=input voltage VIN), and decreases while the pulse signal output from the switch terminal TSW is at L level (=0V).

[0027] The DC bias signal generator 183 generates a DC bias signal, which is a direct current voltage. As shown in FIG. 2, the adder 184 outputs a reference signal VS obtained by adding the slope compensation signal, the current signal, and the DC bias signal. This type of control, in which the current signal component is included in the reference signal VS, is called current mode control. The DC / DC converter 1 under current mode control has the advantages of simple phase compensation design and high feedback loop stability, enabling a fast load transient response. The DC bias signal is also included in the reference signal VS to set the reference signal VS at an operable voltage (e.g., 0.2 V or higher) for the PWM comparator 17 and other devices.

[0028] The overcurrent detection unit 19 compares the voltage generated between the current detection terminal TSNS1 and the current detection terminal TSNS2, which corresponds to the coil current IL flowing through the coil L1, with a threshold voltage, and outputs the comparison result to the PWM control unit 20.

[0029] The PWM control unit 20 outputs pulse signals having a duty cycle corresponding to the comparison signal VCOM to the driver units 131 and 132 to control the on / off of the transistors Q1 and Q2. In this embodiment, the PWM control unit 20 can operate in two modes: a forced PWM mode (hereinafter referred to as "FCM") and a discontinuous mode (hereinafter referred to as "DCM").

[0030] Before explaining FCM and DCM, we will next explain the relationship between the load current flowing through load 2 and the coil current IL. When transistors Q1 and Q2 are alternately turned on, the coil current IL becomes a ripple current that increases and decreases around the load current. When the load current (half the ripple current ΔIL (see Figure 2) flowing through coil L1) is large, as shown in Figure 2, when transistors Q1 and Q2 are alternately turned on, the coil current IL increases and decreases around the load current, but does not fall below 0 A, and current continues to flow from coil L1 to output capacitor C1.

[0031] However, when the load current (half the ripple current ΔIL) is small, the coil current IL falls below 0 A as the transistors Q1 and Q2 alternately turn on and decrease, as shown in Figure 3, and a reverse current flows from the output capacitor C1 to the coil L1.

[0032] In FCM, the PWM control unit 20 continues to alternately turn on and off the transistors Q1 and Q2 even when a reverse current occurs. As a result, when the load current is small, a reverse current occurs in the coil L1, as shown in Figure 3. In other words, FCM is a control that allows the occurrence of a reverse current and ensures that the coil current IL flows continuously.

[0033] In contrast, in DCM, the PWM control unit 20 turns off transistor Q1 when it detects a reverse current. That is, transistor Q1 operates as if it were a Schottky barrier diode. As a result, as shown in FIG. 4, transistor Q1 immediately turns off and is shut off when a reverse current occurs, and no reverse current flows through coil L1. In DCM, no reverse current flows through coil L1 when the load current is small, and no conduction loss occurs in coil L1 and transistor Q2, improving efficiency.

[0034] The control of the FCM and DCM can be switched externally. For example, by providing a switching terminal (not shown) in the switching power supply device 12, switching can be performed by an input voltage input to the switching terminal. Alternatively, by providing a communication terminal (not shown) in the switching power supply device 12, switching can be performed by a communication signal such as SPI input to the communication terminal.

[0035] However, when DCM is performed in the above-mentioned current mode control, there is a problem in that the load transient response deteriorates when changing from no load to a heavy load. It was found that the cause of this problem is that in the conventional DC / DC converter 1, the DC bias signal component included in the reference signal VS is always set to the same value.

[0036] That is, as shown in Fig. 3, a reverse current occurs in an FCM, so the DC bias signal component is set higher to make the reference signal VS an operable voltage (for example, 0.2 V or higher). In contrast, since a reverse current does not occur in a DCM, if the same DC bias signal component as in an FCM is set, the reference signal VS will be set higher, as shown in Fig. 4.

[0037] Next, problems that arise when the DC bias signal component and reference signal VS are set relatively high will be described with reference to FIG. 5. As shown in the figure, consider the case where the load current changes from no load (0 A) to a heavy load (5 A) and then from 5 A to 0 A. When the load current is 0 A, as soon as the pulse signal output from switch terminal TSW becomes high (input voltage VIN), the output voltage VOUT immediately exceeds the target voltage, causing the error signal VERR to decrease and frequently falling below the reference signal VS. Therefore, PWM control unit 20 operates in pulse skip mode, outputting a high-level pulse signal from switch terminal TSW only once every few cycles.

[0038] If the load current increases in this state, the output voltage VOUT will drop below the target voltage, causing the error signal VERR to rise. However, because the reference signal VS is set high, the output voltage VOUT will not exceed the reference signal VS until the output voltage VOUT drops to a certain extent and the error signal VERR rises significantly. For this reason, when the load current switches from no load to a heavy load, the output voltage VOUT will fluctuate greatly, resulting in poor transient response.

[0039] Furthermore, when the load current changes from a heavy load (5 A) to no load (0 A) and decreases, the output voltage VOUT rises and exceeds the target voltage, causing the error signal VERR to fall. In this case, the PWM control unit 20 cannot transition to pulse skip operation until the error signal VERR, which has risen significantly, falls to around 0 V. Therefore, when the load current switches from a heavy load to no load, the output voltage VOUT also fluctuates significantly, resulting in poor transient response.

[0040] Therefore, in this embodiment, a DC bias changing unit 21 is provided, which changes the DC bias signal component included in the reference signal VS so that the DC bias signal component in the DCM is lower than the DC bias signal component in the FCM. This reduces the change in the error signal VERR when the load current changes from no load to heavy load and from heavy load to no load in the DCM, suppresses fluctuations in the output voltage VOUT, and improves the load transient response in the DCM.

[0041] Next, the effects of the above-described embodiment will be described with reference to Fig. 6. As shown in Fig. 6, consider a case where the load current changes from no load (0 A) to a heavy load (5 A) and then changes from 5 A to 0 A. When the load current becomes 0 A, the PWM control unit 20 enters pulse skip mode, as in the conventional DC / DC converter 1, and operates so as to output an H-level pulse signal from the switch terminal TSW only once every few cycles.

[0042] If the load current increases in this state, the output voltage VOUT will drop below the target voltage, causing the error signal VERR to rise. Because the reference signal VS is set appropriately, when the error signal VERR rises, it exceeds the reference signal VS relatively quickly. As a result, when the load current switches from no load to a heavy load, the output voltage VOUT does not fluctuate greatly, improving the transient response.

[0043] Furthermore, when the load current changes from a heavy load (5 A) to no load (0 A) and decreases, the output voltage VOUT rises and exceeds the target voltage, causing the error signal VERR to fall. In this case, because the error signal VERR does not rise significantly under heavy load conditions, it quickly falls to near 0 V, allowing the PWM control unit 20 to transition to pulse skip operation. Therefore, in DCM, even when the load current switches from a heavy load to no load, the output voltage VOUT does not fluctuate significantly, enabling improved load transient response in DCM.

[0044] Next, a detailed circuit for changing the above-mentioned DC bias signal component will be described with reference to Fig. 7. Fig. 7 is a circuit diagram showing details of the DC bias signal generation unit 183 and the addition unit 184 shown in Fig. 1. The addition unit 184 includes V / I conversion circuits 1841-1843 that perform voltage / current (V / I) conversion of the current signal, slope compensation signal, and DC bias signal, and current mirror circuits 1844-1846.

[0045] The DC bias signal generating unit 183 is provided with a variable direct current DC bias signal. The DC bias changing unit 21 controls the DC bias signal generating unit 183 so that the DC bias signal output from the DC bias signal generating unit 183 in the DCM is lower than the DC bias signal output from the DC bias signal generating unit 183 in the FCM.

[0046] The V / I conversion circuit 1841, which serves as a second voltage / current conversion circuit, is a circuit that performs V / I conversion on a current signal and includes an operational amplifier OP1, a transistor Q4, and a resistor R4 serving as a second resistor. When a current signal is supplied to the non-inverting input terminal of the operational amplifier OP1, a current corresponding to the current signal flows through the resistor R4 due to the operation of the operational amplifier OP1 and the transistor Q4.

[0047] The V / I conversion circuit 1842 is a circuit that performs V / I conversion on the slope compensation signal, and includes an operational amplifier OP2, a transistor Q5, and a resistor R5. When a slope compensation signal is supplied to the non-inverting input terminal of the operational amplifier OP2, a current corresponding to the slope compensation signal flows through the resistor R5 due to the operation of the operational amplifier OP2 and the transistor Q5.

[0048] The V / I conversion circuit 1843, which serves as a first voltage / current conversion circuit, is a circuit that performs V / I conversion of a DC bias signal and includes an operational amplifier OP3, a transistor Q6, resistors R61 and R62 as a first resistor, and a switch SW1. The switch SW1 is connected to both ends of the resistor R61 and can change the resistance value connected between the transistor Q6 and ground depending on whether the switch SW1 is turned on or off.

[0049] More specifically, when switch SW1 is turned off, both resistors R61 and R62 are connected between transistor Q6 and ground, increasing the resistance. When switch SW1 is turned on, only resistor R62 is connected between transistor Q6 and ground, decreasing the resistance.

[0050] Furthermore, when a DC bias signal is supplied to the non-inverting input terminal of the operational amplifier OP3, a current corresponding to the DC bias signal flows through both resistors R61 and R62 or only resistor R62 due to the operation of the operational amplifier OP3 and transistor Q6.

[0051] Current mirror circuit 1844, which serves as a second current mirror circuit, is a circuit that mirrors a current corresponding to a current signal flowing through resistor R4 and supplies it to resistor R7, which serves as a third resistor. Current mirror circuit 1844 has transistors Q71 and Q72, whose gates and drains are connected together. The gates of transistors Q71 and Q72 are connected together and their sources are connected together. The drain of transistor Q72 is connected to resistor R7.

[0052] Current mirror circuit 1845 is a circuit that mirrors the current that flows through resistor R5 according to the slope compensation signal and supplies it to resistor R7. Current mirror circuit 1845 has transistor Q81 and transistor Q82, whose gates and drains are connected together. The gates of transistors Q81 and Q82 are connected together and their sources are connected together. The drain of transistor Q82 is connected to resistor R7.

[0053] Current mirror circuit 1846, acting as a first current mirror circuit, is a circuit that reflects a current corresponding to a DC bias signal flowing through both resistors R61 and R62 or through resistor R62, and supplies the reflected current to resistor R7. Current mirror circuit 1846 includes transistor Q91, whose gate and drain are connected, transistors Q92 and Q93, and switch SW2. Transistor Q91 and transistors Q92 and Q93 have their gates connected to each other and their sources connected to each other. The drains of transistors Q92 and Q93 are connected to resistor R7. Switch SW2 is connected between the drain of transistor Q93 and resistor R7. The current supplied from current mirror circuit 1846 to resistor R7 can be increased or decreased by turning switch SW2 on or off.

[0054] With the above configuration, a current that is the sum of a current corresponding to the current signal, a current corresponding to the slope compensation signal, and a current corresponding to the DC bias signal flows through resistor R7. Therefore, a reference signal VS that is the sum of the current signal, slope compensation signal, and DC bias signal is generated in resistor R7, and this reference signal VS is supplied to the inverting input of PWM comparator 17.

[0055] The DC bias change unit 21 turns off the switch SW1 of the V / I conversion circuit 1843 in the DCM, and turns on the switch SW1 of the V / I conversion circuit 1843 in the FCM. As a result, the current flowing through resistors R61 and R62 in the DCM decreases, and the current flowing through resistor R62 in the FCM increases, so that the DC bias signal component in the DCM becomes lower than the DC bias signal component in the FCM.

[0056] Furthermore, the DC bias change unit 21 turns off the switch SW2 of the current mirror circuit 1846 in the DCM, and turns on the switch SW2 of the current mirror circuit 1846 in the FCM. As a result, the current folded back by the current mirror circuit 1846 in the DCM decreases, and the current folded back by the current mirror circuit 1846 in the FCM increases, so that the DC bias signal component in the DCM becomes lower than the DC bias signal component in the FCM.

[0057] 7, the DC bias change unit 21 changes the DC bias signal component by executing three operations: changing the DC bias signal generated by the DC bias signal generation unit 183, turning on / off the switch SW1, and turning on / off the switch SW2. However, the present invention is not limited to this. The DC bias signal component may be changed by executing any one or any two of the three operations.

[0058] Next, another circuit for changing the above-mentioned DC bias signal will be described with reference to Fig. 8. Fig. 8 is a circuit showing the details of the current signal generation unit 182 shown in Fig. 1. The current signal generation unit 182 is made up of resistors R81 to R84 and an instrumentation amplifier having an operational amplifier OP4, and outputs a current signal obtained by amplifying the voltage between the current detection terminals TSNS1 and TSNS2.

[0059] The inverting input terminal of the operational amplifier OP4 is connected to the current detection terminal TSNS1 via resistor R81. The non-inverting input terminal of the operational amplifier OP4 is connected to the current detection terminal TSNS2 via resistor R82. The inverting input terminal of the operational amplifier OP4 is connected to the output via resistor R83. The non-inverting input terminal of the operational amplifier OP4 is connected to the reference power supply 1821 via resistor R84. If the voltage generated between the current detection terminals TSNS1 and TSNS2 is VIL and the reference voltage generated by the reference power supply 1821 is VREF2, the current signal is expressed by the following equation (1).

[0060] Current signal = VREF2 + Gain × VIL …(1)

[0061] The gain is set by resistors R81 to R84. It can be seen from equation (1) that by increasing or decreasing the reference voltage VREF2, the DC component of the current signal can be increased or decreased, thereby changing the DC bias signal.

[0062] Therefore, in this embodiment, the DC bias changer 21 sets the reference voltage VREF2 in the DCM lower than the reference voltage VREF in the FCM, and sets the DC bias signal component in the DCM lower than the DC bias signal component in the FCM.

[0063] In the first embodiment described above, in addition to the change of the DC bias signal by the DC bias signal generating unit 183 and the adding unit 184 shown in Fig. 7, the change of the DC bias signal by the current signal generating unit 182 shown in Fig. 8 is performed, but this is not limited to this. Only one of the change of the DC bias signal by the DC bias signal generating unit 183 and the adding unit 184 and the change of the DC bias signal by the current signal generating unit 182 may be performed.

[0064] (Second embodiment) Next, a DC / DC converter 1 according to a second embodiment will be described. In the first embodiment described above, the DC bias change unit 21 changes the DC bias signal depending on whether the converter is in DCM or FCM, but this is not limiting. The DC bias change unit 21 may also change the DC bias signal depending on the magnitude of the ripple current ΔIL of the coil current IL. Specifically, the DC bias change unit 21 changes the DC bias signal component so that the DC bias signal component increases as the ripple current ΔIL increases.

[0065] As mentioned above, when the load current becomes half or less of the ripple current ΔIL, a reverse current occurs in the coil L1. Therefore, the larger the ripple current ΔIL, the more likely a reverse current will occur, and the more likely the coil current IL will fall below 0. As mentioned above, the DC bias signal component is set higher as the ripple current ΔIL increases, so the DC bias signal can be set so that the reference signal VS remains at an operable voltage even when the coil current IL becomes negative.

[0066] On the other hand, the smaller the ripple current ΔIL, the less likely a reverse current is to occur, and the less likely the coil current IL is to fall below 0. As described above, as the ripple current ΔIL becomes smaller, the DC bias signal component is set lower, which improves the load transient response when the load current fluctuates in DCM.

[0067] The present invention is not limited to the above-described embodiments, and can be appropriately modified, improved, etc. Furthermore, the material, shape, size, number, location, etc. of each component in the above-described embodiments are arbitrary and not limited as long as they can achieve the present invention.

[0068] According to the above-described embodiment, the high-side transistor Q2 is configured as an N-channel transistor and is turned on and off using the bootstrap unit 14. However, the present invention is not limited to this. The high-side transistor Q2 may be configured as a P-channel transistor, and the bootstrap unit 14 may not be provided.

[0069] In the above-described embodiment, the reference signal Vs includes a slope compensation signal component, but this is not limiting. The reference signal Vs only needs to include at least a DC bias signal component and a current signal component, and does not necessarily need to include a slope compensation signal component.

[0070] According to the above-described embodiment, the output unit 11 is configured as a step-down type, but this is not limited to this. The output unit 11 may also be configured as a step-up type that converts the input voltage VIN into a step-up voltage. [Explanation of symbols]

[0071] 11 Output section 12 Switching power supply 16 Error detection section 17 PWM Comparator 18 Reference signal generation section 20 PWM control unit (control unit) 21 DC bias change section 182 Current signal generation section 183 DC bias signal generator 184 Addition section 1841 V / I conversion circuit (second voltage / current conversion circuit) 1843 V / I conversion circuit (first voltage / current conversion circuit) 1844 Current mirror circuit (second current mirror circuit) 1846 Current mirror circuit (first current mirror circuit) IL Coil current L1 coil R4 Resistor (second resistor) R61, R62 Resistors (first resistor) R7 Resistor (third resistor) Q1 Low-side transistor Q2 High-side transistor VCOM comparison signal VERR error signal VREF2 reference voltage VS reference signal

Claims

1. A switching power supply device that controls an output unit that outputs an output voltage obtained by converting an input voltage, a low-side transistor and a high-side transistor connected in series with each other; an error detection unit that outputs an error signal corresponding to the error between the output voltage and a target voltage; a reference signal generating unit that generates a reference signal including a DC bias signal component and a current signal component corresponding to a coil current flowing through a coil included in the output unit; a PWM comparator that compares the reference signal with the error signal and outputs a comparison signal; a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor at a duty cycle corresponding to the comparison signal, the DC bias signal component included in the reference signal is variably set; the control unit is provided to be switchable between a discontinuous mode in which the low-side transistor is turned off when a reverse current flows through the coil, and a forced PWM control mode in which the low-side transistor and the high-side transistor are alternately kept on even when the reverse current flows through the coil, a DC bias changing unit that changes the DC bias signal component so that the DC bias signal component in the discontinuous mode is lower than the DC bias signal component in the forced PWM control mode; Switching power supply.

2. A switching power supply device that controls an output section that outputs an output voltage obtained by converting an input voltage, a low-side transistor and a high-side transistor connected in series with each other; an error detection unit that outputs an error signal corresponding to the error between the output voltage and a target voltage; a reference signal generating unit that generates a reference signal including a DC bias signal component and a current signal component corresponding to a coil current flowing through a coil included in the output unit; a PWM comparator that compares the reference signal with the error signal and outputs a comparison signal; a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor at a duty cycle corresponding to the comparison signal, the DC bias signal component included in the reference signal is variably set; a DC bias changing unit that changes the DC bias signal component so that the DC bias signal component increases as the ripple current of the coil current increases; Switching power supply.

3. 3. The switching power supply device according to claim 1, the reference signal generating unit includes a DC bias signal generating unit that generates a DC bias signal, a current signal generating unit that generates a current signal, and an adding unit that adds the DC bias signal and the current signal to generate the reference signal; The DC bias signal generating unit is provided so that the DC bias signal is variable. Switching power supply.

4. A switching power supply device that controls an output section that outputs an output voltage obtained by converting an input voltage, a low-side transistor and a high-side transistor connected in series with each other; an error detection unit that outputs an error signal corresponding to the error between the output voltage and a target voltage; a reference signal generating unit that generates a reference signal including a DC bias signal component and a current signal component corresponding to a coil current flowing through a coil included in the output unit; a PWM comparator that compares the reference signal with the error signal and outputs a comparison signal; a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor at a duty cycle corresponding to the comparison signal, the DC bias signal component included in the reference signal is variably set; the reference signal generating unit includes a DC bias signal generating unit that generates a DC bias signal, a current signal generating unit that generates a current signal, and an adding unit that adds the DC bias signal and the current signal to generate the reference signal; the adder unit includes a first voltage / current conversion circuit having a first resistor through which a current corresponding to the DC bias signal flows, a second voltage / current conversion circuit having a second resistor through which a current corresponding to the current signal flows, a first current mirror circuit that returns the current flowing through the first resistor and supplies it to a third resistor, and a second current mirror circuit that returns the current flowing through the second resistor and supplies it to the third resistor; The resistance value of the first resistor is set to be variable. Switching power supply.

5. A switching power supply device that controls an output section that outputs an output voltage obtained by converting an input voltage, a low-side transistor and a high-side transistor connected in series with each other; an error detection unit that outputs an error signal corresponding to the error between the output voltage and a target voltage; a reference signal generating unit that generates a reference signal including a DC bias signal component and a current signal component corresponding to a coil current flowing through a coil included in the output unit; a PWM comparator that compares the reference signal with the error signal and outputs a comparison signal; a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor at a duty cycle corresponding to the comparison signal, the DC bias signal component included in the reference signal is variably set; the reference signal generating unit includes a DC bias signal generating unit that generates a DC bias signal, a current signal generating unit that generates a current signal, and an adding unit that adds the DC bias signal and the current signal to generate the reference signal; the adder unit includes a first voltage / current conversion circuit having a first resistor through which a current corresponding to the DC bias signal flows, a second voltage / current conversion circuit having a second resistor through which a current corresponding to the current signal flows, a first current mirror circuit that returns the current flowing through the first resistor and supplies it to a third resistor, and a second current mirror circuit that returns the current flowing through the second resistor and supplies it to the third resistor; the first current mirror circuit is provided so that a current that is folded back to the third resistor is variable; Switching power supply.

6. A switching power supply device that controls an output section that outputs an output voltage obtained by converting an input voltage, a low-side transistor and a high-side transistor connected in series with each other; an error detection unit that outputs an error signal corresponding to the error between the output voltage and a target voltage; a reference signal generating unit that generates a reference signal including a DC bias signal component and a current signal component corresponding to a coil current flowing through a coil included in the output unit; a PWM comparator that compares the reference signal with the error signal and outputs a comparison signal; a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor at a duty cycle corresponding to the comparison signal, the DC bias signal component included in the reference signal is variably set; the reference signal generating unit includes a DC bias signal generating unit that generates a DC bias signal, a current signal generating unit that generates a current signal, and an adding unit that adds the DC bias signal and the current signal to generate the reference signal; The current signal generating unit has an instrumentation amplifier that amplifies a voltage value corresponding to the current flowing through the coil, and a reference voltage supplied to the instrumentation amplifier is variably set. Switching power supply.

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