JP2009100604A - Piezoelectric transformer drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric transformer drive circuit having a protection circuit capable of stopping a drive circuit by performing abnormality detection of an output current more surely than before in a multi-lamp piezoelectric transformer drive circuit having a plurality of discharge tubes. <P>SOLUTION: Cold cathode tubes 10 are respectively connected to the output side of a plurality of piezoelectric transformers, and current determination circuits 12 are branched from wiring for current input to load current comparison circuits 14 to be connected to the respective terminals 11 on the load low voltage side. All the outputs of the current determination circuits 12 are input into an OR circuit 13. The current determination circuits 12 determine whether or not the output current of each load satisfies a predetermined current value, and output their results. In the OR circuit 13, an abnormal stop signal is output to the drive circuit 20 to stop operation of the drive circuit 20 when at least one of the outputs of the current determination circuits 12 is determined to have a current value equal to or lower than a specified value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piezoelectric transformer drive circuit that generates an AC voltage for the purpose of lighting a discharge tube as a load, and more particularly to a piezoelectric transformer drive circuit having a function of detecting and protecting an abnormality in a discharge tube or a piezoelectric transformer. It is.

  In general, a piezoelectric transformer is provided with primary and secondary electrodes on a piezoelectric material, and an input AC voltage near the resonance frequency of the piezoelectric transformer is applied to the primary electrode to resonate the piezoelectric transformer, and the secondary side is mechanically vibrated. It is an element for extracting the output AC voltage generated at the electrode.

  As a piezoelectric transformer driving circuit for driving this type of piezoelectric transformer, for example, a circuit described in Patent Document 1 is known. FIG. 7 is a block diagram of a conventional piezoelectric transformer driving circuit described in Patent Document 1. In FIG. In FIG. 7, the drive circuit 201 is connected to the primary electrode 106 of the piezoelectric transformer 102, converts the frequency sweep signal from the frequency sweep oscillator 205 into an AC waveform necessary for driving the piezoelectric transformer 102, and drives the piezoelectric transformer 102. To do. The secondary electrode 107 of the piezoelectric transformer 102 is connected to the load high-voltage side terminal 108 of the load 103 which is a discharge tube, and gives the voltage boosted by the piezoelectric transformer 102 to the load high-voltage side terminal 108. The load low-voltage side terminal 109 of the load 103 is connected to the load current comparison circuit 3104, and the outflow current from the load flows into the load current comparison circuit 3104. The load current comparison circuit 3104 converts the incoming load current into a voltage and compares it with a reference voltage VrefA110 corresponding to a preset set current value. The load current comparison circuit 3104 is connected to the frequency sweep oscillator 205 and gives the comparison result to the frequency sweep oscillator 205. The frequency sweep oscillator 205 determines the direction of frequency sweep according to the comparison result of the load current comparison circuit 3104.

  Further, in FIG. 7, an output voltage comparison circuit 3206 is connected to the secondary electrode 107 of the piezoelectric transformer 102, and the determination result of the output voltage comparison circuit 3206 is given to the frequency sweep oscillator 205. The output voltage comparison circuit 3206 has a function of voltage-dividing and rectifying the voltage output to the secondary electrode 107 of the piezoelectric transformer 102, and compares the voltage obtained by voltage-dividing and rectification with a preset reference voltage VrefB212. Thus, it has a function of determining whether or not the voltage output to the secondary electrode 107 exceeds a preset output voltage, and the determination result is given to the frequency sweep oscillator 205. When the frequency sweep oscillator 205 determines that the determination result of the output voltage comparison circuit 3206 has exceeded the preset output voltage, the frequency sweep oscillator 205 reverses the frequency sweep direction from the direction in which the frequency decreases to the direction in which the frequency increases. It has a function to switch the sweep direction. With this function, when the load becomes open for some reason, the drive frequency of the piezoelectric transformer 102 shifts to a low step-up ratio and decreases the output voltage.

  The time division drive control circuit 306 generates a signal whose output duty is controlled at a frequency lower than 1/100 of the drive frequency of the piezoelectric transformer in accordance with a duty control voltage Vduty 307 given from outside. The drive circuit 201 has a function of temporarily stopping the output of the drive voltage applied to the primary electrode 106 of the piezoelectric transformer 102 by the drive stop signal from the time division drive control circuit 306, and the average output power of the piezoelectric transformer is controlled. Is done.

  FIG. 8 shows an example of a conventional piezoelectric transformer driving circuit having a protection circuit that stops the driving circuit for protecting the piezoelectric transformer and the discharge tube when the load current is abnormal. As shown in FIG. 8, the protection circuit 200 is connected to the load low-voltage side terminal 109 side of the load 103, and the load current input thereto is monitored, and when the current value does not reach a preset current value, the drive circuit 201. Stop.

Japanese Patent No. 2751842

  Conventionally, when a drive circuit for a piezoelectric transformer has the above-described protection circuit, the conventional protection circuit has only one discharge tube even if it is a multi-lamp type piezoelectric transformer drive circuit having a plurality of discharge tubes as loads. Only the output current is monitored, and the drive circuit is stopped when the value is less than the preset current value. In a piezoelectric transformer drive circuit, all the piezoelectric transformers connected to a plurality of discharge tubes controlled by a single drive circuit are driven at the same frequency by frequency control, so the output of one piezoelectric transformer is monitored and controlled. This is because monitoring of only one output is sufficient because the current value of the piezoelectric transformer that controls the output of other piezoelectric transformers is almost the same.

  However, when only the output of one discharge tube is monitored in this way, if there is a variation in the characteristics of the piezoelectric transformer, the output current in the discharge tube other than the discharge tube being monitored is below the set value. May not be detected. Even if the characteristics of the piezoelectric transformer are uniform, detection cannot be performed even if a problem such as deterioration occurs in a discharge tube other than the discharge tube being monitored and the output current does not reach the set value. That is, the conventional protection circuit has a problem that the function is insufficient.

  Therefore, an object of the present invention is to provide a piezoelectric device having a protection circuit capable of detecting an abnormality in output current more reliably and stopping the drive circuit in a multi-lamp type piezoelectric transformer drive circuit having a plurality of discharge tubes. It is to provide a transformer driving circuit.

  In order to solve the above problems, a piezoelectric transformer drive circuit according to the present invention includes a plurality of piezoelectric transformers each including a primary electrode to which an input AC voltage is applied and a secondary electrode that is insulated from the primary electrode and outputs an output AC voltage. A drive circuit that outputs and drives an AC waveform necessary for the primary electrode of the piezoelectric transformer, a frequency sweep oscillator that outputs a frequency signal of the AC waveform to the drive circuit, and a secondary electrode of the piezoelectric transformer, respectively. A plurality of loads to which one terminal is connected, and the current flowing out from the other terminal of the load is input to convert it into a voltage, and the value is compared with a first reference voltage that is set in advance. A load current comparison circuit for providing a signal for determining a sweep direction of a frequency of the sweep oscillator; a second reference voltage having a preset value obtained by inputting and dividing the output from the secondary electrode of the piezoelectric transformer; A piezoelectric transformer drive circuit comprising an output voltage comparison circuit for providing a signal for determining a frequency sweep direction of the frequency sweep oscillator according to the comparison result, and detecting currents flowing out from the other terminals of the plurality of loads, respectively. And a protection circuit for stopping the drive circuit when at least one of the current values is less than a preset current value.

  Also, a plurality of piezoelectric transformers having a primary electrode to which an input AC voltage is applied and a secondary electrode that is insulated from the primary electrode and outputs an output AC voltage, and outputs an AC waveform necessary for the primary electrode of the piezoelectric transformer Driving circuit, a frequency sweep oscillator that outputs the frequency signal of the AC waveform to the driving circuit, a plurality of loads each having one terminal connected to the secondary electrode of the piezoelectric transformer, A load current that inputs a current flowing out from the other terminal, converts it into a voltage, and compares the value with a preset first reference voltage to give a signal for determining the frequency sweep direction of the frequency sweep oscillator. The frequency sweep of the frequency sweep oscillator is obtained by comparing the comparison circuit and the output from the secondary electrode of the piezoelectric transformer, dividing the voltage, and comparing the value with a preset second reference voltage. A piezoelectric transformer driving circuit including an output voltage comparison circuit for providing a signal for determining a direction, detecting a total value of currents flowing out from the other terminal of the plurality of loads, and setting the total value of the currents in advance. A protective circuit for stopping the drive circuit when the current value is not reached may be provided.

  Also, a plurality of piezoelectric transformers having a primary electrode to which an input AC voltage is applied and a secondary electrode that is insulated from the primary electrode and outputs an output AC voltage, and outputs an AC waveform necessary for the primary electrode of the piezoelectric transformer Driving circuit, a frequency sweep oscillator that outputs the frequency signal of the AC waveform to the driving circuit, a plurality of loads each having one terminal connected to the secondary electrode of the piezoelectric transformer, A load current that inputs a current flowing out from the other terminal, converts it into a voltage, compares the value with a first reference voltage that is set in advance, and gives a signal for determining a frequency sweep direction of the frequency sweep oscillator The frequency sweep of the frequency sweep oscillator is obtained by comparing the comparison circuit and the output from the secondary electrode of the piezoelectric transformer, dividing the voltage, and comparing the value with a preset second reference voltage. A piezoelectric transformer driving circuit including an output voltage comparison circuit for providing a signal for determining a direction; a means for respectively detecting currents flowing out from the other terminal of the plurality of loads; and a means for detecting the current from the other terminal of the plurality of loads. A protection circuit having means for detecting a total value of the discharged current, and stopping the drive circuit when at least one of the respective current values or the total value of the currents is less than a preset current value You may have.

  Further, the protection circuit compares the voltage value obtained by converting the current flowing out from the other terminal of the load with a predetermined reference voltage value to determine whether the current value is less than the preset current value. It may be determined whether or not.

  Further, the operation of the protection circuit may be stopped during the period when the drive circuit is not driven, or the protection circuit may be configured not to output an output for stopping the drive circuit.

  As described above, according to the present invention, in a multi-lamp type piezoelectric transformer drive circuit having a plurality of discharge tubes, each current of each load is monitored or the total value of currents of each load is monitored. Thus, the abnormality of the output current is determined and the drive circuit is stopped, so that a piezoelectric transformer drive circuit including a protection circuit that can detect the abnormality of the output current and stop the drive circuit more reliably than before can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a configuration diagram showing a part of a piezoelectric transformer drive circuit and a protection circuit according to Embodiment 1 of the present invention. This embodiment is similar to the conventional piezoelectric transformer drive circuit shown in FIG. 7 in that a plurality of piezoelectric transformers, a drive circuit that drives these piezoelectric transformers, and a frequency sweep oscillator that outputs a frequency signal to the drive circuit A plurality of loads each having one terminal connected to the secondary electrode of the piezoelectric transformer, a current flowing out from the other terminal of the load, and converted into a voltage, and the value is preset. A load current comparison circuit for providing a signal for determining a frequency sweep direction of the frequency sweep oscillator in comparison with a reference voltage of 1, and an output from a secondary electrode of the piezoelectric transformer, and voltage-dividing and rectifying the value in advance. An output voltage comparison circuit for providing a signal for determining a frequency sweep direction of the frequency sweep oscillator based on a result of comparison with a set second reference voltage. In FIG. 1, a piezoelectric transformer, an output voltage comparison circuit, a frequency sweep transmitter, and the like are omitted.

  In FIG. 1, a plurality of cold cathode tubes 10 as a plurality of loads are connected to the output sides of a plurality of piezoelectric transformers, and wirings for current input to a load current comparison circuit 14 are connected to the respective load low-voltage side terminals 11. The current determination circuit 12 is branched and connected. All outputs of the current determination circuit 12 are input to the OR circuit 13. The current determination circuit 12 determines whether or not the output current of each load satisfies a preset current value, and outputs the result. When the OR circuit 13 determines that the current value is equal to or less than the specified value even if the output of the current determination circuit 12 is one, an abnormal stop signal is output to the drive circuit 20 to stop the operation of the drive circuit 20. That is, in this embodiment, the current determination circuit 12 and the OR circuit 13 constitute a protection circuit.

  The current determination circuit 12 according to the present embodiment includes a current-voltage conversion circuit and a comparator. An example of a current-voltage conversion circuit used in the current determination circuit 12 of the present embodiment is shown in FIGS. 2A and 2B, and an example of a comparator is shown in FIG. 2A and 2B, the current input from the input terminal 21 or 23 is converted into a voltage by the input resistor 25 and the ground resistor 26, and the output is determined by the ratio of the resistance values of the input resistor and the ground resistor. A voltage value is output from the output terminal 22 or 24. In FIG. 3, the comparator is composed of an operational amplifier 31. A reference voltage is applied to the inverting input terminal 32, and the output terminal 22 or 24 of the current-voltage conversion circuit is connected to the non-inverting input terminal 33, and the output voltage value is compared with the reference voltage to obtain a result. Output from the output terminal 34.

  As described above, in the present embodiment, for example, in a piezoelectric transformer driving circuit for lighting a liquid crystal display using a plurality of cold cathode tubes, when one of the plurality is in an abnormal state such as breakage, the current The determination circuit 12 compares the threshold voltage with a reference voltage, and when it is determined that there is an abnormality, the drive circuit is stopped.

  In a backlight such as a liquid crystal display having n cold cathode fluorescent lamps, n current determination circuits for monitoring a current flowing out from a load (hereinafter referred to as a tube current) are provided, and any one of the tube current values is set in advance. If it is smaller than the threshold value, it is determined that there is an abnormality and the drive circuit is stopped.

  A setting example of the tube current threshold and a measurement example of the tube current in the current determination circuit when the present embodiment is applied to a liquid crystal backlight having four cold cathode tubes are shown below.

Tube current threshold Steady tube current Tube current when cold cathode tube 1 is abnormal Cold cathode tube 1 3mA 6mA Crack 0mA
Cold cathode tube 2 3mA 6mA 6mA
Cold cathode tube 3 3mA 6mA 6mA
Cold cathode tube 4 3mA 6mA 6mA

  When there is an abnormality that the cold cathode tube 1 breaks, the tube current output from the cold cathode tube 1 becomes 0, and thus falls below a set threshold value. As a result, it is determined that there is an abnormality, and the drive circuit is stopped.

  In the present embodiment, the current that branches from the load low-voltage side terminal 11 to the current determination circuit 12 and is input to the load current comparison circuit 14 is converted into a voltage by converting one of the output currents into a voltage. It may be compared with the voltage and fed back to the drive frequency, or all output currents may be combined and converted to a voltage and compared with the first reference voltage and fed back to the drive frequency.

(Embodiment 2)
FIG. 4 is a configuration diagram showing a part of the piezoelectric transformer driving circuit and the protection circuit according to the second embodiment of the present invention. The piezoelectric transformer drive circuit of the present embodiment is the same as that of the first embodiment except for the configuration of the protection circuit. In FIG. 4, a plurality of cold cathode tubes 10, which are a plurality of loads, are connected to the output sides of a plurality of piezoelectric transformers, and a current determination circuit 42 is connected to each load low-voltage side terminal 11. Here, the current determination circuit 42 includes the current-voltage conversion circuit in FIG. 2B and the comparator in FIG. All outputs of the current determination circuits 42 are input to the OR circuit 43. The current determination circuit 42 determines whether or not the output current of each load satisfies a preset current value, and outputs the result. In the OR circuit 13, even if one current determination circuit 12 is present, the current value is less than a specified value. Is output, an abnormal stop signal is output to the drive circuit 20 to stop the operation of the drive circuit 20. That is, in this embodiment, the current determination circuit 42 and the OR circuit 43 constitute a protection circuit.

  In the present embodiment, the current-voltage conversion circuit in the load current comparison circuit 44 is shared with the current-voltage conversion circuit of the current determination circuit 42 and is the same voltage as the voltage input to the comparator of the current determination circuit 42. Is input to the load current comparison circuit 44, and one or more of these voltages are compared with the first reference voltage and fed back to the drive frequency.

(Embodiment 3)
FIG. 5 is a configuration diagram showing a part of the piezoelectric transformer driving circuit and the protection circuit according to the third embodiment of the present invention. The piezoelectric transformer drive circuit of the present embodiment is the same as that of the first embodiment except for the configuration of the protection circuit. In FIG. 5, a plurality of cold cathode tubes 10 which are a plurality of loads are connected to the output sides of a plurality of piezoelectric transformers, and output currents are taken out from the respective load low voltage side terminals 11 and inserted into the respective lines. The outputs are combined via the connected diode 55 and connected to the current determination circuit 52.

  In the present embodiment, in a backlight such as a liquid crystal display having a plurality of cold cathode tubes, the current determination circuit 52 that monitors the tube current of each load has a circuit for determining based on the total current of the tube current When the total tube current value is smaller than a preset total tube current threshold value, an abnormality stop signal for stopping the drive circuit 20 is output. Here, the current determination circuit 52 is basically composed of a combination of the current-voltage comparison circuit shown in FIG. 2 and the comparator shown in FIG.

  A setting example of the tube current threshold and a measurement example of the tube current in the current determination circuit 52 when the present embodiment is applied to a liquid crystal backlight having four cold cathode tubes are shown below.

Threshold steady-state total tube current Current value of cold-cathode tube abnormality Total tube current 20mA 24mA Crack 18mA

  Here, the tube current in a steady state per cold cathode tube was 6 mA, the total tube current value was 24 mA, and the threshold was 20 mA. In this case, the total tube current value when one cold-cathode tube is damaged is 18 mA, which is below the threshold value, so that it is determined to be abnormal, and the drive circuit is stopped.

(Embodiment 4)
FIG. 6 is a configuration diagram showing a part of the piezoelectric transformer driving circuit and the protection circuit according to the fourth embodiment of the present invention. The piezoelectric transformer drive circuit of the present embodiment is the same as that of the first embodiment except for the configuration of the protection circuit. In FIG. 6, a plurality of cold cathode tubes 10, which are a plurality of loads, are connected to the output sides of a plurality of piezoelectric transformers, respectively, and output currents are taken out from the respective load low-voltage side terminals 11. A current determination circuit 62 for determining a current value is connected. Furthermore, in this embodiment, the output current is taken out separately from each load low-voltage side terminal 11, the output is merged via the diode 65 inserted in each line, and the total tube current value Is connected to a current judgment circuit 66 for judging the above.

  All the outputs of the individual current determination circuits 62 are input to the OR circuit 63. The current determination circuit 62 determines whether each individual tube current satisfies a preset current value and outputs the result. In the OR circuit 63, even if one current determination circuit 12 is present, the current value is less than a specified value. Is output, an abnormal stop signal is output to the drive circuit 60, and the operation of the drive circuit 60 is stopped. On the other hand, when the total tube current value is smaller than a preset total tube current threshold value, the current determination circuit 66 determines that it is abnormal and outputs an abnormal stop signal for stopping the drive circuit 60.

  As described above, in the present embodiment, it is determined whether or not each current flowing out from a plurality of loads individually satisfies a preset current value, and at the same time, the respective current values are summed to obtain the value. Is provided with a protection circuit which is determined by comparing with another reference, and the drive circuit is stopped based on the result of both.

  A setting example of tube current thresholds and a measurement example of tube current in the current determination circuits 62 and 66 when the present embodiment is applied to a liquid crystal backlight having four cold cathode tubes are shown below. Here, an abnormality in the cold cathode tube impedance is assumed, and a case where current flows even if the cold cathode tube is abnormal is taken as an example.

Setting value / measurement value in current judgment circuit 62
Threshold Steady tube current Abnormal tube current Cold cathode tube 1 5mA 6mA 3mA
Cold cathode tube 2 5mA 6mA 6mA
Cold cathode tube 3 5mA 6mA 6mA
Cold cathode tube 4 5mA 6mA 6mA

Setting value / measurement value in current judgment circuit 66
Threshold Steady state current value Abnormal current value Total tube current 20mA 24mA 21mA

  Since each tube current is individually determined and further determined by the total current value, in the case of the above example, an abnormality cannot be detected only by the determination with the total tube current. Is detected.

  Next, a setting example of the tube current threshold when the tube current is unbalanced and a measurement example of the tube current will be described.

Setting value / measurement value in current judgment circuit 62
Threshold Steady tube current Abnormal tube current Cold cathode tube 1 3mA 6mA 4.5mA
Cold cathode tube 2 3mA 6mA 6mA
Cold cathode tube 3 3mA 6mA 4mA
Cold cathode tube 4 3mA 6mA 5mA

Setting value / measurement value in current judgment circuit 66
Threshold value Steady state current value Abnormal current value Total tube current 20mA 24mA 19.5mA

  In this case, since each tube current is not determined to be lower than the threshold value only, the abnormality is not detected, but the total tube current value is determined to be abnormal below the threshold value.

  By determining the abnormality based on both the individual tube current value and the total tube current value as in the present embodiment, the threshold setting is changed depending on the mode assuming various abnormal modes. The corresponding abnormal mode can be detected.

(Embodiment 5)
In the present embodiment, the operation of the protection circuit including the current determination circuit and the OR circuit is stopped during the period when the drive circuit is not driven, or the output for stopping the drive circuit is not output from the protection circuit. This is a piezoelectric transformer drive circuit. In the case of having a time-division drive control circuit that periodically stops driving of the drive circuit in order to control the average output power of the piezoelectric transformer and provide a dimming function as in the conventional piezoelectric transformer drive circuit shown in FIG. In addition, since the tube current becomes 0 during the stop time of the drive circuit, the purpose is to prevent the protection circuit from outputting an abnormal signal and stopping the drive circuit until then.

  The specific configuration of the present embodiment is basically the same as that of the first to fourth embodiments described above, but in this embodiment, a drive circuit stop signal from the time division drive control circuit is input and A difference is that a circuit for stopping the operation of the protection circuit during the stop signal period or a circuit for cutting off the output of the stop signal at the time of abnormality from the protection circuit is provided during the stop signal period.

  As described above, in the present invention, in the piezoelectric transformer driving circuit having a plurality of discharge tubes, the current of each load is monitored, the total value of the currents of each load, or both are monitored. As a result, the abnormality of the output current is determined and the drive circuit is stopped. Therefore, the abnormality of the output current can be detected more reliably and the drive circuit can be stopped than in the past.

  Needless to say, the present invention is not limited to the above-described embodiment, and a specific circuit configuration or the like can be changed in design according to the purpose of use.

The block diagram which shows a part of piezoelectric transformer drive circuit of Embodiment 1 of this invention, and a protection circuit. The figure which shows an example of the current-voltage conversion circuit used for a current determination circuit. The figure which shows an example of a comparator. The block diagram which shows a part of piezoelectric transformer drive circuit of Embodiment 2 of this invention, and a protection circuit. The block diagram which shows a part of piezoelectric transformer drive circuit of Embodiment 3 of this invention, and a protection circuit. The block diagram which shows a part of piezoelectric transformer drive circuit of Embodiment 4 of this invention, and a protection circuit. The block diagram of the conventional piezoelectric transformer drive circuit. The figure which shows an example of the conventional piezoelectric transformer drive circuit which has a protection circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cold cathode tube 11, 109 Load low voltage side terminal 12, 42, 52, 62, 66 Current determination circuit 13, 43, 63 OR circuit 20, 60, 201 Drive circuit 14, 44, 54, 64, 3104 Load current comparison circuit 55, 65 Diodes 21, 23 Input terminal 22, 24 Output terminal 25 Input resistor 26 Ground resistor 31 Operational amplifier 32 Inverted input terminal 33 Non-inverted input terminal 34 Output terminal 200 Protection circuit 102 Piezoelectric transformer
103 Load 106 Primary electrode 107 Secondary electrode 108 Load high voltage side terminal 205 Frequency sweep oscillator 3206 Output voltage comparison circuit 306 Time division drive control circuit 110 Reference voltage VrefA
212 Reference voltage VrefB
307 Duty control voltage Vduty

Claims (5)

A plurality of piezoelectric transformers each having a primary electrode to which an input AC voltage is applied and a secondary electrode that is insulated from the primary electrode and outputs an output AC voltage; and outputs an AC waveform necessary for the primary electrode of the piezoelectric transformer. A driving circuit for driving, a frequency sweep oscillator that outputs the frequency signal of the AC waveform to the driving circuit, a plurality of loads each having one terminal connected to a secondary electrode of the piezoelectric transformer, and the other of the loads A load current comparison circuit for inputting a current flowing out from a terminal, converting it into a voltage, comparing the value with a first reference voltage set in advance, and providing a signal for determining the frequency sweep direction of the frequency sweep oscillator And the output of the secondary electrode of the piezoelectric transformer is input and voltage-divided rectified, and the value is compared with a preset second reference voltage to determine the frequency sweep direction of the frequency sweep oscillator. A piezoelectric transformer drive circuit and an output voltage comparator circuit which gives a constant signal,
A protection circuit that detects currents flowing out from the other terminals of the plurality of loads, and stops the drive circuit when at least one of the current values is less than a preset current value; Piezoelectric transformer drive circuit. A plurality of piezoelectric transformers each having a primary electrode to which an input AC voltage is applied and a secondary electrode that is insulated from the primary electrode and outputs an output AC voltage; and outputs an AC waveform necessary for the primary electrode of the piezoelectric transformer. A driving circuit for driving, a frequency sweep oscillator that outputs the frequency signal of the AC waveform to the driving circuit, a plurality of loads each having one terminal connected to a secondary electrode of the piezoelectric transformer, and the other of the loads A load current comparison circuit for inputting a current flowing out from a terminal, converting it into a voltage, comparing the value with a first reference voltage set in advance, and providing a signal for determining the frequency sweep direction of the frequency sweep oscillator And the output of the secondary electrode of the piezoelectric transformer is input and voltage-divided rectified, and the value is compared with a preset second reference voltage to determine the frequency sweep direction of the frequency sweep oscillator. A piezoelectric transformer drive circuit and an output voltage comparator circuit which gives a constant signal,
A protection circuit that detects a total value of currents flowing out from the other terminal of the plurality of loads and stops the drive circuit when the total value of the currents does not satisfy a preset current value; A piezoelectric transformer drive circuit. A plurality of piezoelectric transformers each having a primary electrode to which an input AC voltage is applied and a secondary electrode that is insulated from the primary electrode and outputs an output AC voltage; and outputs an AC waveform necessary for the primary electrode of the piezoelectric transformer. A driving circuit for driving, a frequency sweep oscillator that outputs the frequency signal of the AC waveform to the driving circuit, a plurality of loads each having one terminal connected to a secondary electrode of the piezoelectric transformer, and the other of the loads A load current comparison circuit for inputting a current flowing out from a terminal, converting it into a voltage, comparing the value with a first reference voltage set in advance, and providing a signal for determining the frequency sweep direction of the frequency sweep oscillator And the output of the secondary electrode of the piezoelectric transformer is input and voltage-divided rectified, and the value is compared with a preset second reference voltage to determine the frequency sweep direction of the frequency sweep oscillator. A piezoelectric transformer drive circuit and an output voltage comparator circuit which gives a constant signal,
Means for detecting each of the currents flowing out from the other terminal of the plurality of loads, and means for detecting a total value of the currents flowing out from the other terminal of the plurality of loads. A piezoelectric transformer drive circuit comprising: a protection circuit that stops the drive circuit when at least one of current values or a total value of the currents is less than a preset current value.   The protection circuit determines whether or not the preset current value is satisfied by comparing a voltage value obtained by converting the current flowing out from the other terminal of the load with a predetermined reference voltage value. The piezoelectric transformer drive circuit according to claim 1, wherein the piezoelectric transformer drive circuit is determined.   5. The device according to claim 1, wherein during the period when the drive circuit is not driven, the operation of the protection circuit is stopped, or the protection circuit does not output an output for stopping the drive circuit. A piezoelectric transformer driving circuit according to 1.

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