JP6295397B1 - Switching power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply circuit for holding an output voltage constant with high accuracy by a step-up / step-down operation. A switching circuit 8 in which switching elements SW1 to SW4 are switched at a predetermined timing, an error amplifying circuit 1 that generates an error voltage that is a difference between a reference voltage Vref and a feedback voltage from an output terminal VO, and a coil current The coil current emulation circuit 4 for detecting the output voltage VC similar to IL, the adder circuit 3 for adding the output voltage VC to the error voltage, the reference voltage Vref and the added output voltage of the adder circuit 3 are compared, and the coil current is compared. Comparison circuit 5 for detecting a peak for detecting the peak at which IL becomes maximum, and switching control of switching elements SW1 to SW4 based on a peak detection signal output from comparison circuit 5 allows predetermined step-up / step-down voltage via switching circuit 8 And an output voltage VC similar to the coil current IL flowing through the coil L. Having a coil current emulation circuit 4 that. [Selection] Figure 1

Description

  The present invention relates to a switching power supply circuit, and is particularly useful when applied to a step-up / step-down DC / DC converter circuit.

  A switching regulator with a peak detection topology, which can use a low ESR capacitor such as a ceramic capacitor for the load capacity, can operate stably even at oscillation frequencies of several MHz or higher, and can provide high load stability and a large layout area. Patent Document 1 is known as a switching power supply circuit that can be made small.

  However, since the switching power supply circuit disclosed in Patent Document 1 is dedicated to step-down conversion, there is a problem that it cannot be used under conditions where the input voltage is higher or lower than the output voltage.

  On the other hand, Patent Document 2 is publicly known as a switching power supply circuit that can use a low ESR capacitor such as a ceramic capacitor as a load capacity in a step-up / step-down switching power supply circuit and that can stably operate even at an oscillation frequency of several MHz or more. ing.

  By the way, the switching power supply circuit according to Patent Document 2 is of a so-called current mode control system that detects a coil current and controls a switching operation based on the detected coil current. Therefore, in this type of switching power supply circuit, it is necessary to detect the coil current.

  In the prior art including Patent Document 2, when a coil current is detected, one using a coil current sense circuit is widely used. For example, a sense resistor is inserted in series with a coil, both ends thereof are amplified by a current amplifier, and the output of the current amplifier is connected to the output of the error amplifier via a coupling capacitor.

Japanese Patent No. 5997348

JP 2014-39472 A

  Incidentally, in the coil current detection circuit as described above, a sense resistor having a small value must be selected in order to reduce the influence on the output voltage conversion efficiency. As a result, the current amplifier must use an amplifier with a small offset voltage corresponding to a small input voltage, and it is necessary to make adjustments by increasing the number of transistors of the input differential pair, arranging a plurality of transistors, or trimming. Therefore, the problem that the influence on the layout pattern is large arises. For this reason, the circuit scale of the coil current detection circuit is increased, and at the same time, a high-speed comparator is driven, so that current consumption increases. Furthermore, it becomes a factor that hinders the speeding up of the switching frequency in this type of switching power supply circuit.

  In view of the above prior art, the present invention can use a low ESR capacitor as a load capacity, can operate stably even at an oscillation frequency of several MHz or more, and can obtain a high load stability, and can be output by step-up / step-down operation. An object of the present invention is to provide a switching power supply circuit capable of holding a voltage constant with high accuracy.

The first aspect of the present invention for achieving the above object is as follows:
A first switching element connected between an input terminal to which an input voltage is applied and one terminal of the coil, and a second switching element connected between a ground potential and the one terminal or the first switching element , A third switching element connected between the ground potential and the other terminal of the coil, and a fourth switching element or second connected between the output terminal and the other terminal. A switching circuit having a diode;
A coil current emulation circuit that generates an output voltage similar to the coil current flowing through the coil;
The switching is performed so that an output voltage generated at the output terminal of the switching circuit becomes a predetermined set voltage based on a feedback voltage representing an output voltage which is a voltage of the output terminal and an output voltage of the coil current emulation circuit. And a control circuit for performing a predetermined step-up / step-down operation by controlling on / off of the circuit,
The coil current emulation circuit is:
A CR integration circuit and an output terminal that outputs an output voltage similar to the coil current between the capacitor and the resistor constituting the CR integration circuit,
Further, one of the three voltages is applied to one terminal of the CR integrating circuit according to the selection associated with the on / off operation of the switch means, and a voltage proportional to the output voltage is applied to the other terminal of the CR integrating circuit. Is applied,
The three kinds of voltages are a voltage proportional to an input voltage, a ground voltage, and a voltage proportional to a sum of the input voltage and the output voltage. On / off control of the switch means is performed by the one terminal of the coil and the voltage This is performed by a control signal output from the control circuit in accordance with the state of the other terminal.

The second aspect is
In the switching power supply circuit described in the first aspect,
The control circuit includes:
An error amplifying circuit for amplifying an error representing a difference between the predetermined reference voltage and the feedback voltage to generate an error voltage;
A peak detection circuit for detecting a peak at which the coil current becomes maximum based on an output voltage similar to the coil current, the error voltage, and the reference voltage;
A peak detection signal output from the peak detection circuit and a switching signal for performing switching control of the switching element at a preset timing are generated based on a clock signal defining a control cycle, and the switching circuit is generated. And a switch control unit that performs a predetermined step-up / step-down operation via the control signal .

The third aspect is
In the switching power supply circuit described in the second aspect,
The peak detection circuit is
An adder circuit that adds an output voltage similar to the coil current to the error voltage to generate an added output voltage;
A comparison circuit for peak detection for comparing the added output voltage and the reference voltage to detect the peak, or an adder circuit for adding a voltage based on the coil current to the reference voltage to generate an added output voltage; A comparison circuit for detecting a peak for detecting the peak by comparing the added output voltage and the error voltage.

The fourth aspect is
In the switching power supply circuit described in the second or third aspect,
The timing is defined based on any of the output voltage, the input voltage, and the reference voltage.

  According to the present invention, since the coil current is detected based on the output voltage similar to the coil current, it is not necessary to provide a sense resistor for detecting the coil current, and the configuration for detecting the coil current is simplified. Therefore, the coil current can be detected properly even when the switching frequency is increased. As a result, a low ESR capacitor can be used as a load capacity in any of the step-up / step-down modes, and stable operation is possible even at an oscillation frequency of several MHz or more.

It is a block diagram which shows the switching power supply circuit which concerns on embodiment of this invention. FIG. 2 is an explanatory diagram illustrating timing of a step-down operation in the switching power supply circuit illustrated in FIG. 1. FIG. 2 is an explanatory diagram illustrating timing of a step-up / step-down operation in the switching power supply circuit illustrated in FIG. 1. FIG. 2 is an explanatory diagram illustrating timing of a step-up / step-down operation in the switching power supply circuit illustrated in FIG. 1. FIG. 2 is an explanatory diagram illustrating timing of a step-up / step-down operation in the switching power supply circuit illustrated in FIG. 1. FIG. 2 is an explanatory diagram illustrating timing of a boost operation in the switching power supply circuit illustrated in FIG. 1. It is a circuit diagram which shows the specific example of a coil current emulation circuit. It is explanatory drawing which shows the timing of the pressure | voltage fall operation | movement in the switching power supply circuit containing a coil current emulation part circuit. It is explanatory drawing which shows the timing of the pressure | voltage rise / fall operation | movement in the switching power supply circuit containing a coil current emulation part circuit. It is explanatory drawing which shows the timing of the pressure | voltage rise / fall operation | movement in the switching power supply circuit containing a coil current emulation part circuit. It is explanatory drawing which shows the timing of the pressure | voltage rise / fall operation | movement in the switching power supply circuit containing a coil current emulation part circuit. It is explanatory drawing which shows the timing of the pressure | voltage rise operation in the switching power supply circuit containing a coil current emulation circuit. It is a schematic diagram which shows the aspect at the time of full bridge operation | movement in the switching power supply circuit shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a switching power supply circuit according to an embodiment of the present invention. As shown in the figure, the switching power supply circuit according to this embodiment includes a control circuit I, a coil current emulation circuit 4 and a switching circuit 8. further,
The control circuit I sets the output voltage VO generated at the output terminal OUT of the switching circuit 8 to a predetermined setting based on the feedback voltage representing the output voltage VO that is the voltage of the output terminal OUT and the output voltage VC of the coil current emulation circuit 4. The switching circuit 8 is ON / OFF controlled so as to have a voltage, and a predetermined step-up / step-down operation is performed. Therefore, the control circuit I according to this embodiment includes a peak detection circuit II including an error amplification circuit 1, a reference voltage generation circuit 2, an addition circuit 3, and a comparison circuit 5, a switch control unit 6, and an oscillation circuit 7.

  Here, the output voltage VO is divided by the feedback resistors FR 1 and FR 2 and input to the inverting input terminal of the error amplifier circuit 1. On the other hand, the reference voltage Vref generated by the reference voltage generation circuit 2 and set in advance is input to the non-inverting input terminal of the error amplifier circuit 1. Thus, the error amplifying circuit 1 compares the reference voltage Vref and the output voltage VO divided by the feedback resistors FR1 and FR2, amplifies the error that is the difference between the two, and outputs the error voltage Verr.

  The peak detection circuit I is supplied with the output voltage VC, error voltage Verr, and reference voltage Vref of the coil current emulation circuit 4 similar to the coil current IL flowing through the coil L. Based on the output voltage VC, the error voltage Verr, and the reference voltage Vref, the peak at which the coil current IL is maximized is detected to generate the peak detection signal Comp_out.

  The peak detection circuit II in this embodiment includes an addition circuit 3 and a comparison circuit 5. In the adder circuit 3, an output voltage VC similar to the coil current IL is added to the error voltage Verr that is the output of the error amplifier circuit 1 to generate an added output voltage Vadd. The output voltage VC is generated by the coil current emulation circuit 4, and the configuration will be described in detail later.

  The reference voltage Vref, which is the output of the reference voltage generation circuit 2, is input to the inverting input terminal of the comparison circuit 5, and the addition output voltage Vadd, which is the output of the addition circuit 3, is input to the non-inverting input terminal. As a result, the comparison circuit 5 generates a peak detection signal Comp_out that represents the time when the added output voltage Vadd of the adder circuit 3 exceeds the reference voltage Vref, that is, the time when the coil current IL becomes the largest value. Comp_out is output to the switch control unit 6. The peak detection signal Comp_out is a state signal representing two states, Hi and Lo.

  As described above, in the present embodiment, the peak detection circuit II is formed by the combination of the addition circuit 3 and the comparison circuit 5, but the present invention is not limited to this. As long as the peak at which the coil current IL is maximized is detected based on the output voltage VC similar to the coil current IL, the error voltage Verr, and the reference voltage Vref, there is no further special limitation. In this embodiment, the adder circuit 3 is configured to add the output voltage VC to the error voltage Verr and to compare the added output voltage Vadd of the adder circuit 3 with the reference voltage Vref. However, the present invention is not limited to this. is not. The adder circuit 3 may add the output voltage VC to the reference voltage Vref, and may compare the added output voltage Vadd of the adder circuit 3 with the error voltage Verr.

The switch control unit 6 controls the switching circuit 8 based on the timing indicating the elapsed time (which will be described later in detail) set in advance based on the clock signal CLK having a constant frequency generated by the oscillation circuit 7 and the state change of the peak detection signal Comp_out. Controls ON / OFF of the switching elements SW1, SW2, SW3, SW4. As a result, the step-down mode, the step-up / step-down mode, and the step-up mode are appropriately switched, and the output voltage VO is controlled to be constant. Here, the switch control unit 6 performs predetermined switching control on the coil current emulation circuit 4. The specific contents of such switching control will be described in detail later. Note that the peak detection signal Comp_out that is the output of the comparison circuit 5 is normally Lo, and becomes Hi when the peak point is detected.

  The switching circuit 8 is formed by combining four switching elements SW1 to SW4 and a coil L in an H shape. More specifically, the switching element SW1 is connected between an input terminal IN to which an input voltage VIN, which is a power supply voltage, is applied and one terminal LX1 of the coil L, and the switching element SW2 is connected to the ground potential and one terminal LX1. The switching element SW3 is connected between the ground potential and the other terminal LX2 of the coil L, and the switching element SW4 is connected between the output terminal OUT and the other terminal LX2. Here, a smoothing capacitor C is connected to the output terminal OUT. In this embodiment, a low ESR capacitor such as a ceramic capacitor can be used as the capacitor C.

  A control operation of the switch control unit 6 in each of the step-down mode, the step-up / step-down mode, and the step-up mode will be described based on the waveform diagrams of FIGS. 2 to 6, (a) is a clock signal, (b) is a peak detection signal Comp_out, (c) is a voltage at one terminal LX1, (d) is a voltage at the other terminal LX2, (e) Indicates the waveform of the coil current IL.

<Step-down mode>
FIG. 2 is a waveform diagram in the step-down mode. As shown in the figure, first, the peak detection signal Comp_out which is the output of the comparison circuit 5 for peak detection is reset by the clock signal CLK of the oscillation circuit 7. As a result, the peak detection signal Comp_out becomes Lo.

  Next, the peak detection signal Comp_out is set to Hi before the first timing t1 out of two timings set in advance in the switch control unit 6 according to the input voltage VIN, the output voltage VO, or the reference voltage Vref. When changed, one terminal LX1 of the coil L is switched from Hi level to Lo level (switching element SW1 is turned OFF). This period is an off period in which the coil current IL gradually decreases due to the terminal LX1 being at the Lo level.

  Next, the terminal LX1 is switched to the Hi level at the second timing t2, and the on period is set. Here, since the first timing t1 is later than the switching of the peak detection signal Comp_out, it becomes invalid. Further, during such a series of operations, the terminal LX2 is fixed to Hi. By repeating this operation, it operates as a step-down converter and stabilizes the output voltage VO.

  3 to 5 are timing charts in the step-up / step-down mode. In either step-up / step-down mode, FIG. 3 shows a state where the input voltage VIN is higher than the output voltage VO, FIG. 4 shows a state where the input voltage VIN is equal to the output voltage VO, and FIG. Each state is lower than VO.

<Buck-boost mode>
As shown in FIGS. 3 to 5, in the step-up / step-down mode, as in the step-down mode, the peak detection signal Comp_out is reset by the clock signal CLK, and the terminal LX2 is switched from the Hi level to the Lo level at the first timing t1. The on period. As a result, the coil current IL increases.

  In the step-up / step-down mode, unlike the step-down mode, when the peak detection circuit I detects a peak point prior to the second timing t2, the terminal LX1 is switched to Lo level and the terminal Lx2 is switched to Hi level.

  Next, the terminal LX1 is returned to the Hi level at the second timing t2. This operation is repeated to operate as a buck-boost converter and stabilize the output voltage VO.

  In this embodiment, the step-up / step-down operation is realized by combining the step-down operation in which one terminal LX1 is switched and the step-up operation in which the other terminal LX2 is switched. However, both the one terminal LX1 and the other terminal LX2 are Hi. By providing the level period, it is possible to suppress the change smaller than the change in the coil current IL due to the full bridge operation. For this reason, it has contributed to the improvement of the conversion efficiency of the said switching power supply circuit. In addition, since the operation mode shifts depending on the presence or absence of a fine pulse at the other terminal LX2 at the boundary between the step-down mode and the step-up / step-down mode, a large change in coil current due to the mode difference does not occur and continuity can be maintained. Therefore, it can contribute to stable operation. This point will be described in detail with reference to FIG. FIG. 13A shows a switching circuit 8 (see FIG. 1; the same applies hereinafter) similar to that of the present embodiment. When the switching circuit 8 is driven by a full bridge operation in which the ON state of the switching elements SW1 and SW3 and the ON state of the switching elements SW2 and SW4 are alternately repeated, the coil current IL becomes large as shown in FIG. The amount of loss is also increased. Therefore, in this embodiment, as shown in FIG. 13C, the switching elements SW1 and SW3 are turned on at a predetermined timing after the coil current IL is lower than the predetermined output current IO in the ON state of the switching elements SW2 and SW4. In the ON state, there is a period during which the switching elements SW1 and SW4 are in the ON state until a predetermined timing before the coil current IL exceeds the output current IO. That is, a period in which the switching elements SW1, SW4 are turned on is provided between a period in which the switching elements SW2, SW4 are turned on and a period in which the switching elements SW1, SW3 are turned on. As a result, the coil current IL in the full bridge period can be suppressed to a constant small value. As a result, the loss can be greatly reduced.

<Boosting mode>
FIG. 6 is a waveform diagram in the boost mode. As shown in the figure, in this mode, the peak detection signal Comp_out of the peak detection circuit I is reset by the clock signal CLK that is the output of the oscillation circuit 7. After the reset by the clock signal CLK, the terminal LX2 is switched from the Hi level to the Lo level at the first timing t1. At this time, the terminal LX1 remains at the Hi level. Since the terminal LX1 becomes the Lo level, the on-period in which the coil current IL gradually increases is entered.

  The peak detection circuit I detects the peak point, switches the output level of the peak detection signal Comp_out to Hi and latches it, and switches the terminal LX2 to the Hi level. As a result, an off period in which the coil current IL gradually decreases is obtained.

  Next, the peak detection signal Comp_out is reset by the clock signal CLK, and a new cycle starts. Here, the second timing t2 becomes invalid because it is earlier than the switching of the peak detection signal Comp_out. This operation is repeated to operate as a step-down converter and stabilize the output voltage VO.

  With the operation described above, the switching power supply circuit according to this embodiment operates as a step-up / step-down switching regulator.

  Next, detection of the coil current IL will be described. When the coil current IL is detected using a sense resistor, the problem described in the above paragraph [0009] occurs. Therefore, in this embodiment, the coil current emulation circuit 4 generates an output voltage VC similar to the coil current IL, and information on the predetermined coil current IL is obtained by using the output voltage VC.

  However, the switching power supply circuit according to the present embodiment causes the switching circuit 8 constituting the H-type bridge to perform a predetermined switching operation and operate in all modes of the buck-boost. Therefore, when an integrating circuit is simply connected between one terminal LX1 and the other terminal LX2 of the switching circuit 8, since both of the terminals LX1 and LX2 are switched nodes, the waveform obtained as it is is the coil current. It is no longer similar to IL.

  For this reason, in this embodiment, it is necessary to fix one end of the CR integration circuit and apply a voltage proportional to the potential difference between both ends of the coil L as the potential difference between both ends. In consideration of this point, the coil current emulation circuit 4 is configured in this embodiment. Specifically, it is as follows.

  As shown in FIG. 7, the coil current emulation circuit 4 in the present embodiment has a CR integration circuit 9 in which a capacitor C1 and a resistor R1 are connected in series, and is similar to the coil current IL between the capacitor C1 and the resistor R1. Assume that the output terminal generates an output voltage VC.

  Here, one of three kinds of voltages is applied to one terminal V1 of the CR integration circuit 9 by selection of the switch means S1, S2, S3, and the output voltage VO (FIG. 1) is applied to the other terminal V2 of the CR integration circuit. A voltage (A × VO) proportional to reference (hereinafter the same) is applied. The three types of voltages are the voltage proportional to the input voltage VIN (A x VIN), the ground voltage, the voltage proportional to the sum of the input voltage VIN (refer to Fig. 1 below) and the output voltage VO (A x (VIN + VO )).

  In the coil current emulation circuit 4, when both the one terminal LX1 (see FIG. 1: same below) and the other terminal LX2 (see FIG. 1: same below) of the switching circuit 8 (see FIG. 1 below) are at the Hi level. The switch means S1 is turned on and a voltage (A × VIN) proportional to the input voltage VIN is applied to one end of the integrating circuit 9. When one terminal LX1 is at Lo level and the other terminal Lx2 is at Hi level, the switch means S2 is turned on to apply the GND voltage to one end of the integrating circuit 9. Further, when one end LX1 is at the Hi level and the other end LX2 is at the LO level, the switch means S3 is turned on and a voltage proportional to the sum of the input voltage VIN and the output voltage VO is applied to one end of the integrating circuit 9. A × (VIN + VO)) is applied. Here, each proportional coefficient A is set to the same value.

  Each of the switch means S1 to S3 of the coil current emulation circuit 4 is turned on / off by a control signal from the switch control unit 6 (see FIG. 1, the same applies hereinafter) according to the state of one terminal LX1 and the other terminal LX2 of the coil 1. OFF controlled.

  Here, when the voltage at one end of the resistor R1 is V1, the voltage at the other end of the capacitor C1 is V2, and the switching cycle is sufficiently shorter than the time constant of the CR integrating circuit 9, the potential difference ΔVC across the capacitor C1 is expressed by the following equation ( 1).

同様にコイル電流ΔｉＬは次式（２）で表される。

Similarly, the coil current ΔiL is expressed by the following equation (2).

  Specifically, when both the one terminal LX1 and the other terminal LX2 are at the Hi level, the switch means S1 is turned on. Therefore, the potential difference ΔVC is expressed by the following equation (3), and the coil current ΔiL is expressed by the following equation (4). Respectively.

  Next, when one terminal LX1 is at the Lo level and the other terminal LX2 is at the Hi level, the switch means S2 is turned on. Therefore, when the Lo level is set to 0 V, the potential difference ΔVC is expressed by the following equation (5): The current ΔiL is represented by the following equation (6).

  Next, when one terminal LX1 is at the Hi level and the other terminal LX2 is at the Lo level, the switch means S3 is turned on. Therefore, when the Lo level is set to 0 V, the potential difference ΔVC is expressed by the following equation (7): The current ΔiL is expressed by the following equation (8).

  In the above-described coil current emulation circuit 4, the Hi level of one terminal LX1 is substantially equal to the input voltage VIN, and the Hi level of the other terminal LX2 is substantially equal to the output voltage VO. Further, the proportionality coefficient A, the resistance value of the resistor R1, the capacitance of the capacitor C1, and the inductance of the coil L are constants. Therefore, it can be seen that a potential difference ΔVC similar to the coil current ΔiL is obtained from the output terminal VC of the coil current emulation circuit 4.

  8 to 12 are waveform diagrams of step-down, step-up / step-down, and step-up operations including the coil current emulation circuit 4 of the switching power supply circuit according to this embodiment. In these figures, FIGS. 8 to 12 correspond to FIGS. 2 to 6, respectively. Moreover, (f) of each figure is the voltage of one terminal V1 (refer FIG. 7), (g) is the voltage of the other terminal V2 (refer FIG. 7), (h) is output voltage VC (refer FIG. 7). It is a wave form diagram which shows a waveform.

The switching power supply circuit according to the above-described embodiment is a so-called current mode control system that controls the switching operation of the switching elements SW1 to SW4 based on the coil current IL, but is not limited thereto. If the switching circuit 8 and the coil current emulation circuit 4 are combined with a control unit that performs ON / OFF control of the switching circuit 8, no further limitation is required. Therefore, the present invention can also be applied to a so-called voltage mode control type switching power supply circuit and a hysteresis control type switching power supply circuit. In the voltage mode control method, basically, a feedback voltage and a reference voltage are compared, and a PWM signal that performs switching according to an error between the two is generated. Therefore, a control circuit that conforms to this can be constructed. .
In the hysteresis control method, the output ripple is basically detected and a control signal for switching is generated, so that a control circuit suitable for this can be constructed.

DESCRIPTION OF SYMBOLS 1 Error amplification circuit 2 Reference voltage generation circuit 3 Addition circuit 4 Coil current emulation circuit 4A Coil current emulation circuit 5 Comparison circuit 6 Switch control part 7 Oscillation circuit 8 Switching circuit 9 Integration circuit

Claims (4)

A first switching element connected between an input terminal to which an input voltage is applied and one terminal of the coil, and a second switching element connected between a ground potential and the one terminal or the first switching element , A third switching element connected between the ground potential and the other terminal of the coil, and a fourth switching element or second connected between the output terminal and the other terminal. A switching circuit having a diode;
A coil current emulation circuit that generates an output voltage similar to the coil current flowing through the coil;
The switching is performed so that an output voltage generated at the output terminal of the switching circuit becomes a predetermined set voltage based on a feedback voltage representing an output voltage which is a voltage of the output terminal and an output voltage of the coil current emulation circuit. And a control circuit for performing a predetermined step-up / step-down operation by controlling on / off of the circuit,
The coil current emulation circuit is:
A CR integration circuit and an output terminal that outputs an output voltage similar to the coil current between the capacitor and the resistor constituting the CR integration circuit,
Further, one of the three voltages is applied to one terminal of the CR integrating circuit according to the selection associated with the on / off operation of the switch means, and a voltage proportional to the output voltage is applied to the other terminal of the CR integrating circuit. Is applied,
The three kinds of voltages are a voltage proportional to an input voltage, a ground voltage, and a voltage proportional to a sum of the input voltage and the output voltage. On / off control of the switch means is performed by the one terminal of the coil and the voltage A switching power supply circuit comprising: a control signal output from the control circuit according to a state of the other terminal. In the switching power supply circuit according to claim 1,
The control circuit includes:
An error amplifying circuit for amplifying an error representing a difference between the predetermined reference voltage and the feedback voltage to generate an error voltage;
A peak detection circuit for detecting a peak at which the coil current becomes maximum based on an output voltage similar to the coil current, the error voltage, and the reference voltage;
A peak detection signal output from the peak detection circuit and a switching signal for performing switching control of the switching element at a preset timing are generated based on a clock signal defining a control cycle, and the switching circuit is generated. And a switch control unit for performing a predetermined step-up / step-down operation via the control signal . In the switching power supply circuit according to claim 2,
The peak detection circuit includes:
An adder circuit that adds an output voltage similar to the coil current to the error voltage to generate an added output voltage;
A comparison circuit for peak detection for comparing the added output voltage and the reference voltage to detect the peak, or an adder circuit for adding a voltage based on the coil current to the reference voltage to generate an added output voltage; A switching power supply circuit comprising: a peak detection comparison circuit that detects the peak by comparing the added output voltage with the error voltage. In the switching power supply circuit according to claim 2 or 3,
The switching power supply circuit characterized in that the timing is defined based on any one of the output voltage, the input voltage, and the reference voltage.

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