JP2023146577A - Switching power supply device - Google Patents

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

The present invention relates to a switching power supply device.

2. Description of the Related Art A switching power supply device is known that generates a desired output voltage from an input voltage by turning on and off transistors. In switching power supply devices, a current mode control method is widely known in which output feedback control is performed by detecting both an output voltage and a coil current (Patent Document 1). In addition, there are known switching power supplies using current mode control that can be switched between a discontinuous mode that prevents reverse current from flowing through the coil, and a forced PWM mode that allows reverse current to flow through the coil. . In this case, there was a problem in that the load transient response deteriorated in the discontinuous mode.

Japanese Patent Application Publication No. 2015-171214

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a switching power supply device with improved load transient response in discontinuous mode.

In order to achieve the above-mentioned object, the switching power supply device according to the present invention is characterized by the following [1] to [7].
[1]
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 according to the error between the output voltage and the target voltage;
a reference signal generation 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 comparing the reference signal and the error signal;
a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor with a duty cycle according to the comparison signal,
the DC bias signal component included in the reference signal is variably provided;
Must be a switching power supply.
[2]
In the switching power supply device according to [1],
The control unit operates in a discontinuous mode in which the low-side transistor is turned off when a reverse current flows through the coil, and in a forced mode in which the low-side transistor and the high-side transistor are alternately kept on even when the reverse current flows in the coil. It is provided so that it can be switched to PWM control mode,
comprising 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;
Must be a switching power supply.
[3]
In the switching power supply device according to [1],
comprising 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;
Must be a switching power supply.
[4]
In the switching power supply device according to any one of [1] to [3],
The reference signal generation unit includes a DC bias signal generation unit that generates a DC bias signal, a current signal generation unit that generates a current signal, and an addition unit that adds the DC bias signal and the current signal to generate the reference signal. and has a
The DC bias signal generation section is configured to variably provide the DC bias signal.
Must be a switching power supply.
[5]
In the switching power supply device according to any one of [1] to [3],
The reference signal generation unit includes a DC bias signal generation unit that generates a DC bias signal, a current signal generation unit that generates a current signal, and an addition unit that adds the DC bias signal and the current signal to generate the reference signal. and has a
The adding section includes a first voltage/current conversion circuit having a first resistor through which a current according to the DC bias signal flows, and a second voltage/current converting circuit having a second resistor through which a current according to the current signal flows. /a current conversion circuit; a first current mirror circuit that folds back the current flowing through the first resistor and supplies the current to the third resistor; and a first current mirror circuit that folds back the current flowing through the second resistor and supplies the current to the third resistor. a second current mirror circuit,
The resistance value of the first resistor is set to be variable.
Must be a switching power supply.
[6]
In the switching power supply device according to any one of [1] to [3],
The reference signal generation unit includes a DC bias signal generation unit that generates a DC bias signal, a current signal generation unit that generates a current signal, and an addition unit that adds the DC bias signal and the current signal to generate the reference signal. and has a
The adding section includes a first voltage/current conversion circuit having a first resistor through which a current according to the DC bias signal flows, and a second voltage/current converting circuit having a second resistor through which a current according to the current signal flows. /a current conversion circuit; a first current mirror circuit that folds back the current flowing through the first resistor and supplies the current to the third resistor; and a first current mirror circuit that folds back the current flowing through the second resistor and supplies the current to the third resistor. a second current mirror circuit,
The first current mirror circuit is configured to variably provide a current that is reflected back to the third resistor.
Must be a switching power supply.
[7]
In the switching power supply device according to any one of [1] to [3],
The reference signal generation unit includes a DC bias signal generation unit that generates a DC bias signal, a current signal generation unit that generates a current signal, and an addition unit that adds the DC bias signal and the current signal to generate the reference signal. and has a
The current signal generation unit includes an instrumentation amplifier that amplifies a voltage value according to the current flowing through the coil, and a reference voltage supplied to the instrumentation amplifier is variably provided.
Must be a switching power supply.

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

The present invention has been briefly described above. Furthermore, the details of the present invention will be further clarified by reading the mode for carrying out the invention (hereinafter referred to as "embodiment") described below with reference to the accompanying drawings. .

FIG. 1 is a circuit diagram showing a DC/DC converter incorporating a switching power supply device of the present invention. FIG. 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. FIG. 3 is a time chart of the switch terminal potential, coil current, and reference signal in the FCM. FIG. 4 is a time chart of the switch terminal potential, coil current, and reference signal in the DCM. 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. 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. FIG. 7 is a circuit diagram showing details of the DC bias signal generation section and addition section shown in FIG. 1. FIG. 8 is a circuit diagram showing details of the current signal generation section shown in FIG. 1.

(First embodiment)
A first embodiment of the present invention will be described below with reference to each figure.

The DC/DC converter 1 of this embodiment supplies the load 2 with an output voltage VOUT obtained by stepping down the input voltage VIN. Input voltage VIN is supplied from DC power supply 3. The DC/DC converter 1 includes an output section 11 that step-down converts an input voltage VIN and outputs it as an output voltage VOUT, and a switching section that supplies a pulsed input voltage VIN to the output section 11 to control the output section 11. It includes a power supply device 12 and a bootstrap capacitor CB.

The output section 11 includes a coil L1 and an output capacitor C1. Coil L1 is connected between switch terminal TSW of switching power supply device 12 and load 2. The load 2 has one end connected to the coil L1 via a resistor R3, and the other end connected to ground. The output capacitor C1 has one end connected to the load 2 and the other end connected to ground.

The switching power supply device 12 is composed of an IC chip. The switching power supply device 12 includes a low-side transistor Q1 (hereinafter sometimes abbreviated as "transistor Q1"), a high-side transistor Q2 (hereinafter sometimes abbreviated as "transistor Q2"), and a driver section (in FIG. (referred to as "DRV") 131, 132, bootstrap section 14, voltage detection section 15, error detection section 16, PWM comparator 17, reference signal generation section 18, overcurrent detection section 19, control section A PWM control section 20 and a DC bias changing section 21 are provided.

The transistors Q1 and Q2 are composed of 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 high-side transistor Q2 has a source connected to the switch terminal TSW and the drain of the transistor Q1, and a drain connected to the input terminal TIN. An input voltage VIN supplied from the DC power supply 3 is input to the input terminal TIN.

As shown in FIG. 2, when the transistor Q2 is turned on and the transistor Q1 is turned off, the input voltage VIN is output from the switch terminal TSW. On the other hand, when the transistor Q2 is turned off and the transistor Q1 is turned on, a ground potential of 0V is output from the switch terminal TSW. By alternately turning on the transistors Q1 and Q2, the switch terminal TSW outputs a pulse signal (=pulse input voltage VIN) in which the H level is the input voltage VIN and the L level is 0V. By inputting this pulse signal to the output section 11 and smoothing it using the coil L1 and the output capacitor C1, it is possible to supply the load 2 with an output voltage VOUT according to the duty cycle of the pulse signal.

Note that when switching on and off the transistors Q1 and Q2, a dead time DT is provided in which both the transistors Q1 and Q2 are turned off in order to prevent short-circuiting of the DC power supply 3. During the dead time DT, the potential of the switch terminal TSW is -0.7V, that is, a potential lower than the ground potential 0V by 0.7V of the forward voltage of the parasitic diode of the transistor Q1.

As shown in FIG. 1, the driver section 131 is a circuit that is connected to the gate of the transistor Q1 and drives the transistor Q1 to turn on and off. The driver section 131 operates upon being supplied with a gate drive voltage VG from a gate drive power source (denoted as "LDO" in FIG. 1) 141.

The driver section 132 is a circuit that is connected to the gate of the transistor Q2 and 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 in the same way as the transistor Q1, the transistor Q2 cannot be kept turned on. Therefore, the driver section 132 operates upon receiving power supply from the bootstrap section 14, which will be described later.

The bootstrap unit 14 is a circuit that uses the bootstrap capacitor CB to generate a boot voltage VB that is the sum of the voltage across the bootstrap capacitor CB and the potential of the switch terminal TSW (ie, the source potential of the transistor Q2). The voltage across the bootstrap capacitor CB becomes approximately equal to the gate drive voltage VG.

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

The voltage detection section 15 outputs a detection voltage VR corresponding to the output voltage VOUT to an error detection section 16, which will be described later. The voltage detection section 15 includes 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 section 11 via the feedback terminal TFB. A detection voltage VR obtained by dividing the output voltage VOUT by the resistors R1 and R2 is output to the connection point between the resistors R1 and R2.

The error detection unit 16 outputs an error signal VERR, which is an amplified error (difference) between the detection voltage VR and the reference voltage VREF, to the PWM comparator 17. The reference voltage VREF is set to be equal to the detection voltage VR output from the voltage detection section 15 when the output voltage VOUT reaches the target voltage.

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

The reference signal generation unit 18 generates a reference signal VS including a slope compensation signal component, a current signal component, and a DC bias signal component. The reference signal generation section 18 includes a slope compensation signal generation section 181 that generates a slope compensation signal, a current signal generation section 182 that generates a current signal, a DC bias signal generation section 183 that generates a DC bias signal, and a slope compensation signal generation section 182 that generates a current signal. , a current detection signal, and a DC bias signal to output a reference signal VS.

As shown in FIG. 2, the slope compensation signal generation unit 181 outputs a sawtooth slope compensation signal that increases from 0V over one period of the pulse signal and returns to 0V after one period.

The current signal generation unit 182 generates a current signal according to the coil current IL flowing through the coil L1. The current signal generation unit 182 outputs the voltage across the resistor R3 connected between the coil L1 and the load 2 as a current signal. To explain in detail, the current signal generation section 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 generation unit 182 amplifies the voltage generated between the current detection terminals TSNS1 and TSNS2 and outputs the amplified voltage as a current signal.

As shown in FIG. 2, the coil current IL increases while the pulse signal output from the switch terminal TSW is at the H level (=input voltage VIN), and the pulse signal output from the switch terminal TSW increases when the pulse signal is at the L level (=input voltage VIN). 0V). Similarly, the current signal obtained by converting the coil current IL to IV increases while the pulse signal output from the switch terminal TSW increases while the H level (=input voltage VIN), and the pulse signal output from the switch terminal TSW increases during the L level (=input voltage VIN). = 0V).

The DC bias signal generation section 183 generates a DC bias signal that is a DC 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. Control in which the reference signal VS includes a current signal component in this manner is called current mode control. The current mode controlled DC/DC converter 1 has the advantage of being able to provide a fast load transient response because the phase compensation design is simple and the feedback loop is highly stable. Further, the DC bias signal is included in the reference signal VS in order to set the reference signal VS to a voltage (for example, 0.2 V or higher) at which the PWM comparator 17 and the like can operate.

The overcurrent detection unit 19 compares the voltage generated between the current detection terminal TSNS1 and the current detection terminal TSNS2 according to the coil current IL flowing through the coil L1 with a threshold voltage, and transmits the comparison result to the PWM control unit 20. Output for.

The PWM control section 20 outputs a pulse signal with a duty cycle according to the comparison signal VCOM to the driver sections 131 and 132 to control on/off of the transistors Q1 and Q2. In this embodiment, the PWM control unit 20 can operate by switching between two modes: forced PWM mode (hereinafter referred to as "FCM") and discontinuous mode (hereinafter referred to as "DCM").

Next, before explaining FCM and DCM, the relationship between the load current flowing through the load 2 and the coil current IL will be explained. The coil current IL becomes a ripple current that increases and decreases around the load current when the transistors Q1 and Q2 are turned on alternately. When the load current (1/2 of the ripple current ΔIL (see Figure 2) flowing through the coil L1) is large, the coil current IL will increase around the load current when transistors Q1 and Q2 are turned on alternately, as shown in Figure 2. Although the current increases and decreases, the current continues to flow from the coil L1 to the output capacitor C1 without falling below 0A.

However, when the load current (1/2 of the ripple current ΔIL) is small, the coil current IL falls below 0A as transistors Q1 and Q2 are alternately turned on and decreases, as shown in FIG. 3, and the output capacitor A reverse current flows from C1 to coil L1.

In the FCM, the PWM control unit 20 continues to alternately turn on and off the transistors Q1 and Q2 even if a reverse current occurs. As a result, as shown in FIG. 3, when the load current is small, a reverse current is generated in the coil L1. That is, FCM is a control that allows generation of reverse current and causes coil current IL to flow continuously.

On the other hand, in the DCM, the PWM control section 20 turns off the transistor Q1 when detecting a reverse current. That is, the transistor Q1 operates as if it were a Schottky barrier diode. As a result, as shown in FIG. 4, as soon as a reverse current is generated, the transistor Q1 is turned off and cut off, and no reverse current is generated in the coil L1. The DCM can improve efficiency because no reverse current is generated in the coil L1 when the load current is small, and no conduction loss occurs in the coil L1 and the transistor Q2.

Control of the FCM and DCM can be switched externally. For example, the switching power supply device 12 can be provided with a switching terminal (not shown), and switching can be performed using an input voltage input to the switching terminal. Further, the switching power supply device 12 is provided with a communication terminal (not shown), and switching can be performed by a communication signal such as SPI input to the communication terminal.

However, when DCM is performed in the above-described current mode control, there is a problem in that the load transient response deteriorates when the load is changed from no load to heavy load. 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, and this was found to be the cause.

That is, as shown in FIG. 3, since a reverse current occurs in the FCM, the DC bias signal component is set high so that the reference signal VS becomes an operable voltage (for example, 0.2 V or more). On the other hand, since no reverse current is generated in the DCM, if the same DC bias signal component as in the FCM is set, the reference signal VS is set to be higher as shown in FIG.

Next, a problem when the DC bias signal component and the reference signal VS are set high will be explained with reference to FIG. 5. As shown in the figure, consider a case where the load current changes from no load (0A) to heavy load (5A), and then from 5A to 0A. When the load current is 0A, when the pulse signal output from the switch terminal TSW becomes H level (input voltage VIN), the output voltage VOUT immediately exceeds the target voltage, so the error signal VERR decreases and the reference signal There are many situations where the value is below VS. Therefore, the PWM control unit 20 performs a pulse skip operation and operates to output an H level pulse signal from the switch terminal TSW only once every few cycles.

When the load current increases in this state, the output voltage VOUT decreases and becomes below the target voltage, so the error signal VERR increases. However, since the reference signal VS is set high, the error signal VERR cannot exceed the reference signal VS unless the output voltage VOUT decreases to some extent and the error signal VERR increases significantly. For this reason, when the load current switches from no load to heavy load, the output voltage VOUT fluctuates greatly, resulting in poor transient response.

Further, when the load current changes from heavy load (5 A) to no load (0 A) and the load current decreases, the output voltage VOUT increases and exceeds the target voltage, so the error signal VERR decreases. In this case, the PWM control section 20 cannot shift to pulse skip operation unless the error signal VERR, which has increased significantly, decreases to around 0V. For this reason, even when the load current is switched from heavy load to no load, the output voltage VOUT fluctuates greatly, resulting in poor transient response.

Therefore, in this embodiment, the DC bias changing section 21 is provided, and the DC bias changing section 21 changes the DC bias signal component included in the reference signal VS so that the DC bias signal component in DCM is lower than the DC bias signal component in FCM. Change the bias signal components. This reduces the change in the error signal VERR when the load current changes from no load to heavy load or from heavy load to no load in DCM, suppresses fluctuations in output voltage VOUT, and improves load transient response in DCM. can be done.

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

When the load current increases in this state, the output voltage VOUT decreases and becomes below the target voltage, so the error signal VERR increases. Since the reference signal VS is appropriately set, when the error signal VERR rises, it exceeds the reference signal VS relatively quickly. Therefore, when the load current switches from no load to heavy load, the output voltage VOUT does not fluctuate greatly, and the transient response can be improved.

Further, when the load current changes from heavy load (5 A) to no load (0 A) and the load current decreases, the output voltage VOUT increases and exceeds the target voltage, so the error signal VERR decreases. In this case, since the error signal VERR does not rise much during heavy load, it quickly drops to around 0V, and the PWM control unit 20 can shift to pulse skip operation. Therefore, in the DCM, even when the load current is switched from heavy load to no load, the output voltage VOUT does not fluctuate greatly, and the load transient response can be improved in the DCM.

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

The DC bias signal generation section 183 is provided with a variable DC bias signal. The DC bias change unit 21 generates a DC bias signal so that the DC bias signal output from the DC bias signal generation unit 183 in DCM is lower than the DC bias signal output from the DC bias signal generation unit 183 in FCM. 183.

The V/I conversion circuit 1841 as a second voltage/current conversion circuit is a circuit that converts a current signal to V/I, and includes an operational amplifier OP1, a transistor Q4, and a resistor R4 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 functions of the operational amplifier OP1 and the transistor Q4.

The V/I conversion circuit 1842 is a circuit that converts the slope compensation signal to V/I, 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 functions of the operational amplifier OP2 and the transistor Q5.

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

To explain in detail, when the switch SW1 is turned off, both the resistors R61 and R62 are connected between the transistor Q6 and the ground, and the resistance value increases. When the switch SW1 is turned on, only the resistor R62 is connected between the transistor Q6 and the ground, and the resistance value becomes low.

Further, when a DC bias signal is supplied to the non-inverting input terminal of the operational amplifier OP3, a current according to the DC bias signal flows through both the resistors R61 and R62 or only through the resistor R62 due to the functions of the operational amplifier OP3 and the transistor Q6.

A current mirror circuit 1844 as a second current mirror circuit is a circuit that returns a current according to a current signal flowing through resistor R4 and supplies it to resistor R7 as a third resistor. The current mirror circuit 1844 includes a transistor Q71 and a transistor Q72 whose gate and drain are connected. The gates and sources of the transistors Q71 and Q72 are connected to each other. The drain of transistor Q72 is connected to resistor R7.

The current mirror circuit 1845 is a circuit that returns a current according to the slope compensation signal flowing through the resistor R5 and supplies it to the resistor R7. Current mirror circuit 1845 includes a transistor Q81 and a transistor Q82 whose gate and drain are connected. The gates and sources of the transistors Q81 and Q82 are connected to each other. The drain of transistor Q82 is connected to resistor R7.

A current mirror circuit 1846 as a first current mirror circuit is a circuit that returns a current according to a DC bias signal flowing through both resistors R61 and R62 or resistor R62 and supplies it to resistor R7. The current mirror circuit 1846 includes a transistor Q91 whose gate and drain are connected, transistors Q92 and Q93, and a switch SW2. The gates and sources of the transistor Q91 and the transistors Q92 and Q93 are 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 the current mirror circuit 1846 to the resistor R7 can be increased or decreased depending on whether the switch SW2 is turned on or off.

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

The DC bias changing unit 21 turns off the switch SW1 of the V/I conversion circuit 1843 in DCM, and turns on the switch SW1 of the V/I conversion circuit 1843 in FCM. As a result, the current flowing through the resistors R61 and R62 in the DCM decreases, and the current flowing through the 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.

Further, the DC bias changing unit 21 turns off the switch SW2 of the current mirror circuit 1846 in DCM, and turns on the switch SW2 of the current mirror circuit 1846 in FCM. As a result, the current mirrored by the current mirror circuit 1846 in the DCM decreases, the current mirrored by the current mirror circuit 1846 in the FCM increases, and the DC bias signal component in the DCM becomes lower than the DC bias signal component in the FCM.

In the example shown in FIG. 7, the DC bias changing unit 21 executes three things: changing the DC bias signal generated by the DC bias signal generating unit 183, turning on/off the switch SW1, and turning on/off the switch SW2. Although the DC bias signal component is changed in this case, the present invention is not limited to this. Any one or any two of the three may be executed to change the DC bias signal component.

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

A current detection terminal TSNS1 is connected to the inverting input terminal of the operational amplifier OP4 via a resistor R81. A current detection terminal TSNS2 is connected to the non-inverting input terminal of the operational amplifier OP4 via a resistor R82. The inverting input terminal of the operational amplifier OP4 is connected to the output via a resistor R83. A non-inverting input terminal of operational amplifier OP4 is connected to reference power supply 1821 via resistor R84. Assuming that 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).

Current signal = VREF2 + gain × VIL … (1)

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

Therefore, in the present embodiment, the DC bias changing unit 21 sets the reference voltage VREF2 in the DCM lower than the reference voltage VREF in the FCM, so that the DC bias signal component in the DCM is lower than the DC bias signal component in the FCM. Set.

In addition, in the first embodiment described above, in addition to changing the DC bias signal by the DC bias signal generation section 183 and addition section 184 shown in FIG. 7, the DC bias signal is changed by the current signal generation section 182 shown in FIG. We are doing this, but it is not limited to this. The DC bias signal generation section 183 and the addition section 184 may change the DC bias signal, or the current signal generation section 182 may change the DC bias signal.

(Second embodiment)
Next, a DC/DC converter 1 in a second embodiment will be explained. In the first embodiment described above, the DC bias changing unit 21 changes the DC bias signal depending on whether it is DCM or FCM, but the present invention is not limited to this. The DC bias changing unit 21 may change the DC bias signal depending on the magnitude of the ripple current ΔIL of the coil current IL. Specifically, the DC bias changing unit 21 changes the DC bias signal component so that the DC bias signal component becomes higher as the ripple current ΔIL becomes larger.

As described above, when the load current becomes 1/2 or less of the ripple current ΔIL, a reverse current is generated in the coil L1. Therefore, the larger the ripple current ΔIL is, the more likely a reverse current will occur, and the more likely the coil current IL will be below zero. As mentioned above, as the ripple current ΔIL increases, the DC bias signal component is set higher, so even if the coil current IL becomes negative, the DC bias signal is set so that the reference signal VS becomes an operable voltage. can do.

On the other hand, the smaller the ripple current ΔIL is, the less likely a reverse current will occur and the less likely the coil current IL will be below zero. As described above, as the ripple current ΔIL becomes smaller, the DC bias signal component is set lower, so that the load transient response when the load current fluctuates in the DCM can be improved.

Note that the present invention is not limited to the embodiments described above, and can be modified, improved, etc. as appropriate. In addition, the material, shape, size, number, arrangement location, etc. of each component in the above-described embodiments are arbitrary as long as the present invention can be achieved, and are not limited.

According to the embodiment described above, the high-side transistor Q2 is configured from an Nch transistor, and the bootstrap section 14 is used to turn on and off the high-side transistor Q2, but the present invention is not limited to this. The high-side transistor Q2 may be configured from a Pch transistor, and the bootstrap section 14 may not be provided.

According to the embodiments described above, the reference signal VS includes a slope compensation signal component, but the present invention is not limited to this. The reference signal VS only needs to contain at least a DC bias signal component and a current signal component, and does not need to contain a slope compensation signal component.

According to the embodiment described above, the output section 11 is configured of a step-down type, but the output section 11 is not limited to this. The output section 11 may be configured as a step-up type converter that converts the input voltage VIN into a step-up type.

11 Output section 12 Switching power supply device 16 Error detection section 17 PWM comparator 18 Reference signal generation section 20 PWM control section (control section)
21 DC bias changing section 182 Current signal generating section 183 DC bias signal generating section 184 Adding 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 Resistance (second resistance)
R61, R62 resistance (first resistance)
R7 resistance (third resistance)
Q1 Low-side transistor Q2 High-side transistor VCOM Comparison signal VERR Error signal VREF2 Reference voltage VS Reference signal

Claims (7)

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 according to the error between the output voltage and the target voltage;
a reference signal generation 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 comparing the reference signal and the error signal;
a control unit that controls the output unit by alternately turning on the low-side transistor and the high-side transistor with a duty cycle according to the comparison signal,
the DC bias signal component included in the reference signal is variably provided;
Switching power supply. The switching power supply device according to claim 1,
The control unit operates in a discontinuous mode in which the low-side transistor is turned off when a reverse current flows through the coil, and in a forced mode in which the low-side transistor and the high-side transistor are alternately kept on even when the reverse current flows in the coil. It is provided so that it can be switched to PWM control mode,
comprising 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. The switching power supply device according to claim 1,
comprising 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. In the switching power supply device according to any one of claims 1 to 3,
The reference signal generation unit includes a DC bias signal generation unit that generates a DC bias signal, a current signal generation unit that generates a current signal, and an addition unit that adds the DC bias signal and the current signal to generate the reference signal. and has a
The DC bias signal generation section is configured to variably provide the DC bias signal.
Switching power supply. In the switching power supply device according to any one of claims 1 to 3,
The reference signal generation unit includes a DC bias signal generation unit that generates a DC bias signal, a current signal generation unit that generates a current signal, and an addition unit that adds the DC bias signal and the current signal to generate the reference signal. and has a
The adding section includes a first voltage/current conversion circuit having a first resistor through which a current according to the DC bias signal flows, and a second voltage/current converting circuit having a second resistor through which a current according to the current signal flows. /a current conversion circuit; a first current mirror circuit that folds back the current flowing through the first resistor and supplies the current to the third resistor; and a first current mirror circuit that folds back the current flowing through the second resistor and supplies the current to the third resistor. a second current mirror circuit,
The resistance value of the first resistor is set to be variable.
Switching power supply. In the switching power supply device according to any one of claims 1 to 3,
The reference signal generation unit includes a DC bias signal generation unit that generates a DC bias signal, a current signal generation unit that generates a current signal, and an addition unit that adds the DC bias signal and the current signal to generate the reference signal. and has a
The adding section includes a first voltage/current conversion circuit having a first resistor through which a current according to the DC bias signal flows, and a second voltage/current converting circuit having a second resistor through which a current according to the current signal flows. /a current conversion circuit; a first current mirror circuit that folds back the current flowing through the first resistor and supplies the current to the third resistor; and a first current mirror circuit that folds back the current flowing through the second resistor and supplies the current to the third resistor. a second current mirror circuit,
The first current mirror circuit is configured to variably provide a current that is reflected back to the third resistor.
Switching power supply. In the switching power supply device according to any one of claims 1 to 3,
The reference signal generation unit includes a DC bias signal generation unit that generates a DC bias signal, a current signal generation unit that generates a current signal, and an addition unit that adds the DC bias signal and the current signal to generate the reference signal. and has a
The current signal generation unit includes an instrumentation amplifier that amplifies a voltage value according to the current flowing through the coil, and a reference voltage supplied to the instrumentation amplifier is variably provided.
Switching power supply.

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