Boost circuit, step-up / step-down system

Abstract

To provide a boost circuit capable of accommodating a wide range of input voltages.SOLUTION: A boost circuit includes a switch-controlled first DCDC converter using a transformer to boost an input voltage, a second DCDC converter that boosts the input voltage using a method different from that of the first DCDC converter, an input voltage measuring unit that measures the input voltage, and a control unit that controls the first DCDC converter and the second DCDC converter on the basis of the measurement result of the input voltage measuring unit.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a boost circuit and a buck-boost system.

Background Art

[0002] Conventionally, a flyback converter capable of operating at an extremely low input voltage has been known. (See, for example, Patent Documents 1 and 2). [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent Translation Publication No. 2015-532580 [Patent Document 2] U.S. Patent No. 7,170,762

Summary of the Invention

Problems to be Solved by the Invention

[0003] The boost circuit preferably can handle a wide range of input voltages.

Means for Solving the Problems

[0004] In a first aspect of the present invention, a boost circuit is provided. The boost circuit may include a switch-controlled first DC-DC converter using a transformer to boost the input voltage. Any of the boost circuits may include a second DC-DC converter that boosts the input voltage by a method different from that of the first DC-DC converter. Any of the boost circuits may include an input voltage measurement unit that measures the input voltage. Any of the boost circuits may include a control unit that controls the first DC-DC converter and the second DC-DC converter based on the measurement result of the input voltage measurement unit.

[0005] In a second aspect of the present invention, a boost circuit is provided. The boost circuit may include a switch-controlled first DC-DC converter using a transformer to boost an input voltage. Any of the boost circuits may include a second DC-DC converter that boosts the input voltage. Any of the boost circuits may include an input voltage measurement unit that measures the input voltage. Any of the boost circuits may include a control unit that controls the first DC-DC converter and the second DC-DC converter based on the measurement result of the input voltage measurement unit. In any of the boost circuits, when the ratio of the maximum voltage generated by the DC-DC converter to the input voltage is defined as the generated voltage ratio, the generated voltage ratio of the second DC-DC converter may be smaller than the generated voltage ratio of the first DC-DC converter.

[0006] In any of the boost circuits, the control unit may control whether to operate the first DC-DC converter and the second DC-DC converter based on the measurement result. In any of the boost circuits, the second DC-DC converter may be a switch-controlled DC-DC converter using a transformer. In any of the boost circuits, the turns ratio of the transformer of the second DC-DC converter may be smaller than the turns ratio of the transformer of the first DC-DC converter.

[0007] In any of the boost circuits, the control unit may boost the input voltage using the first DC-DC converter when the value of the input voltage is equal to or greater than a first threshold and equal to or less than a second threshold. In any of the boost circuits, the control unit may boost the input voltage using the second DC-DC converter when the value of the input voltage is equal to or greater than the second threshold.

[0008] In any of the boost circuits, the first threshold when the input voltage is increasing may be greater than the first threshold when the input voltage is decreasing.

[0009] Any of the above boost circuits may further include a timer unit that transmits a monitor signal to the control unit. In any of the above boost circuits, the control unit may acquire the measurement result of the input voltage measurement unit according to the timing of the monitor signal.

[0010] Any of the above boost circuits may further include an output voltage measurement unit that measures the output voltage boosted by the boost circuit. In any of the above boost circuits, the control unit may control the first DC-DC converter and the second DC-DC converter based on the measurement result of the output voltage measurement unit during the period from receiving the monitor signal from the timer unit to receiving the next monitor signal.

[0011] Any of the above boost circuits may further include an output voltage measurement unit that measures the output voltage boosted by the boost circuit. In any of the above boost circuits, the control unit may control the first DC-DC converter and the second DC-DC converter based on the measurement result of the output voltage measurement unit.

[0012] In a second aspect of the present invention, a buck-boost system is provided. The above buck-boost system may include a power supply. Any of the above buck-boost systems may include any of the above boost circuits that boost the voltage of the power supply to an output voltage. Any of the above buck-boost systems may include a storage element charged by the output voltage.

[0013] Note that the above summary of the invention does not list all the necessary features of the present invention. Also, sub-combinations of these feature groups may also be inventions.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 2D

Figure 3A

Figure 3B

Figure 3C

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

MODE FOR CARRYING OUT THE INVENTION

[0015] Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution means of the invention. Also, for the same configuration in each figure, the description may be omitted by attaching the same reference numerals.

[0016] In this specification, expressions such as "connected" shall include not only being directly connected without passing through other elements, but also being indirectly connected through other elements. Also, in this specification, expressions such as "connected between... and...", "provided between... and...", or "arranged between... and..." do not limit the physical arrangement, but shall mean "electrically connected between... and...".

[0017] FIG. 1 is a diagram showing a step-up / down system 10 according to an embodiment of the present invention. The step-up / down system 10 includes a power supply 12, a step-up circuit 14, and a power storage element 16. The step-up / down system 10 extracts electric power from various power supplies 12 and charges the power storage element 16 with a desired output voltage or output current. In this specification, a case where the voltage of the power supply 12 is stepped up in the step-up / down system 10 will be described, but in the step-up / down system 10, a step-down operation may be performed. In FIG. 1, the illustration of the load is omitted.

[0018] The power supply 12 is, as an example, a thermoelectric element. A typical thermoelectric element, a Peltier element, has a characteristic that the generated output voltage is small because the output resistance is small. Depending on the environment in use, the output voltage may be about several tens of mV. Therefore, the step-up circuit 14 described later is configured to be able to step up from an extremely low voltage. However, the power supply 12 is not limited to a thermoelectric element. The power supply 12 may be a photovoltaic element using light energy such as sunlight as an energy source, a vibration power generation element using vibration generated by a machine or vibration of a bridge, road, etc. as an energy source, etc. The power supply 12 may generally be one whose output voltage is stepped up and used. In FIG. 1, the open-circuit voltage of the power supply 12 is represented by Voc and the internal resistance is represented by Rs.

[0019] The power of the power supply 12 is charged to the energy storage element 16. The energy storage element 16 is charged by the output voltage VOUT boosted by the boost circuit 14. The energy storage element 16 is, for example, a capacitor or a lithium-ion battery (LIB). The power charged to the energy storage element 16 may be supplied to the load.

[0020] The boost circuit 14 boosts the input voltage VIN to the output voltage VOUT and outputs it to the energy storage element 16. Here, the input voltage VIN is the name seen from the boost circuit 14 and is the same as the output voltage of the power supply 12. The boost circuit 14 in this example includes an input terminal 18, an output terminal 19, a capacitor 22, a first DC-DC converter 24, a second DC-DC converter 26, an input voltage measurement unit 28, and a control unit 30.

[0021] The input terminal 18 is connected to the power supply 12, and the output voltage of the power supply 12 is applied. That is, the voltage of the input terminal 18 is the input voltage VIN of the boost circuit 14. The capacitor 22 is provided between the wiring to which the input voltage VIN is applied and the ground terminal. The capacitor 22 has a capacitance for stabilizing the input voltage VIN.

[0022] The first DC-DC converter 24 boosts the input voltage VIN to the first output voltage VOUT1. The first DC-DC converter 24 may be a switch-controlled DC-DC converter. In other words, the first DC-DC converter 24 may be a separately-excited oscillation type DC-DC converter rather than a self-excited oscillation type. By using a switch-controlled DC-DC converter, a highly efficient boosting operation can be performed. The first DC-DC converter 24 in this example is a switch-controlled DC-DC converter using a transformer. The transformer may be a high turns ratio transformer in which the ratio of the number of turns of the secondary winding to the number of turns of the primary winding is large. The turns ratio may be 10 or more, may be 30 or more, or may be 50 or more. The voltage boosted by the transformer is proportional to the turns ratio. Therefore, by using a high turns ratio transformer as the first DC-DC converter 24, it is possible to boost the voltage to a voltage capable of charging the energy storage element 16 even from an extremely low voltage. The first output voltage VOUT1 is output to the output terminal 19.

[0023] The second DC-DC converter 26 boosts the input voltage VIN to the second output voltage VOUT2. The second output voltage VOUT2 is output to the output terminal 19. The second DC-DC converter 26 may be a switch-controlled DC-DC converter using the same transformer as the first DC-DC converter 24, or may be a DC-DC converter of a different type from the first DC-DC converter 24. The second DC-DC converter 26 may be a DC-DC converter that does not use a transformer. The second DC-DC converter 26 may be a switch-controlled DC-DC converter that does not use a transformer. The second DC-DC converter 26 in this example is a boost chopper. The second DC-DC converter 26 may include an element that stores energy from the power supply 12 and a switch that switches whether to output the energy stored in the element to the output terminal 19. The element is, for example, a coil.

[0024] The output terminal 19 is connected to the energy storage element 16. The boost circuit 14 outputs the output voltage VOUT to the energy storage element 16 via the output terminal 19. Here, the output voltage VOUT may be the first output voltage VOUT1 or the second output voltage VOUT2. For example, when the first DC-DC converter 24 is operating, the output voltage VOUT becomes the first output voltage VOUT1, and when the second DC-DC converter 26 is operating, the output voltage VOUT becomes the second output voltage VOUT2. The output voltage VOUT may be the voltage of the output terminal 19.

[0025] The input voltage measurement unit 28 measures the input voltage VIN. The input voltage measurement unit 28 outputs information regarding the measured input voltage VIN to the control unit 30.

[0026] The control unit 30 controls the first DC-DC converter 24 and the second DC-DC converter 26 based on the measurement result of the input voltage measurement unit 28. The control unit 30 may select which of the first DC-DC converter 24 and the second DC-DC converter 26 to use based on the measurement result of the input voltage measurement unit 28. The control unit 30 may control the first DC-DC converter 24 and the second DC-DC converter 26 by controlling the on / off of the switches of the first DC-DC converter 24 and the second DC-DC converter 26.

[0027] FIG. 2A is a diagram showing an example of the first DC-DC converter 24. The first DC-DC converter 24 in this example is a flyback type DC-DC converter. The first DC-DC converter 24 in this example has a transformer Tr, a switch SW11, and a switch SW12. One end of the switch SW11 is connected to the primary side of the transformer Tr, and the other end is connected to the ground terminal. One end of the switch SW12 is connected to the secondary side of the transformer Tr, and the other end is connected to the ground terminal.

[0028] The + terminal on the primary side of transformer Tr is connected to input terminal 18, and input voltage VIN is applied. The - terminal on the secondary side of transformer Tr is connected to output terminal 19. By turning on switch SW11, transformer Tr is charged, and then by turning off switch SW11, an output voltage VOUT1 and an output current flowing from the + terminal to the - terminal are generated on the secondary side of transformer Tr. By turning on switch SW12 while the output current is flowing, a high-efficiency boost operation with reduced losses becomes possible. The display 1:N in the figure represents the turns ratio between the primary and secondary sides of transformer Tr. Since the primary and secondary sides of the flyback type DCDC converter are insulated, the input impedance of the first DCDC converter 24 is determined by the on-time of switch SW11.

[0029] Here, let the maximum value of the voltage generated by the boost operation of the DCDC converter be the maximum voltage. The maximum voltage may refer to the instantaneous high voltage generated by the boost operation of the coil or transformer. The maximum voltage may be higher than the output voltage. In this example, the peak of the instantaneous voltage generated on the secondary side of transformer Tr due to the switching of switch SW11 may be taken as the maximum voltage.

[0030] Figure 2B is a diagram showing another example of the first DCDC converter 24. The first DCDC converter 24 in this example is different from the first DCDC converter 24 shown in Figure 2A in the arrangement of switch SW12.

[0031] The switch SW12 in this example is arranged between the - terminal on the secondary side of transformer Tr and output terminal 19. Also in the first DCDC converter 24 of this example, a boost operation can be performed by controlling switch SW11 and switch SW12.

[0032] Figure 2C is a diagram showing another example of the first DCDC converter 24. The first DCDC converter 24 in this example is different from the first DCDC converter 24 shown in Figure 2A in that switch SW12 is replaced by diode Di1.

[0033] FIG. 2D is a diagram showing another example of the first DC-DC converter 24. The first DC-DC converter 24 in this example is different from the first DC-DC converter 24 shown in FIG. 2C in that the diode Di1 is arranged between the - terminal on the secondary side of the transformer Tr and the output terminal 19. The first DC-DC converter 24 configured as shown in FIGS. 2C and 2D can also perform a boosting operation.

[0034] FIG. 3A is a diagram showing an example of the second DC-DC converter 26. The second DC-DC converter 26 in this example is a boost chopper. The second DC-DC converter 26 in this example includes a coil I1, a switch SW21, and a switch SW22. One end of the coil I1 is connected to the input terminal 18 to which the input voltage VIN is applied. The other end of the coil I1 is connected to one side terminals of the switch SW21 and the switch SW22. The other end of the switch SW21 is connected to the ground terminal. The other end of the switch SW22 is connected to the output terminal 19.

[0035] By turning on the switch SW21, the coil I1 can be charged, and then by turning off the switch SW21 and turning on the switch SW22, the energy charged in the coil I1 can be output to the output terminal 19. The instantaneous peak voltage generated in the coil I1 when the current flowing through the coil I1 is changed may be used as the maximum voltage in the boost chopper.

[0036] FIG. 3B is a diagram showing another example of the second DC-DC converter 26. The second DC-DC converter 26 in this example is different from the second DC-DC converter 26 shown in FIG. 3A in that the switch SW22 is replaced by a diode Di1. Also in the second DC-DC converter 26 in this example, a boosting operation can be performed by switching the on / off of the switch SW21.

[0037] FIG. 3C is a diagram showing another example of the second DC-DC converter 26. The second DC-DC converter 26 in this example is a switch control type DC-DC converter using a transformer. The second DC-DC converter 26 in this example has a different winding ratio of the transformer Tr compared to the first DC-DC converter 24 shown in FIG. 2A. That is, the winding ratio (1:M) of the transformer Tr of the second DC-DC converter 26 is smaller than the winding ratio (1:N) of the transformer Tr of the first DC-DC converter 24. Since the maximum voltage described above increases according to the winding ratio of the transformer Tr, the maximum voltage of the second DC-DC converter 26 in this example is smaller than the maximum voltage of the first DC-DC converter 24.

[0038] FIG. 4 is a diagram showing specific examples of the first DC-DC converter 24 and the second DC-DC converter 26 in the step-up / step-down system 10 of FIG. 1. As the first DC-DC converter 24 in this example, the first DC-DC converter 24 shown in FIG. 2A is used, and as the second DC-DC converter 26 in this example, the second DC-DC converter 26 shown in FIG. 3A is used. Also, an analog-to-digital converter (A / D) is used as the input voltage measurement unit 28. However, the input voltage measurement unit 28 is not limited to this, and for example, a comparator may be used as the input voltage measurement unit 28.

[0039] The control unit 30 in this example selects the DC-DC converter to be used by controlling the switches SW11 and SW12 of the first DC-DC converter 24 and the switches SW21 and SW22 of the second DC-DC converter 26.

[0040] In the boost circuit 14 of this example, by using a transformer Tr with a high turns ratio as the first DC-DC converter 24, boosting can be performed from an extremely low voltage. On the other hand, since a transformer Tr with a high turns ratio is used, when the input voltage VIN increases, the above-mentioned maximum voltage increases. The maximum voltage in this example is the voltage between both terminals on the secondary side of the transformer Tr. When the input voltage VIN on the primary side of the transformer Tr and the turns ratio N of the transformer Tr are considered, a voltage of (VIN × N) + VOUT is generated at the + terminal on the secondary side of the transformer Tr when the switch SW11 on the primary side is on. As an example, when VIN = 0.5V, N = 50, and VOUT = 3V, the peak voltage (maximum voltage) on the secondary side is 28V.

[0041] Therefore, when only the first DC-DC converter 24 is used, a switch with a high breakdown voltage characteristic capable of handling a high voltage is used as the switch SW12 on the secondary side. Furthermore, the range of the input voltage VIN is restricted so that the + terminal on the secondary side of the transformer Tr does not exceed the breakdown voltage of the switch SW12. The restriction of the input voltage VIN means, for example, when the power supply 12 is a thermoelectric element, the restriction of the output voltage that the thermoelectric element can handle, that is, the temperature difference at which the boosting operation is possible is limited.

[0042] The ratio of the maximum voltage generated by the DCDC converter with respect to the input voltage VIN is defined as the generated voltage ratio. That is, generated voltage ratio = maximum voltage / input voltage VIN. The generated voltage ratio of the second DCDC converter 26 in this example is smaller than that of the first DCDC converter 24. In the boost circuit 14 of this example, the first DCDC converter 24 and the second DCDC converter 26 are controlled based on the value of the input voltage VIN. As an example, as will be described later, when the input voltage VIN is equal to or less than a predetermined value, the first DCDC converter 24 is used to perform a boost operation, and when the value of the input voltage VIN is equal to or greater than the predetermined value, the second DCDC converter 26 is used to perform a boost operation. Thereby, even when the input voltage VIN increases to such an extent that the maximum voltage of the first DCDC converter 24 becomes equal to or greater than the breakdown voltage of the switch SW12, a boost operation can be performed. That is, the boost circuit 14 can correspond to a wide range of values of the input voltage VIN. Also, a switch with a low breakdown voltage can be used as the switch SW12. Furthermore, since the breakdown voltage of the switch SW22 of the second DCDC converter 26 can be lowered, the first DCDC converter 24 and the second DCDC converter 26 can be configured with switches having a low breakdown voltage.

[0043] FIG. 5 is a diagram showing an example of the state transition of the first DCDC converter 24 and the second DCDC converter 26 of the embodiment shown in FIG. 4. FIG. 6 is a diagram showing a timing chart of the state transition in FIG. 5. The boost circuit 14 of this example has three states: a state where both the first DCDC converter 24 and the second DCDC converter 26 are off (DCDC1: OFF, DCDC2: OFF), a state where the first DCDC converter 24 is on and the second DCDC converter 26 is off (DCDC1: ON, DCDC2: OFF), and a state where the first DCDC converter 24 is off and the second DCDC converter 26 is on (DCDC1: OFF, DCDC2: ON).

[0044] The description starts from the case where the input voltage VIN is 0V. When the input voltage VIN is 0V or higher and equal to or lower than the first threshold (Von_H), both the first DCDC converter 24 and the second DCDC converter 26 are in the off state (t0: see FIG. 6. The same applies hereinafter).

[0045] When the input voltage VIN is equal to or higher than the first threshold value (Von_H) and equal to or lower than the second threshold value (Vth_H), the first DC-DC converter 24 is in the on state and the second DC-DC converter 26 is in the off state (t1). That is, the boost circuit 14 boosts the input voltage VIN using the first DC-DC converter 24.

[0046] When the input voltage VIN is equal to or higher than the second threshold value (Vth_H), the first DC-DC converter 24 is in the off state and the second DC-DC converter 26 is in the on state (t2). That is, the boost circuit 14 boosts the input voltage VIN using the second DC-DC converter 26.

[0047] When the input voltage VIN, which was equal to or higher than the second threshold value (Vth_H), becomes equal to or lower than the second threshold value (Vth_L), the boost circuit 14 again has the first DC-DC converter 24 in the on state and the second DC-DC converter 26 in the off state (t3). Further, when the input voltage VIN becomes equal to or lower than the first threshold value (Von_L) from that state, both the first DC-DC converter 24 and the second DC-DC converter 26 are in the off state (t4).

[0048] The first threshold value may be a value corresponding to the input voltage VIN at which the first DC-DC converter 24 can operate. The second threshold value may be a value corresponding to the breakdown voltage of the switch SW12.

[0049] The first threshold value and the second threshold value may have hysteresis. That is, the first threshold value (Von_H) when the input voltage VIN is increasing may be greater than the first threshold value (Von_L) when the input voltage VIN is decreasing. Similarly, the second threshold value (Vth_H) when the input voltage VIN is increasing may be greater than the second threshold value (Vth_L) when the input voltage VIN is decreasing. Thereby, when minute fluctuations such as noise occur in the input voltage VIN, excessive state transitions (chattering operations) can be suppressed, and a more stable state transition of the DCDC converter becomes possible. However, the first threshold value (Von_H) and the first threshold value (Von_L) may be equal, and the second threshold value (Vth_H) and the second threshold value (Vth_L) may be equal.

[0050] FIG. 7 is a diagram showing a modified example of an embodiment of the present invention. The boost circuit 14 in this example has a timer unit 32 in addition to the configuration shown in FIG. 1. Since other configurations are the same as those in FIG. 1, the description thereof is omitted.

[0051] The timer unit 32 transmits a monitor signal Sm to the control unit 30. The control unit 30 may acquire the measurement result of the input voltage measurement unit 28 according to the timing of the monitor signal Sm. That is, the control unit 30 controls the first DCDC converter 24 and the second DCDC converter 26 according to the timing of the monitor signal Sm. The control unit 30 may compare the value of the input voltage VIN with the above-mentioned threshold value according to the timing of the monitor signal Sm and select the DCDC converter to be used. In any of the above operations, the control unit 30 turns off both the first DCDC converter 24 and the second DCDC converter 26, and the input voltage measurement unit 28 may measure the open-circuit voltage Voc of the power supply 12.

[0052] FIG. 8 is a flowchart of the operation of the boost circuit 14 in the modified example of FIG. 7. When the control unit 30 receives the monitor signal Sm from the timer unit 32, it acquires the measurement result from the input voltage measurement unit 28 (Step1). The control unit 30 in this example turns off both the first DCDC converter 24 and the second DCDC converter 26 and acquires the open-circuit voltage Voc of the power supply 12 from the input voltage measurement unit 28.

[0053] Subsequently, the control unit 30 compares the input voltage VIN with a predetermined threshold value (Step 2). In this example, the control unit 30 compares the open-circuit voltage Voc with the first threshold value Von. The first threshold value Von may be the first threshold value (Von_H) or the first threshold value (Von_L) described with reference to FIGS. 5 and 6.

[0054] In Step 2, if the open-circuit voltage Voc is greater than the first threshold value Von (Yes), the control unit 30 compares the open-circuit voltage Voc with the second threshold value Vth (Step 3). The second threshold value Vth may be the second threshold value (Vth_H) or the second threshold value (Vth_L) described with reference to FIGS. 5 and 6.

[0055] In Step 2, if the open-circuit voltage Voc is less than the first threshold value Von (No), the control unit 30 turns off both the first DC-DC converter 24 and the second DC-DC converter 26 (Step 4).

[0056] In Step 3, if the open-circuit voltage Voc is greater than the second threshold value Vth (Yes), the control unit 30 turns off the first DC-DC converter 24 and turns on the second DC-DC converter 26 (Step 4). In Step 3, if the open-circuit voltage Voc is less than the second threshold value Vth (No), the control unit 30 turns on the first DC-DC converter 24 and turns off the second DC-DC converter 26 (Step 4). The control unit 30 may repeat the flowchart of FIG. 8 each time it receives the monitor signal Sm.

[0057] FIG. 9 is a diagram showing a timing chart of the operation of the modification in FIG. 7. When the control unit 30 receives the monitor signal Sm from the timer unit 32, it turns off both the first DC-DC converter 24 and the second DC-DC converter 26 (t0). As a result, the input voltage VIN rises to the open-circuit voltage Voc. The control unit 30 acquires the voltage value of the risen input voltage VIN and selects the DC-DC converter to be used (t1). In the case of this example, at time t1, since the input voltage VIN is equal to or higher than the first threshold value (Von_H) and equal to or lower than the second threshold value (Vth_H), the control unit 30 turns on the first DC-DC converter 24 and turns off the second DC-DC converter 26. The length from time t0 to time t1 may be appropriately set according to the type of the power supply 12 and the like.

[0058] At the next timing, when the control unit 30 receives the monitor signal Sm from the timer unit 32, it turns off both the first DC-DC converter 24 and the second DC-DC converter 26 again (t2). The control unit 30 acquires the voltage value of the risen input voltage VIN and selects the DC-DC converter to be used (t3). In the case of this example, at time t3, since the input voltage VIN is equal to or higher than the second threshold value (Vth_H), the control unit 30 turns off the first DC-DC converter 24 and turns on the second DC-DC converter 26.

[0059] At the next timing, when the control unit 30 receives the monitor signal Sm from the timer unit 32, it turns off both the first DC-DC converter 24 and the second DC-DC converter 26 again (t4). The control unit 30 acquires the voltage value of the risen input voltage VIN and selects the DC-DC converter to be used (t5). In the case of this example, at time t3, since the input voltage VIN is equal to or lower than the first threshold value (Von_H), the control unit 30 turns off both the first DC-DC converter 24 and the second DC-DC converter 26.

[0060] In the step-up / step-down system 10, the open-circuit voltage Voc of the power supply 12 is periodically measured, and high-efficiency step-up can be achieved by matching (matching) the impedance of the step-up circuit 14 to the variation in the impedance of the power supply 12. By providing a timer unit 32 and periodically measuring the open-circuit voltage Voc, impedance matching and selection of the DCDC converter can be performed together.

[0061] FIG. 10 is a diagram showing another modification example in the embodiment of the present invention. The step-up circuit 14 in this example includes an output voltage measurement unit 34 in addition to the configuration shown in FIG. 1. Since other configurations are the same as those in FIG. 1, the description thereof is omitted.

[0062] The output voltage measurement unit 34 measures the output voltage VOUT, which is the voltage of the output terminal 19. The output voltage VOUT is the voltage stepped up by the step-up circuit 14. The output voltage VOUT may be the first output voltage VOUT1 when the first DCDC converter 24 is operating, or may be the second output voltage VOUT2 when the second DCDC converter 26 is operating. The output voltage measurement unit 34 outputs the measurement result to the control unit 30. The output voltage measurement unit 34 may have the same configuration as the input voltage measurement unit 28.

[0063] The control unit 30 in this example controls the first DCDC converter 24 and the second DCDC converter 26 based on the measurement result of the output voltage measurement unit 34. The control unit 30 may select which DCDC converter to use or turn both off based on the measurement result of the output voltage measurement unit 34.

[0064] FIG. 11 is a diagram showing an example of the state transition of the first DCDC converter 24 and the second DCDC converter 26 in the modification example shown in FIG. 10. The portion surrounded by the dotted line is the same as that in FIG. 5, so the description thereof is omitted.

[0065] The control unit 30 may control the first DC-DC converter 24 and the second DC-DC converter 26 by comparing the output voltage VOUT with the third threshold value Vov. When the output voltage VOUT is higher than the third threshold value Vov, the control unit 30 may turn off both the first DC-DC converter 24 and the second DC-DC converter 26. When the output voltage VOUT is lower than the third threshold value Vov, the control unit 30 may perform the state transition described in FIG. 5.

[0066] The third threshold value Vov may be determined based on the breakdown voltage of the element to which the output voltage VOUT is applied among the elements constituting the boost circuit 14 and the energy storage element 16. Also, the third threshold value Vov may be different when the output voltage VOUT is increasing and when it is decreasing. That is, when the output voltage VOUT is increasing, the control unit 30 may compare the output voltage VOUT with the third threshold value Vov_H, and when the output voltage VOUT is decreasing, the control unit 30 may compare the output voltage VOUT with the third threshold value Vov_L. The third threshold value Vov_H may be larger than the third threshold value Vov_L.

[0067] FIG. 12 is a diagram showing another modification example in the embodiment of the present invention. The boost circuit 14 in this example has an output voltage measurement unit 34 in addition to the configuration shown in FIG. 7. Since the other configurations are the same as those in FIG. 7, the description thereof is omitted.

[0068] In the boost circuit 14 of this example, the control unit 30 acquires the input voltage VIN (or the open-circuit voltage Voc) according to the monitor signal Sm received from the timer unit 32 and controls the first DC-DC converter 24 and the second DC-DC converter 26. Further, the control unit 30 controls the first DC-DC converter 24 and the second DC-DC converter 26 based on the measurement result of the output voltage measurement unit 34.

[0069] FIG. 13 is a diagram showing an example of state transitions of the first DC-DC converter 24 and the second DC-DC converter 26 of the modification shown in FIG. 12. Similar to the example shown in FIG. 5, the boost circuit 14 in this example has three states: both the first DC-DC converter 24 and the second DC-DC converter 26 are off (DCDC1: OFF, DCDC2: OFF), the first DC-DC converter 24 is on and the second DC-DC converter 26 is off (DCDC1: ON, DCDC2: OFF), and the first DC-DC converter 24 is off and the second DC-DC converter 26 is on (DCDC1: OFF, DCDC2: ON).

[0070] In this example, the operating states of the first DC-DC converter 24 and the second DC-DC converter 26 transition according to the value of the output voltage VOUT. Now, let's start the explanation from the case where the output voltage VOUT is low. When the output voltage VOUT is equal to or lower than the fourth threshold value (Von4_H), both the first DC-DC converter 24 and the second DC-DC converter 26 are in the off state.

[0071] When the output voltage VOUT is equal to or higher than the fourth threshold value (Von4_H) and equal to or lower than the fifth threshold value (Vth5_H), the first DC-DC converter 24 is in the on state and the second DC-DC converter 26 is in the off state. That is, the boost circuit 14 boosts the input voltage VIN using the first DC-DC converter 24.

[0072] When the output voltage VOUT is equal to or higher than the fifth threshold value (Vth5_H), the first DC-DC converter 24 is in the off state and the second DC-DC converter 26 is in the on state. That is, the boost circuit 14 boosts the input voltage VIN using the second DC-DC converter 26.

[0073] When the output voltage VOUT, which was equal to or higher than the fifth threshold value (Vth5_H), becomes equal to or lower than the fifth threshold value (Vth5_L), the first DC-DC converter 24 is again in the on state and the second DC-DC converter 26 is in the off state. Further, when the output voltage VOUT becomes equal to or lower than the fourth threshold value (Von4_L) from that state, both the first DC-DC converter 24 and the second DC-DC converter 26 are in the off state.

[0074] The state transition shown in FIG. 13 may be performed while the control unit 30 receives the monitor signal Sm from the timer unit 32 until the next monitor signal Sm is received. In other words, it may be performed during the periods from time t1 to t2, from t3 to t4, and after t5 in FIG. 9. Thereby, while periodically measuring the input voltage VIN (open circuit voltage Voc) using the timer unit 32, even when the input voltage VIN fluctuates during the measurement interval, the DCDC converter can be controlled and the elements of the first DCDC converter 24 can be protected. The state transition shown in FIG. 13 may not be performed when measuring the input voltage VIN (open circuit voltage Voc).

[0075] Here, the fourth threshold value and the fifth threshold value may have hysteresis. That is, the fourth threshold value (Von4_H) when the output voltage VOUT is increasing may be larger than the fourth threshold value (Von4_L) when the output voltage VOUT is decreasing. Similarly, the fifth threshold value (Vth5_H) when the output voltage VOUT is increasing may be larger than the fifth threshold value (Vth_L) when the output voltage VOUT is decreasing. However, the fourth threshold value (Von_H) and the fourth threshold value (Von_L) may be equal, and the fifth threshold value (Vth_H) and the fifth threshold value (Vth_L) may be equal.

[0076] As described above, the present invention has been described using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. It is obvious to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the description of the claims that forms with such changes or improvements can also be included in the technical scope of the present invention.

[0077] In the claims, the specification, and the drawings, the execution order of each process such as operations, procedures, steps, and stages in the apparatus, system, flowchart, and method shown is not explicitly indicated as "earlier than", "preceding", etc., and it should be noted that it can be realized in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the specification, and the drawings, even if it is described for convenience using "first", "next", etc., it does not mean that it is essential to implement in this order.

Explanation of Signs

[0078] 10 ··· Step-up / down system, 12 ··· Power supply, 14 ··· Step-up circuit, 16 ··· Energy storage element, 18 ··· Input terminal, 19 ··· Output terminal, 22 ··· Capacitor, 24 ··· First DC / DC converter, 26 ··· Second DC / DC converter, 28 ··· Input voltage measurement unit, 30 ··· Control unit, 32 ··· Timer unit, 34 ··· Output voltage measurement unit

Claims

1. A first switch-controlled DC-DC converter using a transformer to boost an input voltage, a second DC-DC converter that boosts the input voltage in a manner different from that of the first DC-DC converter, an input voltage measurement unit that measures the input voltage, and a control unit that controls the first DC-DC converter and the second DC-DC converter based on the measurement result of the input voltage measurement unit A boosting circuit comprising the same.

2. A first switch-controlled DC-DC converter using a transformer to boost an input voltage, a second DC-DC converter that boosts the input voltage, an input voltage measurement unit that measures the input voltage, and a control unit that controls the first DC-DC converter and the second DC-DC converter based on the measurement result of the input voltage measurement unit Comprising, When the ratio of the maximum voltage generated by the DC-DC converter to the input voltage is defined as the generated voltage ratio, the generated voltage ratio of the second DC-DC converter is smaller than the generated voltage ratio of the first DC-DC converter A boosting circuit.

3. The control unit controls whether to operate the first DC-DC converter and the second DC-DC converter based on the measurement result The boosting circuit according to Claim 1 or Claim 2.

4. The second DC-DC converter is a switch-controlled DC-DC converter using a transformer, and the turns ratio of the transformer of the second DC-DC converter is smaller than the turns ratio of the transformer of the first DC-DC converter The boosting circuit according to Claim 2.

5. When the value of the input voltage is equal to or greater than a first threshold value and equal to or less than a second threshold value, the control unit boosts the input voltage using the first DC-DC converter, and when the value of the input voltage is equal to or greater than the second threshold value, the control unit boosts the input voltage using the second DC-DC converter The boosting circuit according to Claim 1 or Claim 2.

6. The first threshold value when the input voltage is increasing is greater than the first threshold value when the input voltage is decreasing The boosting circuit according to Claim 5.

7. The control unit further comprises a timer unit that transmits a monitor signal, and the control unit acquires the measurement result of the input voltage measurement unit according to the timing of the monitor signal The boosting circuit according to Claim 1 or Claim 2.

8. The boosting circuit further comprises an output voltage measurement unit that measures the output voltage boosted by the boosting circuit, The control unit controls the first DC-DC converter and the second DC-DC converter based on the measurement result of the output voltage measurement unit between receiving the monitor signal from the timer unit and receiving the next monitor signal. The boost circuit according to claim 7.

9. The boost circuit further includes an output voltage measurement unit that measures the output voltage boosted by the boost circuit. The control unit controls the first DC-DC converter and the second DC-DC converter based on the measurement result of the output voltage measurement unit. The boost circuit according to claim 1 or claim 2.

10. A power source, The boost circuit according to claim 1 or claim 2 that boosts the voltage of the power source to an output voltage, and a storage element charged by the output voltage. A buck-boost system comprising the same.

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