JP5861810B1 - Power supply - Google Patents

Abstract

An inverter circuit (11) that converts a DC voltage into an AC voltage, a pulse signal generation circuit (12) that controls the inverter circuit (11) at a set drive frequency, and an AC voltage output from the inverter circuit (11) Insulating piezoelectric transformer (15) for stepping down, parallel resonant circuit (14) connected between inverter circuit (12) and piezoelectric transformer (15), piezoelectric transformer (15), and the output side thereof And a parallel resonant circuit (152) having the same resonant frequency as the parallel resonant circuit (14). The process of sweeping the drive frequency and detecting the resonance frequency of the piezoelectric transformer (15) caused by the parallel resonance circuit (14) and the parallel resonance circuit (152) on the input side of the piezoelectric transformer (15) is executed at a predetermined cycle. . The detected resonance frequency is set as a drive frequency.

Description

  The present invention relates to a power supply device using a piezoelectric transformer.

  Generally, a power supply device includes a winding transformer for stepping up or stepping down. Since the winding transformer is limited in size by the output voltage, it is difficult to reduce the size and thickness. Therefore, in order to realize a reduction in size and thickness, an inverter power supply for a liquid crystal backlight using a Rosen-type piezoelectric transformer has been proposed. However, the Rosen-type piezoelectric transformer cannot structurally insulate the circuit on the input side and the output side because of its structure, and cannot sufficiently take measures against noise.

  Patent Document 1 discloses a constant frequency / constant voltage generator using an insulating piezoelectric transformer capable of insulating a circuit on an input side and an output side. In the device described in Patent Document 1, the piezoelectric transformer is an insulating type, but the ground is shared between the primary side and the secondary side of the piezoelectric transformer. For this reason, there is a possibility that noise wraps around the ground.

  Patent Document 2 discloses a power supply circuit using a piezoelectric transformer whose output voltage can be controlled. The power supply circuit described in Patent Literature 2 is configured to detect the output voltage of the piezoelectric transformer and feed back a control signal according to the detection result to control the output voltage.

JP-A-6-86552 Japanese Patent No. 2961851

  However, in Patent Document 2, so-called feedback control is performed in which the output voltage of the piezoelectric transformer is detected and the sine wave of the voltage input to the piezoelectric transformer is controlled based on the output voltage. Become.

  Therefore, an object of the present invention is to provide a power supply device that can always be controlled at an optimum frequency without using a complicated circuit configuration.

  A power supply apparatus according to the present invention includes an inverter circuit that converts a DC voltage into an AC voltage, a PWM control circuit that PWM-controls the inverter circuit at a set drive frequency, and boosts or reduces the AC voltage output from the inverter circuit. A piezoelectric transformer that steps down, a first resonance circuit connected between the inverter circuit and the piezoelectric transformer, the piezoelectric transformer, and an element connected to an output side of the piezoelectric transformer, the first transformer A second resonance circuit having the same resonance frequency as that of the resonance circuit, and sweeping the drive frequency to obtain a resonance frequency of the piezoelectric transformer caused by the first resonance circuit and the second resonance circuit. A resonance frequency detection unit that executes processing to be detected on the input side of the transformer at a predetermined cycle, and a resonance frequency detected by the resonance frequency detection unit. Characterized in that a drive frequency setting unit that sets the number.

  In this configuration, an insulation type piezoelectric transformer is used, but the characteristics of the piezoelectric transformer change due to self-heating caused by driving. For this reason, if the resonance frequency of the first resonance circuit and the second resonance circuit is set to the drive frequency, an efficient power supply device can be realized. However, as the power supply device is continuously driven, the resonance frequency shifts and the characteristics are increased. Deteriorates. In the configuration according to the present invention, the resonance frequency of the piezoelectric transformer is periodically detected and the resonance frequency is set as the drive frequency, so that it is possible to always control the power supply device at the optimum operating point (drive frequency). In addition, since the periodic resonance frequency is detected on the input side of the piezoelectric transformer, feedback control from the output side to the input side of the insulation-side piezoelectric transformer is not required, so that the circuit configuration is not complicated. .

  The resonance frequency detection unit preferably lengthens the predetermined period as the amount of change in the resonance frequency detected at different timings decreases.

  In this configuration, if the amount of change in the resonance frequency is small, the period of the resonance frequency detection process is lengthened. Thereby, the influence by the unnecessary noise which arises by sweeping a frequency (sweep) can be prevented.

  A current detection unit configured to detect a current flowing through the inverter circuit, wherein the resonance frequency detection unit detects the resonance frequency based on a frequency characteristic of a current value detected by the current detection unit when the drive frequency is swept; It is preferable to do.

  In this configuration, since the resonance frequency is detected by detecting the current flowing through the inverter circuit, the resonance frequency can be detected without directly monitoring the state of the piezoelectric transformer.

  An output power detection unit that outputs an AC voltage boosted or lowered by the piezoelectric transformer to a constant resistance load and detects output power of the inverter circuit, and the first resonance circuit and the second resonance according to output power A storage unit that stores a detection condition of a resonance frequency of the circuit, wherein the resonance frequency detection unit acquires a detection condition according to the output power detected by the power detection unit from the storage unit, and acquires the detection condition Preferably, the resonance frequency is detected based on the frequency characteristics of the current value detected by the current detection unit when the drive frequency is swept.

  Since the frequency characteristic of the current value detected by the current detection unit varies depending on the output power of the inverter circuit, the detection condition of the resonance frequency corresponding to the output power of the inverter circuit is stored in advance as in the above configuration. Thus, even if the output power of the inverter circuit changes, an appropriate resonance frequency can be easily detected without directly monitoring the piezoelectric transformer.

  The piezoelectric transformer outputs an AC voltage stepped up or down to a constant resistance load, and the resonance frequency detector resonates based on a minimum value of the current value detected by the current detector when the drive frequency is swept. It is preferable to detect the frequency.

  In this configuration, an appropriate resonance frequency can be easily detected without directly monitoring the piezoelectric transformer.

  According to the present invention, since the resonance frequency of the piezoelectric transformer is periodically detected and the resonance frequency is set as the drive frequency, the power supply apparatus is always controlled at the optimum operating point (drive frequency) even when the resonance frequency is shifted. can do. In addition, since the periodic resonance frequency is detected on the input side of the piezoelectric transformer, feedback control from the output side to the input side of the insulation-side piezoelectric transformer is not required, so that the circuit configuration is not complicated. .

Circuit diagram of power supply apparatus according to Embodiment 1 The figure which shows the equivalent circuit of FIG. The figure which shows the connection structure of the piezoelectric transformer shown in FIG. Perspective view of piezoelectric transformer Sectional view taken along line VV in FIG. Sectional view taken along line VI-VI in FIG. Functional block diagram of control circuit The figure which shows the frequency characteristic of input electric current IDC The figure which shows the power conversion efficiency to the change of the drive frequency of the inverter circuit The figure which shows the input current IDC with respect to the change of the gate signal width of an inverter circuit The figure which shows the power conversion efficiency with respect to the change of the gate signal width of the inverter circuit The flowchart which shows the process which a control part performs Flow chart showing drive frequency setting process Circuit diagram of another example of a power supply Circuit diagram of power supply device according to Embodiment 2 Functional block diagram of control circuit The figure which shows the frequency characteristic of input electric current IDC The figure which shows the transformation ratio with respect to the change of the frequency of the output voltage from an inverter circuit when it is a constant resistance load. 7 is a flowchart showing drive frequency setting processing according to the second embodiment.

(Embodiment 1)
FIG. 1 is a circuit diagram of a power supply device according to the first embodiment. FIG. 2 is a diagram showing an equivalent circuit of FIG.

  In the power supply device 1 according to the present embodiment, the commercial power supply 101 is connected to the input terminals Pi1 and Pi2, and the constant power load RL1 is connected to the output terminals Po1 and Po2. The power supply device 1 receives an AC voltage (for example, 100 to 240 V) from the commercial power supply 101, converts the AC voltage to a DC voltage (for example, 19 V), and outputs the DC voltage to the constant power load RL1. Examples of the constant power load RL1 include a secondary battery such as a mobile phone or a personal computer.

  The power supply device 1 includes a diode bridge circuit DB including four diodes and a smoothing capacitor C1. The diode bridge circuit DB performs full-wave rectification on the AC voltage input from the commercial power supply 101.

  In FIG. 1, the power supply device 1 is configured to include the diode bridge circuit DB and the smoothing capacitor C1, but may not include these. That is, when a DC voltage output from a battery, a DC-DC converter, or the like is input to the power supply device 1, the diode bridge circuit DB and the smoothing capacitor C1 are unnecessary.

  The power supply device 1 includes an inverter circuit 11. The inverter circuit 11 includes MOS-FET switching elements Q1, Q2, Q3, and Q4. In the inverter circuit 11, the switch elements Q1 and Q2 are connected in series, and the switch elements Q3 and Q4 are connected in series. A connection point between the switch elements Q1 and Q2 and a connection point between the switch elements Q3 and Q4 are connected to an input terminal of a parallel resonance circuit 14 described later.

  Each switch element Q1, Q2, Q3, Q4 of the inverter circuit 11 is driven by the pulse signal generation circuit 12. In FIG. 2, the pulse signal generation circuit 12 is not shown. The pulse signal generation circuit 12 alternately inputs signals to the gates of the switch elements Q1 and Q4 and the switch elements Q2 and Q3, and alternately turns on and off the switch elements Q1 and Q4 and the switch elements Q2 and Q3. Thereby, the inverter circuit 11 converts a DC voltage into an AC voltage.

  The pulse signal generation circuit 12 generates a pulse signal input to the gates of the switch elements Q1, Q2, Q3, and Q4. The pulse signal generation circuit 12 generates a pulse signal having a frequency based on a command from the control circuit 13.

  The power supply device 1 includes a control circuit 13 (not shown in FIG. 2). The control circuit 13 causes the pulse signal generation circuit 12 to generate a pulse signal having a predetermined frequency. The control circuit 13 will be described in detail later.

  The parallel resonance circuit 14 has an input terminal connected to a connection point between the switch elements Q1 and Q2 and a connection point between the switch elements Q3 and Q4. The parallel resonance circuit 14 includes a capacitor C2 and an inductor L1 that are connected in parallel. In the present embodiment, the parallel resonance circuit 14 is set so that the resonance frequency is about 472 kHz. The parallel resonance circuit 14 corresponds to a “first resonance circuit” according to the present invention.

  A piezoelectric transformer 15 is connected to the parallel resonant circuit 14 via capacitors C31 and C32. The piezoelectric transformer 15 shown in FIG. 1 is illustrated in a simplified manner, and the detailed structure will be described later. The piezoelectric transformer 15 is an insulating type and has input electrodes E1 and E2 and output electrodes E3 and E4. The input electrode E1 is connected to one end of the parallel resonant circuit 14 via a capacitor C31, and the input electrode E2 is connected to the other end of the parallel resonant circuit 14 via a capacitor C32. The output electrodes E3 and E4 are connected to the rectifying / smoothing circuit 16. The piezoelectric transformer 15 steps down the voltage input from the input electrodes E1 and E2 and outputs it from the output electrodes E3 and E4.

  The capacitors C31 and C32 are elements for limiting the input current to the piezoelectric transformer 15. If the current flowing through the piezoelectric transformer 15 becomes excessive, an abnormal operation may occur. Therefore, the capacitors C31 and C32 are provided to limit the current so that the piezoelectric transformer 15 operates normally. Capacitors C31 and C32 have the same capacitance, and preferably have a larger capacitance than capacitor C41, which is an equivalent input capacitance of piezoelectric transformer 15. If the input current to the piezoelectric transformer 15 is small and there is no possibility of being excessive, the capacitors C31 and C32 are not necessarily required, and the parallel resonant circuit 14 and the piezoelectric transformer 15 may be directly connected. An inductor may be provided in place of the capacitors C31 and C32.

  As shown in FIG. 2, the piezoelectric transformer 15 is equivalently represented by capacitors C41 and C42, a capacitor Cp, an inductor Lp, a resistor Rp, an ideal transformer Ts, and the like. The capacitor C41 is an equivalent input capacity of the piezoelectric transformer 15, and the capacitor C42 is an equivalent output capacity of the piezoelectric transformer 15. The capacitor Cp and the inductor Lp are parameters representing electromechanical coupling.

  The resonance frequency of the piezoelectric transformer 15 is determined mainly by the resonance of the series resonance circuit 151 by the capacitor Cp and the inductor Lp. Since electrical energy conversion is via elastic vibration, it has a natural resonance frequency determined by the elastic wave propagation velocity and dimensions of the piezoelectric ceramic. The circuit constants are set so that the series resonant circuit 151 and the parallel resonant circuit 14 of the piezoelectric transformer 15 have the same resonant frequency.

  An inductor L 2 is connected to the output side of the piezoelectric transformer 15, and this inductor L 2 constitutes a parallel resonance circuit 152 together with a capacitor C 42 that is an equivalent output capacity of the piezoelectric transformer 15. The inductor L2 has a circuit constant set so that the parallel resonant circuit 152 has the same resonance frequency as the parallel resonant circuit 14 and the series resonant circuit 151. The parallel resonance circuit 152 corresponds to a “second resonance circuit” according to the present invention.

  The piezoelectric transformer 15 self-heats with driving, and the temperature rises with time. This heat generation affects the constant of each element that is equivalently expressed, such as the capacitor Cp of the piezoelectric transformer 15. In the present embodiment, in a state where the piezoelectric transformer 15 is not generating heat (that is, in a state where the piezoelectric transformer 15 is cooled), the series resonant circuit 151 and the parallel resonant circuit 152 have circuit constants so that the resonant frequencies are the same. Is set.

  The voltage stepped down by the piezoelectric transformer 15 is output to the rectifying and smoothing circuit 16. The rectifying / smoothing circuit 16 includes a smoothing circuit including a capacitor and an inductor, and a diode bridge. The rectifying / smoothing circuit 16 rectifies and smoothes the AC voltage and outputs it to the constant power load RL1. The rectifying / smoothing circuit 16 may be connected to a DC-DC converter that converts the voltage into a predetermined value and outputs the voltage.

  Hereinafter, the piezoelectric transformer 15 will be described in detail.

  FIG. 3 is a diagram showing a connection configuration of the piezoelectric transformer 15 shown in FIG. FIG. 4 is a perspective view of the piezoelectric transformer 15. 5 is a cross-sectional view taken along line VV in FIG. 6 is a cross-sectional view taken along line VI-VI in FIG.

  The piezoelectric transformer 15 includes a rectangular plate-shaped piezoelectric plate 30. The piezoelectric plate 30 is formed by stacking, for example, PZT ceramic sheets. Hereinafter, the length direction of the piezoelectric transformer 15 is defined as the X-axis direction, the width direction is defined as the Y-axis direction, and the thickness direction is defined as the Z-axis direction.

  The piezoelectric transformer 15 is assumed to vibrate in the length direction in the (7λ / 2) resonance mode. Here, λ is one wavelength of vibration in the length direction. Therefore, the length of the piezoelectric transformer 15 in the X-axis direction is (7λ / 2). Here, the width in the Y-axis direction and the thickness in the Z-axis direction are preferably less than (λ / 2). By doing so, the vibration in the width direction and the thickness direction is not coupled with the vibration in the length direction, and the vibration of the entire piezoelectric transformer 15 is not unstable.

  The piezoelectric plate 30 includes a first low voltage region 31, a first high voltage region 32, a second high voltage region 33, a second low voltage region 34, a third high voltage region 35, a fourth, along the X-axis direction. A high voltage region 36 and a third low voltage region 37 are formed. The lengths of the regions 31 to 37 in the X-axis direction are all λ / 2.

  In FIG. 3, the polarization direction of each area | region 31-37 is shown. The first low voltage region 31, the second low voltage region 34, and the third low voltage region 37 are polarized in the Z-axis direction (thickness direction). The first low voltage region 31 and the third low voltage region 37 are polarized in the same direction, and the second low voltage region 34 is polarized in the opposite direction to the first low voltage region 31 and the third low voltage region 37. . Examples of the polarization treatment method include a method of applying a voltage of 2 kV / mm to the piezoelectric plate in insulating oil at 170 ° C.

  In the first low voltage region 31, a pair of first output electrodes E31 and E32 are provided on the side surface of the piezoelectric plate 30 so as to face each other in the Y-axis direction. The first low voltage region 31 is provided with a plurality of internal electrodes E33 stacked in the Z-axis direction. As shown in FIG. 6, the internal electrodes E33 are alternately connected to the first output electrodes E31 and E32.

  Similarly, in the second low voltage region 34 and the third low voltage region 37, the pair of second output electrodes E41 and E42 and the third output electrodes E51 and E52 are arranged so as to face each other in the Y-axis direction. It is provided on the side surface of the plate 30. The second low voltage region 34 and the third low voltage region 37 are provided with a plurality of internal electrodes E43 and E53 stacked in the Z-axis direction. The internal electrodes E43 are alternately connected to the second output electrodes E41 and E42, and the internal electrodes E53 are alternately connected to the third output electrodes E51 and E52.

  The first high voltage region 32, the second high voltage region 33, the third high voltage region 35, and the fourth high voltage region 36 are polarized in the X-axis direction. In the first high voltage region 32, a pair of second input electrodes E21 and E22 are provided on the side surface of the piezoelectric plate 30 so as to face each other in the Y-axis direction. The first high voltage region 32 is provided with a plurality of internal electrodes E23 stacked in the Z-axis direction. The internal electrode E23 is connected to each of the second input electrodes E21 and E22.

  In the fourth high voltage region 36, a pair of first input electrodes E11 and E12 are provided on the side surface of the piezoelectric plate 30 so as to face each other in the Y-axis direction. The fourth high voltage region 36 is provided with a plurality of internal electrodes E13 stacked in the Z-axis direction. The internal electrode E13 is connected to each of the first input electrodes E11 and E12.

  In the piezoelectric transformer 15 configured as described above, the first input electrodes E11 and E12 correspond to the input electrode E1 shown in FIG. The second input electrodes E21 and E22 correspond to the input electrode E2 shown in FIG. The first input electrodes E11 and E12 are connected to the parallel resonant circuit 14 via the capacitor C31, and the second input electrodes E21 and E22 are connected to the parallel resonant circuit 14 via the capacitor C31.

  The first output electrode E31, the second output electrode E41, and the third output electrode E51 correspond to the output electrode E3 shown in FIG. The first output electrode E32, the second output electrode E42, and the third output electrode E52 correspond to the output electrode E4 shown in FIG. The first output electrode E31, the second output electrode E41, the third output electrode E51, and the first output electrode E32, the second output electrode E42, and the third output electrode E52 are connected to the rectifying and smoothing circuit 16. .

  When a voltage is applied to the first input electrodes E11, E12 and the second input electrodes E21, E22, a voltage is applied in the X-axis direction (length direction) of the piezoelectric plate 30. Therefore, an electric field is applied to the first high voltage region 32, the second high voltage region 33, the third high voltage region 35, and the fourth high voltage region 36 in the polarization direction. The longitudinal vibration is excited in the direction along the polarization direction by the inverse piezoelectric effect, that is, in the X-axis direction of the piezoelectric plate 30.

  When longitudinal vibration is excited, mechanical distortion occurs in the Z-axis direction (polarization direction) in the first low-voltage region 31, the second low-voltage region 34, and the third low-voltage region 37, and in the polarization direction due to the piezoelectric transverse effect. A potential difference occurs. Due to this potential difference, the low voltages extracted from the first low voltage region 31, the second low voltage region 34, and the third low voltage region 37 are combined in parallel and applied to the constant power load RL1.

  FIG. 7 is a functional block diagram of the control circuit 13. The control circuit 13 includes a microcomputer and has functions of an IDC detection unit 131, a frequency control unit 132, a control unit 133, and the like.

  The IDC detection unit 131 detects the input current IDC. Specifically, a current detection resistor R1 is connected between the diode bridge circuit DB and the inverter circuit 11, and the IDC detection unit 131 detects the input current IDC flowing in the inverter circuit 11 by the voltage drop of the resistor R1. To do. The IDC detection unit 131 corresponds to a “current detection unit” according to the present invention.

  The frequency control unit 132 outputs a control signal to the pulse signal generation circuit 12 so that the inverter circuit 11 is driven at a predetermined drive frequency. The pulse signal generation circuit 12 generates a pulse signal having a frequency corresponding to the input control signal and drives the inverter circuit 11. The frequency control unit 132 sweeps (sweeps) the frequency at which the pulse signal generation circuit 12 controls the drive of the inverter circuit 11. For example, when the pulse signal generation circuit 12 drives the inverter circuit 11 at a frequency of 470 kHz, the frequency ranges of 468, 469, 470, 471, 472 kHz and 470 ± 2 kHz are swept in increments of 1 kHz.

  The control unit 133 controls operations of the IDC detection unit 131 and the frequency control unit 132. The control unit 133 sets the frequency for driving the inverter circuit 11 based on the frequency characteristics of the input current IDC detected by the IDC detection unit 131 when the frequency control unit 132 performs frequency sweep. The control unit 133 corresponds to a “resonance frequency detection unit” and a “drive frequency setting unit” according to the present invention.

  FIG. 8 is a diagram illustrating frequency characteristics of the input current IDC. In FIG. 8, the horizontal axis represents the drive frequency of the inverter circuit 11, and the vertical axis represents the input current IDC. As shown in FIG. 8, the input current IDC has a minimum value in the vicinity of the resonance frequency of about 472 kHz.

  The control unit 133 sets the frequency (about 472 kHz) at which the input current IDC takes the minimum value as the drive frequency of the inverter circuit 11 from the frequency characteristics of the input current IDC. Then, the frequency control unit 132 outputs a control signal to the pulse signal generation circuit 12 so that the pulse signal generation circuit 12 drives the inverter circuit 11 at the drive frequency.

  FIG. 9 is a diagram illustrating the power conversion efficiency with respect to a change in the drive frequency of the inverter circuit 11. The horizontal axis in FIG. 9 is the drive frequency of the inverter circuit 11, and the vertical axis is the power conversion efficiency. The drive frequency of the inverter circuit 11 is the drive frequency of the switch elements Q1 to Q4 of the inverter circuit 11. The power conversion efficiency is the conversion efficiency between the input terminals Pi1, Pi2 and the output terminals Po1, Po2. From FIG. 9, it can be seen that the power conversion efficiency is maximum at a resonance frequency of about 472 kHz.

  Note that the pulse signal generation circuit 12 may drive and control the inverter circuit 11 by changing the pulse width of the output pulse signal (the gate signal width of the inverter circuit 11).

  FIG. 10 is a diagram illustrating the input current IDC with respect to the change in the gate signal width of the inverter circuit. The horizontal axis of FIG. 10 is the ratio of the gate signal width of the inverter circuit 11, that is, the ratio of the time during which the gate signal is ON in one period when one period of the gate signal of the inverter circuit is 1. The axis is the input current IDC. As shown in FIG. 10, the input current IDC has a minimum value when the gate signal width is about 0.42.

  From the frequency characteristic of the input current IDC, the control circuit 17 generates a pulse signal so that the pulse signal generation circuit 12 controls the inverter circuit 11 with a gate signal width (about 0.42) when the input current IDC takes a minimum value. A control signal is output to the circuit 12.

  FIG. 11 is a diagram illustrating the power conversion efficiency with respect to a change in the gate signal width of the inverter circuit 11. The horizontal axis of FIG. 11 is the gate signal width of the inverter circuit 11, and the vertical axis is the power conversion efficiency. It can be seen from FIG. 11 that the power conversion efficiency is maximum when the gate signal width is about 0.42.

  As described above, the piezoelectric transformer 15 self-heats with driving and the resonance condition is shifted. For this reason, with the passage of time, the resonance frequency shifts from the drive frequency, and the conversion efficiency between the input terminals Pi1, Pi2 and the output terminals Po1, Po2 decreases. Therefore, in this embodiment, the resonance frequency is periodically detected and the drive frequency is corrected as needed. Thereby, the power supply device 1 is always controlled at the optimum driving frequency. In addition, since the resonance frequency is detected by a circuit unit before the piezoelectric transformer 15, a so-called feedback control in which the result of direct monitoring of the piezoelectric transformer 15 or the result of detection on the output side of the piezoelectric transformer 15 is fed back to the input side. Therefore, the circuit configuration is not complicated.

  Below, the setting method of a drive frequency is demonstrated.

  FIG. 12 is a flowchart illustrating processing executed by the control unit 133. The process illustrated in FIG. 12 is started, for example, when the commercial power supply 101 and the constant power load RL1 are connected to the power supply device 1.

  The control unit 133 executes the drive frequency setting process shown in FIG. 13 (S1). FIG. 13 is a flowchart showing the drive frequency setting process. The frequency control unit 132 controls each switch element Q1 to Q4 of the inverter circuit 11 and sweeps the frequency of the output voltage of the inverter circuit 11 (S11). For example, when the current frequency is 470 kHz, sweeping is performed in increments of 1 kHz from 468 kHz to 472 kHz, 468, 469, 470, 471, 472 kHz.

  Each time the frequency control unit 132 performs a frequency sweep, the IDC detection unit 131 detects the input current IDC, and the control unit 133 acquires the frequency characteristics of the input current IDC (S12). The control unit 132 detects the input current IDC, and acquires the frequency at which the input current IDC takes a minimum value. And the control part 132 sets the acquired frequency to the drive frequency of the inverter circuit 11 (S13).

  When the inverter circuit 11 is driven by changing the pulse width of the pulse signal, the pulse signal width when the input current IDC takes the minimum value in the processing shown in FIG. 13 by sweeping (sweeping) the pulse signal width. And the inverter circuit 11 is driven with the pulse signal width.

  Returning to FIG. 12, the control unit 133 determines whether or not to end the process (S2). For example, when the power supply device 1 is disconnected from the commercial power supply 101 or the constant power load RL1, or when the remote signal becomes invalid, the processing in FIG. 12 ends. Alternatively, when the commercial power supply 101 or the constant power load RL1 is disconnected from the power supply device 1 during the execution of the process of FIG. 12, this process may be forcibly terminated.

  Next, the control unit 133 determines whether or not the time T has elapsed since the drive frequency was set (S3). This time T can be appropriately changed, for example, 10 s. When the time T has not elapsed (S3: NO), the control unit 133 executes the process of S2. When the time T has elapsed (S3: YES), the control unit 133 executes a drive frequency setting process (S4). This drive frequency setting process is the process shown in FIG. Thus, in the present embodiment, the drive frequency is set every time T.

  When the piezoelectric transformer 15 is continuously driven, the piezoelectric transformer 15 self-heats with time, and the resonance frequency fluctuates due to the influence. For this reason, when the piezoelectric transformer 15 is continuously driven at the same drive frequency even if time elapses, the efficiency of power supply to the constant power load RL1 decreases. Therefore, the drive frequency is reset (corrected) every time T. Thereby, even if the resonance frequency of the piezoelectric transformer 15 shifts, the drive frequency is reset according to the shift, so that it is possible to continue supplying power to the constant power load RL1 efficiently.

  After resetting the drive frequency, the control unit 133 determines the voltage value obtained by the product of the value of the input current IDC before resetting the drive frequency and the resistance value of the detection resistor R1, and the value of the input current IDC after reset. It is determined whether or not the difference from the voltage value obtained by the product of the resistance value of the detection resistor R1 is equal to or greater than a threshold value (for example, 50 mV) (S5). If it is equal to or greater than the threshold value (S5: YES), the control unit 133 executes the process of S2. When it is not more than a threshold value (S5: NO), the control part 133 sets T to T + (DELTA) t (S6). That is, when it is determined that the change in the resonance frequency detected periodically is small, the period for performing the drive frequency setting process is lengthened. Thereby, generation | occurrence | production of the unnecessary noise by performing a drive frequency setting process frequently can be prevented.

  In addition, when the change of the resonance frequency detected periodically is small, the detection period of the resonance frequency is lengthened, but the change of the resonance frequency detected periodically becomes large again, and the difference between the voltage values is a threshold value. When it becomes above, you may make it shorten a detection period.

  As described above, in this embodiment, since the resonance frequency, that is, the drive frequency is shifted due to self-heating of the piezoelectric transformer 15, the resonance frequency is periodically detected and the drive frequency is reset, so that the resonance frequency is reset. It is possible to suppress a decrease in power conversion efficiency due to the deviation. Further, since the resonance frequency is detected from the input current IDC, it is not necessary to monitor the piezoelectric transformer 15 directly. For this reason, control is easy and the circuit is not complicated.

  In the present embodiment, the piezoelectric transformer 15 has been described as a step-down transformer, but may be a step-up transformer. In this case, the connection configuration of the piezoelectric transformer 15 is different from that of the present embodiment. Specifically, in FIG. 3, the first output electrodes E31, E32 and the third output electrodes E51, E52 are connected to the parallel resonant circuit 14 via the capacitor C31, and the second output electrodes E41, E42 are connected to the capacitor C32. To the parallel resonant circuit 14. The first input electrode E11 and the second input electrode E21, and the first input electrode E12 and the second input electrode E22 are connected to the rectifying and smoothing circuit 16. When a voltage is applied to the first output electrodes E31, E32, the second output electrodes E41, E42, and the third output electrodes E51, E52, the first input electrode E11, the second input electrode E21, and the second input electrode E21. The low voltage is taken out from the second input electrode E22 and applied to the constant power load RL1.

  In this embodiment, the resonance frequency is detected from the input current IDC. However, the voltage output from the inverter circuit 11 and applied to the piezoelectric transformer 15 is detected, and the resonance frequency is detected from the voltage. Also good.

  Further, in the present embodiment, when setting the circuit constants so that the resonance frequencies are the same, the piezoelectric transformer 15 is not generating heat (that is, the piezoelectric transformer 15 is cooled). The circuit constants may be set in a state where the heat is generated in 15 (the temperature of the piezoelectric transformer 15 is increased).

  The power supply device 1 uses the parallel resonance circuits 14 and 152. When the power supply device 1 is a constant resistance load with little variation in the resistance value of the load, when the constant voltage is desired to be output, the parallel resonance circuits 14 and 152 are used. May be replaced with a series resonant circuit.

  FIG. 14 is a circuit diagram of another example of the power supply device 1. In FIG. 14, the diode bridge DB, the smoothing capacitor C1, the input terminals Pi1 and Pi2, the output terminals Po1 and Po2, and the like shown in FIGS. 1 and 2 are not shown.

  In this example, a series resonance circuit 18 is connected to the inverter circuit 11. The series resonance circuit 18 includes an inductor L3 and a capacitor C2. Further, an inductor L4 is connected to the output side of the piezoelectric transformer 15, and this inductor L4 constitutes a series resonance circuit 153 together with a capacitor C42 which is an equivalent output capacity of the piezoelectric transformer 15. The circuit constants of the series resonance circuit 18 and the series resonance circuit 153 are set so that the resonance frequency is the same as that of the series resonance circuit 151. In this configuration, the impedance of the inverter circuit 11 viewed from the series resonant circuit 18 side can be set to be inductive. For this reason, the power loss in the inverter circuit 11 can be reduced.

(Embodiment 2)
FIG. 15 is a circuit diagram of the power supply device according to the second embodiment. In the power supply device 2 according to the present embodiment, the commercial power supply 101 is connected to the input terminals Pi1 and Pi2, and the constant resistance load RL2 is connected to the output terminals Po1 and Po2. The constant resistance load RL2 includes, for example, an electric lamp. The basic configuration of the power supply device 2 is the same as that of the first embodiment. Hereinafter, only differences from the first embodiment will be described.

  The power supply device 2 includes a control circuit 17. Capacitors C41 and C42 are connected to the output side of the inverter circuit 11. The output voltage V1 of the inverter circuit 11 is divided by the capacitors C41 and C42. The control circuit 17 rectifies the capacity-divided AC voltage and detects the output voltage V1.

  Further, a resistor R2 for current detection is connected to the output side of the inverter circuit 11. The control circuit 17 detects the output current I1 of the inverter circuit 11, which is a current flowing through the resistor R2. The control circuit 17 acquires input power to the piezoelectric transformer 15 from the output current I1 and the output voltage V1.

  FIG. 16 is a functional block diagram of the control circuit 17. The control circuit 17 includes a microcomputer and has functions of an IDC detection unit 171, a power acquisition unit 172, a frequency control unit 173, a storage unit 174, a control unit 175, and the like.

  The IDC detection unit 171 detects the input current IDC, similarly to the IDC detection unit 131 of the first embodiment. The IDC detection unit 171 corresponds to a “current detection unit” according to the present invention.

  The power acquisition unit 172 acquires the output voltage V1 and the output current I1 of the inverter circuit 11, and acquires the input power to the piezoelectric transformer 15 from the voltage V1 and the current I1. The power acquisition unit 172 is an example of the “output power detection unit” according to the present invention.

  Note that the input power to the piezoelectric transformer 15 may be obtained from the input voltage to the inverter circuit 11 and the input voltage IDC detected by the IDC detection unit 171 and the input voltage.

  Similarly to the frequency control unit 132 of the first embodiment, the frequency control unit 173 outputs a control signal to the pulse signal generation circuit 12 so that the inverter circuit 11 is driven at a predetermined drive frequency. The pulse signal generation circuit 12 drives the inverter circuit 11 at a frequency corresponding to the input control signal. Further, the frequency control unit 173 sweeps (sweeps) the frequency at which the pulse signal generation circuit 12 drives the inverter circuit 11. For example, when the pulse signal generation circuit 12 drives the inverter circuit 11 at a frequency of 470 kHz, the frequency ranges of 468, 469, 470, 471, 472 kHz and 470 ± 2 kHz are swept in increments of 1 kHz.

  The storage unit 174 stores setting conditions (detection conditions) for setting the drive frequency. Specifically, the storage unit 174 stores a plurality of setting conditions according to the input power to the piezoelectric transformer 15. This setting condition is used when the control unit 175 sets the drive frequency from the frequency characteristic of the input current IDC.

  The control unit 175 controls the operations of the IDC detection unit 171, the power acquisition unit 172, and the frequency control unit 173. The control unit 175 sets the drive frequency based on the input current IDC detected by the IDC detection unit 171 when the frequency control unit 173 performs frequency sweep, that is, based on the frequency characteristics of the input current IDC.

  As shown in FIG. 17, the frequency characteristic of the input current IDC varies depending on the output power from the inverter circuit 11. FIG. 17 is a diagram illustrating frequency characteristics of the input current IDC. The horizontal axis in FIG. 17 is the drive frequency of the inverter circuit 11, and the vertical axis is the input current IDC. The four different plots show the characteristics when the value of the constant resistance load RL2 is changed. As shown in FIG. 17, the characteristic curve of the frequency characteristic varies depending on the size of the load.

  In the setting conditions stored in the storage unit 174, for example, it is determined whether to set the frequency that takes the maximum value of the characteristic curve of the obtained frequency characteristic as the driving frequency or to set the frequency that takes the minimum value as the driving frequency. It has been. The control unit 175 acquires the setting condition corresponding to the power acquired by the power acquisition unit 172 from the storage unit 174, and sets the drive frequency from the setting condition and the frequency characteristics of the input current IDC. Then, the frequency control unit 173 outputs a control signal to the pulse signal generation circuit 12 so that the pulse signal generation circuit 12 drives the inverter circuit 11 at the drive frequency. Thus, since the setting conditions corresponding to the output power from the inverter circuit 11 are stored in advance, even if the input power to the piezoelectric transformer 15 changes, an appropriate resonance frequency can be easily detected.

  The control unit 175 corresponds to a “resonance frequency detection unit” and a “drive frequency setting unit” according to the present invention.

  FIG. 18 shows the transformation ratio with respect to the change in the frequency of the output voltage from the inverter circuit 11, that is, the change in the ratio between the output voltage Vout of the piezoelectric transformer 15 and the output voltage V1 of the inverter circuit when the value of the constant resistance load RL2 is different. FIG. The horizontal axis in FIG. 18 is the frequency, and the vertical axis is the transformation ratio. The four different plots show the frequency characteristics of the transformation ratio when the value of the constant resistance load RL2 is different. From FIG. 18, it can be seen that in the vicinity of the resonance frequency of about 470 kHz, the transformation ratio is constant regardless of the value of the constant resistance load RL2, that is, the output voltage is constant if V1 is constant.

  Below, the setting method of the drive frequency in the power supply device 2 which concerns on this embodiment is demonstrated. The driving frequency setting method is different from the first embodiment in the driving frequency setting process shown in FIG. 13 described in the first embodiment.

  FIG. 19 is a flowchart illustrating a drive frequency setting process according to the second embodiment.

  The control unit 175 controls the pulse signal generation circuit 12 that controls the switch elements Q1 to Q4 of the inverter circuit 11, and sweeps the drive frequency of the inverter circuit 11 (S21). For example, when the current frequency is 470 kHz, sweeping is performed in increments of 1 kHz from 468 kHz to 472 kHz, 468, 469, 470, 471, 472 kHz.

  Each time the frequency control unit 173 performs a frequency sweep, the IDC detection unit 171 detects the input current IDC, and the control unit 175 acquires the frequency characteristics of the input current IDC (S22). The control unit 175 acquires the input power to the piezoelectric transformer 15 from the output voltage V1 from the inverter circuit 11 and the output current I1 from the inverter circuit 11 (S23). The control unit 175 acquires a setting condition opposite to the input power from the storage unit 174 (S24). The control unit 175 sets the drive frequency from the frequency characteristic acquired in S22 and the setting condition acquired in S24 (S25).

  The frequency characteristic of the input current IDC varies depending on the output power from the inverter circuit 11. For this reason, the resonance frequency is detected according to the setting condition corresponding to the output power from the inverter circuit 11, and the detected resonance frequency is set as the drive frequency. For example, in the frequency characteristic shown in FIG. 17, when the frequency characteristic obtained by detection is the characteristic curve RC1, and the acquired setting condition is a condition that the maximum value of the obtained frequency is set as the drive frequency, The maximum value of the characteristic curve RC1 shown in FIG. 17, that is, the frequency of 470 kHz is set as the drive frequency. Further, when the frequency characteristic obtained by the detection is the characteristic curve RC2, and the acquired setting condition is a condition that the minimum value of the obtained frequency is set as the drive frequency, the minimum of the characteristic curve RC2 shown in FIG. A value, that is, a frequency of 470 kHz is set as a driving frequency.

  Note that other processes executed by the control unit 175 are the same as those in the first embodiment, and thus the description thereof is omitted.

  As described above, in this embodiment, since the resonance frequency, that is, the drive frequency is shifted due to self-heating of the piezoelectric transformer 15, the resonance frequency is periodically detected and the drive frequency is reset, so that the resonance frequency is reset. It is possible to suppress a decrease in power conversion efficiency due to the deviation. Further, since the resonance frequency is detected from the input current IDC, it is not necessary to monitor the piezoelectric transformer 15 directly. For this reason, control is easy and the circuit is not complicated.

DESCRIPTION OF SYMBOLS 1, 2 ... Power supply device 11 ... Inverter circuit 12 ... Pulse signal generation circuit 13 ... Control circuit 14 ... Parallel resonance circuit 15 ... Piezoelectric transformer 16 ... Rectification smoothing circuit 18 ... Series resonance circuit 30 ... Piezoelectric board 31 ... First low voltage Region 32 ... First high voltage region 33 ... Second high voltage region 34 ... Second low voltage region 35 ... Third high voltage region 36 ... Fourth high voltage region 37 ... Third low voltage region 101 ... Commercial power supply 131 ... IDC Detection unit 132 ... frequency control unit 133 ... control unit 151 ... series resonance circuit 152 ... parallel resonance circuit 153 ... series resonance circuit 171 ... IDC detection unit 172 ... power acquisition unit 173 ... frequency control unit 174 ... storage unit 175 ... control unit C1 ... smoothing capacitor C2 ... capacitors C31 and C32 ... capacitors C41 and C42 ... capacitor Cp ... capacitor DB ... diode bridge circuit E1 ... input electrode E1 , E12 ... first input electrodes E13, E23, E33, E43 ... internal electrodes E2 ... input electrodes E21, E22 ... second input electrodes E3 ... output electrodes E31, E32 ... first output electrodes E4 ... output electrodes E41, E42 ... first 2 output electrodes E51, E52 ... 3rd output electrode E53 ... internal electrodes L1, L2, Lp ... inductors Pi1, Pi2 ... input terminals Po1, Po2 ... output terminals Q1, Q2, Q3, Q4 ... switch elements R1, R2, Rp ... Resistor RL1 ... Constant power load RL2 ... Constant resistance load

Claims (5)

An inverter circuit for converting a DC voltage into an AC voltage;
A pulse signal generation circuit for driving the inverter circuit at a set drive frequency;
An insulating piezoelectric transformer that boosts or lowers the AC voltage output from the inverter circuit;
A first resonant circuit connected between the inverter circuit and the piezoelectric transformer;
A second resonance circuit including the piezoelectric transformer and an element connected to the output side of the piezoelectric transformer, and having the same resonance frequency as the first resonance circuit;
Resonance that sweeps the drive frequency and detects the resonance frequency of the piezoelectric transformer caused by the first resonance circuit and the second resonance circuit on the input side of the piezoelectric transformer at a predetermined period. A frequency detector;
A drive frequency setting unit for setting the resonance frequency detected by the resonance frequency detection unit to the drive frequency;
Power supply unit with The resonance frequency detector is
As the amount of change in the resonance frequency detected at different timings becomes smaller, the predetermined period is lengthened.
The power supply device according to claim 1. A current detection unit for detecting a current flowing in the inverter circuit;
The resonance frequency detection unit detects the resonance frequency based on a frequency characteristic of a current value detected by the current detection unit when the drive frequency is swept.
The power supply device according to claim 1 or 2. Output the AC voltage boosted or stepped down by the piezoelectric transformer to a constant resistance load,
An output power detector for detecting output power of the inverter circuit;
A storage unit for storing a detection condition of a resonance frequency of the first resonance circuit and the second resonance circuit according to output power;
With
The resonance frequency detector is
The detection condition according to the output power detected by the output power detection unit is acquired from the storage unit, the acquired detection condition, and the frequency characteristic of the current value detected by the current detection unit when the drive frequency is swept To detect the resonant frequency based on
The power supply device according to claim 3. Output the AC voltage boosted or stepped down by the piezoelectric transformer to a constant power load,
The resonance frequency detector is
Based on the minimum value of the current value detected by the current detection unit when the drive frequency is swept, the resonance frequency is detected.
The power supply device according to claim 3.

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