Self-excited oscillating circuit and energy harvesting system

Abstract

To provide a self-excited oscillating circuit with high conversion efficiency in input voltage of a wide range and leading to no intermittent oscillation preferably.SOLUTION: A self-excited oscillating circuit boosting input voltage supplied from an input source has a transformer having a primary winding and a secondary winding, a first switching element connected to the primary winding and controlling DC current supplied from the input source to the primary winding, and an impedance adjustment circuit adjusting an impedance of a secondary side circuit to which the secondary winding of the transformer is connected based on the input voltage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a self-excited oscillation circuit and an energy harvesting system.

Background Art

[0002] Conventionally, even if the starting resistance is increased to lengthen the period of intermittent oscillation, a switching power supply device that can smoothly start the device regardless of the load size and continue oscillation stably during start-up or during a droop state when the output power increases is known. (For example, see Patent Document 1). [Prior Art Document] [Patent Document] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-128453

Summary of the Invention

Problems to be Solved by the Invention

[0003] The self-excited oscillation circuit preferably has high conversion efficiency over a wide range of input voltages and does not reach intermittent oscillation.

Means for Solving the Problems

[0004] In a first aspect of the present invention, a self-excited oscillation circuit is provided. The self-excited oscillation circuit may boost an input voltage supplied from an input source. Any of the self-excited oscillation circuits may include a transformer having a primary winding and a secondary winding. Any of the self-excited oscillation circuits may include a first switching element connected to the primary winding of the transformer and controlling a direct current supplied from the input source to the primary winding. Any of the self-excited oscillation circuits may include an impedance adjustment circuit that adjusts the impedance of a secondary-side circuit to which the secondary winding of the transformer is connected based on the input voltage.

[0005] In any of the self-excited oscillation circuits, the impedance adjustment circuit may be connected to a control terminal of the first switching element.

[0006] Any of the above self-excited oscillation circuits may further include a first resistor provided between the secondary winding of the transformer and the ground terminal. In any of the above self-excited oscillation circuits, the impedance adjustment circuit may include a second resistor provided in parallel with the first resistor. In any of the above self-excited oscillation circuits, the impedance adjustment circuit may include a second switching element provided in series with the second resistor. In any of the above self-excited oscillation circuits, the input voltage may be input to the control terminal of the second switching element.

[0007] In any of the above self-excited oscillation circuits, the impedance adjustment circuit may further include a third resistor provided in parallel with the first resistor and the second resistor. In any of the above self-excited oscillation circuits, the impedance adjustment circuit may further include a third switching element provided in series with the third resistor. In any of the above self-excited oscillation circuits, the input voltage may be input to the control terminal of the third switching element.

[0008] In any of the above self-excited oscillation circuits, the threshold voltage of the third switching element and the threshold voltage of the second switching element may be different.

[0009] Any of the above self-excited oscillation circuits may further include a first resistor having one end connected to the secondary winding of the transformer and the other end connected between the input terminal to which the input source is connected and the primary winding of the transformer. In any of the above self-excited oscillation circuits, the impedance adjustment circuit may include a second resistor provided in parallel with the first resistor. In any of the above self-excited oscillation circuits, the impedance adjustment circuit may include a second switching element provided in series with the second resistor. In any of the above self-excited oscillation circuits, the control terminal of the second switching element may be connected to the ground terminal.

[0010] In any of the above self-excited oscillation circuits, the impedance adjustment circuit may reduce the impedance of the secondary-side circuit when the input voltage becomes equal to or higher than the threshold voltage.

[0011] In a second aspect of the present invention, an energy harvesting system is provided. The energy harvesting system may include the input source. Any of the energy harvesting systems may include any of the self-oscillating circuits.

[0012] Note that the above summary of the invention does not list all of the necessary features of the present invention. Also, sub-combinations of these feature groups may also be inventions.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0014] 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.

[0015] 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. Further, 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...".

[0016] FIG. 1 is a diagram showing an energy harvesting system 10 according to one embodiment of the present invention. The energy harvesting system 10 includes an input source 12, a self-excited oscillation circuit 14, a first diode Di1, and a second capacitor C2.

[0017] The energy harvesting system 10 extracts power from various input sources 12 and charges a power storage element or supplies power to a load at a desired output voltage or output current. In the example of FIG. 1, the voltage of the input source 12 is boosted to charge the second capacitor C2.

[0018] In FIG. 1, the power supply voltage of the input source 12 is denoted as Vsource, and the internal resistance is denoted as Rsource. The input source 12 may be an environmental power source or a rectenna in wireless power feeding. The environmental power source is, for example, photovoltaic power generation using light energy such as sunlight, incandescent lamps, fluorescent lamps, and LEDs as an energy source, thermoelectric power generation using thermal energy such as heat generated by a machine or environmental temperature as an energy source, vibration power generation using vibrations generated by a machine or vibrations of a bridge, road, etc. as an energy source, electromagnetic wave power generation using electromagnetic waves, radio waves, etc. as an energy source, or biological power generation that converts the activity amount of organisms represented by a microbial fuel cell into energy. The input source 12 may be one in which the power supply voltage Vsource varies due to ambient environmental changes. The current output from the input source 12 may be a direct current.

[0019] The self-excited oscillation circuit 14 boosts the input voltage Vin supplied from the input source 12. The self-excited oscillation circuit 14 includes a transformer TR1, a first switching element M1, a first capacitor C1, a first resistor R1, an impedance adjustment circuit 16, an input terminal 18, and an output terminal 20. The input terminal 18 is connected to the positive side of the input source 12. The input voltage Vin may be the voltage of the input terminal 18, may be the voltage from the input terminal 18 to the primary winding Np of the transformer TR1 described later, or may be the voltage from the input terminal 18 to the first switching element M1. The input voltage Vin may be the power supply voltage Vsource of the input source 12, or may be the voltage obtained by voltage drop of the power supply voltage Vsource due to an internal resistor Rsource or the like.

[0020] The transformer TR1 has a primary winding Np and a secondary winding Ns. The primary winding Np and the secondary winding Ns in this example have opposite polarities. One end of the primary winding Np is connected to the input terminal 18, and the other end is connected to the first switching element M1. One end of the secondary winding Ns is connected to the first capacitor C1. The other end of the secondary winding Ns is connected to the output terminal 20, and the voltage boosted by the transformer TR1 is output to the second capacitor C2 via the output terminal 20. In this specification, the circuit to which the primary winding Np is connected is referred to as the primary side circuit 21, and the circuit to which the secondary winding Ns is connected is referred to as the secondary side circuit 22. The first diode Di1 is a rectifying diode for supplying current to the output terminal 20 during boosting.

[0021] The first switching element M1 is connected to the primary winding Np of the transformer TR1 and controls the DC current supplied from the input source 12 to the primary winding Np. The first switching element M1 may control whether or not to allow the DC current to flow, or may control the magnitude of the current value of the DC current. The other end of the first switching element M1 is connected to the negative side of the input source 12 and the ground terminal. By switching the first switching element M1, the current flowing through the primary winding Np of the transformer TR1 is controlled, and boosting is performed. The first switching element M1 may be a semiconductor device switch, and as an example, it is a depletion type n-type MOSFET.

[0022] The control terminal G1 of the first switching element M1 is connected to the node N1 of the secondary circuit 22. That is, whether the first switching element M1 is in the on state or the off state is determined according to the voltage of the node N1. In this example, the node N1 is connected to the secondary winding Ns of the transformer TR1 via the first capacitor C1.

[0023] The first capacitor C1 is provided between the secondary winding Ns of the transformer TR1 and the node N1. The first capacitor C1 adjusts the voltage of the node N1 based on the boosting operation of the transformer TR1. Since the voltage of the node N1 is input to the control terminal G1 of the first switching element M1, self-excited oscillation for controlling the switching of the primary circuit 21 based on the voltage generated by the boosting operation of the transformer TR1 is performed.

[0024] The first resistor R1 is provided between the secondary winding Ns of the transformer TR1 and the ground terminal. In this example, the first resistor R1 is provided between the node N1 and the ground terminal. The higher the resistance value (impedance) of the first resistor R1, the larger the amplitude of the node N1. Therefore, even when the power supply voltage Vsource of the input source 12 is low, a voltage of the node N1 sufficient to turn on the first switching element M1 can be ensured. As a result, even when the power supply voltage Vsource is low, the conversion efficiency in boosting becomes high. In this specification, the amplitude of the voltage may be simply referred to as the amplitude.

[0025] On one hand, at node N1, for example, an ESD protection element with a range on the negative side is used to achieve Class AB operation that is advantageous in terms of efficiency. Therefore, when the amplitude of the voltage at node N1 increases, the center value (common voltage) of the amplitude moves to the negative side. As a result, if the amplitude of the voltage at node N1 becomes too large, the Gm (mutual conductance) of the first switching element M1 decreases, and the switching operation of the first switching element M1 stops, falling into so-called intermittent oscillation. Intermittent oscillation, since it intermittently stops the switching operation, may contribute to low power consumption. However, in applications where power generation is desired to continue, such as the input source 12 in this example, intermittent oscillation hinders energy harvesting and is thus not preferable.

[0026] The self-oscillating circuit 14 in this example includes an impedance adjustment circuit 16. The impedance adjustment circuit 16 in this example is connected to the control terminal G1 of the first switching element M1. The impedance adjustment circuit 16 in this example is provided between node N1 and the ground terminal in parallel with the first resistor R1.

[0027] The impedance adjustment circuit 16 adjusts the impedance of the secondary circuit 22 to which the secondary winding Ns of the transformer TR1 is connected based on the input voltage Vin. The secondary circuit 22 to which the secondary winding Ns is connected may be a part where the voltage fluctuates due to the step-up operation of the transformer TR1, and may be a circuit connected to either one of the secondary windings Ns of the transformer TR1. Also, among the above circuits, it may be a part connected to the control terminal G1 of the first switching element M1.

[0028] The impedance adjustment circuit 16 in this example includes a second resistor R2 provided in parallel with the first resistor R1, and a second switching element M2 provided in series with the second resistor R2. And the input voltage Vin is input to the control terminal G2 of the second switching element M2. The second switching element M2 is, as an example, an n-type MOSFET.

[0029] When the input voltage Vin becomes equal to or higher than the threshold voltage, the second switching element M2 turns on, reducing the impedance of the secondary circuit 22. Thereby, fluctuations in the common voltage of the oscillation amplitude at node N1 can be suppressed, and intermittent oscillation can be prevented. Thereafter, when the input voltage Vin becomes lower than the threshold voltage, the second switching element M2 turns off, and the impedance of the secondary circuit 22 increases.

[0030] According to this example, by switching the impedance of the secondary circuit 22 by the impedance adjustment circuit 16, it is possible to boost the voltage with high conversion efficiency even when the input voltage Vin is low, and to prevent intermittent oscillation when the input voltage Vin is high. Furthermore, since the impedance is adjusted based on the voltage of the primary circuit 21, the impedance can be adjusted immediately before the secondary circuit 22 is charged with power by the boosting operation. In addition, since the power of the primary circuit 21 before conversion is used instead of the power of the secondary circuit 22 after conversion (boosting), there is no loss due to conversion, which also contributes to improving the total conversion efficiency of the self-excited oscillation circuit 14.

[0031] The threshold voltage of the second switching element M2 may be selected according to the voltage at which the first switching element M1 starts intermittent oscillation. The resistance value of the second resistor R2 may be equal to or less than the resistance value of the first resistor R1. The second switching element M2 may be configured such that two MOSFETs are connected in series. In that case, the bulk of each MOSFET may be connected to the source terminal. Also, the drain terminal of each MOSFET may be connected to the node N1, and the source terminal may be connected to the ground terminal. Further, each MOSFET may have a body diode, and the anode of each body diode may be connected to the ground terminal, and the cathode may be connected to the node N1. In this case, since the body diodes of each MOSFET are multi-stage, the threshold voltage at which the body diode turns on is doubled. Therefore, the limitation of the amplitude on the negative side of the node N1 can be relaxed, and the efficiency can be increased when the voltage Vsource of the input source 12 is high and the amplitude of the node N1 becomes large. The second switching element M2 may be configured such that three or more MOSFETs are connected in series.

[0032] FIG. 2 is a diagram showing a modified example of the energy harvesting system 10 in the embodiment. In the energy harvesting system 10 of this example, the configuration of the transformer TR1 of the self-oscillation circuit 14, the secondary circuit 22, and the configuration after the output terminal 20 are different from those of the energy harvesting system 10 shown in FIG. 1. Since other parts are the same as those of the energy harvesting system 10 in FIG. 1, the description thereof is omitted.

[0033] In the transformer TR1 of this example, the primary winding Np and the secondary winding Ns have the same polarity. One end of the secondary winding Ns is connected to the ground terminal. The other end of the secondary winding is connected to the output terminal 20 to output a boosted voltage.

[0034] In this example, the first capacitor C1 is connected to the high-potential side of the secondary winding Ns. With such a configuration, the same effect as in the case of FIG. 1 can be obtained. That is, the impedance adjustment circuit 16 can be used for the self-excited oscillation circuit 14 that controls the switching of the primary-side circuit 21 based on the voltage generated by the step-up operation of the transformer TR1 regardless of the circuit configuration of the secondary-side circuit 22.

[0035] The energy harvesting system 10 includes a first diode Di1, a second diode Di2, a second capacitor C2, and a third capacitor C3 as the configuration after the output terminal 20. The third capacitor C3 is a capacitor for cutting off the DC voltage. The first diode Di1 and the second diode Di2 are rectifying diodes for rectifying the amplitude of the output voltage and supplying it to the second capacitor C2. Also in this example, the self-excited oscillation circuit 14 boosts the voltage of the input source 12 and charges the second capacitor C2.

[0036] FIG. 3 is a diagram showing a modified example of the impedance adjustment circuit 16 in the embodiment. The impedance adjustment circuit 16 in this example further includes a third resistor R3 and a third switching element M3 in addition to the second resistor R2 and the second switching element M2. Since other parts are the same as the self-excited oscillation circuit 14 shown in FIG. 1, the description thereof is omitted.

[0037] The third resistor R3 is provided in parallel with the first resistor R1 and the second resistor R2. The third switching element M3 is provided in series with the third resistor R3. Then, the input voltage Vin is input to the control terminal G3 of the third switching element M3. The third switching element M3 also turns on when the input voltage Vin becomes equal to or higher than the threshold voltage, and reduces the impedance of the secondary-side circuit 22. As a result, the voltage of the node N1 decreases, and intermittent oscillation can be prevented. The third switching element M3 is an n-type MOSFET as an example.

[0038] The threshold voltage of the third switching element M3 and the threshold voltage of the second switching element M2 may be different. For example, as the second switching element M2, a MOSFET having a normal threshold voltage may be used, and as the third switching element M3, a MOSFET having a low threshold voltage lower than the threshold voltage of the second switching element M2 may be used. Thereby, the impedance of the secondary circuit 22 can be finely adjusted according to the variation of the input voltage Vin.

[0039] The threshold voltage of the third switching element M3 may be lower than the threshold voltage of the second switching element M2, and the resistance value of the third resistor R3 may be equal to or greater than the resistance value of the second resistor R2. Thereby, the impedance of the secondary circuit 22 can be adjusted more finely.

[0040] The third switching element M3 may also be configured such that two MOSFETs are connected in series. In that case, the bulk of each MOSFET may be connected to the source terminal. Also, the drain terminal of each MOSFET may be connected to the node N1 side, and the source terminal may be connected to the ground terminal side. Further, each MOSFET may have a body diode. Thereby, as described above, the limitation of the amplitude on the negative side of the node N1 can be relaxed, and the efficiency can be increased when the voltage Vsource of the input source 12 is high and the amplitude of the node N1 becomes large. The third switching element M3 may also be configured such that three or more MOSFETs are connected in series.

[0041] In addition to the above-described configuration, the impedance adjustment circuit 16 in this example may further include a resistor provided in parallel with the first resistor R1 or the like and a switching element provided in series with the resistor. In that case, the threshold voltages of all the switching elements of the impedance adjustment circuit 16 may be different from each other. Also, the resistance values of all the resistors included in the impedance adjustment circuit 16 may be smaller than the resistance value of the first resistor R1.

[0042] FIG. 4 is a diagram showing an example in which a modified example of the impedance adjustment circuit 16 shown in FIG. 3 is applied to the energy harvesting system 10 shown in FIG. 2. Among the self-oscillation circuits 14 in this example, those other than the impedance adjustment circuit 16 are the same as those in FIG. 2, and the impedance adjustment circuit 16 is the same as that in FIG. 3.

[0043] Even with such a configuration, the same effects as in the case of FIG. 2 can be obtained. That is, the impedance adjustment circuit 16 can be used for the self-oscillation circuit 14 that controls the switching of the primary-side circuit 21 based on the voltage generated by the step-up operation of the transformer TR1 regardless of the circuit configuration of the secondary-side circuit 22.

[0044] FIG. 5 is a diagram showing a modified example of the self-oscillation circuit 14 in the embodiment. The self-oscillation circuit 14 in this example is different from the self-oscillation circuit 14 shown in FIG. 1 in the arrangement of the first resistor R1 and the configuration of the impedance adjustment circuit 16. Since other parts are the same as the self-oscillation circuit 14 shown in FIG. 1, the description thereof is omitted.

[0045] One end of the first resistor R1 in this example is connected to the secondary winding Ns of the transformer TR1 and is connected between the input terminal 18 and the primary winding Np of the transformer TR1. More specifically, the first resistor R1 in this example is connected to the node N1 and is connected to the secondary winding Ns via the first capacitor C1.

[0046] The impedance adjustment circuit 16 in this example includes a second resistor R2 provided in parallel with the first resistor R1 and a second switching element M2 provided in series with the second resistor R2. That is, similar to the first resistor R1, one end of the impedance adjustment circuit 16 in this example is connected to the secondary winding Ns of the transformer TR1, and the other end is connected between the input terminal 18 and the primary winding Np of the transformer TR1.

[0047] The control terminal G2 of the switching element M2 in this example is connected to the ground terminal. The switching element M2 in this example is, as an example, a p-type MOSFET. When the input voltage Vin becomes equal to or higher than the threshold voltage, the second switching element M2 turns on, reducing the impedance of the secondary circuit 22. As a result, the voltage at node N1 decreases, and the same effect as in the case of FIG. 1 can be obtained.

[0048] The MOSFET of the second switching element M2 may also have a body diode. Also in this example, the second switching element M2 may be configured such that two MOSFETs are connected in series. In that case, the sources or drains of the two MOSFETs may be connected to each other. Also, the bulk may be connected to the source or drain in both MOSFETs. That is, the connection of the bulk may be symmetric. In other words, the MOSFETs may be connected such that the directions of the body diodes are opposite to each other. Thereby, the reverse flow of current from node N1 to the input terminal 18 can be prevented, and the amplitude of node N1 can be prevented from being limited.

[0049] However, the body diodes may be connected in cascade in the same direction. That is, the anode of each body diode may be connected to the ground terminal side, and the cathode may be connected to the node N1 side. Thereby, as described above, the limitation of the amplitude on the negative side of node N1 can be relaxed. The second switching element M2 in this example may also be configured such that three or more MOSFETs are connected in series.

[0050] Also in this example, the impedance adjustment circuit 16 may further include resistors and switching elements having the same configuration. In that case, as described with reference to FIG. 3, the threshold voltages of the respective switching elements may be different. Also, the resistance values of the respective resistors may be equal to or less than the resistance value of the first resistor R1.

[0051] FIG. 6 is a diagram showing an example in which a modified example of the impedance adjustment circuit 16 shown in FIG. 5 is applied to the energy harvesting system 10 shown in FIG. 2. Among the self-excited oscillation circuits 14 in this example, those other than the impedance adjustment circuit 16 are the same as those in FIG. 2, and the impedance adjustment circuit 16 is the same as that in FIG. 5.

[0052] Even with such a configuration, the same effects as in the case of FIG. 2 can be obtained. That is, the impedance adjustment circuit 16 can be used for the self-excited oscillation circuit 14 that controls the switching of the primary-side circuit 21 based on the voltage generated by the step-up operation of the transformer TR1, regardless of the circuit configuration of the secondary-side circuit 22.

[0053] 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.

Explanation of Reference Numerals

[0054] 10... Energy harvesting system, 12... Input source, 14... Self-excited oscillation circuit, 16... Impedance adjustment circuit, 18... Input terminal, 20... Output terminal, 21... Primary-side circuit, 22... Secondary-side circuit

Claims

1. A self-excited oscillation circuit that boosts an input voltage supplied from an input source, comprising: A transformer having a primary winding and a secondary winding; A first switching element connected to the primary winding of the transformer and controlling a direct current supplied from the input source to the primary winding; An impedance adjustment circuit that adjusts the impedance of a secondary circuit to which the secondary winding of the transformer is connected based on the input voltage. A self-excited oscillation circuit comprising the above components.

2. The impedance adjustment circuit is connected to a control terminal of the first switching element. The self-excited oscillation circuit according to Claim 1.

3. The self-excited oscillation circuit further comprises a first resistor provided between the secondary winding of the transformer and a ground terminal. The impedance adjustment circuit comprises: A second resistor provided in parallel with the first resistor; A second switching element provided in series with the second resistor. The control terminal of the second switching element is supplied with the input voltage. The self-excited oscillation circuit according to Claim 1 or 2.

4. The impedance adjustment circuit further comprises: A third resistor provided in parallel with the first resistor and the second resistor; A third switching element provided in series with the third resistor. The control terminal of the third switching element is supplied with the input voltage. The self-excited oscillation circuit according to Claim 3.

5. The threshold voltage of the third switching element is different from the threshold voltage of the second switching element. The self-excited oscillation circuit according to Claim 4.

6. The self-excited oscillation circuit further comprises a first resistor having one end connected to the secondary winding of the transformer and the other end connected between an input terminal to which the input source is connected and the primary winding of the transformer. The impedance adjustment circuit comprises: A second resistor provided in parallel with the first resistor; A second switching element provided in series with the second resistor. The control terminal of the second switching element is connected to a ground terminal. The self-excited oscillation circuit according to Claim 1.

7. When the input voltage is equal to or higher than a threshold voltage, the impedance adjustment circuit reduces the impedance of the secondary circuit. The self-excited oscillation circuit according to Claim 1.

8. An energy harvesting system comprising: The input source; The self-excited oscillation circuit according to Claim 1. ​ ​ ​ ​

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