JP2016167896A - Dc/dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC/DC converter that enables both of boosting and step-down with a simple circuit configuration.SOLUTION: When a time ratio control amount Ds reaches a first predetermined value at a switching point between boosting and step-down, every period interval determined based on the correlation between a predetermined time ratio control amount Ds and an ON-frequency f, a control circuit 27 performs ON-control on a boosting switching element or step-down switching element which has not been subjected pulse-width modulation control under a state that the ON-period of one of two switching elements connected in series is fixed, and performs OFF-control on the boosting switching element or the step-down switching element under a state that the OFF-period of the other of the two switching elements connected in series is fixed. Then, when the time ratio control amount Ds reaches a second predetermined value, the control circuit 27 exchanges the operations of the boosting switching element and the step-down switching element by each other. Then, when the time ratio control amount Ds reaches a third predetermined value, the control circuit 27 performs the boosting operation by the boosting switching element, and the step-down operation by the step-down switching element.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a DC / DC converter capable of performing both step-up voltage conversion and step-down voltage conversion.

  Conventionally, for example, Patent Document 1 proposes a step-up / step-down DC / DC converter capable of obtaining a desired output voltage by stepping up and stepping down an input voltage.

  FIG. 18 shows a schematic diagram of a buck-boost switching regulator that is this step-up / step-down DC / DC converter. The power supply 101 includes a synchronous switching adjuster 103 and a control circuit 105. The synchronous switching regulator 103 receives the input voltage Vin and provides a regulated output voltage Vout. The input voltage Vin can be higher, lower or substantially the same as the output voltage Vout. The control circuit 105 can operate the synchronous switching regulator 103 in the buck mode, the boost mode, or the buck-boost mode. Synchronous switching regulator 103 has four switches coupled between Vin and Vout. These switches 107, 109, 111, 113 control the supply voltage of the current to the output node at Vout, so that the output voltage can be held at an adjusted value. The control circuit 105 receives the output voltage Vout and provides four drive signals (Va, Vb, Vc, and Vd) that control switching of the four switches 107, 109, 111, and 113 in the synchronous switching regulator 103. . Control circuit 105 includes resistors 115 and 117, error amplifier 119, pulse width modulator 121, and logic circuit 123. Pulse width modulator 121 includes a signal generator 125 and comparators 127 and 129.

  Next, the operation of the power supply 101 will be described with reference to the exemplary signal graph of FIG. In the graph of FIG. 19, the horizontal axis indicates time, and the vertical axis indicates bolt. FIG. 19 also shows a timing chart.

  The graph of FIG. 19 shows an example of the waveform signals Vx and Vy and the control voltage VCL shown in FIG. The waveform signal Vx has a period T and is a triangular waveform having a minimum value V1 and a maximum value V3. The waveform signal Vy has a period T and is a triangular waveform having a minimum value V2 and a maximum value V4. Further, as shown in FIG. 19, V1 <V2 <V3 <V4. When V1 <VCL ≦ V2, the synchronous switching regulator 103 controlled by the control circuit 105 operates in the back mode. When V2 <VCL <V3, the synchronous switching regulator 103 controlled by the control circuit 105 is When operating in the buck-boost mode and V3 ≦ VCL <V4, the synchronous switching regulator 103 controlled by the control circuit 105 operates in the boost mode. When VCL ≦ V1 or VCL ≧ V4, the synchronous switching regulator 103 operates in the degenerate mode. By such an operation, the control signals Vz1 and Vz2 and the drive signals Va, Vb, Vc, and Vd change as shown in the timing chart of FIG.

Japanese Patent No. 4903945

  According to the above-described buck-boost switching regulator (power supply 101), as shown in FIG. 19, the buck-boost mode operation is performed when switching between the boost mode and the buck mode. At this time, as is apparent from the graph of FIG. 19, two types of control signals Vz1 and Vz2 are required. Since these are based on two types of waveform signals Vx and Vy (triangular waves), a circuit for generating these waveform signals Vx and Vy is required, and there is a problem that the circuit configuration becomes complicated.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a DC / DC converter capable of both stepping up and stepping down with a simple circuit configuration.

  In order to solve the above-described conventional problems, a DC / DC converter according to the present invention includes two step-down switching elements that are electrically connected in series between an input terminal and a ground terminal and perform complementary operations, and an output terminal. Two step-up switching elements that are electrically connected in series between each other and the ground terminal and perform complementary operations, a connection point between the two step-down switching elements, and two step-up switching elements An inductor electrically connected to a connection point; an output voltage detection circuit which is electrically connected to the output terminal and detects an output voltage (Vo) of the output terminal; the step-down switching element; A boosting switching element, and a control circuit electrically connected to the output voltage detection circuit. Then, when switching between the step-up operation and the step-down operation, the control circuit performs the pulse width modulation control when the duty ratio control amount (Ds) reaches a first predetermined value at which pulse width modulation control cannot be performed. No two step-up switching elements or two step-down switching elements are connected in series for each period determined based on a predetermined correlation between the duty ratio control amount (Ds) and the ON frequency (f). On-control is performed in a state where one on-period of the switching elements is fixed, and off-control is performed in a state where the other off-period of the two switching elements in series is fixed. The control circuit, when the duty ratio control amount (Ds) reaches a second predetermined value when the step-up switching element and the step-down switching element are ON / OFF controlled in substantially the same period, The operations of the step-up switching element and the step-down switching element are interchanged. When the duty ratio control amount (Ds) reaches the third predetermined value at which the pulse width modulation control can be resumed, the control circuit performs the step-up operation by the step-up switching element or the step-down switching element. Thus, the step-down operation is performed.

  The DC / DC converter according to the present invention includes two step-down switching elements that are electrically connected in series between an input terminal and a ground terminal and perform complementary operations, and an output terminal and the ground terminal. Two step-up switching elements that are electrically connected in series and perform complementary operations, and between the connection points of the two step-down switching elements and the connection points of the two step-up switching elements. An inductor connected to the output terminal, an output voltage detection circuit that is electrically connected to the output terminal and detects an output voltage (Vo) of the output terminal, the step-down switching element, the step-up switching element, and the output A control circuit electrically connected to the voltage detection circuit. The control circuit performs the pulse width modulation control when the duty ratio control amount (Ds) reaches a first predetermined value at which the pulse width modulation control cannot be performed when switching between the step-up operation and the step-down operation. Two booster switching elements or two step-down switching elements are connected in series for each period determined based on a predetermined correlation between the duty ratio control amount (Ds) and the on-frequency (f). On-control is performed in a state where one on-period of the switching elements is fixed, and off-control is performed in a state where the other off-period of the two switching elements in series is fixed. The control circuit, when the duty ratio control amount (Ds) reaches a second predetermined value when the step-up switching element and the step-down switching element are ON / OFF controlled in substantially the same period, The operations of the step-up switching element and the step-down switching element are interchanged. The control circuit performs the step-up operation by the step-up switching element or the step-down operation by the step-down switching element when the duty ratio control amount (Ds) reaches the third predetermined value. It is a thing.

  According to the DC / DC converter of the present invention, the control circuit performs step-up / step-down switching by controlling a total of four switching elements based on the correlation. Since this control only changes the on / off period at the time of switching, a circuit for obtaining two triangular waves is not required as in the prior art, and a DC / DC converter capable of step-up / step-down with a simple configuration is obtained. There is an effect.

1 is a block circuit diagram of a DC / DC converter according to Embodiment 1 of the present invention. 2 is a timing chart of each switching element during step-up of the DC / DC converter according to Embodiment 1 of the present invention, (a) is a pulse waveform diagram of the first step-down switching element, and (b) is the second step-down switching element. (C) is a pulse waveform diagram of the first boosting switching element, and (d) is a pulse waveform diagram of the second boosting switching element. FIG. 5 is a timing chart when the first and second step-down switching elements are four times as long as the first and second step-up switching elements at the time of step-up / step-down switching of the DC / DC converter according to Embodiment 1 of the present invention; a) is a pulse waveform diagram of the first step-down switching element, (b) is a pulse waveform diagram of the second step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a second waveform diagram. Pulse waveform diagram of step-up switching element FIG. 6 is a timing chart when the first and second step-down switching elements are twice as long as the first and second step-up switching elements at the time of step-up / step-down switching of the DC / DC converter according to Embodiment 1 of the present invention; a) is a pulse waveform diagram of the first step-down switching element, (b) is a pulse waveform diagram of the second step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a second waveform diagram. Pulse waveform diagram of step-up switching element FIG. 5 is a timing chart when the first and second step-down switching elements and the first and second step-up switching elements are in the same period when the DC / DC converter according to the first embodiment of the present invention performs step-up / step-down switching. ) Is a pulse waveform diagram of the first step-down switching element, (b) is a pulse waveform diagram of the second step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a second step-up switching element. Waveform diagram of switching element FIG. 4 is a timing chart when the first and second step-up switching elements are twice as long as the first and second step-down switching elements at the time of step-up / step-down switching of the DC / DC converter according to Embodiment 1 of the present invention; a) is a pulse waveform diagram of the first step-down switching element, (b) is a pulse waveform diagram of the second step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a second waveform diagram. Pulse waveform diagram of step-up switching element FIG. 6 is a timing chart when the first and second step-up switching elements are four times as long as the first and second step-down switching elements at the time of step-up / step-down switching of the DC / DC converter according to Embodiment 1 of the present invention; a) is a pulse waveform diagram of the first step-down switching element, (b) is a pulse waveform diagram of the second step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a second waveform diagram. Pulse waveform diagram of step-up switching element 2 is a timing chart of each switching element at the time of step-down of the DC / DC converter according to Embodiment 1 of the present invention, (a) is a pulse waveform diagram of the first step-down switching element, and (b) is a second step-down switching element. (C) is a pulse waveform diagram of the first boosting switching element, and (d) is a pulse waveform diagram of the second boosting switching element. Correlation diagram between duty ratio control amount Ds and on-frequency f of the DC / DC converter in Embodiment 1 of the present invention 4 is a timing chart of each switching element during step-up of the DC / DC converter according to Embodiment 2 of the present invention, where (a) is a pulse waveform diagram of the first step-down switching element, and (b) is the second step-down switching element. (C) is a pulse waveform diagram of the first boosting switching element, and (d) is a pulse waveform diagram of the second boosting switching element. FIG. 7 is a timing chart when the ON period of the first boost switching element is extended every four periods when the step-up / step-down switching of the DC / DC converter according to the second embodiment of the present invention is performed. FIG. (B) is a pulse waveform diagram of the first step-up switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a pulse waveform of the second step-up switching element. Figure FIG. 7 is a timing chart when the ON period of the first boost switching element is extended every two cycles when the DC / DC converter according to the second embodiment of the present invention is switched in the step-up / step-down mode, and FIG. (B) is a pulse waveform diagram of the first step-up switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a pulse waveform of the second step-up switching element. Figure 6 is a timing chart when the ON period of the first boost switching element is maximum when the DC / DC converter is switched in step-up / step-down mode according to the second embodiment of the present invention. FIG. 5A is a pulse waveform of the first step-down switching element. (B) is a pulse waveform diagram of the second step-up switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a pulse waveform diagram of the second step-up switching element. It is a timing chart when the ON period of the second step-down switching element is extended every two cycles at the time of step-up / step-down switching of the DC / DC converter in Embodiment 2 of the present invention, (a) is for the first step-down step. (B) is a pulse waveform diagram of the first step-up switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a pulse waveform of the second step-up switching element. Figure It is a timing chart at the time of extending the ON period of the second step-down switching element every four cycles at the time of step-up / step-down switching of the DC / DC converter in Embodiment 2 of the present invention, (a) is for the first step-down step. (B) is a pulse waveform diagram of the first step-up switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a pulse waveform of the second step-up switching element. Figure 5 is a timing chart of each switching element at the time of step-down of the DC / DC converter according to Embodiment 2 of the present invention, where (a) is a pulse waveform diagram of the first step-down switching element, and (b) is the second step-down switching element. (C) is a pulse waveform diagram of the first boosting switching element, and (d) is a pulse waveform diagram of the second boosting switching element. Correlation diagram between duty ratio control amount Ds and on-frequency f of the DC / DC converter in Embodiment 2 of the present invention Schematic diagram of a conventional buck-boost switching regulator Exemplary signal graph of a conventional buck-boost switching regulator

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block circuit diagram of a DC / DC converter according to Embodiment 1 of the present invention. FIG. 2 is a timing chart of each switching element at the time of boosting of the DC / DC converter according to Embodiment 1 of the present invention. FIG. 2A is a pulse waveform diagram of the first step-down switching element, and FIG. FIG. 5C is a pulse waveform diagram of the step-down switching element, FIG. 5C is a pulse waveform diagram of the first step-up switching element, and FIG. 5D is a pulse waveform diagram of the second step-up switching element. FIG. 3 is a timing chart when the first and second step-down switching elements are in the four cycles of the first and second step-up switching elements when the DC / DC converter according to Embodiment 1 of the present invention performs step-up / step-down switching. (A) is a pulse waveform diagram of the first step-down switching element, (b) is a pulse waveform diagram of the second step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d). FIG. 6 is a pulse waveform diagram of a second boosting switching element. FIG. 4 is a timing chart when the first and second step-down switching elements are in two cycles of the first and second step-up switching elements at the time of step-up / step-down switching of the DC / DC converter according to Embodiment 1 of the present invention. (A) is a pulse waveform diagram of the first step-down switching element, (b) is a pulse waveform diagram of the second step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d). FIG. 6 is a pulse waveform diagram of a second boosting switching element. FIG. 5 is a timing chart when the first and second step-down switching elements and the first and second step-up switching elements are in the same period at the time of step-up / step-down switching of the DC / DC converter according to Embodiment 1 of the present invention. (A) is a pulse waveform diagram of the first step-down switching element, (b) is a pulse waveform diagram of the second step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d). FIG. 6 is a pulse waveform diagram of a second boosting switching element. FIG. 6 is a timing chart when the first and second step-up switching elements are in two cycles of the first and second step-down switching elements at the time of step-up / step-down switching of the DC / DC converter according to Embodiment 1 of the present invention. (A) is a pulse waveform diagram of the first step-down switching element, (b) is a pulse waveform diagram of the second step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d). FIG. 6 is a pulse waveform diagram of a second boosting switching element. FIG. 7 is a timing chart when the first and second step-up switching elements are four cycles of the first and second step-down switching elements at the time of step-up / step-down switching of the DC / DC converter according to Embodiment 1 of the present invention. (A) is a pulse waveform diagram of the first step-down switching element, (b) is a pulse waveform diagram of the second step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d). FIG. 6 is a pulse waveform diagram of a second boosting switching element. FIG. 8 is a timing chart of each switching element at the time of step-down of the DC / DC converter according to Embodiment 1 of the present invention. FIG. 8 (a) is a pulse waveform diagram of the first step-down switching element, and FIG. FIG. 5C is a pulse waveform diagram of the step-down switching element, FIG. 5C is a pulse waveform diagram of the first step-up switching element, and FIG. 5D is a pulse waveform diagram of the second step-up switching element. FIG. 9 is a correlation diagram between the duty ratio control amount Ds and the on-frequency f of the DC / DC converter according to Embodiment 1 of the present invention.

  In FIG. 1, two DC / DC converters 11 are electrically connected in series between an input terminal 15 and a ground terminal 17, a step-down switching element that performs a complementary operation, an output terminal 19, and a ground terminal 17. Between two step-up switching elements that are electrically connected in series and perform complementary operations, a connection point between the two step-down switching elements, and a connection point between the two step-up switching elements And an inductor 21 electrically connected to. The DC / DC converter 11 is electrically connected to the input terminal 15, is electrically connected to the input terminal 15 for detecting the input voltage Vi of the input terminal 15, and the output terminal 19. And an output voltage detection circuit 25 for detecting the output voltage Vo. A control circuit 27 electrically connected to the step-down switching element, the step-up switching element, the input voltage detection circuit 23, and the output voltage detection circuit 25 is provided.

  When the control circuit 27 switches between the step-up operation and the step-down operation, and the duty ratio control amount Ds reaches a first predetermined value at which the pulse width modulation control cannot be performed, the step-up switching not performing the pulse width modulation control. One on-period of the two switching elements in series is obtained for each period obtained based on the correlation between the predetermined time ratio control amount Ds and the on-frequency f for the element or the step-down switching element. On-control is performed in a fixed state, and off-control is performed in a state in which the other off period of the two switching elements in series is fixed. When the duty ratio control amount Ds reaches the second predetermined value when the step-up switching element and the step-down switching element are ON / OFF controlled in substantially the same cycle, the control circuit 27 The operations of the switching element and the step-down switching element are interchanged. Then, when the time ratio control amount Ds reaches the third predetermined value at which the pulse width modulation control can be resumed, the control circuit 27 performs the step-up operation by the step-up switching element or the step-down operation by the step-down switching element. I do.

  Accordingly, the control circuit 27 performs step-up / step-down switching by controlling a total of four switching elements based on the correlation. Since the control only changes the ON / OFF cycle at the time of switching, a circuit for obtaining two triangular waves is not required as in the prior art, and a DC / DC converter 11 capable of step-up / step-down with a simple configuration is obtained. .

  Hereinafter, the configuration and operation of the first embodiment will be described more specifically.

  In FIG. 1, a solar cell 28 is electrically connected between the input terminal 15 and the ground terminal 17 of the DC / DC converter 11. Therefore, the DC / DC converter 11 has a function of outputting a stable output voltage Vo that is not easily affected by the weather and shadows by increasing or decreasing the voltage (input voltage Vi) in the power generated by the solar cell 28.

  Further, between the output terminal 19 and the ground terminal 17, for example, a load, a secondary battery, or an inverter for supplying power to commercial system power can be connected. There is no particular limitation.

  Next, details of the internal configuration of the DC / DC converter 11 will be described.

  First, the step-down switching element has a configuration in which two switching elements are connected in series. Here, a field effect transistor (hereinafter referred to as FET) is used as the switching element. Accordingly, a parasitic diode 29 is formed in each switching element. The switching element is not limited to the FET, and may be another semiconductor switching element. Of the two step-down switching elements, one that is electrically connected to the input terminal 15 is the first step-down switching element 30 and the one that is electrically connected to the ground terminal 17 is the second step-down switching element. This is referred to as switching element 31.

  The first step-down switching element 30 and the second step-down switching element 31 perform complementary operations. Here, the complementary operation is basically defined as an operation in which the on / off operations of the two step-down switching elements are inverted. However, when the two step-down switching elements, which will be described later, are simultaneously turned off within a short period, the complementary operation is temporarily lost. Defined as being included in complementary operations.

  Similarly, the boosting switching element has a configuration in which two switching elements (FETs) are connected in series. Here, of the two boosting switching elements, the one that is electrically connected to the output terminal 19 is the first boosting switching element 33 and the one that is electrically connected to the ground terminal 17 is the second boosting element. This is referred to as switching element 35.

  A smoothing capacitor 37 is electrically connected between the output terminal 19 and the ground terminal 17. The smoothing capacitor 37 may be omitted when a secondary battery having a very large capacity is connected between the output terminal 19 and the ground terminal 17.

  Next, the input voltage detection circuit 23 has a function of detecting the input voltage Vi with reference to the ground terminal 17 and outputting it to the control circuit 27. Similarly, the output voltage detection circuit 25 has a function of detecting the output voltage Vo with reference to the ground terminal 17 and outputting it to the control circuit 27.

  The control circuit 27 includes a microcomputer, a peripheral circuit, a memory, and the like. The control circuit 27 takes in the input voltage Vi and the output voltage Vo, and includes a first step-down switching element 30, a second step-down switching element 31, and a first step-up voltage. The switching element 33 and the second boosting switching element 35 are controlled to be turned on / off by switch signals SW1, SW2, SW3, and SW4, respectively.

  Next, the operation of such a DC / DC converter 11 will be described.

  First, a case where the DC / DC converter 11 is performing a boosting operation will be described. 2A to 2D show the ON / OFF states of the first step-down switching element 30, the second step-down switching element 31, the first step-up switching element 33, and the second step-up switching element 35 over time at this time. ) Respectively. In the step-up operation, the control circuit 27 causes the first step-up switching element 33 and the second step-up switching element 35 to operate in a complementary manner, as shown in FIGS. Here, complementary operation means that when the first boost switching element 33 is on, the second boost switching element 35 is off, and when the first boost switching element 33 is off, the second boost switching element 33 is off. In the following, it is defined that the element 35 operates so as to be turned on, that is, to be in an inverted state. With such an operation, the DC / DC converter 11 boosts the input voltage Vi and outputs the output voltage Vo. At this time, the control circuit 27 sets the time ratio between the first boost switching element 33 and the second boost switching element 35 so that the output voltage Vo detected by the output voltage detection circuit 25 becomes a desired set voltage (see FIG. 2 (c) and (d) are defined as the ratio of the ON period to one cycle). The amount for adjusting the time ratio is hereinafter referred to as a time ratio control amount Ds. In the case of FIGS. 2C and 2D, since the on period and the off period are equal, the duty ratio is 0.5. The control for adjusting the step-up ratio by changing the time ratio and setting the output voltage Vo to a desired set voltage is called pulse width modulation control. In the following description, pulse width modulation control is abbreviated as PWM control.

  On the other hand, in the step-up operation, the control circuit 27 turns on the first step-down switching element 30 so that the step-down switching element does not perform ON / OFF control and the input voltage Vi is directly applied to the inductor 21. The second step-down switching element 31 is turned off so that the input terminal 15 and the ground terminal 17 are not short-circuited. Accordingly, as shown in FIGS. 2A and 2B, the first step-down switching element 30 remains on and the second step-down switching element 31 remains off, respectively.

  Such control is performed when the amount of solar radiation to the solar cell 28 is insufficient and the input voltage Vi is lower than the desired output voltage Vo, for example, when sunrise, dusk, cloudy weather, or shadows appear. .

  Next, the case where the solar radiation amount to the solar cell 28 is improved and the input voltage Vi increases will be described. In this case, since the DC / DC converter 11 needs to switch from the step-up operation to the step-down operation, the operation will be described below.

  In the DC / DC converter 11 according to the first embodiment, a predetermined correlation between the duty ratio control amount Ds and the on-frequency f is stored in the memory. Details of the ON frequency f will be described later. When switching the step-up / step-down operation of the DC / DC converter 11, the switching operation is controlled by the control circuit 27 based on the correlation. Therefore, first, the correlation shown in FIG. 9 will be described. In FIG. 9, the horizontal axis represents the duty ratio control amount Ds, and the vertical axis represents the on-frequency f.

  First, the state of FIG. 2 will be described with reference to FIG. Since only the boosting operation is performed in FIG. 2, the time ratio control amount Ds is equal to or greater than the time ratio control amount Ds1 (first predetermined value) in FIG. Here, it is assumed that the state in FIG. 2 is the time ratio control amount Ds1 that is the first predetermined value. In this case, as described above, the first boost switching element 33 and the second boost switching element 35 are PWM-controlled so as to perform complementary operations. Accordingly, as indicated by the duty ratio control amount Ds1 in FIG. 9, the first boosting switching element 33 and the second boosting switching element 35 (thick solid line in FIG. 9) are turned on and off at a constant on-frequency f1. Yes.

  Here, the ON frequency f on the vertical axis in FIG. 9 is a frequency that generates an ON period in PWM control of the first boost switching element 33 when the duty ratio is 0.5, for example. In the first embodiment, in the region where the first step-up switching element 33 is PWM-controlled, the ON frequency f1 is set to 80 kilohertz (hereinafter referred to as kHz). Therefore, since the period of 80 kHz is 12.5 μsec, a pulse waveform with a time ratio of 0.5 is generated every 12.5 μsec. This corresponds to FIGS. 2C and 2D. Here, since the ON frequency f1 is 80 kHz and the duty ratio is 0.5, the ON period is 6.25 μsec. Therefore, the first step-up switching element 33 repeats on / off every 6.25 μsec every 12.5 μsec. Since the second boosting switching element 35 operates in a complementary manner to the first boosting switching element 33, as shown in FIG. 2D, a waveform obtained by shifting the phase of the operation in FIG. Become.

  On the other hand, since the first step-down switching element 30 is in the on state and the second step-down switching element 31 is in the off state as described above, as shown by the thick broken line in FIG. The on-frequency f is 0 hertz (hereinafter referred to as Hz).

  In addition, with respect to the first step-down switching element 30 and the second step-down switching element 31, the duty ratio control amount Ds1 shows two points of the on-frequency f of 0 Hz and the audible frequency f0. Is a white circle, and in this case, it is defined that the numerical value of the black circle is adopted. Therefore, when the duty ratio control amount Ds is slightly smaller than the duty ratio control amount Ds1, the on-frequency f rapidly increases to a frequency slightly higher than the audible frequency f0.

  When the correlation is determined continuously from the black circle points, the ON frequency f may be included in the audible frequency band (approximately 20 Hz to 18 kHz) depending on the value of the duty ratio control amount Ds. As a result, noise may be generated from the DC / DC converter 11. Similarly, in the PWM control, if the on / off frequency is included in the audible frequency band, it becomes a noise factor, so the frequency of the PWM control (here, 80 kHz) is also set to a value outside the audible frequency band. As described above, in the first embodiment, the frequency in the pulse width modulation control and the on-frequency f are set to 0 hertz or higher than the audible frequency f0. In addition, when noise does not become a problem, it is good also as an above-mentioned continuous correlation.

  Next, it is assumed that the amount of solar radiation to the solar cell 28 increases and the difference between the output voltage Vo and the input voltage Vi approaches. Here, the first predetermined value is defined as a value at which PWM control of the step-down switching element cannot be performed. Therefore, when the difference becomes small, the DC / DC converter 11 performs a normal PWM control by varying the time ratio at a constant cycle (frequency) by the time ratio control amount Ds for controlling the output voltage Vo to the target value. Cannot be done. The threshold at which PWM control cannot be performed is the first predetermined value.

  Here, the duty ratio control amount Ds is reduced until the control circuit 27 cannot perform the PWM control. In this case, the control circuit 27 performs the on / off operation of the first step-down switching element 30 and the second step-down switching element 31 that maintain the on state or the off state based on the correlation shown in FIG. The control circuit 27 can know from the difference in the output voltage Vo with respect to the target value that the PWM control cannot be performed. That is, when the output voltage Vo matches the target value within the error range of measurement and control, the control circuit 27 determines that PWM control is being performed. On the other hand, when the difference is different beyond the error range, the control circuit 27 determines that the PWM control cannot be performed. In this case, the control circuit 27 continues the operation by fixing the time ratio of the step-up switching element that is performing the on / off operation, and starts the on-off operation of the step-down switching element. In this operation, the time ratio control amount Ds of the step-down switching element is based on the proportional integration amount in the first embodiment. Therefore, when it becomes smaller than the first predetermined value, the duty ratio control amount Ds is assumed to be a proportional integral amount of the step-down switching element. The duty ratio control amount Ds here is not limited to the proportional integral amount, and may be a proportional integral derivative amount, for example. In this case, although the control is complicated, the accuracy of the output voltage Vo is increased.

  Next, a specific operation when the duty ratio control amount Ds becomes smaller than the first predetermined value will be described below.

  First, in the process in which the time ratio control amount Ds decreases to the time ratio control amount Ds2, the first step-down switching element 30 and the second step-down switching element 31 are turned on and off based on the ON frequency f obtained from the thick broken line in FIG. The operation is performed gradually. When the duty ratio control amount Ds2 is reached, the on-frequency f2 is 20 kHz as shown in FIG. 9, so the first step-down switching element 30 and the second step-down switching element 31 perform the on-off operation based on the on-frequency f2 of 20 kHz. Do.

  This is shown in FIG. FIGS. 3A to 3D are timing charts of the same switching elements as FIGS. 2A to 2D, respectively.

  First, as shown in FIGS. 3C and 3D, the first boosting switching element 33 and the second boosting switching element 35 operate in the same manner as in FIGS. 2C and 2D, respectively. Accordingly, the boosting operation is the same as when the duty ratio control amount Ds is the first predetermined value. Therefore, as shown by the thick solid line in FIG. 9, the first boost switching element 33 and the second boost switching element 35 are both turned on and off at the on frequency f1 (= 80 kHz) with the phase shifted by 180 degrees. repeat.

  Thereafter, the first boost switching element 33 and the second boost switching element 35 continue to operate at the ON frequency f1 of 80 kHz until the time ratio control amount Ds reaches a time ratio control amount Ds4 (second predetermined value) described later. The on / off operation is repeated with the duty ratio of 0.5.

  On the other hand, as shown in FIG. 3A, the first step-down switching element 30 is turned off from time t2 to time t3, from time t10 to time t11, and so on. Since the second step-down switching element 31 operates complementarily to the first step-down switching element 30, a period during which the second step-down switching element 31 is turned on at the above time occurs as shown in FIG.

  Here, as indicated by a thick broken line in FIG. 9, the on-frequency f2 of the first step-down switching element 30 and the second step-down switching element 31 at the time ratio control amount Ds2 is 20 kHz, so the on-frequency f2 is The ON frequency f1 (80 kHz) of the first boost switching element 33 and the second boost switching element 35 is ¼. Therefore, the period is quadrupled. Accordingly, the first step-down switching element 30 is off-controlled by the control circuit 27 every four times the period of the first step-up switching element 33, and the second step-down switching element 31 operating in a complementary manner is the control circuit 27. Thus, the on-control is performed every four times the period of the second boosting switching element 35. At this time, the ON period in which the ON control is performed is fixed to the same value as the ON period (6.25 μsec) of the second boost switching element 35. Further, the off period of the first boosting switching element 33 that performs a complementary operation with the second boosting switching element 35 is also fixed to 6.25 μsec.

  From the above, the first step-down switching element 30 and the second step-down switching element 31 are, as shown in FIGS. 3A and 3B, the first step-up switching element 33 and the second step-up switching element. Each cycle is four times 35, and is turned on or off. That is, for example, every time the first step-up switching element 33 is turned off four times, the first step-down switching element 30 is turned off once. Both off periods are substantially equal within the error range of the control circuit 27. Similarly, every time the second step-up switching element 35 is turned on four times, the second step-down switching element 31 is turned on once, and both ON periods are substantially equal within an error range.

  Here, the control circuit 27 obtains the second step-down switching element 31 that is not performing the PWM control based on a predetermined correlation between the duty ratio control amount Ds and the ON frequency f (FIG. 9). The ON control is performed in a state where the ON period is fixed at every cycle, but the first step-down switching element 30 performs OFF control. This is because the first step-down switching element 30 and the second step-down switching element 31 perform complementary operations. Therefore, when the first step-down switching element 30 and the second step-down switching element 31 are collectively referred to as step-down switching elements, one of them (here, the second step-down switching element 31) performs ON control. As a whole, it is described that ON control is performed. Since the first step-down switching element 30 performs a complementary operation with respect to the second step-down switching element 31, one of the two step-down switching elements that is not on-controlled is necessarily off-controlled. become. When the first boosting switching element 33 and the second boosting switching element 35 are collectively referred to as a boosting switching element, the same definition as above is used.

  Next, when the duty ratio control amount Ds further decreases, the on-frequency f gradually increases as shown by the thick broken line in FIG. When the duty ratio control amount Ds3 is reached, the on-frequency f becomes a portion where the duty ratio control amount Ds3 and the thick broken line intersect, that is, the on-frequency f3 (= 40 kHz). Therefore, the on-frequency f3 is half of the on-frequency f1 (= 80 kHz) of the first boost switching element 33 and the second boost switching element 35 that are PWM-controlled, so that the second step-down switching element 31 is on-controlled. The period in which the second step-up switching element 35 is turned on is twice as long.

  Timing charts at this time are shown in FIGS. These timing charts are for the same switching elements as in FIGS.

  As described above, the period during which the second step-down switching element 31 is on-controlled is doubled. Also in FIGS. 4B and 4D, as described with reference to FIG. Since it is 25 μs and is substantially equal within the error range, the second step-down switching element 31 is turned on once every time the second step-up switching element 35 is turned on twice. As shown in FIG. 4A, the first step-down switching element 30 performs an operation complementary to the second step-down switching element 31. Further, as shown in FIG. 4C, the first boosting switching element 33 performs an operation complementary to the second boosting switching element 35.

  Thereafter, when the duty ratio control amount Ds decreases, the on-frequency f gradually increases, the second step-down switching element 31 is turned on, and the first step-down switching element 30 is turned off, as shown by the thick broken line in FIG. In addition, the controlled period becomes shorter. In other words, since the off period of the first step-down switching element 30 is fixed at 6.25 μsec, the on period in one cycle becomes shorter as the time ratio control amount Ds decreases. Since the second step-down switching element 31 performs an operation complementary to that of the first step-down switching element 30, the OFF period in one cycle becomes shorter as the time ratio control amount Ds decreases.

  Then, when the duty ratio control amount Ds becomes substantially zero within the error range of voltage detection or calculation, that is, when the input voltage Vi and the output voltage Vo become substantially equal within the error range, the step-down control is performed from FIG. The on-frequency f of the switching element for switching is substantially equal to the on-frequency f1 of the switching element for boosting within an error range. Timing charts at this time are shown in FIGS. Note that the switching elements in the timing charts of FIGS. 5A to 5D correspond to FIGS. 2A to 2D, respectively.

  As is apparent from FIG. 5, in the case of the duty ratio control amount Ds4 (= 0), FIG. 5A, that is, the timing chart of the first step-down switching element 30, and FIG. The timing chart of the switching element 33 has the same waveform. Similarly, the timing chart of FIG. 5B, that is, the second step-down switching element 31, and the timing chart of FIG. 5D, ie, the second step-up switching element 35, have the same waveform.

  This state corresponds to the DC / DC converter 11 performing the step-up operation and the step-down operation at the same time under the same conditions, and as described above, the input voltage Vi is controlled as it is to the output voltage Vo.

  In this way, while the duty ratio control amount Ds is between the first predetermined value and the second predetermined value, the second step-down switching element 31 operates as shown in FIGS. 2 (b) to 5 (b). The smaller the ratio control amount Ds, the shorter the turn-on period, and the more the number of turns on. Therefore, while the duty ratio control amount Ds is between the first predetermined value and the second predetermined value, control is performed so that the number of pulses of the step-down switching element (second step-down switching element 31) increases. This can be realized by proportional-integral control by the control circuit 27. This control may be proportional-integral-derivative control as described above.

  Next, the amount of solar radiation to the solar cell 28 further increases, and the input voltage Vi becomes higher than the output voltage Vo. In this case, the duty ratio control amount Ds becomes negative, and as shown by a thick solid line in FIG. 9, this time, the correlation is such that the ON frequency f of the step-up switching element gradually decreases. At the same time, the step-down switching element has a correlation in which the ON frequency f1 (= 80 kHz) is a constant value. In this operation, when the duty ratio control amount Ds reaches the second predetermined value, that is, the duty ratio control amount Ds4, the control circuit 27 switches the operations of the step-up switching element and the step-down switching element.

  In practice, the on-frequency f is for the second boost switching element 35, and the first boost switching element 33 performs a complementary operation to the second boost switching element 35. Here, by describing that the ON frequency f of the step-up switching element gradually decreases, the whole operation including the complementary operations of the step-up switching element is shown.

  When the time ratio control amount Ds decreases to the time ratio control amount Ds5, the on-state of the second boost switching element 35 is set to the on frequency f3 (= 40 kHz) based on the correlation shown by the thick solid line in FIG. Is controlled. At this time, the step-down switching element is ON / OFF controlled at an ON frequency f1 (= 80 kHz). Accordingly, the second step-up switching element 35 is controlled so as to be turned on at a cycle twice that of the second step-down switching element 31.

  Timing charts in these cases are shown in FIGS. Comparing FIG. 6B and FIG. 6D, the second step-up switching element 35 has a period twice that of the second step-down switching element 31 in a state where the ON period (6.25 μsec) is fixed. It is controlled to turn on in (25 μsec). As shown in FIG. 6A, the first step-down switching element 30 performs an operation complementary to the second step-down switching element 31, and as shown in FIG. 6C, the first step-up switching element 30 33 performs an operation complementary to the second boosting switching element 35.

  Thereafter, similarly, when the duty ratio control amount Ds decreases and reaches the duty ratio control amount Ds6, the second boost switching element 35 operates at the on-frequency f2 (= 20 kHz) from FIG. Timing charts at this time are shown in FIGS. Comparing FIG. 7B and FIG. 7D, the second step-up switching element 35 is controlled so as to be turned on at a period four times that of the second step-down switching element 31. Then, as shown in FIG. 7A, the first step-down switching element 30 performs an operation complementary to the second step-down switching element 31, and as shown in FIG. 7C, the first step-up switching element 30 33 performs an operation complementary to the second boosting switching element 35.

  When the time ratio control amount Ds further decreases and reaches the time ratio control amount Ds7 which is the third predetermined value, the first boost switching element 33 and the second boost switching element 35 are shown in the correlation of FIG. Stops the on / off operation, and only the first step-down switching element 30 and the second step-down switching element 31 perform the on / off operation. As a result, the DC / DC converter 11 performs a step-down operation using only the step-down switching element. When the duty ratio control amount Ds becomes smaller than the duty ratio control amount Ds7, the control circuit 27 performs the PWM control at the fluctuation time ratio on the step-down switching element, so that the control circuit 27 makes the output voltage Vo become a desired voltage value. To control.

  A timing chart at this time is shown in FIG. As shown in FIG. 8C, the first boosting switching element 33 maintains the on state, and as shown in FIG. 8D, the second boosting switching element 35 maintains the off state. Then, as shown in FIGS. 8A and 8B, the first step-down switching element 30 and the second step-down switching element 31 continue on and off complementarily.

  In this way, while the duty ratio control amount Ds is between the second predetermined value and the third predetermined value, the second boosting switching element 35 operates as shown in FIGS. 5 (c) to 8 (c). The smaller the ratio control amount Ds, the longer the cycle of turning off, and the number of times of turning off. Therefore, while the duty ratio control amount Ds is between the second predetermined value and the third predetermined value, the pulse of the boosting switching element (first boosting switching element 33) is controlled to decrease. This can be realized by proportional-integral control by the control circuit 27.

  When the duty ratio control amount Ds increases from a small value, that is, when the step-up operation is performed from the step-down operation, the DC / DC converter 11 performs the operation opposite to the above description. In this case, the first predetermined value replaces the duty ratio control amount Ds7, and the third predetermined value replaces the duty ratio control amount Ds1.

  The control by the control circuit 27 when switching from the step-up operation to the step-down operation is summarized as follows. When the time ratio control amount Ds reaches the first predetermined value, the control circuit 27 determines a predetermined time ratio control amount for the step-up switching element or the step-down switching element that is not subjected to pulse width modulation control. For each period obtained based on the correlation between Ds and the ON frequency f, one of the two switching elements in series (here, when the time ratio control amount Ds is 0 or more, the second step-down switching element 31 and the time ratio control). When the amount Ds is less than 0, on-control is performed with the on-period of the first step-up switching element 33 fixed, and the other of the two switching elements in series (here, the time ratio control amount Ds is 0 or more is the first). When the step-down switching element 30 and the duty ratio control amount Ds are less than 0, the OFF control is performed with the off-period of the second step-up switching element 35) fixed. Then, when the duty ratio control amount Ds reaches the second predetermined value, the control circuit 27 switches the operations of the step-up switching element and the step-down switching element. When the duty ratio control amount Ds reaches the third predetermined value, the step-up operation is performed by the step-up switching element, or the step-down operation is performed by the step-down switching element.

  By operating in this way, the DC / DC converter 11 can switch the step-up / step-down operation smoothly. Furthermore, since the four switching elements are turned on / off only when the voltage difference in the vicinity of switching the step-up / step-down operation, that is, when the duty ratio control amount Ds is close to 0, the step-up / step-down operation is performed. Only the on / off operation of one switching element is required. Therefore, the efficiency of the DC / DC converter 11 is improved. Further, when switching the step-up / step-down operation, on-control is performed for each period obtained based on the correlation between the duty ratio control amount Ds and the on-frequency f, so that it is not necessary to use two triangular waves. Therefore, a simple circuit configuration can be obtained.

  With the above-described configuration and operation, the control circuit 27 performs PWM control on the step-up switching element when only boosting is performed and on the step-down switching element when stepping down only. The control circuit 27 can perform step-up / step-down switching by controlling a total of four switching elements based on the correlation. Since the control only changes the ON / OFF cycle at the time of switching, a circuit for obtaining two triangular waves is not required as in the prior art, and a DC / DC converter 11 capable of step-up / step-down with a simple configuration is obtained. .

  In the first embodiment, when the control circuit 27 controls the step-up switching element and the step-down switching element in a complementary manner, the on / off states of the control circuit 27 depend on the response of the control circuit 27 or the switching element. Control is performed so as to switch simultaneously within the error range. However, this operation may include a period in which the two step-up switching elements are simultaneously turned off and a period in which the two step-down switching elements are simultaneously turned off. In this case, it is possible to reduce the possibility of a short circuit when there is substantially no period of simultaneous OFF. The reason is as follows.

  First, when the first boosting switching element 33 and the second boosting switching element 35 are switched at substantially the same time, there is a possibility that both of them are simultaneously turned on for a moment depending on an error. As a result, the output terminal 19 and the ground terminal “17 may be short-circuited, and the output voltage Vo may become unstable. Depending on the capacitance of the smoothing capacitor 37 due to the occurrence of a short-circuit, a large current may be generated from the smoothing capacitor 37. There is a possibility that the step-up switching element deteriorates.

  Next, even when the first step-down switching element 30 and the second step-down switching element 31 are switched at substantially the same time, both of them may be turned on simultaneously for a moment depending on the error. As a result, the input voltage Vi becomes unstable, and may cause a malfunction particularly during the buck-boost control. Furthermore, since the positive electrode and the negative electrode (both not shown) of the solar cell 28 are short-circuited, the life of the solar cell 28 may be affected.

  From these facts, a configuration may be adopted in which a period in which the two step-up switching elements are simultaneously turned off is interposed and a period in which the two step-down switching elements are simultaneously turned off.

  However, since the simultaneous off period affects the stability of the output voltage Vo during that period, it is desirable that the simultaneous off period exceeds the error range and is set as short as possible as compared to the on period. Further, depending on the control speed of the control circuit 27 and the response speed of each switching element, the ON / OFF state may be switched simultaneously without interposing the simultaneous OFF period.

  As described above, the necessity of the intervening OFF period may be determined as appropriate depending on the device to be used, its performance, the stability of the required output voltage Vo, and the like.

  Further, in the first embodiment, when the time ratio control amount Ds is substantially, that is, when the time ratio control amount Ds4 reaches the same period within the error range, the step-up switching element and the step-down switching element Although the operations are switched, this is not limited to such operations. Specific examples thereof will be described below.

  First, when the time ratio control amount Ds reaches the time ratio control amount Ds3, the control circuit 27 switches the operation of the step-up switching element and the step-down switching element. Then, the timing chart of each switching element becomes FIG. Originally, the waveform of FIG. 6 is a waveform when the duty ratio control amount Ds reaches the duty ratio control amount Ds5. Therefore, until the duty ratio control amount Ds reaches from the duty ratio control amount Ds3 to the duty ratio control amount Ds5, The output voltage Vo deviates from a desired value. However, depending on the application of the DC / DC converter 11, the amount of deviation may be within an allowable range. Therefore, the timing at which the operations of the step-up switching element and the step-down switching element are interchanged does not have to be exactly the time when the time ratio control amount Ds reaches the time ratio control amount Ds4.

  Therefore, if the amount of deviation of the output voltage Vo falls within the allowable range, it can be regarded that the on / off control is performed in substantially the same cycle even if the time ratio control amount Ds is not exactly the time ratio control amount Ds4. it can. Here, the term “substantially” is defined to include an allowable range in the amount of deviation of the output voltage Vo in addition to the above error range of voltage measurement and calculation. Accordingly, if the deviation of the output voltage Vo falls within the allowable range in the process of the duty ratio control amount Ds toward the duty ratio control amount Ds4, the control circuit 27 is regarded as being in a state where the on / off control is performed at substantially the same cycle. The operations of the step-up switching element and the step-down switching element are interchanged. Even with such a configuration, a conventional circuit for obtaining two triangular waves is not required, and the DC / DC converter 11 capable of step-up / step-down with a simple configuration is obtained.

(Embodiment 2)
FIG. 10 is a timing chart of each switching element at the time of step-up of the DC / DC converter according to Embodiment 2 of the present invention. FIG. 10 (a) is a pulse waveform diagram of the first step-down switching element, and FIG. FIG. 5C is a pulse waveform diagram of the step-down switching element, FIG. 5C is a pulse waveform diagram of the first step-up switching element, and FIG. 5D is a pulse waveform diagram of the second step-up switching element. FIG. 11 is a timing chart when the on-period of the first boosting switching element is extended every four periods when the step-up / step-down switching of the DC / DC converter according to the second embodiment of the present invention is performed. (B) is a pulse waveform diagram of the first step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a second step-up switching element. It is a pulse waveform figure of an element. FIG. 12 is a timing chart when the ON period of the first boosting switching element is extended every two cycles at the time of step-up / step-down switching of the DC / DC converter according to the second embodiment of the present invention. (B) is a pulse waveform diagram of the first step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a second step-up switching element. It is a pulse waveform figure of an element. FIG. 13 is a timing chart when the ON period of the first step-up switching element is maximum at the time of step-up / step-down switching of the DC / DC converter according to Embodiment 2 of the present invention, and (a) is the first step-down switching. (B) is a pulse waveform diagram of the second step-up switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a pulse waveform diagram of the second step-up switching element. It is. FIG. 14 is a timing chart when the ON period of the second step-down switching element is extended every two cycles at the time of step-up / step-down switching of the DC / DC converter according to Embodiment 2 of the present invention. (B) is a pulse waveform diagram of the first step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a second step-up switching element. It is a pulse waveform figure of an element. FIG. 15 is a timing chart when the ON period of the second step-down switching element is extended every four periods when the step-up / step-down switching of the DC / DC converter according to Embodiment 2 of the present invention is performed. (B) is a pulse waveform diagram of the first step-down switching element, (c) is a pulse waveform diagram of the first step-up switching element, and (d) is a second step-up switching element. It is a pulse waveform figure of an element. FIG. 16 is a timing chart of each switching element at the time of step-down of the DC / DC converter according to Embodiment 2 of the present invention. FIG. 16 (a) is a pulse waveform diagram of the first step-down switching element, and FIG. FIG. 5C is a pulse waveform diagram of the step-down switching element, FIG. 5C is a pulse waveform diagram of the first step-up switching element, and FIG. 5D is a pulse waveform diagram of the second step-up switching element. FIG. 17 is a correlation diagram between the duty ratio control amount Ds and the on-frequency f of the DC / DC converter according to Embodiment 2 of the present invention.

  Since the configuration of the DC / DC converter 11 in the second embodiment is the same as that in FIG. 1 of the first embodiment, the same components are denoted by the same reference numerals and will be briefly described.

  Two DC / DC converters 11 are electrically connected in series between the input terminal 15 and the ground terminal 17, and a step-down switching element that performs a complementary operation, and an electric current between the output terminal 19 and the ground terminal 17. Two step-up switching elements that are connected in series and perform complementary operations, electrically connected between a connection point of the two step-down switching elements and a connection point of the two step-up switching elements. And an inductor 21 to be connected. The DC / DC converter 11 is electrically connected to the input terminal 15, is electrically connected to the input terminal 15 for detecting the input voltage Vi of the input terminal 15, and the output terminal 19. And an output voltage detection circuit 25 for detecting the output voltage Vo. A control circuit 27 electrically connected to the step-down switching element, the step-up switching element, the input voltage detection circuit 23, and the output voltage detection circuit 25 is provided.

  Next, an operation that characterizes the second embodiment will be described. When switching between the step-up operation and the step-down operation, the control circuit 27 performs the pulse width modulation control when the duty ratio control amount (Ds) reaches a first predetermined value at which the pulse width modulation control cannot be performed. One switching element in series for each period determined based on a correlation between a predetermined duty ratio control amount Ds and an on-frequency f for the switching element for step-down or the switching element for step-down. On-control is performed with the period fixed, and off-control is performed with the other off-period of the two switching elements in series fixed. Then, when the duty ratio control amount Ds reaches the second predetermined value when the on / off control is performed in substantially the same cycle, the control circuit 27 switches the operations of the step-up switching element and the step-down switching element. When the duty ratio control amount Ds reaches the third predetermined value, the control circuit 27 performs the step-up operation by the step-up switching element or the step-down operation by the step-down switching element.

  Accordingly, the control circuit 27 performs step-up / step-down switching by controlling a total of four switching elements based on the correlation. At the time of this switching, only the on control and the off control are performed with the on period and the off period fixed, so that a circuit for obtaining two triangular waves is not required as in the prior art, and the step-up / step-down circuit has a simple configuration. A DC / DC converter 11 capable of performing the above is obtained.

  Hereinafter, the operation of the second embodiment will be described more specifically. Since the configuration is the same as that in FIG. 1, detailed description thereof is omitted.

  First, a case where the DC / DC converter 11 is performing a boosting operation will be described. 10A to 10D show the ON / OFF states of the first step-down switching element 30, the second step-down switching element 31, the first step-up switching element 33, and the second step-up switching element 35 over time at this time. ) Respectively. Since FIGS. 10A to 10D are the same as FIGS. 2A to 2D, detailed descriptions of FIGS. 10A to 10D are omitted. 10C and 10D, the duty ratio is 0.5, and PWM control is performed at 80 kHz. The duty ratio control amount Ds used for this PWM control is assumed to be a first predetermined value (the duty ratio control amount Ds11).

  Next, the case where the input voltage Vi increases will be described. In this case, since the DC / DC converter 11 switches from the step-up operation to the step-down operation, the detailed operation will be described below.

  In the DC / DC converter 11 according to the second embodiment, a predetermined correlation between the duty ratio control amount Ds and the on-frequency f is stored in the memory. Details of the ON frequency f will be described later. When switching the step-up / step-down operation of the DC / DC converter 11, the switching operation is controlled by the control circuit 27 based on the correlation. Therefore, here, the state of FIG. 10 will be described with reference to the correlation shown in FIG. In FIG. 17, the horizontal axis represents the duty ratio control amount Ds, and the vertical axis represents the on-frequency f. The duty ratio control amount Ds is the same as that described in the first embodiment.

  First, in FIG. 10, since only the boosting operation is performed as described above, in FIG. 17, the time ratio control amount Ds is equal to or greater than the time ratio control amount Ds11 (first predetermined value). Now, let us assume that the state of FIG. 10 is the time ratio control amount Ds11 that is the first predetermined value. In this case, the first boost switching element 33 and the second boost switching element 35 are PWM-controlled so as to perform complementary operations. Here, it can be seen from the thick solid line in FIG. 17 that the on-frequency f1 of the first boosting switching element 33 and the second boosting switching element 35 in the duty ratio control amount Ds11 is 80 kHz. Accordingly, the boosting switching element is complementarily controlled on and off at a period of 12.5 kHz.

  Here, the on-frequency f that is the vertical axis in FIG. 17 is a frequency that generates an on-period in the PWM control of the first boost switching element 33 as described above. Accordingly, when the on-frequency f at the first predetermined value of the first step-down switching element 30 and the second step-down switching element 31 is read from FIG. 17, it becomes 0 Hz. When the on-frequency f is 0 Hz, the cycle is infinite, and thus the on / off operation is not performed. Therefore, as shown in FIGS. 10A and 10B, when the time ratio control amount Ds is equal to or greater than the time ratio control amount Ds11, the first step-down switching element 30 remains on and the second step-down switching element 31 remains on. Remains off.

  Thereafter, when the duty ratio control amount Ds becomes smaller than the duty ratio control amount Ds11, the on-frequency f decreases as shown by a thick solid line in FIG. The duty ratio control amount Ds reaches the duty ratio control amount Ds12. It can be seen from the intersection with the thick solid line at this time that the ON frequency f4 is 60 kHz. Therefore, the control circuit 27 controls the on / off of the second step-up switching element 35 at a cycle corresponding to the frequency of 60 kHz. The specific control will be described with reference to FIG.

  First, since the cycle of the on-frequency f4 (60 kHz) is about 16.67 μsec, the second boosting switching element 35 performs an operation of turning on for a fixed period of 6.25 μsec. This waveform is shown in FIG. In FIG. 11D, for example, the period from time t1 to time t31 is one cycle, and the period from time t21 to time t31 is the ON period of the second boost switching element 35. Therefore, the control for extending the off period is performed, and as a result, the number of pulses is reduced. By repeating such an operation, the control circuit 27 controls the boost ratio to decrease. At this time, the first boosting switching element 33 performs a complementary operation with the second boosting switching element 35, and thus has a waveform shown in FIG. Note that the first step-down switching element 30 and the second step-down switching element 31 both have an ON frequency f of 0 Hz as shown by a thick broken line in the time ratio control amount Ds12 in FIG. To maintain. Therefore, the aging characteristics of both remain on or off as shown in FIGS. 11A and 11B, respectively.

  Next, when the duty ratio control amount Ds reaches the duty ratio control amount Ds13, the ON frequency f3 of the second boost switching element 35 is 40 kHz from the intersection with the thick solid line in FIG. In this case, since the period is twice that in the case of 80 kHz, the time is 25 μs, and the on-fixed period is 6.25 μs. Therefore, 1/4 of the period is the on period. This is shown in FIG. One cycle is, for example, from time t1 to time t5, of which time t4 to time t5 is a fixed on period. As shown in FIG. 12C, the first boosting switching element 33 has a complementary operation to the second boosting switching element 35. Further, from the thick broken line of FIG. 17, even in the duty ratio control amount Ds13, the on-frequency f is 0 Hz, so the on / off state of the step-down switching element is as shown in FIGS. 12 (a) and 12 (b). The former remains on and the latter remains off. Therefore, it can be seen that the control circuit 27 performs control to further lower the boost ratio.

  Next, when the time ratio control amount Ds reaches the time ratio control amount Ds14 which is the second predetermined value, the intersection with the thick solid line in FIG. 17 at that time becomes a white circle (18 kHz). The meaning of the white circle is the same as that in FIG. 9 and does not include the white circle value, but includes the black circle value. Therefore, in the duty ratio control amount Ds14, the ON frequency f of the step-up switching element is 0 Hz. That is, when the duty ratio control amount Ds reaches the second predetermined value, the on-frequency f immediately becomes 0 Hz. As a result, the second boost switching element 35 is turned off as shown in FIG. 13D, and the first boost switching element 33 is turned on as shown in FIG. 13C. Controlled by the circuit 27. Further, as shown in FIGS. 13A and 13B, the step-down switching element also maintains the on state and the off state. From these facts, in the time ratio control amount Ds14, as described in the first embodiment, the input voltage Vi and the output voltage Vo are substantially equal. By turning on only the switching element 33 and the first step-down switching element 30, the input terminal 15 and the output terminal 19 are directly connected. Therefore, the switching operation is not performed only at the time ratio control amount Ds14, so that the efficiency is improved as compared with the first embodiment.

  The reason why the on-frequency f is controlled so as to suddenly change from 18 kHz to 0 Hz in the duty ratio control amount Ds14 is to reduce noise as described in the first embodiment.

  Next, when the duty ratio control amount Ds becomes slightly smaller than the duty ratio control amount Ds14 (second predetermined value), as shown in FIG. Symmetric to f). This is because when the duty ratio control amount Ds reaches the second predetermined value when the boosting switching element and the step-down switching element are on / off controlled in substantially the same cycle, the control circuit 27 causes the boosting control element 27 to The operations of the switching element and the step-down switching element are interchanged. Therefore, as shown in FIGS. 14C, 14D, 15C, 15D, and 16C, 16D, when the time ratio control amount Ds is on the step-down operation side, The first boosting switching element 33 maintains the on state, and the second boosting switching element 35 maintains the off state. Therefore, the description of the operation of the boosting switching element is omitted in the following description.

  Note that the definition of a state in which on / off control is performed at substantially the same cycle is the same as in the first embodiment. Therefore, the timing for switching the operation of the step-up switching element and the step-down switching element does not have to be exactly when the time ratio control amount Ds reaches the time ratio control amount Ds14. However, as shown in FIG. 17, when the duty ratio control amount Ds is equal to or greater than the duty ratio control amount Ds14, the step-down switching element is used. When the duty ratio control amount Ds is equal to or less than the duty ratio control amount Ds14, the step-up switching is performed. Since each element is controlled to be turned on or off, the period becomes infinite. However, for example, if the first step-down switching element 30 remains on and the second step-down switching element 31 remains off, the period is infinite. In other words, it includes a state in which on / off control is performed in the same cycle. Therefore, it is defined herein that the on / off control includes on only control and off only control.

  When the duty ratio control amount Ds decreases and reaches the duty ratio control amount Ds15, the on-frequency f3 is 40 kHz from the thick broken line in FIG. This is the same as FIG. 12, but since it is a thick broken line, the control to turn on the second step-down switching element 31 for a fixed on period (6.25 μsec) at a cycle (25 μsec) with respect to 40 kHz is repeated. It is. The first step-down switching element 30 performs an operation complementary to the second step-down switching element 31. Accordingly, the waveforms are as shown in FIGS. 14 (a) and 14 (b), respectively.

  Next, when the duty ratio control amount Ds is further reduced and reaches the duty ratio control amount Ds16, the ON frequency f4 is 60 kHz from the thick broken line in FIG. This is the same as FIG. 11, but since it is a thick broken line, the second step-down switching element 31 is turned on for a fixed on period (6.25 μsec) with a period (16.67 μsec) with respect to 60 kHz. Is repeated. The first step-down switching element 30 performs an operation complementary to the second step-down switching element 31. Accordingly, the waveforms are as shown in FIGS. 15A and 15B, respectively.

  Next, when the duty ratio control amount Ds further decreases and reaches the duty ratio control amount Ds17 that is the third predetermined value, the on-frequency f1 is 80 kHz from the thick broken line in FIG. This is the same as FIG. 10, but since it is a thick broken line, the second step-down switching element 31 is turned on for a fixed on period (6.25 μsec) with a period (12.5 μsec) with respect to 80 kHz. Is repeated. The first step-down switching element 30 performs an operation complementary to the second step-down switching element 31. Accordingly, the waveforms are as shown in FIGS. 16 (a) and 16 (b), respectively.

  At this time point, the ON frequency f reaches 80 kHz used for PWM control. Therefore, when the duty ratio control amount Ds is smaller than that, the ON frequency f is maintained at 80 kHz as shown by a thick broken line in FIG. Then, the step-down operation is performed by the fluctuation ratio PWM control using only the step-down switching element.

  To summarize the operations up to here, when the power generation amount of the solar cell 28 increases from a small state, the step-up / step-down pressure when the DC / DC converter 11 is smoothly switched from the step-up operation to the step-down operation through the step-up / step-down operation. In operation, based on the correlation between the duty ratio control amount Ds and the ON frequency f, the period of the pulse waveform of the switching element under PWM control is increased or decreased with the ON period fixed. Switching is possible.

  In addition, what is necessary is just to perform operation | movement contrary to said description, when the electric power generation amount of the solar cell 28 decreases from the large state. In this case, the first predetermined value replaces the duty ratio control amount Ds17, and the third predetermined value replaces the duty ratio control amount Ds11.

  The control by the control circuit 27 when switching from the step-up operation to the step-down operation is summarized as follows. When switching between the step-up operation and the step-down operation, the control circuit 27 performs the pulse width modulation control when the duty ratio control amount (Ds) reaches a first predetermined value at which the pulse width modulation control cannot be performed. One switching element in series for each period determined based on a correlation between a predetermined duty ratio control amount Ds and an on-frequency f for the switching element for step-down or the switching element for step-down. On-control is performed with the period fixed, and off-control is performed with the other off-period of the two switching elements in series fixed. Then, when the duty ratio control amount Ds reaches the second predetermined value when the on / off control is not substantially performed, the control circuit 27 switches the operations of the step-up switching element and the step-down switching element. When the duty ratio control amount Ds reaches the third predetermined value, the control circuit 27 performs the step-up operation by the step-up switching element or the step-down operation by the step-down switching element.

  With the above-described configuration and operation, the control circuit 27 performs pulse width modulation control on the step-up switching element when only boosting is performed and on the step-down switching element when stepping down only. The control circuit 27 can perform step-up / step-down switching by controlling a total of four switching elements based on the correlation. At the time of this switching, since only the on period is fixed and the on control and the off control are performed for each period determined based on the correlation between the predetermined duty ratio control amount Ds and the on frequency f, Thus, a circuit for obtaining two triangular waves is not required, and the DC / DC converter 11 capable of step-up / step-down with a simple configuration is obtained.

  The differences between the first embodiment and the second embodiment are summarized as follows.

  First, in the first embodiment, the ON control of the second step-down switching element 31 that has not performed the ON / OFF operation in FIGS. 2B to 5B is performed in the ON period (6.25 μsec). It is performed in a fixed state. And the frequency is calculated | required from the correlation of FIG. Therefore, in the first embodiment, when the operation is switched from step-up to step-down, first, the control for increasing the number of pulses for turning on the second step-down switching element 31 is performed. Since the first step-down switching element 30 has an operation complementary to that of the second step-down switching element 31, the number of OFF pulses is increased.

  Next, as shown in FIG. 6C to FIG. 8C, when the duty ratio control amount Ds becomes negative, the ON control of the first boost switching element 33 is performed in the ON period (6.25 μsec). This is done in a fixed state. And the frequency is calculated | required from the correlation of FIG. Therefore, in the first embodiment, when the operation is switched from step-up to step-down, if the time ratio control amount Ds becomes negative, the number of pulses for turning on the first step-up switching element 33 is increased. Then, the second boost switching element 35 has more pulses to be turned off.

  As described above, in the first embodiment, as indicated by an arrow at the bottom of FIG. 9, when switching from step-up to step-down, the pulse of the switching element (the step-down switching element) that is not PWM-controlled is increased to perform step-down operation. If it enters, PWM control is performed. The switching element that has been PWM controlled (the step-up switching element) performs the reverse operation of the step-down switching element.

  On the other hand, in the second embodiment, when switching from step-up to step-down, the on-period is set in the first step-up switching element 33 in which PWM control is performed from FIG. 10 (c) to FIG. 13 (c). The fixed and on period is determined by the correlation in FIG. This is an operation to reduce the pulse. Then, as shown in FIG. 14C to FIG. 16C, when the step-down operation is started, the first step-up switching element 33 is kept in the ON state. This operation is indicated by the second arrow from the bottom in FIG. The second boosting switching element 35 performs an operation complementary to the first boosting switching element 33. Further, the step-down switching element performs the reverse operation of the step-up switching element as indicated by the arrow at the bottom of FIG.

  Therefore, to summarize the differences between the first embodiment and the second embodiment, the former performs the step-up / step-down switching by controlling the pulse of the switching element not subjected to the PWM control for performing the step-up operation or the step-down operation. The latter is different in that the step-up / step-down switching is performed by controlling the pulse of the switching element that is PWM controlled to perform the step-up operation or the step-down operation. However, no matter which control is adopted, the effect of enabling switching of the step-up / step-down with a simple configuration can be obtained.

  In the second embodiment, as in the first embodiment, a period in which the two step-up switching elements are simultaneously turned off is interposed, and the two step-down switching elements are simultaneously turned off. You may determine suitably so that a period may be interposed.

  In the second embodiment, the control circuit 27 uses the step-down switching element when the time ratio control amount Ds is equal to or greater than the time ratio control amount Ds14, and the time ratio control amount Ds is equal to or less than the time ratio control amount Ds14. Each of the step-up switching elements is controlled to be turned on or off, but this may be controlled to be turned on / off, for example, at an upper limit audible frequency f0 (= 18 kHz). In this case, the audible frequency f0 in the duty ratio control amount Ds14 in FIG. 17 is a black circle.

  Further, in the first and second embodiments, in the correlation, the portion where the on-frequency f changes with the duty ratio control amount Ds is a linear relationship, but the present invention is not limited to this, and the DC / DC converter 11 Depending on the specifications and the like, the correlation other than the linear relationship may be determined as appropriate.

  In the first and second embodiments, the configuration in which the solar cell 28 is connected to the DC / DC converter 11 has been described. However, the configuration is not limited to this configuration, and the input voltage Vi with respect to the desired output voltage Vo. However, the present invention may be applied to a configuration requiring a step-up / step-down operation, such as a charge / discharge circuit of a secondary battery.

  Since the DC / DC converter according to the present invention can perform both step-up voltage conversion and step-down voltage conversion, it is particularly useful as a DC / DC converter for a solar cell having a large input voltage variation. .

11 DC / DC converter 15 Input terminal 17 Ground terminal 19 Output terminal 21 Inductor 23 Input voltage detection circuit 25 Output voltage detection circuit 27 Control circuit 30 First step-down switching element 31 Second step-down switching element 33 First step-up switching element 35 Second Boosting Switching Element

Claims (4)

Two step-down switching elements that are electrically connected in series between the input terminal and the ground terminal and perform complementary operations;
Two step-up switching elements that are electrically connected in series between the output terminal and the ground terminal and perform complementary operations;
An inductor electrically connected between a connection point of the two step-down switching elements and a connection point of the two step-up switching elements;
An output voltage detection circuit that is electrically connected to the output terminal and detects an output voltage (Vo) of the output terminal;
A control circuit electrically connected to the step-down switching element, the step-up switching element, and the output voltage detection circuit;
When the control circuit switches between step-up operation and step-down operation,
When the time ratio control amount (Ds) reaches the first predetermined value at which the pulse width modulation control cannot be performed, the boosting switching element that is not performing the pulse width modulation control or the step-down switching element is determined in advance. On-control is performed in a state in which one on-period of the two switching elements in series is fixed for each period obtained based on the correlation between the duty ratio control amount (Ds) and the on-frequency (f). In addition, off control is performed with the other off period of the two switching elements in series fixed.
When the duty ratio control amount (Ds) reaches a second predetermined value when the step-up switching element and the step-down switching element are ON / OFF controlled in substantially the same cycle, the step-up switching element and the step-up switching element Replacing the operation of the step-down switching element,
When the duty ratio control amount (Ds) reaches the third predetermined value at which pulse width modulation control can be resumed, the step-up operation is performed by the step-up switching element, or the step-down operation is performed by the step-down switching element. DC / DC converter. Two step-down switching elements that are electrically connected in series between the input terminal and the ground terminal and perform complementary operations;
Two step-up switching elements that are electrically connected in series between the output terminal and the ground terminal and perform complementary operations;
An inductor electrically connected between a connection point of the two step-down switching elements and a connection point of the two step-up switching elements;
An output voltage detection circuit that is electrically connected to the output terminal and detects an output voltage (Vo) of the output terminal;
A control circuit electrically connected to the step-down switching element, the step-up switching element, and the output voltage detection circuit;
When the control circuit switches between step-up operation and step-down operation,
When the duty ratio control amount (Ds) reaches a first predetermined value at which the pulse width modulation control cannot be performed, the boosting switching element or the step-down switching element performing the pulse width modulation control is determined in advance. On-control is performed in a state in which one on-period of the two switching elements in series is fixed for each period obtained based on the correlation between the duty ratio control amount (Ds) and the on-frequency (f). In addition, off control is performed with the other off period of the two switching elements in series fixed.
When the duty ratio control amount (Ds) reaches a second predetermined value when the step-up switching element and the step-down switching element are ON / OFF controlled in substantially the same cycle, the step-up switching element and the step-up switching element Replacing the operation of the step-down switching element,
A DC / DC converter configured to perform the step-up operation by the step-up switching element or the step-down operation by the step-down switching element when the duty ratio control amount (Ds) reaches the third predetermined value. 3. The DC / DC converter according to claim 1, wherein the frequency in the pulse width modulation control and the on-frequency (f) are frequencies higher than 0 Hz or an audible frequency (f 0). The control circuit interposes a period in which the two boost switching elements are simultaneously turned off when controlling the boost switching element and the step-down switching element in a complementary manner, and the two step-down switching elements. The DC / DC converter according to claim 1, wherein a period during which the switching elements for the power supply are simultaneously turned off is interposed.

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