JP5885544B2 - Piezoelectric transformer drive circuit, power supply device, and piezoelectric transformer drive method - Google Patents

Description

  The present invention relates to a driving circuit for a piezoelectric transformer that drives a piezoelectric transformer to generate an AC output voltage, a power supply device including the driving circuit, and a driving method for the piezoelectric transformer.

  As a drive circuit and drive method for this type of piezoelectric transformer, a drive circuit and drive method for a piezoelectric transformer disclosed in the following Patent Document 1 are known. As shown in FIG. 1, the piezoelectric transformer drive circuit 51 includes a pulse generation unit 52 and a full bridge circuit unit 3.

  In this case, the full bridge circuit unit 3 includes a pair of complementary push-pull circuits (hereinafter also referred to as “push-pull circuits”) 11 and 12, and generates an AC rectangular wave voltage V 1 between the push-pull circuits 11 and 12. . Specifically, the push-pull circuit 11 includes switch elements 13 and 14 such as transistors, and is connected between the power supply voltage Vcc and the ground potential in a state where the switch element 13 is disposed on the power supply voltage Vcc side. Has been. The push-pull circuit 12 includes switch elements 15 and 16 such as transistors, and is connected between the power supply voltage Vcc and the ground potential in a state where the switch element 15 is disposed on the power supply voltage Vcc side. .

  The pulse generator 52 generates the drive pulses S1 and S2 at the timing shown in FIG. 6 and outputs the drive pulse S1 to the switch elements 14 and 15 as shown in FIG. By outputting to 16, the group of switch elements 14 and 15 and the group of switch elements 13 and 16 are alternately shifted to the ON state.

  In the drive circuit 51, the push-pull circuit 11 is one primary side electrode 22 of the pair of primary side electrodes 22, 23 formed on one end side of the piezoelectric vibrating body 21 in the piezoelectric transformer 4. The push-pull circuit 12 is connected to the other primary side electrode 23.

  With the above configuration, in the drive circuit 51, the switch elements 13, 14, 15, 16 of the full bridge circuit unit 3 are turned on at the timing shown in FIG. 6 by the drive pulses S1, S2 output from the pulse generation unit 52. By repeating the off-state, as shown in the figure, an AC rectangular wave voltage V1 having a positive peak value of Vcc and a negative peak value of −Vcc is generated, and a pair of 1 of the piezoelectric transformer 4 is generated. Output between the secondary electrodes 22 and 23. As a result, in the piezoelectric transformer 4, the piezoelectric vibrating body 21 generates an AC output voltage V2 at the secondary electrode 24 formed at the other end, and between the secondary electrode 24 and the ground potential. Output to connected load 5.

  In the full bridge circuit unit 3, the switch elements 13 and 14 constituting the push-pull circuit 11 are not simultaneously turned on (so that the power supply voltage Vcc is not short-circuited to the ground potential), and the push-pull circuit 12 is It is necessary that the switch elements 15 and 16 to be configured do not simultaneously shift to the on state. For this reason, the pulse generation unit 52 is between the stop of the output of the drive pulse S1 and the start of the output of the drive pulse S2, and between the stop of the output of the drive pulse S2 and the start of the output of the drive pulse S1. The drive pulses S1 and S2 are output in a state in which the dead time (short-circuit prevention period) Td having the same length is provided.

JP 2001-86758 A (pages 5-6, FIGS. 12-13)

  By the way, the AC output from the piezoelectric transformer 4 under the condition that the type of the piezoelectric transformer 4 to be used, the power supply voltage Vcc used for the full bridge circuit unit 3, and the period and duty ratio of the drive pulses S1 and S2 are not changed. If the voltage value of the output voltage V2 can be increased, the applicable range of the piezoelectric transformer 4 can be further expanded, which is preferable.

  Under the above conditions, the inventor of the present application has an off period from the stop of the output of the drive pulse S1 to the start of the output of the drive pulse S2, and from the stop of the output of the drive pulse S2 to the start of the output of the drive pulse S1. An experiment in which the balance of the lengths of the off-periods is changed within a range in which the short circuit does not occur in the full-bridge circuit unit 3 (one off period is lengthened and the other off-period is shortened). As a result, the phenomenon was found that the AC output voltage V2 was higher when both off periods were made the same length (when they were the same). did.

  The present invention has been made to solve such a problem, and a piezoelectric transformer driving circuit capable of increasing the voltage value of an AC output voltage output from the piezoelectric transformer, a power supply device including the piezoelectric transformer and the driving circuit, And it aims at providing the drive method of a piezoelectric transformer.

  In order to achieve the above object, the piezoelectric transformer drive circuit according to claim 1 generates an AC rectangular wave voltage and applies the AC rectangular wave voltage between the primary electrodes of the piezoelectric transformer. A drive circuit for a piezoelectric transformer that generates an AC output voltage on a secondary side electrode, wherein a pair of negative square waves that form a voltage waveform of the AC rectangular wave voltage are output before and after the negative rectangular wave The alternating current in a state in which an off period mainly composed of a short-circuit prevention period is interposed between any one of the positive rectangular waves and the one of the positive rectangular waves is unevenly distributed on the one positive rectangular wave side Generate a square wave voltage.

  According to a second aspect of the present invention, in the piezoelectric transformer driving circuit according to the first aspect, the off period is constituted only by the short-circuit prevention period.

  According to a third aspect of the present invention, there is provided a power supply apparatus comprising: the piezoelectric transformer drive circuit according to the first or second aspect; and the piezoelectric transformer, and an output for a load based on the AC output voltage generated by the piezoelectric transformer. Generate and output voltage.

  According to a fourth aspect of the present invention, there is provided a piezoelectric transformer driving method in which an AC rectangular wave voltage is applied between primary electrodes of a piezoelectric transformer to generate an AC output voltage on the secondary electrode of the piezoelectric transformer. A driving method, wherein a negative rectangular wave constituting a voltage waveform of the AC rectangular wave voltage is a positive rectangular of one of a pair of positive rectangular waves output before and after the negative rectangular wave The AC rectangular wave voltage is generated in a state where an off period mainly composed of a short-circuit prevention period is interposed between the waves and the wave is unevenly distributed on the one positive rectangular wave side.

  In the piezoelectric transformer drive circuit according to claim 1, the power supply device according to claim 3, and the piezoelectric transformer drive method according to claim 4, the negative-side rectangular wave constituting the voltage waveform of the AC rectangular wave voltage is converted into the negative-side rectangular wave. An off period mainly composed of a short-circuit prevention period is interposed between any one of the pair of positive rectangular waves output before and after the side rectangular wave, and this one positive side An AC rectangular wave voltage is generated while being unevenly distributed on the rectangular wave side, and is output between the pair of primary electrodes of the piezoelectric transformer.

  Therefore, according to this piezoelectric transformer drive circuit, power supply device, and piezoelectric transformer drive method, the positive side rectangle that forms the AC rectangular wave voltage with the type of the piezoelectric transformer and the power supply voltage used for the full-bridge circuit section being constant. An AC output voltage with an increased voltage value can be output from the piezoelectric transformer under the condition that the period and duty ratio (pulse width of each rectangular wave) of the wave and the negative rectangular wave are constant.

  According to the piezoelectric transformer drive circuit of the second aspect, since the off period is configured only by the short-circuit prevention period, the AC output voltage having the highest voltage value can be output from the piezoelectric transformer.

2 is a configuration diagram showing a configuration of a power supply device PS including a drive circuit 1 (51) for a piezoelectric transformer 4. FIG. 4 is a timing chart for explaining the operation of the drive circuit 1 and the method for driving the piezoelectric transformer 4. 4 is a timing chart for explaining the contents of an experiment regarding a driving method of the piezoelectric transformer 4. The piezoelectric transformer 4 shows how the voltage value of the AC output voltage V2 generated by the piezoelectric transformer 4 changes when T3 / T1 is changed while maintaining T2 / T1 of the AC rectangular wave voltage V1 at 0.3. It is an output characteristic figure. The piezoelectric transformer 4 shows how the voltage value of the AC output voltage V2 generated by the piezoelectric transformer 4 changes when T3 / T1 is changed while maintaining T2 / T1 of the AC rectangular wave voltage V1 at 0.1. It is an output characteristic figure. 6 is a timing chart for explaining a conventional method for driving a piezoelectric transformer 4.

  Embodiments of a piezoelectric transformer driving circuit, a power supply device, and a piezoelectric transformer driving method will be described below with reference to the accompanying drawings.

  First, the configuration of the piezoelectric transformer drive circuit 1 and the power supply device PS including the drive circuit 1 will be described with reference to the drawings.

  As shown in FIG. 1, the power supply device PS includes a drive circuit 1 and a piezoelectric transformer 4, and generates an AC output voltage V2, and generates an output voltage for the load 5 based on the generated AC output voltage V2. Thus, the load 5 can be output. In this example, as an example, the AC output voltage V2 generated by the piezoelectric transformer 4 is output to the load 5 as it is as the output voltage for the load 5.

  The drive circuit 1 includes a pulse generation unit 2 and a full bridge circuit unit 3 as shown in FIG. The pulse generator 2 includes a drive pulse S1 for driving each switch element 14 and 15, which will be described later, constituting the full bridge circuit section 3, and a drive pulse S2 for driving each switch element 13, 16 which will be described later. Generate and output.

  Specifically, as shown in FIG. 2, the pulse generator 2 generates one of the pair of drive pulses S1 output before and after the drive pulse S2 (in this example, the subsequent drive). An off period (a period in which none of the drive pulses S1 and S2 are output) Toff1 is interposed between the pulse S1) and the drive pulse S2, and this drive pulse is mainly composed of a short-circuit prevention period (dead time) Td. The drive pulses S1 and S2 are generated in a state where S2 is unevenly distributed on the drive pulse S1 side. In other words, the pulse generation unit 2 is one of the start end and the end of the drive pulse S1 (start end (left end as an example in the figure)) and the drive pulse of the start end and end of the drive pulse S2. While maintaining the state in which the one end (starting end) in S1 and one end (terminal end (right end in the figure)) of a different type appear continuously across the off period Toff1, In this example, the drive pulses S1 and S2 are generated in a state where the drive pulse S2 is unevenly distributed on the side of the subsequent drive pulse S1 between the pair of drive pulses S1 output before and after the drive pulse S2.

  In this case, during this short-circuit prevention period Td, the switch elements 13 and 14 constituting the push-pull circuit 11 which will be described later constituting the full bridge circuit unit 3 do not shift to the ON state simultaneously (the power supply voltage Vcc is applied to the push-pull circuit 11). And the switch elements 15 and 16 constituting the push-pull circuit 12 to be described later are not simultaneously turned on (the power supply voltage Vcc is not short-circuited to the ground potential via the push-pull circuit 12). It is defined as a minimum length (time interval). Further, the off period Toff1 is defined to have a length substantially equal to the short-circuit prevention period Td (specifically, the length of the short-circuit prevention period Td occupying the off-period Toff1 is 80% or more, preferably 90% or more). By doing so, it is mainly configured with a short-circuit prevention period Td.

  In addition, another off period is also present between the other driving pulse S1 (the previous driving pulse S1 in this example) of the pair of driving pulses S1 output before and after the driving pulse S2 and the driving pulse S2. Although Toff2 is present, the other off-period Toff2 is always longer than the above-mentioned off-period Toff1 because the drive pulse S2 is unevenly distributed to the subsequent drive pulse S1 as described above. Maintained.

  With this configuration, when the duty ratio of the drive pulse S1 is set, the pulse generator 2 uses the above-mentioned one end (starting end in FIG. 2) of the drive pulse S1 as a reference and the pulse width T2 (one end) 2 to the other end (the time from the end (right end) in FIG. 2) is changed as indicated by an arrow A. Further, when setting the duty ratio of the drive pulse S2, the pulse generator 2 sets the pulse width T2 (from one end to the other with reference to the one end (the end in FIG. 2) of the drive pulse S2. 2 (time until the start end (left end) in FIG. 2) is changed as indicated by an arrow A. That is, the length of the other off period Toff2 is changed.

  The full bridge circuit unit 3 includes a pair of complementary push-pull circuits (hereinafter also referred to as “push-pull circuits”) 11 and 12, and generates an AC rectangular wave voltage V 1 between the push-pull circuits 11 and 12. Specifically, the push-pull circuit 11 includes switch elements (for example, field effect transistors) 13 and 14, the switch element 13 is disposed on the power supply voltage Vcc side, and the switch element 14 is disposed on the ground potential side. In this state, it is connected between the power supply voltage Vcc and the ground potential. The push-pull circuit 12 includes switch elements (for example, field effect transistors) 15 and 16, with the switch element 15 disposed on the power supply voltage Vcc side and the switch element 16 disposed on the ground potential side. Are connected between the power supply voltage Vcc and the ground potential.

  In addition, among the switch elements 13 to 16 of the push-pull circuits 11 and 12, the switch elements 14 and 15 are driven by the drive pulse S1 output from the pulse generator 2, and the drive pulse S1 is input. It shifts to an on state during a period, and shifts to an off state during other periods. Further, the switch elements 13 and 16 are driven by the drive pulse S2, and shift to the on state during the period when the drive pulse S2 is input, and shift to the off state during the other periods.

  Further, in the full bridge circuit unit 3, the connection point A of the switch elements 13 and 14 in the push-pull circuit 11 and the connection point B of the switch elements 15 and 16 in the push-pull circuit 12 are respectively an AC rectangular wave voltage V1. And is connected to primary electrodes 22 and 23 (to be described later) of the piezoelectric transformer 4.

  The piezoelectric transformer 4 includes a piezoelectric vibrating body 21, a pair of primary-side electrodes 22 and 23 formed on one end side of the piezoelectric vibrating body 21 and spaced apart in the thickness direction of the piezoelectric vibrating body 21, and the piezoelectric vibrating body 21. A secondary side electrode 24 formed on the other end side is provided. In the piezoelectric transformer 4 configured in this way, the mechanical vibration is applied to the primary side electrodes 22 and 23 of the piezoelectric vibrating body 21 in a state where the AC rectangular wave voltage V1 is input between the primary side electrodes 22 and 23. Excited to the formation site side, this mechanical vibration is converted into a voltage on the formation site side of the secondary electrode 24 in the piezoelectric vibrator 21 to generate an AC output voltage V2. The generated AC output voltage V2 is output from the output terminal C (output terminal in the power supply device PS) connected to the secondary electrode 24 to the outside of the power supply device PS.

  Next, a method for driving the piezoelectric transformer 4 by the drive circuit 1 together with operations of the power supply device PS and the drive circuit 1 will be described with reference to the drawings.

  In the power supply device PS, as shown in FIG. 2, the pulse generation unit 2 has a drive pulse S1 between the drive pulse S1 and the drive pulse S1 after the drive pulse S1 output before and after the drive pulse S2. The drive pulses S1 and S2 are generated and output to the full bridge circuit unit 3 in a state where the off-period Toff1 is interposed and the drive pulse S2 is unevenly distributed on the subsequent drive pulse S1 side.

  In the full bridge circuit unit 3, the switch element 14 of the push-pull circuit 11 and the switch element 15 of the push-pull circuit 12 are alternately and alternately switched on and off in accordance with the drive pulse S1, and pushed in accordance with the drive pulse S2. The switch element 13 of the pull circuit 11 and the switch element 16 of the push-pull circuit 12 are alternately and repeatedly turned on and off.

  Thus, as shown in FIG. 2, when the drive pulse S1 is input, the connection point A is connected to the ground potential via the switch element 14 in the on state, and the connection point B is connected to the ground element via the switch element 15 in the on state. When the drive pulse S2 is input, the connection point A is connected to the power supply voltage Vcc via the switch element 13 in the on state, and the connection point B is connected via the switch element 16 in the on state. Connected to ground potential. For this reason, the full bridge circuit section 3 has a positive peak value Vcc as shown in FIG. 2 between the connection points A and B as a pair of output terminals, and a negative peak value −Vcc. The AC rectangular wave voltage V1 is generated, and this AC rectangular wave voltage V1 is applied (output) between the primary electrodes 22 and 23 of the piezoelectric transformer 4.

  The piezoelectric transformer 4 generates an AC output voltage V2 at the secondary side electrode 24 by applying an AC rectangular wave voltage V1 between the primary side electrodes 22 and 23, and outputs the generated AC output voltage V2 to the output terminal C. Output to the load 5 via

  In the drive circuit 1, as described above, in each of the drive pulses S1 and S2, between the drive pulse S1 and the drive pulse S2 after the pair of drive pulses S1 output before and after the drive pulse S2. An off period Toff1 mainly composed of the short-circuit prevention period Td is interposed, and the state where the drive pulse S2 is unevenly distributed on the subsequent drive pulse S1 side is maintained. Further, when setting the duty ratio of the drive pulses S1, S2, the pulse width T2 of each of the drive pulses S1, S2 is changed as indicated by the arrow A while maintaining this state.

  Therefore, also in the AC rectangular wave voltage V1 generated by the full bridge circuit unit 3, as shown in FIG. 2, this voltage output before and after the negative rectangular wave Vm constituting the voltage waveform of the AC rectangular wave voltage V1. A short-circuit prevention period between one positive rectangular wave Vp (in this example, the subsequent positive rectangular wave Vp in this example) of the pair of positive rectangular waves Vp constituting the waveform and the negative rectangular wave Vm. An off period Toff1 mainly composed of Td is interposed, and the state where the negative-side rectangular wave Vm is unevenly distributed on the one positive-side rectangular wave Vp side is maintained. When setting the duty ratios of the positive side rectangular wave Vp and the negative side rectangular wave Vm, the pulse width T2 of the positive side rectangular wave Vp and the negative side rectangular wave Vm is indicated by an arrow A while maintaining this state. Changed as shown.

  As shown in FIG. 3, the inventor of the present application has a positive rectangular shape in a state where the period T1 of the AC rectangular wave voltage V1 is constant (that is, the positive rectangular wave Vp and the negative rectangular wave Vm are also constant at the period T1). While maintaining the pulse width T2 of the wave Vp and the negative rectangular wave Vm constant, one end of the positive rectangular wave Vp (starting end (left end) in the figure) and one of the negative rectangular wave Vm The time interval T3 to the end of the figure (the end (right end) in the figure) is changed from the state shown in the upper part of the figure (time interval T3 = short-circuit prevention period Td) to the state shown in the middle part (negative The state shown in the lower stage (a state in which the side rectangular wave Vm is output at an intermediate point between the front and rear positive rectangular waves Vp) (a pair of positive rectangular waves output before and after the negative rectangular wave Vm) Prevent short circuit between the positive square wave Vp in front of Vp and the negative square wave Vm. When only the interval Td is present and the negative rectangular wave Vm is gradually increased until the negative rectangular wave Vm is unevenly distributed to the previous positive rectangular wave Vp side (the positive and negative before and after the negative rectangular wave Vm). The state of change in the AC output voltage V2 (when gradually approaching the front positive rectangular wave Vp of the side rectangular waves Vp) was measured by experiment.

  The state shown in the lower part of FIG. 3 means that the pulse generator 2 is between the previous drive pulse S1 and the drive pulse S2 of the pair of drive pulses S1 output before and after the drive pulse S2. In this state, only the short-circuit prevention period Td is present, and the drive pulses S1 and S2 are generated in a state where the drive pulse S2 is unevenly distributed on the previous drive pulse S1 side. In this experiment, AS-A243T manufactured by Tamura Corporation is used as the piezoelectric transformer 4, the power supply voltage Vcc is regulated to 20V, and the switch elements 13 and 15 constituting the push-pull circuits 11 and 12 are P-channel type. A power MOSFET (TPC8120: manufactured by Toshiba) was used, and an N-channel type power MOSFET (TPC8063-H: manufactured by Toshiba) was used as the switch elements 14 and 16. Further, the cycle T1 of each drive pulse S1, S2 is defined as 10 μs (frequency is 100 kHz).

  Results of this experiment when the ratio (duty ratio) of each pulse width T2 of the positive rectangular wave Vp and the negative rectangular wave Vm to the period T1 of the AC rectangular wave voltage V1 is 0.3 (= T2 / T1) Is shown in FIG. The horizontal axis indicates the ratio of the time interval T3 to the period T1 (= T3 / T1).

  According to the result of this experiment, the voltage value (peak to peak) of the AC output voltage V2 gradually decreases as the time interval T3 becomes longer from the state shown in the upper part of FIG. 3, and the ratio T3 / T1 is When the value is 0.2, that is, when the position of the negative rectangular wave Vm with respect to the positive rectangular wave Vp is in the state shown in the middle of FIG. Further, the voltage value of the AC output voltage V2 gradually increases as the time interval T3 becomes longer from the state shown in the middle stage, and this increase continues until the state shown in the lower stage in the figure. It can be confirmed that it has characteristics.

  This experiment was performed when the ratio (duty ratio) of each pulse width T2 of the positive rectangular wave Vp and the negative rectangular wave Vm to the period T1 of the AC rectangular wave voltage V1 was 0.1 (= T2 / T1). The results are shown in FIG.

  Also in the result of this experiment, the voltage value (peak to peak) of the AC output voltage V2 gradually decreases as the time interval T3 increases from the state shown in the upper part of FIG. 3, and the ratio T3 / T1 is 0. .4, that is, when the position of the negative-side rectangular wave Vm with respect to the positive-side rectangular wave Vp is in the state shown in the middle of FIG. Further, the voltage value of the AC output voltage V2 gradually increases as the time interval T3 becomes longer from the state shown in the middle stage, and this increase continues until the state shown in the lower stage in the figure. It can be confirmed that it has characteristics.

  Thereby, in this power supply device PS, the piezoelectric transformer 4 causes the negative rectangular wave Vm to be output from one positive rectangular wave Vp (of the pair of positive rectangular waves Vp output before and after the negative rectangular wave Vm ( An alternating current that is output in a state in which an off-period Toff1 (a period mainly composed of a short-circuit prevention period Td) is present on the side of the subsequent positive-side rectangular wave Vp and is unevenly distributed on the one-side positive-side rectangular wave Vp side Since it is driven by the rectangular wave voltage V <b> 1, the AC output voltage V <b> 2 (AC output voltage V <b> 2 with the increased voltage value) increased to the state where the voltage value is the highest or close to the highest state is applied to the secondary electrode 24. It can be generated and supplied to the load 5.

  Although not shown, the ratio (duty ratio) of each pulse width T2 of the positive rectangular wave Vp and the negative rectangular wave Vm to the period T1 of the AC rectangular wave voltage V1 is set to 0. 0 in a state where the short-circuit prevention period Td is secured. When approaching 5 (= T2 / T1), the degree to which the negative rectangular wave Vm is biased to one side of the pair of positive rectangular waves Vp output before and after the negative rectangular wave Vm gradually decreases. It has been confirmed that the effect of increasing the AC output voltage V2 gradually decreases because the negative rectangular wave Vm approaches the configuration in which the negative rectangular wave Vm is output at the midpoint of the pair of positive rectangular waves Vp.

  As described above, in the driving circuit 1 of the piezoelectric transformer 4, the power supply device PS having the driving circuit 1, and the driving method of the piezoelectric transformer 4, the negative rectangular wave Vm constituting the voltage waveform of the AC rectangular wave voltage V1 is An off period Toff1 is interposed between any one of the pair of positive side rectangular waves Vp output before and after the negative side rectangular wave Vm, and the one positive side rectangular wave Vm. An AC rectangular wave voltage V <b> 1 is generated in a state of being unevenly distributed on the Vp side and applied (output) to the primary side electrodes 22 and 23 of the piezoelectric transformer 4.

  Therefore, according to the driving method of the driving circuit 1, the power supply device PS, and the piezoelectric transformer 4, the type of the piezoelectric transformer 4 and the power supply voltage Vcc used for the full bridge circuit unit 3 are fixed (without changing) and are driven. The period T1 and the duty ratio (pulse width T2 of each drive pulse S1, S2) of the pulses S1, S2 are made constant (that is, the period of the positive rectangular wave Vp and the negative rectangular wave Vm constituting the AC rectangular wave voltage V1). Under the condition of T1 and the duty ratio (the pulse width T2 of each rectangular wave Vp, Vm is constant), the AC output voltage V2 (the voltage value is the highest or close to the highest state) with the increased voltage value The AC output voltage V2) increased to the state can be output from the piezoelectric transformer 4 to the load 5.

  In the drive circuit 1 described above, the length is approximately equal to the short-circuit prevention period Td (specifically, the length of the short-circuit prevention period Td in the off period Toff1 is 80% or more, preferably 90% or more). The off period Toff1 is defined in FIG. 1, but the length is equal to the short-circuit prevention period Td (specifically, the length of the short-circuit prevention period Td in the off-period Toff1 is 100%), that is, A configuration in which the off period Toff1 is configured only by the short-circuit prevention period Td can also be employed. By adopting this configuration, the off-side period Toff1 (short circuit) is provided on one positive-side rectangular wave Vp side of the pair of positive-side rectangular waves Vp output before and after the negative-side rectangular wave Vm. Since the piezoelectric transformer 4 is driven by the AC rectangular wave voltage V1 that is output in a state in which it is unevenly distributed on the one positive rectangular wave Vp side, the voltage is set to the voltage. The AC output voltage V <b> 2 having the highest value can be generated at the secondary electrode 24 and supplied to the load 5.

  Note that the power supply device PS employs a configuration in which the AC output voltage V2 output from the piezoelectric transformer 4 is output as it is to the load 5 as the output voltage for the load 5, but the secondary side of the piezoelectric transformer 4 is used. By adopting a configuration in which a rectifier (not shown) is disposed between the electrode 24 and the output terminal C, an output voltage for the load 5 is generated based on the AC output voltage V2 (that is, the AC output voltage V2 is changed). It is also possible to adopt a configuration in which an output voltage is generated by converting the direct current voltage into a direct current voltage in the rectifying unit, and then output to the load 5.

DESCRIPTION OF SYMBOLS 1 Drive circuit 2 Pulse generation part 4 Piezoelectric transformer 21 Piezoelectric vibrator 22, 23 Primary side electrode 24 Secondary side electrode PS Power supply device V1 AC rectangular wave voltage V2 AC output voltage Vm Negative side rectangular wave Vp Positive side rectangular wave

Claims (4)

A piezoelectric transformer drive circuit that generates an AC output voltage at the secondary side electrode of the piezoelectric transformer by generating an AC rectangular wave voltage and applying the AC rectangular wave voltage between the primary side electrodes of the piezoelectric transformer. And
The negative rectangular wave constituting the voltage waveform of the AC rectangular wave voltage is short-circuited between one positive rectangular wave of a pair of positive rectangular waves output before and after the negative rectangular wave. A drive circuit for a piezoelectric transformer that generates the AC rectangular wave voltage in a state in which an off period mainly composed of a prevention period is interposed and is unevenly distributed on the one positive rectangular wave side.   The piezoelectric transformer drive circuit according to claim 1, wherein the off period includes only the short-circuit prevention period.   A power supply apparatus comprising the piezoelectric transformer drive circuit according to claim 1 and 2 and the piezoelectric transformer, and generating and outputting an output voltage for a load based on the AC output voltage generated by the piezoelectric transformer. A method of driving a piezoelectric transformer in which an alternating current rectangular wave voltage is applied between primary electrodes of a piezoelectric transformer to generate an alternating current output voltage on a secondary side electrode of the piezoelectric transformer,
The negative rectangular wave constituting the voltage waveform of the AC rectangular wave voltage is short-circuited between one positive rectangular wave of a pair of positive rectangular waves output before and after the negative rectangular wave. A driving method of a piezoelectric transformer that generates the AC rectangular wave voltage in a state in which an off period mainly composed of a prevention period is interposed and unevenly distributed on the one positive rectangular wave side.

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