JP2010011606A - Power supply circuit using piezoelectric transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply circuit which can simplify its circuit constitution, with its parts count small. <P>SOLUTION: This power unit includes a piezoelectric transformer 30, a piezoelectric transformer driving circuit part 10, which has a switching element Q1 and drives a piezoelectric transformer 30 by applying a voltage to the piezoelectric transformer 30, and a digital signal processor DSP, which outputs a drive signal for driving the switching element Q1. The piezoelectric transformer 30 includes a detecting electrode 34, which outputs an AC voltage of frequency conforming to the natural resonance frequency of the piezoelectric transformer 30. The digital signal processor DSP computes the frequency of a detected voltage outputted from the detecting electrode 34, and generates a drive signal so that an outputted drive signal may come close to computed frequency. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power supply circuit using a piezoelectric transformer that includes a piezoelectric transformer and boosts and outputs a DC voltage.

  2. Description of the Related Art Conventionally, a power supply circuit that boosts a DC voltage using a piezoelectric transformer has been used in high voltage, low current load applications such as discharge lamps and electrostatic atomizers.

  As this type of power supply circuit, there is one in which a discharge lamp as a load 70 is connected to the secondary electrode 33 of the piezoelectric transformer 30 as shown in FIG. 9 (see Patent Document 1). In this power supply circuit, a pair of primary electrodes provided on the piezoelectric transformer 30 is connected by connecting a pair of series circuits of inductors L2, L3 and switching elements Q2, Q3 via switching element Q4 between both ends of DC power supply E. One of 32 is connected to a connection point between the inductor L2 and the switching element Q2, and the other is connected to a connection point between the inductor L3 and the switching element Q3.

  Each of the switching elements Q2 and Q3 is alternately turned on and off by a drive circuit unit 91 including a transmitter OSC that outputs a triangular wave with a constant frequency and a frequency dividing circuit composed of two flip-flops FF1 and FF2.

  Further, since the load 70 is a discharge lamp, in order to keep the luminance constant, a configuration is adopted in which the lamp current is detected by the current detection circuit 92 and the time ratio (on duty) of the switching element Q4 is feedback controlled. . That is, the on-duty of the switching element Q4 is controlled by comparing the voltage corresponding to the lamp current detected by the current detection circuit 92 with the triangular wave output from the oscillator OSC by the comparator CP1.

  In the configuration shown in FIG. 9, since the frequency of the voltage applied to the piezoelectric transformer 30 is fixedly determined by the output frequency of the oscillator OSC, the resonance frequency of the piezoelectric transformer due to variations in the resonance frequency of the piezoelectric transformer 30 and the environmental temperature. In some cases, the piezoelectric transformer cannot be driven at a frequency at which the conversion efficiency is maximized due to a change in current.

  The basic configuration of the power supply circuit shown in FIG. 10 is the same as that of the power supply circuit shown in FIG. 9, except that a variable oscillation circuit OSC ′ whose output frequency is variable is used instead of the oscillator OSC whose output frequency is fixed. Is different. The output frequency of the variable oscillation circuit OSC ′ is adjusted according to the output of the phase detection circuit 93 that detects the phase difference between the voltage applied to the piezoelectric transformer 30 and the lamp current of the discharge lamp as the load 70. That is, the output frequency of the variable oscillation circuit OSC ′ is controlled so that the phase difference is within the set range (see Patent Document 2).

  The output of the variable oscillation circuit OSC 'is applied to the primary electrode 32 of the piezoelectric transformer 30 through the waveform shaping circuit 10a and the drive circuit 10b after the pulse width is adjusted by the pulse width variable circuit 95. The waveform shaping circuit 10 a has a function of removing high frequency components from the voltage applied to the piezoelectric transformer 30, and the drive circuit 10 b has a function of raising the output of the waveform shaping circuit 10 a to the drive level of the piezoelectric transformer 30. That is, it corresponds to the inductors L2 and L3 and the switching elements Q2 and Q3 in the power supply circuit shown in FIG.

  The lamp current of the load 70 is detected by the current detection circuit 92, and the output of the current detection circuit 92 is input to the pulse width control circuit 94. The pulse width control circuit 94 instructs the pulse width variable circuit 95 to keep the lamp current constant. That is, the pulse width control circuit 94 and the pulse width variable circuit 95 have functions corresponding to the comparator CP1 and the switching element Q4 in the power supply circuit shown in FIG.

  The configuration shown in FIG. 10 makes the frequency of the voltage applied to the primary side electrode 32 of the piezoelectric transformer 30 variable, and sets the phase difference between the voltage applied to the primary side of the piezoelectric transformer 30 and the current on the secondary side. Since the frequency is controlled so as to keep the range, the piezoelectric transformer 30 can be used in a region where the conversion efficiency is high by appropriately selecting the phase difference.

  However, in the configuration of Patent Document 2, since the output frequency of the variable oscillation circuit OSC ′ is determined using information including not only the piezoelectric transformer 30 but also the load 70, the piezoelectric transformer 30 depends on the operating state of the load 70. However, it is not always possible to obtain a drive frequency that maximizes the conversion efficiency.

  As a power supply circuit for solving this type of problem, in order to apply a voltage of the natural resonance frequency of the piezoelectric transformer 30 to the primary electrode 32 of the piezoelectric transformer 30, as shown in FIG. In addition to the side electrode 32 and the secondary electrode 33, a detection electrode (voltage detection electrode) 34 is provided, and self-excited oscillation is performed using the detection voltage at the detection electrode 34 (see Patent Document 3). ).

  In this power supply circuit, a series circuit of an inductor L1 and a switching element Q1 composed of a MOSFET is connected between both ends of a DC power supply E, a capacitor C1 for waveform shaping is connected in parallel to the switching element Q1, and both ends of the capacitor C1 are connected. A voltage is applied to the primary electrode 32 of the piezoelectric transformer 30. The secondary voltage output from the secondary electrode 33 is applied to the load 70.

  As described above, the piezoelectric transformer 30 is provided with the detection electrode 34, and the detection voltage detected by the detection electrode 34 is input to the comparator CP2. The output of the comparator CP2 is used to turn on and off the switching element Q1 through a buffer composed of two transistors Q10 and Q11 connected in a complementary manner. In the comparator CP2, the voltage to be compared with the detection voltage is an average value of the output voltage of the buffer, and a rectangular wave signal is output from the comparator CP2.

In this configuration, on / off of the switching element Q1 is controlled by a rectangular wave signal obtained by comparing the pulsation voltage output from the detection electrode 34 with a constant value voltage. It will be done at the same frequency.
JP 2000-295861 A JP-A-9-135573 JP 2005-184896 A

  By the way, in the configuration described in Patent Document 3, since the comparator CP2 is used for self-excited oscillation, at least resistors R10 to R12, capacitors C10 and C11, and the like are required as external components of the operational amplifier. In addition, many components such as transistors Q10 and Q11, a pull-up resistor, and a voltage adjusting resistor constituting the buffer are used. As described above, the configuration of Patent Document 3 has a problem that the number of parts increases.

  The present invention has been made in view of the above reasons, and its object is to adopt a configuration using a digital signal processor instead of a configuration using a comparator that requires an operational amplifier and an external component. Accordingly, it is an object of the present invention to provide a power supply circuit using a piezoelectric transformer that can reduce the number of parts while driving the piezoelectric transformer with high efficiency.

  The invention according to claim 1 is a power supply circuit that boosts and outputs a DC voltage, and includes a booster and a booster that boost a voltage applied to the primary electrode formed of a pair of primary electrodes and a piezoelectric material. A piezoelectric transformer for taking out the output voltage from the secondary side electrode to the load, a switching element, and a secondary side electrode for outputting the voltage boosted in step S2 and a detection electrode for outputting a voltage corresponding to the deformation amount of the boosting unit. A piezoelectric transformer driving circuit unit for intermittently applying a voltage to the primary electrode; and a digital signal processor for driving on / off of a switching element, wherein the digital signal processor is configured to detect a detection voltage input from the detection electrode. A frequency calculation means for calculating the frequency and a drive signal generation means for generating a drive signal for turning on / off the switching element; A driving signal of the driving frequency is generated after the power is turned on, thereafter, and repeating the operation of calculating the frequency of the detected voltage, the act of generating a driving signal of the calculated frequency.

  According to a second aspect of the present invention, in the first aspect of the invention, the digital signal processor adjusts an output voltage to the load by controlling a time ratio of a drive signal for turning on and off the switching element. .

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the piezoelectric transformer drive circuit unit includes a resonance capacitor connected in parallel to the switching element, and a resonance capacitor. A resonance circuit unit having a resonance coil connected in series, applying a voltage across the resonance capacitor to the primary side electrode of the piezoelectric transformer, and the drive signal generating means switching the on-time of the switching element An initial drive signal which is a minimum time in a range where zero voltage switching is performed when the element is turned on is generated.

  According to the configuration of the first aspect of the invention, since the drive frequency of the drive signal for turning on / off the switching element matches the natural resonance frequency of the piezoelectric transformer, the piezoelectric transformer can be driven at a frequency at which the step-up ratio becomes high. There is.

  In addition, since the drive frequency of the drive signal for driving the switching element is adjusted to the natural resonance frequency of the piezoelectric transformer using a digital signal processor, the external parts that are necessary when using the comparator become unnecessary, and the comparator is used. There is an advantage that the number of parts can be reduced as compared with the conventional configuration.

  In the configuration of the invention of claim 2, since the duty ratio of the switching element is changed by the digital signal processor, there is an advantage that the output voltage can be changed by changing the duty ratio of the switching element without adding components.

  According to the configuration of the invention of claim 3, the drive signal generating means generates an initial drive signal that is a minimum time in a range in which zero voltage switching is performed when the switching element is turned on. Even when driving is started at a low output voltage, the switching element performs zero voltage switching, and there is an advantage that noise generation and switching loss in the piezoelectric transformer can be suppressed.

  In the following embodiments, a power supply circuit that boosts a DC voltage using a piezoelectric transformer and supplies the boosted voltage to a load is exemplified.

(Embodiment 1)
As shown in FIG. 1, the present embodiment includes a piezoelectric transformer 30, a piezoelectric transformer drive circuit unit 10 that includes a switching element Q1 and drives the piezoelectric transformer 30, a digital signal processor DSP that controls on / off of the switching element Q1, A regulator (constant voltage power source) 60 that supplies power to the digital signal processor DSP, a rectifier circuit unit 40 that rectifies the AC voltage output from the piezoelectric transformer 30, and an output detection circuit unit that detects the voltage supplied to the load 70. 50.

  The piezoelectric transformer 30 includes a booster 31 formed of a piezoelectric material such as PZT (lead zirconate titanate), a pair of primary electrodes 32 to which a voltage is applied by the piezoelectric transformer drive circuit unit 10, and a boosted voltage. Is provided with a secondary electrode 33 and a detection electrode 34.

  The step-up part 31 is formed in a rectangular plate shape, the pair of primary side electrodes 32 are respectively provided at the end portions in the longitudinal direction on each surface in the thickness direction, and the secondary side electrode 33 is extended from the primary side electrode 32 in the longitudinal direction. It is provided on one end face of the far side.

  The detection electrode 34 is disposed at one end (the end closer to the secondary electrode 33) of the boosting unit 31 on the surface where the one primary electrode 32 is provided, and corresponds to the amount of deformation of the boosting unit 31. Output voltage. That is, the detection electrode 34 outputs a voltage that fluctuates at a frequency corresponding to the natural resonance frequency of the piezoelectric transformer 30.

  The piezoelectric transformer drive circuit unit 10 includes a resonance circuit unit 20 formed by a resonance coil L1 and a resonance capacitor C1. The resonance coil L1 and the resonance capacitor C1 are connected in series, one end of the resonance coil L1 is connected to the high voltage side of the DC power supply E (for example, 12V), and one end of the resonance capacitor C1 is the low voltage of the DC power supply E. Connected to the side.

  The piezoelectric transformer 30 is connected in parallel to the resonance capacitor C1, and the piezoelectric transformer 30 and the resonance circuit unit 20 form a resonance circuit.

  A MOSFET is used as the switching element Q1, a source is connected to the low voltage side of the DC power supply E, a drain is connected to one end of the resonance capacitor C1, and the switching element Q1 is connected in parallel to the resonance capacitor C1.

  The rectifier circuit unit 40 includes two rectifier diodes D1 and D2 and a smoothing capacitor C2. The cathode of the rectifier diode D1 and the anode of the rectifier diode D2 are connected to the secondary electrode 33, and the anode of the rectifier diode D1 is connected to the low voltage side of the DC power supply E. Both ends of the smoothing capacitor C2 are connected to the cathode of the rectifier diode D2 and the low voltage side of the DC power supply E, respectively.

  One end of the load 70 is connected to one end (high voltage side) of the smoothing capacitor C2 via the resistor R5, and the other end is connected to the low voltage side of the DC power supply E.

  The output detection circuit unit 50 includes a capacitor C3 and voltage dividing resistors R3 and R4. The series circuit composed of the voltage dividing resistors R3 and R4 is connected between both ends of the smoothing capacitor C2, and the capacitor C3 is connected in parallel to the resistor R4 connected to the low voltage side of the DC power source E.

  The input end of the regulator 60 is connected to the high voltage side of the DC power source E, and the output end is connected to the digital signal processor DSP. The regulator 60 steps down the input voltage (for example, 3.3 V) and supplies it to the digital signal processor DSP.

  The digital signal processor DSP is connected to the first signal input terminal 61 connected to the detection electrode 34 via the resistor R2, the second signal input terminal 62 connected to the output detection circuit unit 50, and the gate of the switching element Q1. A signal output terminal 63, a GND terminal 64 connected to the low voltage side of the DC power supply E, and a power supply terminal 65. The first signal input terminal 61 is connected to the low voltage side of the DC power supply E via the capacitor C4.

  When the switching element Q1 is on, a DC voltage is applied to the resonance coil L1, and electromagnetic energy is stored in the resonance coil L1. When the switching element Q1 is switched from on to off, a resonance voltage is generated in a resonance circuit (hereinafter simply referred to as a resonance circuit) formed by the piezoelectric transformer 30 and the resonance circuit unit 20 by the electromagnetic energy stored in the resonance coil 22. Occurs, and a resonance voltage is applied to the primary electrode 32. Here, the resonance coil L1 and the resonance capacitor C1 are set so that the resonance frequency of the resonance circuit is higher than half of the natural resonance frequency of the piezoelectric transformer 30.

  When the switching element Q1 is periodically turned on and off, as shown in FIG. 2A, a resonance voltage is applied to the primary side electrode 32 at a period that matches the period of the switching element Q1.

  The voltage applied to the primary electrode 32 is boosted by the booster 31 and output as an AC voltage from the secondary electrode 33. At this time, the detection electrode 34 outputs a voltage having a frequency that matches the natural resonance frequency of the piezoelectric transformer 30 as shown in FIG.

  The voltage output from the secondary electrode 33 is double-voltage rectified by the rectifier circuit unit 40 and supplied to the load 70 as a DC voltage. Since the load 70 is connected to the smoothing capacitor C2, the voltage across the smoothing capacitor C2 fluctuates in a sawtooth shape as shown in FIG.

  The DC voltage output from the rectifier circuit unit 40 is divided by the voltage dividing resistors R3 and R4, the fluctuation component is removed by the capacitor C3, and the DC voltage is output as a substantially constant DC voltage as shown in FIG. The

  The digital signal processor DSP includes frequency calculation means (not shown) for calculating the natural resonance frequency of the piezoelectric transformer 30 and drive signal generation means (not shown) for generating a drive signal for the switching element Q1. As shown in FIG. 3, the digital signal processor DSP samples the detection voltage output from the detection electrode 34 at a predetermined sampling period T, quantizes the detection voltage, and converts the detection voltage into a digital value. For example, the frequency calculation means calculates the period of the detection voltage from the time when the maximum value and the minimum value of the digitized detection AC voltage are measured, and calculates the natural resonance frequency of the piezoelectric transformer 30. Note that the sampling period T is set sufficiently smaller than the period of the detection voltage.

  The drive control of the switching element Q1 by the digital signal processor DSP will be described with reference to FIG. The drive signal generating means generates an initial drive signal with an initial drive frequency and an initial duty ratio, and the digital signal processor DSP starts driving the switching element Q1 with the initial drive signal (S1). The duty ratio means the on-duty of the drive signal.

  The initial drive signal is set so that the output of the power supply circuit immediately after the start of driving of the switching element Q1 is a value close to the natural resonance frequency of the piezoelectric transformer 30 so that the minimum necessary voltage can be output to the load 70. . For example, if the natural resonance frequency of the piezoelectric transformer 30 is 150 kHz, the initial drive frequency may be set to 140 kHz or the like.

  The initial time ratio is set so that a voltage lower than a target voltage value (hereinafter referred to as a target voltage value) finally supplied to the load 70 is output so that an excessive voltage is not supplied to the load 70 at the start of driving. Is set.

  By the way, the resonance condition in the resonance circuit is determined by the maximum value of the drain current of the resonance coil L1, the resonance capacitor C1, the DC power source E, the switching element Q1, and the like. When the ON time of the switching element Q1 is long and the maximum value of the drain current of the switching element Q1 is sufficiently large, a voltage having a normal waveform as shown in FIG. 4A is applied to the primary side electrode 32.

  However, if the on-time of the switching element Q1 is too short and the maximum value of the drain current of the switching element Q1 becomes too small, the drain voltage does not become 0V or less, and the waveform of the voltage applied to the primary electrode 32 is as shown in FIG. As shown in b), it is distorted and the switching element Q1 does not switch to zero voltage. That is, the switching element Q1 has a minimum on-time for zero voltage switching.

  In the present embodiment, the initial ratio is determined so that the on-time of the switching element Q1 becomes the minimum on-time (for example, the initial ratio is about 0.2). Accordingly, the driving of the piezoelectric transformer 30 is started with an output voltage lower than the target voltage value, and the switching element Q1 performs zero voltage switching from the start of driving of the piezoelectric transformer 30. By performing the zero voltage switching, the generation of noise is suppressed and the switching loss is reduced.

  The initial drive frequency and the initial time ratio are stored in a storage unit (not shown) provided in the digital signal processor DSP when the power supply circuit is manufactured.

  When driving of the switching element Q1 is started and a voltage is applied to the primary electrode 32 of the piezoelectric transformer 30, a detection voltage is input to the first signal input terminal 61 of the digital signal processor DSP, and the digital signal processor DSP As described above, the detection voltage is converted into a digital value, and the output monitoring voltage input to the second signal input terminal 62 is sampled and quantized and converted into a digital value (S2), and then detected by the frequency calculation means. The frequency of the voltage (that is, the natural resonance frequency of the piezoelectric transformer 30) is calculated (S3).

  When the natural resonance frequency is calculated, the drive signal generating means generates a new drive signal by correcting the drive frequency without changing the time ratio, and the digital signal processor DSP switches with the newly generated drive signal. The element Q1 is driven (S4).

  After correcting the drive frequency, the output monitoring voltage is compared with the reference value that is set according to the target voltage value and stored in advance in the storage unit (S5), and when it is determined that the output monitoring voltage is greater than the reference value, Considering an abnormality, the drive signal output is stopped (S6).

  When it is determined in step S5 that the output monitoring voltage is smaller than the reference value, the drive signal generating means increases the time ratio by a ratio determined at the time of design and generates a new drive signal. The digital signal processor DSP drives the switching element Q1 with the newly generated drive signal (S7). After increasing the duty ratio, the drive frequency is corrected again (S8 to S10). The operations in steps S8 to S10 are the same as the operations in steps S2 to S4.

  As described above, in the present embodiment, the driving frequency of the switching element Q1 (that is, the driving frequency of the piezoelectric transformer 30) is gradually brought closer to the natural resonance frequency of the piezoelectric transformer 30, and finally, the piezoelectric element is piezoelectric at the natural resonance frequency of the piezoelectric transformer 30. The transformer 30 is driven.

  In step S11, the output monitoring voltage is compared with the reference value (the operation of S11 is the same as S5), and if it is determined that the output monitoring voltage is smaller than the reference value, the operation of step S12 is performed. The operation in step S12 is the same as that in step S7. Therefore, in this embodiment, the output voltage is gradually increased until the output monitoring voltage reaches the reference value.

  If it is determined in step S11 that the output monitoring voltage is greater than the reference value, the drive signal generating means generates a new drive signal by reducing the time ratio by the ratio determined at the time of design, and the digital signal processor DSP The switching element Q1 is driven with the newly generated drive signal (S13). Therefore, after the output of the power supply circuit is raised to the target voltage value, the output of the power supply circuit maintains a value near the target voltage value.

  In the piezoelectric transformer 30, the step-up ratio, which is the value of the ratio between the voltage applied to the primary electrode 32 and the voltage output from the secondary electrode 33, is applied to the primary electrode 32 as shown in FIG. Depending on the frequency of the applied voltage (hereinafter referred to as the driving frequency of the piezoelectric transformer 30), the driving frequency is highest when the driving frequency of the piezoelectric transformer 30 matches the natural resonance frequency of the piezoelectric transformer 30.

  As described above, in the present embodiment, since the drive frequency of the piezoelectric transformer 30 matches the natural resonance frequency of the piezoelectric transformer 30, the step-up ratio is high and the energy conversion efficiency in the piezoelectric transformer 30 is increased.

  In addition, since the drive frequency of the piezoelectric transformer 30 is adjusted to the natural resonance frequency of the piezoelectric transformer 30 using the digital signal processor DSP, the configuration using the comparator does not require the necessary external parts of the comparator, and is a component compared to the configuration using the comparator. The score can be reduced.

  Further, since the time ratio of the switching element Q1 is changed using the digital signal processor DSP, it is not necessary to add a new part in order to change the time ratio of the switching element Q1, and an increase in the number of parts can be suppressed.

(Embodiment 2)
In the present embodiment, as shown in FIG. 7, the rectifier circuit unit 40 is formed so that the output to the load 70 becomes a negative DC voltage, and the output detection circuit unit 50 has a negative output from the rectifier circuit unit 40. The difference from the first embodiment is that the DC voltage is output as a positive voltage.

  The anode of the rectifier diode D1 and the cathode of the rectifier diode D2 are connected to the secondary electrode 33, and the cathode of the rectifier diode D1 is connected to the low voltage side of the DC power supply E. Both ends of the smoothing capacitor C2 are connected to the anode of the rectifier diode D2 and the low voltage side of the DC power supply E, respectively.

  That is, the direction of the rectifier diodes D1 and D2 is different from that of the first embodiment. Therefore, the potential of one end of the smoothing capacitor C2 (one end opposite to the side connected to the low-voltage side of the DC power supply E) becomes negative, and the power supply circuit outputs a negative DC voltage.

  The voltage dividing resistors R3 and R4 are connected in series, and one end of the voltage dividing resistor R3 is connected to one end of the smoothing capacitor C2 (the side opposite to the side connected to the low voltage side of the DC power supply E), and the voltage dividing resistor R4. Is connected to the output end of the regulator 60.

  The negative DC voltage rectified by the rectifier circuit unit 40 is converted into a low positive DC voltage by the voltage dividing resistors R3 and R4, and is smoothed by the capacitor C3 and input to the second signal input terminal 62. Other configurations of the present embodiment are the same as those of the first embodiment.

  An example in which an electrostatic atomizer is used as the load of the power supply circuit of this embodiment is shown in FIG. The electrostatic atomizer includes an atomizing electrode 71 connected to one end (a negative potential side) of the smoothing capacitor C2, and a counter electrode 72 disposed to face the atomizing electrode 71. The electrostatic atomizer includes water supply means (not shown) for supplying water to the atomization electrode 71. As the water supply means, for example, the atomization electrode 71 is cooled to generate condensed water. There is a cooling means.

  The atomization electrode 71 is connected to one end of the smoothing capacitor C2, and the water supplied to the atomization electrode 71 is negatively charged. The charged water is attracted to the counter electrode 72 by the Coulomb force and discharged from the atomizing electrode 71, and is dispersed into the air as charged fine particle water (nanomicro order water particles). The output voltage of the power supply circuit used for the electrostatic atomizer is set to about -5 kV.

  The micro signal processor DSP includes a third signal input terminal 65 connected to the counter electrode 72 via the resistor R7, detects the discharge current flowing between the atomizing electrode 71 and the counter electrode 72, and keeps the discharge current constant. So as to generate a drive signal and control the amount of water to be atomized.

1 is a circuit diagram of Embodiment 1. FIG. FIG. 3 is a diagram illustrating a time change of a voltage in each part of the first embodiment. It is a figure showing the time change of the voltage which the detection electrode of Embodiment 1 outputs. FIG. 3 is a diagram illustrating a time change of a voltage applied to the piezoelectric transformer according to the first embodiment. 3 is a flowchart illustrating an operation of the digital signal processor according to the first embodiment. It is a figure showing the relationship between the drive frequency of a piezoelectric transformer, and a step-up ratio. FIG. 6 is a circuit diagram of a second embodiment. 6 is a circuit diagram illustrating an example of use of Embodiment 2. FIG. It is a circuit diagram of a conventional example. It is a block diagram of another prior art example. FIG. 10 is a circuit diagram of still another conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piezoelectric transformer drive circuit part 30 Piezoelectric transformer 31 Booster part 32 Primary side electrode 33 Secondary side electrode 34 Detection electrode E DC power supply DSP Digital signal processor Q1 Switching element

Claims (3)

  A power supply circuit that boosts and outputs a DC voltage, which is formed of a pair of primary side electrodes and a piezoelectric material, boosts a voltage applied to the primary side electrode, and outputs a voltage boosted by the boosting unit A secondary electrode, a detection electrode that outputs a voltage corresponding to the amount of deformation of the booster, a piezoelectric transformer that extracts the output voltage from the secondary electrode to the load, and a switching element that intermittently connects to the primary electrode. A piezoelectric transformer driving circuit unit for applying voltage and a digital signal processor for driving on / off of the switching element, wherein the digital signal processor calculates the frequency of the detection voltage input from the detection electrode. And a drive signal generating means for generating a drive signal for turning on / off the switching element, and driving at an initial drive frequency set in advance immediately after the power is turned on No. was generated after the power is turned on, thereafter, the operation of calculating the frequency of the detected voltage, the power supply circuit using a piezoelectric transformer and repeating an operation for generating a driving signal of the calculated frequency.   2. The power circuit using a piezoelectric transformer according to claim 1, wherein the digital signal processor adjusts an output voltage to the load by controlling a time ratio of a drive signal for turning on and off the switching element.   The piezoelectric transformer driving circuit unit includes a resonance circuit unit including a resonance capacitor connected in parallel to the switching element and a resonance coil connected in series to the resonance capacitor, and the voltage across the resonance capacitor is Applied to the primary side electrode of the piezoelectric transformer, the drive signal generating means generates an initial drive signal that is a minimum time in a range in which zero voltage switching occurs when the switching element is turned on. A power supply circuit using the piezoelectric transformer according to claim 1 or 2.

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