JP2001128460A - Piezoelectric transformer drive device and discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric transformer driving device, for which the conversion efficiency of the piezoelectric transformer is improved, the variable control of an output current is stabilized and safety is improved, and to provide a discharge lamp lighting device using this. SOLUTION: By setting the resonance frequency f1 of a series resonance circuit, comprising an inductor L1 and the input static capacitance Cd1 of a piezoelectric transformer 104 to a higher level by 10% or more than the intrinsic resonance frequency (drive frequency) fs of the transformer 104, the transformer 104 is driven by the frequency or higher, at which a load current value I3 becomes the largest. As a result, a resonance current decreases, so that the loss caused by this resonance current can be minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer driving device and a discharge lamp lighting device using the same, and more particularly to improvement of the conversion efficiency of a piezoelectric transformer, stabilization of variable output current control, and improvement of safety. It is.

[0002]

2. Description of the Related Art Conventionally, a compact and lightweight power supply device requiring a high voltage, such as a discharge lamp lighting device for a backlight, a copier, a page printer, a dust collector, a high voltage power source such as an ozone generator, and a DC-DC converter. A piezoelectric transformer has been used to achieve this.

[0003] As an example of a circuit configuration of a drive unit for applying a voltage to the input side of a piezoelectric transformer, a plurality of types are known. As one of them, there is a circuit configuration driven by a single-ended output as disclosed in JP-A-9-74444 and JP-A-11-8082.

[0004] This is, as shown in FIG.
2, two switching elements Q1 and Q2 that are alternately turned on between the power supply and the ground are arranged based on the control signal output from the power supply 1 and the output point of the two switching elements Q1 and Q2. And an inductor L1 forming a sine filter 203.

A voltage is applied from a connection point between the two switching elements Q1 and Q2 to the input side of the piezoelectric transformer 204 via the inductor L3. Further, a current flowing through a load 205 connected to the output side of the piezoelectric transformer 204 is connected to a resistor R
By converting the voltage into a voltage by s and feeding back to the control circuit 201, the control circuit 201 smoothes the feedback voltage,
The switching elements Q1,
The drive control of Q2 is performed.

An example of drive control of the switching elements Q1 and Q2 by the control circuit 201 is disclosed in
There is known a control method using the frequency characteristics of the piezoelectric transformer 204, as disclosed in JP-A-167694, JP-A-8-107678, and JP-A-9-107684. This is because the conversion efficiency of the piezoelectric transformer can be increased by setting the driving frequency (frequency of the applied voltage) of the piezoelectric transformer near the resonance frequency of the piezoelectric transformer.

On the other hand, when a discharge lamp or a fluorescent tube used for backlight illumination of a liquid crystal panel is used as the load 205, in order to widen the dimming range,
JP-A-5-198384, JP-A-9-10768
As disclosed in Japanese Unexamined Patent Publication No. 4 (1993) -104, a well-known burst dimming method of dimming by changing the on / off ratio of the discharge lamp has been used.

When a high voltage is generated by using the piezoelectric transformer 204, the piezoelectric transformer
In some cases, the vibration of the piezoelectric transformer 04 becomes excessive, the output voltage increases, and the piezoelectric transformer is cracked. To avoid this,
As shown in FIG. 3, two resistors R forming a voltage dividing circuit
1, R2, a voltage detection circuit 206, a comparator 207, and a latch circuit 208 to detect an abnormal increase in high-voltage output,
Alternatively, the state of the load 205 is detected and the piezoelectric transformer 2
There is known a protection circuit for stopping or restricting the driving of the drive circuit 04. Here, the voltage detection circuit 206 includes resistors R1, R2
Then, the output voltage of the piezoelectric transformer 204 is detected and output to the comparator 207. The comparator 207 calculates the voltage input from the voltage detection circuit 206 and the threshold voltage Vref.
And outputs the result as a binarized signal. The latch circuit 208 holds the binarized signal output from the comparator 207 at a predetermined timing and controls the control circuit 201.
Output to When the binary signal input from the latch circuit 208 indicates an abnormality, the control circuit 201 stops driving the switching elements Q1 and Q2 and stops voltage application to the piezoelectric transformer 204.

In some cases, the voltage converted by the resistor Rs is input to the voltage detection circuit 206 to perform a protection operation.

Further, as disclosed in Japanese Patent Application Laid-Open No. 10-321928, a temperature protection circuit for protecting against thermal runaway destruction and characteristic deterioration due to self-heating of the piezoelectric transformer 204 due to an abnormality of the load 205 is useful. It has been known.

[0011]

However, the above-described conventional piezoelectric transformer driving device has the following problems.

That is, in the conventional half-bridge type driving unit shown in FIG. 2, the resonance frequency of the series resonance circuit composed of the input capacitance of the piezoelectric transformer 204 and the inductor L1 of the sine filter 203 is determined. Frequency which is the same as the natural resonance frequency of
No. 44), and driving a piezoelectric transformer at the resonance frequency of a series resonance circuit (Japanese Patent Application Laid-Open No. H11-8082).

In these systems, the series resonance circuit is driven at its resonance frequency, so that the impedance of the driven circuit is minimized. For this reason, when a large drive current flows and the piezoelectric transformer 204 having a large input capacitance and a high step-up ratio is driven, there is a problem that the loss due to the resonance current increases and high conversion efficiency cannot be obtained.

In the conventional half-bridge type driving unit, when the drive output is to be PWM-controlled for widening the range of the input DC voltage Vin,
It is suitable only for a single type PWM waveform in which the ON / OFF periods of the switching elements Q1 and Q2 are exclusively changed. For this reason, there is a problem that waveform distortion due to higher harmonic components occurs even through the sine filter 203, resulting in a vertically asymmetric waveform, and the piezoelectric transformer 204 cannot be efficiently driven.

As a control method using the frequency characteristics of the piezoelectric transformer, a control method of adjusting the output using a curve on the right side of the frequency characteristics of the piezoelectric transformer 204 is a well-known technique. This method is also used in a discharge lamp lighting device using a piezoelectric transformer driving device used for backlight illumination of a notebook personal computer (hereinafter, referred to as a notebook PC). However, notebook PC
In this case, the input voltage Vin of the discharge lamp lighting device is required to support a wide input covering the range of the battery and the AC adapter.

Therefore, in the conventional frequency control system, control in the wide input range is often performed only by controlling the drive frequency. Therefore, the higher the input voltage Vin, the lower the conversion efficiency of the piezoelectric transformer 204. Driving is performed at a frequency apart from the frequency at which the maximum point occurs, and there is a problem that the conversion efficiency is reduced.

On the other hand, there is an increasing demand for increasing the dimming range of the backlight illumination toward the dark side for energy saving.

However, in the conventional constant current control using a continuous current, if the lamp current is reduced and the brightness is reduced due to the nature of the discharge lamp, problems such as unstable lighting of the fluorescent tube and extinguishing of the fluorescent tube occur. appear.

Therefore, as described above, instead of the method of continuously reducing the tube current, the tube current is allowed to flow to a stable region, and the lighting of the fluorescent tube is intermittently performed at such a frequency that the eyes do not flicker. A burst dimming method that performs dimming by changing an intermittent duty ratio has been used.

In the case of the burst dimming method, the fluorescent tube current is not a continuous current but a current intermittently flowing at a period of several hundred Hz. However, when the tube current flows intermittently, it is difficult to perform constant current control for stabilizing the brightness of the fluorescent tube.

For this reason, conventionally, a method of controlling the ON / OFF periods of the switching elements Q1 and Q2 at a time ratio without performing constant current control has been used (Japanese Patent Laid-Open No. 5-1983).
No. 84).

However, in this method, since the fluorescent lamp current is not controlled with a constant current, there is a problem that the luminance of the fluorescent tube changes due to a change in input voltage or a change in ambient temperature.

Therefore, a method has been devised in which burst dimming is performed in a state where constant current control of the fluorescent tube current is performed (Japanese Patent Laid-Open Publication No. Hei 1 (1998)).
0-223390).

When the burst dimming is performed by the constant current control as described above, since the fluorescent lamp current flows intermittently, the current detection voltage is high in the portion where the current flows and decreases in the portion where the current does not flow. In a conventional current (voltage) detection circuit, a rectified and smoothed voltage must be detected. Therefore, at the time of burst dimming, the average voltage level of the detection voltage decreases. Further, in the rectifying section for current detection, there is a problem that a pulsating flow of repetition of discharge occurs and control is likely to be unstable.

Therefore, in a conventional example, a system in which current detection in a frequency control loop is performed by a sample-and-hold circuit has been devised (Japanese Patent Laid-Open No. Hei 10-223390).

However, as described above, the driving device for the piezoelectric transformer needs to be equipped with a protection means for detecting an abnormality of the output voltage (current) due to an abnormality such as an open load and restricting the operation of the circuit. In the detection circuit that detects the output voltage of the piezoelectric transformer or the load current,
The sample hold circuit as described above is not provided because the circuit scale becomes large. For this reason, at the time of burst dimming, the voltage detected by using the detection resistor and the rectifier circuit has a pulsating flow as described above, and there is a problem that the protection circuit easily malfunctions, particularly when the dimming level is lowered. .

Further, in the case of a discharge lamp lighting device using a winding transformer, a protection means of a type in which a thermal fuse is thermally coupled to a core of the transformer has been used as protection against heat generation of the transformer in the event of an abnormality. However, in the case of a discharge lamp lighting device using a piezoelectric transformer driving device, since the piezoelectric transformer is a vibrating body, a temperature detecting element cannot be attached to the main body of the piezoelectric transformer. Did not.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a piezoelectric transformer driving device which improves the conversion efficiency of a piezoelectric transformer, stabilizes variable output current control, and improves safety, and a discharge lamp using the same. It is to provide a lighting device.

[0029]

According to the first aspect of the present invention, there is provided a first and a second power supply circuit which are connected in series between an input DC power supply and a ground potential section and are driven alternately. Switching means comprising two switching elements;
Drive control means for alternately controlling on / off driving of the first and second switching elements; and a drive control means connected between a connection point between the first and second switching elements and an input terminal of the piezoelectric transformer. And a resonance frequency of a series resonance circuit including the inductor and the input capacitance of the piezoelectric transformer, wherein the resonance frequency of the series resonance circuit is higher or lower than the natural resonance frequency of the piezoelectric transformer. On the other hand, the present invention proposes a piezoelectric transformer driving device that is set in a frequency band having an efficiency higher than the efficiency at the natural resonance frequency.

According to the piezoelectric transformer driving device, the piezoelectric transformer is driven at a frequency different from the frequency at which the load current value becomes maximum, and the series resonance frequency of the series resonance circuit is set to be lower than the natural resonance frequency of the piezoelectric transformer. One of a high frequency band and a low frequency band, and set to a frequency band of higher efficiency than the efficiency at the natural resonance frequency,
Since it is separated from the driving frequency, the resonance current is reduced, and the loss caused by the resonance current can be reduced. Further, when the series resonance frequency is close to the driving frequency, there is an effect that the input voltage of the piezoelectric transformer increases due to the boosting effect of the inductor, and the input capacitance of the piezoelectric transformer is easily affected by variation and temperature change. When the resonance frequency is separated from the natural resonance frequency of the piezoelectric transformer by a predetermined value or more, the boosting effect of the inductor is reduced, and the variation of the input capacitance of the piezoelectric transformer and the influence of the input capacitance and inductance change due to temperature change are reduced. You.

According to a second aspect of the present invention, in the piezoelectric transformer driving device according to the first aspect, the resonance frequency of the series resonance circuit including the inductor and the input capacitance of the piezoelectric transformer is higher than the natural resonance frequency of the piezoelectric transformer. We propose a piezoelectric transformer drive set at a frequency band that is 4.5% to 16% lower.

According to the piezoelectric transformer driving device, the piezoelectric transformer is driven at a frequency equal to or lower than the frequency at which the load current value becomes maximum, and the series resonance frequency of the series resonance circuit is changed to the natural resonance frequency of the piezoelectric transformer, that is, the driving frequency. Since the frequency band is separated from the frequency band of 4.5% to 16% lower than the frequency, the resonance current is reduced, and the loss generated by the resonance current can be reduced. Further, when the series resonance frequency is close to the driving frequency, there is an effect that the input voltage of the piezoelectric transformer increases due to the boosting effect of the inductor, and the input capacitance of the piezoelectric transformer is easily affected by variation and temperature change. Since the resonance frequency is set to be 4.5% to 16% lower than the natural resonance frequency of the piezoelectric transformer, the boosting effect of the inductor is reduced, and the input capacitance due to the variation in the input capacitance of the piezoelectric transformer and the temperature change. And the effect of inductance change is reduced.

According to a third aspect of the present invention, in the piezoelectric transformer driving device of the first aspect, the resonance frequency of the series resonance circuit including the inductor and the input capacitance of the piezoelectric transformer is higher than the natural resonance frequency of the piezoelectric transformer. We propose a piezoelectric transformer drive set to be higher than 10%.

According to the piezoelectric transformer driving device, the piezoelectric transformer is driven at a frequency equal to or higher than the frequency at which the load current value becomes maximum, and the series resonance frequency of the series resonance circuit is changed to the natural resonance frequency of the piezoelectric transformer, that is, the driving frequency. Since the separation is performed so as to be higher than the frequency by 10% or more, the resonance current is reduced, and the loss generated by the resonance current can be reduced. Further, when the series resonance frequency is close to the driving frequency, there is an effect that the input voltage of the piezoelectric transformer increases due to the boosting effect of the inductor, and the input capacitance of the piezoelectric transformer is easily affected by variation and temperature change. Since the resonance frequency is set to be higher than the natural resonance frequency of the piezoelectric transformer by 10% or more, the boosting effect of the inductor is reduced, and the variation in the input capacitance of the piezoelectric transformer and the change in the input capacitance and the inductance due to the temperature change are reduced. Impact is mitigated.

According to a fourth aspect of the present invention, in the piezoelectric transformer driving device according to the first aspect, a control signal for switching an on / off state is input as the first and second switching elements, and a pulse width of the control signal is provided. And a switching element for which an on-state period and an off-state period are set in accordance with the above. The drive control means makes the on-state period per cycle of each of the first and second switching elements equal. We propose a piezoelectric transformer drive device that controls the pulse width.

According to the piezoelectric transformer driving device, since the on-state periods of the first and second switching elements change evenly, the driving waveform becomes vertically symmetric even when the duty is 50% or less, and the harmonics are increased. The generation of components is reduced. Thereby, the conversion efficiency of the piezoelectric transformer is improved. Further, by changing the length of the ON state period, the input voltage level of the piezoelectric transformer is changed.

According to a fifth aspect of the present invention, in the piezoelectric transformer driving device according to the fourth aspect, a field effect transistor is used as the first and second switching elements, and the first switching element and the second switching element are used. Between the connection point and the input DC power supply and between the connection point and the ground potential, the forward direction is opposite to the energizing direction of the switching element connected in parallel with each switching element and connected in parallel. A piezoelectric transformer driving device provided with a set diode is proposed.

According to the piezoelectric transformer driving device, the insertion of the diode can reduce the loss as compared with the case where only the parasitic diode of the field effect transistor is used.

According to a sixth aspect of the present invention, in the piezoelectric transformer driving device according to the first aspect, voltage detecting means for detecting an input voltage level of the piezoelectric transformer and feeding back the voltage, and detecting the voltage level detected by the voltage detecting means. Based on the above, there is proposed a piezoelectric transformer driving device provided with input voltage level control means for controlling the input voltage level of the piezoelectric transformer to a predetermined constant value.

According to the piezoelectric transformer driving device, the input voltage level to the piezoelectric transformer is maintained at a constant value by the input voltage level control means based on the voltage level detected by the voltage detection means. Thus, the output voltage fluctuation of the piezoelectric transformer is reduced.

According to a seventh aspect of the present invention, in the piezoelectric transformer driving device according to the fourth aspect, a voltage detecting means for detecting an input voltage level of the piezoelectric transformer and feeding back the voltage level;
Pulse generating means for generating a pulse signal at a repetition frequency in the range of not less than 300 Hz and controlling the pulse width of one cycle of the pulse signal in a time ratio; and detecting the pulse signal output from the pulse generating means by the voltage detecting means. Signal superimposing means for superimposing on the voltage detected by the signal superimposing means and outputting the same, and the drive control means so that the voltage level output from the signal superimposing means substantially matches the predetermined voltage level set in advance. A piezoelectric transformer driving device including on-period control means for setting an on-state period per cycle of the repetition frequency of each of the first and second switching elements is proposed.

According to the piezoelectric transformer driving device, the voltage level fed back to the drive control means changes by superimposing the pulse signal by the signal superimposing means. , The input voltage level to the piezoelectric transformer is changed according to the pulse width. Thereby, the output voltage of the piezoelectric transformer is changed. Therefore, variable current control to a load connected to the output side of the piezoelectric transformer can be performed. Accordingly, when a fluorescent tube or a discharge lamp is used as the load, a change in the brightness of the fluorescent tube or the discharge lamp can be suppressed even if the input voltage of the piezoelectric transformer changes.

According to an eighth aspect of the present invention, in the piezoelectric transformer driving device according to the seventh aspect, the voltage detecting means has means for detecting and feeding back only an AC component of an input voltage level of the piezoelectric transformer, The input voltage level control means includes a piezoelectric transformer driving device having means for changing the on-state period of each of the first and second switching elements based on the voltage level of the AC voltage component detected by the voltage detection means. suggest.

According to the piezoelectric transformer driving device, since the level of only the AC component is detected by the voltage detecting means, the amplitude of the input AC voltage of the piezoelectric transformer is stabilized, and
Even if a DC bias component is superimposed on the input voltage waveform of the piezoelectric transformer, the AC voltage level input to the piezoelectric transformer is controlled to a constant level.

According to a ninth aspect of the present invention, in the piezoelectric transformer driving device according to the seventh aspect, a current detecting means for detecting a current value flowing to a load connected to an output side of the piezoelectric transformer, and an output from the pulse generating means. A frequency control feedback loop having frequency control means for changing the driving frequency of the piezoelectric transformer based on the pulse signal to be output, the detection signal output from the output current detection unit, and a predetermined reference signal set in advance. The proposed piezoelectric transformer drive is proposed.

According to the piezoelectric transformer driving device, the pulse signal controlled by the duty ratio generated from the pulse generating means is superimposed on the frequency control feedback loop for detecting the output current of the piezoelectric transformer and controlling the driving frequency. The driving frequency is changed in response to a change in the pulse width or the like of the pulse signal. Thereby, when a fluorescent tube or a discharge lamp is used as the load of the piezoelectric transformer, the efficiency when the output current is reduced by changing the pulse width of the pulse signal is improved. That is, when the output current is changed, the temperature of the fluorescent tube as the load changes. Therefore, when the inner wall temperature of the fluorescent tube changes, the mercury vapor pressure changes to change the impedance of the fluorescent tube, and the load impedance changes to change the optimum driving frequency of the piezoelectric transformer with high efficiency. The driving frequency of the piezoelectric transformer is corrected in accordance with the level of the piezoelectric transformer to approach the optimum driving frequency, thereby improving the efficiency.

According to a tenth aspect of the present invention, in the piezoelectric transformer driving device according to the seventh aspect, an output current detecting means for detecting an output current of the piezoelectric transformer and feeding back a detection signal corresponding to the output current value; Based on a pulse signal output from a pulse generation unit, a detection signal output from the output current detection unit, and a preset reference signal,
The present invention proposes a piezoelectric transformer driving device including a protection unit that stops or restricts driving of the piezoelectric transformer by detecting a load release and an output short circuit on the output side of the piezoelectric transformer.

According to the piezoelectric transformer driving device, when the output side of the piezoelectric transformer is opened or short-circuited by the protection means, the driving of the piezoelectric transformer is stopped or limited. Further, when the pulse signal is changed and the output current of the piezoelectric transformer is reduced, even if the average value of the detection voltage is reduced, the protection unit is configured based on the pulse signal, the detection signal, and the reference signal. Since the open load and the output short circuit on the output side of the piezoelectric transformer are detected, malfunction is prevented. For example, the protection unit may add the pulse signal level and the detection signal level and compare with the reference signal level, or may add the pulse signal level and the reference signal level and add the detection signal level. By performing the comparison, detection is performed according to the output control state of the piezoelectric transformer, so that malfunction is prevented.

In the eleventh aspect, in the piezoelectric transformer driving device according to the seventh aspect, the pulse generating means includes:
A piezoelectric transformer driving device having an operational amplifier having a low processing speed at the final output stage of the pulse signal and outputting the pulse signal from the operational amplifier is proposed.

According to the piezoelectric transformer driving device, by outputting the pulse signal from the low-speed operational amplifier, it is possible to obtain a pulse waveform having a gentle rise and fall. Accordingly, when the output of the piezoelectric transformer is changed by the pulse signal, the rising waveform of the switching element in the ON state period becomes gentle, and it is possible to reduce a low-frequency growling sound generated from the piezoelectric transformer. Further, the stress generated in the piezoelectric transformer is reduced, and the reliability is improved.

According to a twelfth aspect of the present invention, in the piezoelectric transformer driving device of the first aspect, output current detecting means for detecting a current flowing to a load connected to an output side of the piezoelectric transformer, and detecting the detected load current. A current / voltage conversion unit that converts the voltage into a voltage and outputs the voltage and a voltage level output from the current / voltage conversion unit and a reference voltage level, and compares the comparison result and the frequency characteristic curve of the step-up ratio of the piezoelectric transformer. A frequency control feedback loop having frequency control means for changing a drive frequency of the piezoelectric transformer based on the voltage, a voltage detection means for detecting an input voltage level of the piezoelectric transformer, and a detection result of the voltage detection means. Energization time control means for controlling the energization time per cycle to the piezoelectric transformer input terminal so that the input voltage level becomes substantially constant. Together and a voltage level control feedback loop that, the response speed of the frequency control feedback loop,
A piezoelectric transformer driving device set to be slower than the response speed of the voltage level control feedback loop is proposed.

According to the piezoelectric transformer driving device, the load current detected by the output current detecting means is converted into a voltage by the frequency control feedback loop and compared with the reference voltage level. The driving frequency of the piezoelectric transformer is changed based on the frequency characteristic curve of the step-up ratio of the transformer. Further, in parallel with this, the input voltage of the piezoelectric transformer is maintained at a substantially constant value by the voltage level control feedback loop. Further, when performing frequency control using the frequency characteristic curve of the step-up ratio of the piezoelectric transformer, in an attempt to cope with a wide range of input DC voltage, the input voltage of the piezoelectric transformer increases when the input voltage is higher. As a result, the drive frequency moves to the higher frequency side from the point of high efficiency. Further, when the driving frequency exceeds the anti-resonance frequency, the input impedance of the piezoelectric transformer decreases, and the efficiency is significantly reduced. However, since the response speed of the voltage level control feedback loop is set faster than the response speed of the frequency control feedback loop, when changing the output voltage or output current of the piezoelectric transformer using the voltage level control feedback loop, The influence on the frequency control feedback loop can be reduced.

According to a thirteenth aspect of the present invention, in the piezoelectric transformer driving device according to the first aspect, a temperature detecting means for detecting the temperature of the switching element or the vicinity thereof, and a temperature detected by the temperature detecting means is a predetermined threshold value. A piezoelectric transformer driving device provided with a driving stop means for stopping driving of the piezoelectric transformer when a temperature is exceeded.

According to the piezoelectric transformer driving device, when the input power of the piezoelectric transformer increases due to a load abnormality or the like, the heat generation of the switching element increases, and when the temperature of the switching element or its vicinity becomes higher than a predetermined temperature. Since the driving of the piezoelectric transformer is stopped, breakage of the piezoelectric transformer is prevented. A piezoelectric transformer is a device that has the property of decreasing efficiency at high temperatures and may cause thermal runaway. However, since the piezoelectric transformer is a vibrating body, it is difficult to directly detect the temperature of the piezoelectric transformer,
By detecting the temperature of the switching element of the drive unit which is correlated with the input power of the piezoelectric transformer, a protection operation at abnormal temperature can be performed.

According to the present invention, a current flowing through a load connected to the output side of the piezoelectric transformer is detected, the detected load current is converted into a voltage, and the voltage level is compared with a reference voltage level. A frequency control feedback loop having frequency control means for changing a driving frequency of the piezoelectric transformer based on the comparison result and a frequency characteristic curve of a step-up ratio of the piezoelectric transformer; In a piezoelectric transformer driving device including a voltage level control feedback loop for controlling a conduction time per cycle to a transformer input terminal, a response speed of the frequency control feedback loop is higher than a response speed of the voltage level control feedback loop. A piezoelectric transformer drive set late is proposed.

According to the piezoelectric transformer driving device, the load current detected by the output current detecting means is converted into a voltage by the frequency control feedback loop and compared with the reference voltage level. The driving frequency of the piezoelectric transformer is changed based on the frequency characteristic curve of the step-up ratio of the transformer. Further, in parallel with this, the input voltage of the piezoelectric transformer is maintained at a substantially constant value by the voltage level control feedback loop. Further, when performing frequency control using the frequency characteristic curve of the step-up ratio of the piezoelectric transformer, in an attempt to cope with a wide range of input DC voltage, the input voltage of the piezoelectric transformer increases when the input voltage is higher. As a result, the drive frequency moves to the higher frequency side from the point of high efficiency. Further, when the driving frequency exceeds the anti-resonance frequency, the input impedance of the piezoelectric transformer decreases, and the efficiency is significantly reduced. However, since the response speed of the voltage level control feedback loop is set faster than the response speed of the frequency control feedback loop, when changing the output voltage or output current of the piezoelectric transformer using the input level control loop, The influence on the control feedback loop can be reduced.

According to a fifteenth aspect, a pulse generating means for generating a pulse signal of a predetermined frequency for setting a voltage application time per one cycle of the dimming frequency to the piezoelectric transformer by a pulse width, and a pulse width of the pulse signal And a voltage applying means for applying a voltage at a predetermined period to the input side of the piezoelectric transformer based on the pulse signal, wherein the output current of the piezoelectric transformer is detected. An output current detection unit that feeds back a detection signal corresponding to the output current value; a pulse signal output from the pulse generation unit; a detection signal output from the output current detection unit; Based on a reference signal, a load release and an output short circuit on the output side of the piezoelectric transformer are detected to stop or limit the driving of the piezoelectric transformer. Suggest piezoelectric transformer driving apparatus and a protection unit that.

According to the piezoelectric transformer driving device, when the output side of the piezoelectric transformer is opened or short-circuited by the protection means, the driving of the piezoelectric transformer is stopped or limited. Furthermore, when the pulse signal is changed and the output current of the piezoelectric transformer is reduced, even if the average value of the detection voltage is reduced, the protection unit applies the pulse signal, the detection signal, and the reference signal to each other. Since the open circuit and the output short circuit on the output side of the piezoelectric transformer are detected on the basis of this, malfunction is prevented. For example, the protection means includes:
By adding the pulse signal level and the detection signal level and comparing with the reference signal level, or adding the pulse signal level and the reference signal level and comparing with the detection signal level, the piezoelectric transformer Since the detection according to the output control state is performed, malfunction is prevented.

According to another aspect of the present invention, a current detecting means for detecting a value of a current flowing to a load connected to an output side of the piezoelectric transformer, and a detection result of the current value detecting means and a reference value are compared. A frequency control feedback loop having frequency control means for changing the driving frequency of the pulse generator, and a pulse generation means for generating a pulse signal for setting a voltage application time per cycle of the dimming frequency to the piezoelectric transformer by a pulse width; A piezoelectric transformer driving device comprising: a pulse width varying unit that changes a pulse width of the pulse signal; and a voltage application unit that applies a voltage to an input side of the piezoelectric transformer at a predetermined cycle based on the pulse signal. A piezoelectric transformer driving device provided with mixing means for mixing the pulse signal with a feedback signal of a control feedback loop is proposed.

According to the piezoelectric transformer driving device, the pulse signal generated from the pulse generating means is mixed with the feedback signal of the frequency control feedback loop, and the driving frequency is changed with a change in the pulse width of the pulse signal. Is changed. Thereby, when a fluorescent tube or a discharge lamp is used as the load of the piezoelectric transformer, the efficiency when the output current is reduced by changing the pulse width of the pulse signal is improved. That is, when the output current is changed,
The temperature of the fluorescent tube as the load changes. Therefore, when the inner wall temperature of the fluorescent tube changes, the mercury vapor pressure changes to change the impedance of the fluorescent tube, and the load impedance changes to change the optimum driving frequency of the piezoelectric transformer with high efficiency. The driving frequency of the piezoelectric transformer is corrected in accordance with the level of the piezoelectric transformer to approach the optimum driving frequency, thereby improving the efficiency.

According to a seventeenth aspect of the present invention, in the piezoelectric transformer driving device for applying a DC voltage to the input side of the piezoelectric transformer intermittently by a switching element, a temperature detecting means for detecting a temperature of the switching element or a temperature near the switching element. And a means for stopping driving of the piezoelectric transformer when the switching element exceeds a predetermined temperature.

According to the piezoelectric transformer driving device, when the input power of the piezoelectric transformer increases due to a load abnormality or the like and the heat generation of the switching element increases, the temperature of the switching element or its vicinity becomes higher than a predetermined temperature. At this time, the driving of the piezoelectric transformer is stopped, so that the breakage of the piezoelectric transformer is prevented. A piezoelectric transformer is a device that has the property of decreasing efficiency at high temperatures and may cause thermal runaway. However, since the piezoelectric transformer is a vibrating body, it is difficult to directly detect the temperature of the piezoelectric transformer.Therefore, by detecting the temperature of the switching element of the drive unit that is correlated with the input power of the piezoelectric transformer, the abnormal temperature Can be performed.

Further, claim 18 proposes a discharge lamp lighting device using the piezoelectric transformer driving device according to any one of claims 1 to 17.

[0064]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1 and 4 are block diagrams showing electric circuits of the piezoelectric transformer driving device according to the first embodiment of the present invention. The first embodiment corresponds to claim 1 of the present invention. FIG. 4 shows the piezoelectric transformer in the circuit shown in FIG. 1 using an equivalent circuit. In the figure, 101 is a control circuit, 102 is an output circuit, 10
3 is a sine filter, 104 is a piezoelectric transformer, and 105 is a discharge lamp such as a cold cathode fluorescent tube as a load.

The output circuit 102 is a P-channel MOS type F
ET (Q1) and N-channel MOS FET (Q2). The source of the FET (Q1) is connected to the DC power source Vin, and the drain is connected to the drain of the FET (Q2). The source of the FET (Q2) is grounded.

Further, the control voltage Vq output from the control circuit 101 is applied to the gates of these FETs (Q1, Q2).
1 and Vq2 are applied, and the FETs (Q1 and Q2) are alternately turned on between the power supply and the ground based on the control voltages Vq1 and Vq2, and the connection point between them, namely, the drain of the FET (Q1) and the voltage V1 Is output.

The connection point between the FET (Q 1) and the FET (Q 2) is connected to the input terminal of the piezoelectric transformer 104 via the inductor L 1 forming the sine filter 103, and connected to the input terminal of the piezoelectric transformer 104. Is applied with a voltage V2.

The output terminal of the piezoelectric transformer 104 is connected to one electrode of a discharge lamp 105 serving as a load, and the output voltage V3 from the piezoelectric transformer 104 is applied.

The other electrode of the discharge lamp 105 is grounded via a resistor Rs. Energizing current I3 to discharge lamp 105
Is converted to a voltage V3 'by a resistor Rs.
By feeding back 3 'to the control circuit 101, the control circuit 101 smoothes the feedback voltage V3' and controls the driving of the FETs (Q1, Q2) so that the smoothed voltage becomes a constant value.

Further, in the present embodiment, the inductor L1
The resonance frequency of a series resonance circuit including the input capacitance of the piezoelectric transformer 104 is set to be higher than the natural resonance frequency of the piezoelectric transformer 104 by 15% or more.

That is, as shown in FIG.
04 can be represented by an equivalent circuit of an inductor L, a capacitor C, a resistor R, and capacitors Cd1 and Cd2. Cd1 is the primary-side input capacitance of the piezoelectric transformer,
d2 is a value obtained by converting the secondary-side input capacitance of the piezoelectric transformer to the primary-side. The inductor L, the capacitor C, and the resistor R are connected in series, and one end of the series circuit is an input terminal and the other end is an output terminal. Also, the capacitor Cd1
Is connected between the input terminal and ground, and the capacitor Cd2 is connected between the output terminal and ground.

Thus, the inductor L1 of the sine filter 103 and the input capacitance Cd1 of the piezoelectric transformer 104
Constitutes a series resonance circuit. Here, the inductor L1
, The series resonance frequency f1 of the input capacitance Cd1, and the series resonance frequency (natural resonance frequency) fs of the piezoelectric transformer 104.
Is expressed by the following equations (1) and (2), and the values of the inductance of the inductor L1 and the values of the inductor L, the capacitor C, the resistor R, and the capacitors Cd1 and Cd2 are set so as to satisfy the equation (3). Is set.

F1 = 1 / {2π (L1 · Cd1) 1/2} (1) fs = 1 / {2π (LC ′) 1/2} (2) 1.15 × fs ≦ f1 <1. 5 × fs (3) Here, C ′ represents a combined capacitance of C and Cd2. If the influence of Cd2 becomes small and C becomes dominant depending on the conditions of the load 105, C ′ may be replaced by C.

According to the above configuration, the piezoelectric transformer 104 is driven at a frequency higher than the frequency at which the load current value I3 becomes maximum. Further, the series resonance frequency f1 of the series resonance circuit
Are set so as to be at least 15% higher than the natural resonance frequency fs of the piezoelectric transformer 104, that is, the driving frequency of the piezoelectric transformer 104, so that the resonance current is reduced, and the loss generated by the resonance current is reduced. can do.

FIG. 5 shows the results of measuring the measured conversion efficiency when the resonance frequency of the series resonance circuit was changed by changing the constant of the circuit. In FIG. 5, the horizontal axis represents the detuning degree (%) of the input circuit, and the vertical axis represents the efficiency (%). In this measurement, a 4 W fluorescent tube (φ2.3, L300 mm) was used as a load, and the fluorescent tube current was 5 mA.
rms, the inverter circuit supply voltage was set to 8.0 V, and the efficiency characteristics were compared by changing the input inductor value of the piezoelectric transformer. The detuning degree means that the series resonance frequency f1 of the series resonance circuit is equal to the natural resonance frequency f
s, that is, how far from the drive frequency of the piezoelectric transformer 104 is.

In this measurement result, when the degree of detuning is -30%, an efficiency of 85.9% is obtained, and the degree of detuning is -23%.
Is 88.5% efficiency, and detuning degree is -9%, 8
9.3% efficiency, 88.6% efficiency when detuning is 0%, 88.8% efficiency when detuning is 8%, 89.9% when detuning is 12% The efficiency is 90.0% when the detuning degree is 29% and 90.90 when the detuning degree is 58%.
It showed 0% efficiency.

As shown in FIG. 5, the efficiency increases when the resonance frequency f1 is about 10% higher than the natural resonance frequency fs, and becomes substantially flat when the resonance frequency f1 is 12% or less. In the case described above, it is desirable to set it to 15% or more in consideration of the dispersion of parts, temperature characteristics and the like, but it may be set to 10% or more or 12% or more. Further, the resonance frequency f1 may be lower than the natural resonance frequency fs by 4.5% to 16%.

In this measurement, the point at which the resonance frequency f1 of the inductor and input capacitance of the input side of the piezoelectric transformer coincides with the drive frequency (natural resonance frequency) fs is defined as the detuning degree 0 (%). At the point of the detuning degree of 0 (%), the resonance current increases and the loss increases, so that the efficiency including the drive circuit decreases. According to the measured data, the efficiency is improved when the resonance circuit on the input side is detuned to a side 12% higher than the drive frequency. Although there is a difference depending on the type of the piezoelectric transformer used, if the detuning is performed by about 15% or more, the decrease in efficiency due to the influence of the resonance current can be reduced. Even if detuning is performed, the measured data shows good efficiency characteristics. However, if the inductor value is too small, the harmonic component increases and the efficiency decreases, and the load current cannot be reduced. In addition, a large detuning causes a problem that the loss increases when the power supply voltage is increased with a wide input.

The series resonance frequency f1 is equal to the driving frequency f.
When it is close to s, there is an effect that the input voltage V2 of the piezoelectric transformer 104 increases due to the boosting effect of the inductor L1.
For this reason, the piezoelectric transformer 104 is easily affected by variations in the input capacitance Cd1 and changes in the ambient temperature. However, since the series resonance frequency f1 is set to be higher than the natural resonance frequency fs of the piezoelectric transformer 104 by 15% or more, the boosting effect of the inductor L1 is reduced, and the variation in the input capacitance Cd1 of the piezoelectric transformer 104 and In addition, the effects of changes in input capacitance and inductance L1 due to temperature changes can be reduced.

Next, a second embodiment of the present invention will be described.

FIG. 6 is a block diagram showing an electric system circuit of the piezoelectric transformer driving device according to the second embodiment. The second embodiment corresponds to claims 2 and 4 of the present invention.

In the figure, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. The difference between the second embodiment and the first embodiment is that the control circuit 101 is a voltage-controlled oscillation circuit (hereinafter, VC
O) 301, the operation control circuit 30 of the VCO 301
2. A pulse width modulation control circuit (hereinafter, referred to as a PWM control circuit) 303, and resistors R1, R2,
That is, a feedback loop including the voltage detection circuit 106 and the error amplification circuit 107 is provided.

The VCO 301 is an oscillating circuit for outputting a rectangular wave signal of a predetermined frequency.
Is input, and the voltage V3 '
The frequency of the output signal is changed so that the value of 3 'becomes equal to the reference value preset by the operation control circuit 302.

The operation control circuit 302 causes the VCO 301 to output a rectangular wave signal having a frequency about 20% higher than the resonance frequency f1 of the piezoelectric transformer 104 at the time of startup, and the frequency decreases after startup, and the output current i3 of the piezoelectric transformer 104 decreases. When the value reaches a predetermined value, the frequency sweep of the VCO 301 is stopped.

Further, the operation control circuit 302
01 is controlled so that the frequency of the output signal does not become lower than a predetermined frequency. This is so that the maximum point of the efficiency of the piezoelectric transformer 104 is at a frequency slightly higher than the series resonance frequency of the piezoelectric transformer 104, and the output signal frequency of the VCO 301 which is the driving frequency of the piezoelectric transformer 104 does not drop to a frequency with low efficiency. This is to limit.

The PWM control circuit 303 receives the output signal of the VCO 301 and the output voltage V6 of the error amplifier circuit 107, and generates pulse signals Vq1 and Vq2 of a predetermined voltage level that changes with the output signal frequency of the VCO 301. One pulse signal Vq1 is applied to the gate of the FET (Q1), and the other pulse signal Vq2 is applied to the gate of the FET (Q2). Further, the PWM control circuit 303 changes the pulse width of the pulse signals Vq1 and Vq2 so that the level of the voltage V2 becomes a predetermined value.

The resistors R1 and R2 are connected in series, connected between the input terminal of the piezoelectric transformer 104 and the ground, and divide the input voltage V2 to the piezoelectric transformer 104. The voltage V4 divided by these resistors R1 and R2 is input to the voltage detection circuit 106.

The voltage detection circuit 106 detects the input voltage V4
And outputs it as the voltage V5.

The error amplifying circuit 107 includes the voltage detecting circuit 10
6, and outputs a difference from a preset reference voltage Vref1 as a voltage V6.

Here, in this embodiment, the PWM control circuit 303 controls the pulse width so that the ON state period per one cycle of each of the FETs (Q1, Q2) is equal.

That is, as shown in FIG.
(Q1) is in the ON state during period t1 and the other FET (Q
The pulse signals Vq1 and Vq2 are generated such that the periods t2 during which 2) is in the on state are substantially equal and they are shifted by a half cycle.

As described above, by controlling the pulse signal Vq1 input to the gate of the FET (Q1) and the pulse signal Vq2 input to the gate of the FET (Q2), the FET (Q
Since the on-state period of 1) and the FET (Q2) change uniformly, the driving waveform becomes vertically symmetric even when the duty is 50% or less, and the generation of harmonic components is reduced as shown in FIG. Thereby, the piezoelectric transformer 10
4 improves the conversion efficiency.

Further, the output voltage V of the error amplifier 107 is
6, the length of the ON state period is changed, so that the input voltage level of the piezoelectric transformer 104 can be kept constant.

FIG. 7 is a diagram showing each signal waveform when operated so that the duty in the ON state period is changed uniformly at a frequency of 66 KHz and a duty of 25%. Input voltage V2,
The output current I3 of the piezoelectric transformer 104, the output voltage V1 of the output circuit 102, the pulse signal Vq1 input to the gate of the FET (Q2), and the pulse signal Vq2 input to the gate of the FET (Q1) are shown.

FIG. 8 is a diagram showing frequency components obtained by Fourier-transforming the input voltage waveform of the piezoelectric transformer shown in FIG.

In order to confirm the effect of the present embodiment,
FIGS. 9 and 10 show the results of actual measurement of similar signal waveforms in the conventional piezoelectric transformer driving device shown in FIG.

FIG. 9 is a diagram showing each signal waveform when operated so as to exclusively change the duty in the ON state period at a frequency of 66 KHz and a duty of 25%. A voltage V2, an output current I3 of the piezoelectric transformer 104, an output voltage V1 of the output circuit 102, a pulse signal Vq1 input to the gate of the FET (Q2), and a pulse signal Vq2 input to the gate of the FET (Q1) are shown. . FIG. 10 is a diagram showing frequency components obtained by Fourier-transforming the piezoelectric transformer input voltage waveform of FIG.

As can be seen by comparing the waveform of FIG. 8 with the waveform of FIG.
The generation of the second harmonic is reduced.

Next, a third embodiment of the present invention will be described.

FIG. 11 is a block diagram showing an electric circuit of the piezoelectric transformer driving device according to the third embodiment.
The third embodiment corresponds to claims 3 and 4 of the present invention.

In the figure, the same components as those of the above-described second embodiment are denoted by the same reference numerals, and description thereof will be omitted. The difference between the third embodiment and the second embodiment is that the FET (Q1) and the FET
Each FET (Q1, Q2) is connected between the connection point of (Q2) and the input DC power supply Vin and between the connection point and the ground potential, respectively.
2) and the FETs (Q1,
Diodes D1 and D2 whose forward directions are set in the reverse direction to the energizing direction of Q2) are provided.

That is, the cathode of the diode D1 is an FET
(Q1), and the anode of the diode D1 is connected to the drain of the FET (Q1). The cathode of the diode D2 is connected to the drain of the FET (Q2), and the cathode of the diode D2 is connected to the FET (Q2).
(Q2).

According to the above configuration, the diodes D1, D
By providing 2, the loss can be reduced as compared with the case where only the parasitic diodes of the FETs (Q1, Q2) are used.

The loss can be greatly reduced by using a Schottky diode having a small forward voltage as the diodes D1 and D2.

Next, a fourth embodiment of the present invention will be described.

FIG. 12 is a block diagram showing an electric circuit of the piezoelectric transformer driving device according to the fourth embodiment.
The fourth embodiment corresponds to claims 5, 6, and 9 of the present invention.

In the figure, the same components as those in the third embodiment described above are denoted by the same reference numerals, and description thereof will be omitted. Further, the difference between the fourth embodiment and the third embodiment is that the provision of the dimming signal generation circuit 401 makes it possible to supply electric power to the discharge lamp 105 which is a load connected to the output side of the piezoelectric transformer 104. Can be changed arbitrarily.

The dimming signal generation circuit 401 generates a pulse signal V7 at a repetition frequency in the range of 80 Hz to 300 Hz by an external operation, and controls the pulse width of the pulse signal V7 per cycle by time ratio control. Circuit. Further, in the present embodiment, the output stage of the pulse signal V7 controlled for the duty ratio for dimming is constituted by a low-speed operational amplifier.

Output signal V7 of dimming signal generation circuit 401
Is superimposed on the output signal V5 of the voltage detection circuit 106,
The signal V5 ′ obtained by combining these is input to the error amplifier circuit 107.

The error amplifying circuit 107 receives the voltage V5 'and outputs a difference from a preset reference voltage Vref1 as a voltage V6.

According to the above configuration, since the pulse signal V7 is superimposed on the output signal of the voltage detection circuit 106, the pulse signal V7 is fed back to the PWM control circuit 303 by changing the frequency and pulse width of the pulse signal V7 from outside. Since the voltage level changes, the input voltage level to the piezoelectric transformer 104 is changed by the PWM control circuit 303 according to the pulse width of the pulse signal V7.

As a result, the output voltage V3 of the piezoelectric transformer 104 is changed, so that the power supplied to the discharge lamp 105 serving as a load connected to the output side of the piezoelectric transformer 104 can be changed, and even after the change. Stable constant current control is possible.

Thus, when a fluorescent tube or a discharge lamp is used as a load, the input voltage V
Even if the change in occurs, the change in luminance of the fluorescent tube and the discharge lamp can be suppressed to a small value.

Further, since the level of only the AC component is detected by the voltage detection circuit 106, the piezoelectric transformer 10
4, the amplitude of the input AC voltage V2 is stabilized, and even if a DC bias component is superimposed on the waveform of the input voltage V2 of the piezoelectric transformer 104, the level of the AC voltage V2 input to the piezoelectric transformer 104 is controlled to a constant level. be able to.

In the dimming signal generation circuit 401,
Since the pulse signal V7 is output by the low-speed operational amplifier, the rising waveform of the ON period at the time of burst light control becomes gentle, and the piezoelectric transformer 1 at the time of burst light control is used.
It is possible to reduce the low-frequency growling sound generated from the sound signal 04. Further, stress on the piezoelectric transformer 104 is reduced, and reliability can be improved.

Next, a fifth embodiment of the present invention will be described.

FIG. 13 is a block diagram showing an electric circuit of the piezoelectric transformer driving device according to the fifth embodiment.
The fifth embodiment corresponds to claims 7, 10 and 14 of the present invention.

In the figure, the same components as those of the above-described fourth embodiment are denoted by the same reference numerals, and description thereof is omitted. The fifth embodiment is different from the fourth embodiment in that a frequency control feedback loop including a current detection circuit 402, an error amplification circuit 403, and a low-pass filter (hereinafter, referred to as LPF) is provided. .

The current detection circuit 402 receives the voltage V3 'converted by the resistor Rs, smoothes the voltage V3', and outputs it as a voltage V8.

The error amplification circuit 403 includes the current detection circuit 40
2 and the dimming signal generation circuit 401
And outputs a difference between a voltage obtained by adding these voltages and a preset reference voltage Vref2 as a voltage V9.

The LPF 404 receives the voltage V9 output from the error amplifying circuit 403, extracts only the low frequency component of the voltage V9, and outputs it as a voltage V10.

In this embodiment, a VCO 301 'is provided in place of the VCO 301. This VCO 301 ′
The frequency of the output signal is changed so that the output voltage V10 of the PF 404 becomes almost half of the maximum value of the output voltage V10.

Further, in the present embodiment, the current detection circuit 4
02, the response speed of the frequency control feedback loop including the error amplification circuit 403 and the LPF 404 is lower than the response speed of the voltage level control feedback loop including the resistors R1 and R2, the voltage detection circuit 106, and the error amplification circuit 107. Each circuit constant is set as described above.

According to the above configuration, when a fluorescent tube or a discharge lamp is used as the load of the piezoelectric transformer 104, the pulse width of the pulse signal V7 output from the dimming signal generation circuit 401 is changed to change the pulse width of the piezoelectric transformer 104. The efficiency when the output current I3 is reduced can be improved.

That is, the output current I3 of the piezoelectric transformer 104
Is changed, the temperature of the discharge lamp 105, which is a load, changes, so that the inner wall temperature of the discharge lamp changes. This allows
The mercury vapor pressure inside the discharge lamp 105 changes, the impedance of the discharge lamp changes, and the load impedance changes. Further, the optimum driving frequency at which the piezoelectric transformer 104 is efficient also changes.

For this reason, in the present embodiment, by combining the output signal V7 of the dimming signal generation circuit 401 and the output voltage V8 of the current detection circuit 402, the driving frequency of the piezoelectric transformer 104 is changed according to the dimming state. I made it possible.

As a result, the driving frequency of the piezoelectric transformer 104 is corrected according to the level of the output current I3.
Since the driving frequency of the piezoelectric transformer 104 can be made closer to the optimum driving frequency in accordance with the dimming state, the piezoelectric transformer 104 can always be driven with the best efficiency in that state.

The above control method is based on the piezoelectric transformer 10
4 based on the frequency characteristic curve of the step-up ratio of 4.
It is needless to say that the control for changing the drive frequency of the drive signal 04 is also effective.

In the case where the frequency control is performed using the frequency characteristic curve of the step-up ratio of the piezoelectric transformer 104 as described above, in order to cope with a wide range of the input DC voltage, the input of the piezoelectric transformer 104 is increased when the input voltage is higher. The voltage increases, and as a result, the drive frequency moves to the higher frequency side from the point of high efficiency. Further, when the driving frequency exceeds the anti-resonance frequency, the input impedance of the piezoelectric transformer 104 decreases, and the efficiency is significantly reduced. However, as described above, since the response speed of the voltage level control feedback loop is set faster than the response speed of the frequency control feedback loop, the output voltage V3 or the output current I3 of the piezoelectric transformer 104 using the voltage level control feedback loop. Is changed, the influence on the frequency control feedback loop can be reduced.

In this embodiment, the error amplification circuit 403
In the above, the output voltage V8 of the current detection circuit 402 and the voltage of the pulse signal V7 output from the dimming signal generation circuit 401 are added to output a difference from the reference voltage Vref2. Alternatively, the voltage of the pulse signal V7 and the reference voltage Vref2 may be added, and the difference between the sum and the output voltage V8 of the current detection circuit 402 may be output.

Next, a sixth embodiment of the present invention will be described.

FIG. 14 is a block diagram showing an electric circuit of the piezoelectric transformer driving device according to the sixth embodiment.
The sixth embodiment corresponds to claim 8 of the present invention.

In the figure, the same components as those of the above-described fifth embodiment are denoted by the same reference numerals, and description thereof is omitted. The sixth embodiment is different from the fifth embodiment in that an error amplifier circuit 4 as a protection means for preventing a malfunction such as an output-side load opening and an output short-circuit of the piezoelectric transformer 104 is prevented.
05 is provided.

That is, in the present embodiment, the current detection circuit 40
2 receives the voltage V3 'converted by the resistor Rs and outputs voltages V8 and V11 corresponding to the voltage V3'.

The error amplification circuit 405 is connected to the current detection circuit 40
2 and the dimming signal generation circuit 40
The pulse signal V7 output from 1 is input, and a difference between a voltage obtained by adding these voltages and a preset reference voltage Vref3 is obtained. When the difference voltage becomes equal to or less than a predetermined threshold voltage, , The voltage V12 is inverted from a high level to a low level or from a low level to a high level. This voltage V12 is supplied to the voltage detection circuit 1 together with the voltage V7.
The voltage is superimposed on the voltage V5 output from the signal generator 06, and a composite voltage of these voltages is input to the error amplifier circuit 107 as a voltage V5 ″.

The error amplifier 107 receives the voltage V5 ″ and outputs a difference from a preset reference voltage Vref1 as a voltage V6.

According to the above configuration, when the output side of the piezoelectric transformer 104 is opened or short-circuited to the ground, the level of the output voltage V12 of the error amplifier circuit 405 becomes a voltage level indicating an abnormality. Suspended or restricted. When the driving is stopped, the error amplifier circuit 4
05 is subjected to positive feedback, and the output voltage of the error amplification circuit 405 is latched.

Further, the pulse signal V7 output from the dimming signal generation circuit 401 is changed to
When the output current I3 of the current detection circuit 402 decreases, the current detection circuit 402
Error amplification circuit 4
05, the pulse signal V7, the voltage V11 and the reference voltage V
Based on ref3, load open and output short circuit on the output side of the piezoelectric transformer 104 are detected, so that detection according to the output control state of the piezoelectric transformer 104 can be performed.
Malfunction can be prevented.

In the present embodiment, the error amplifier circuit 405 adds the output voltage V11 of the current detection circuit 402 and the voltage of the pulse signal V7 output from the dimming signal generation circuit 401 to calculate the difference between the output voltage V11 and the reference voltage Vref3. Although the output is performed, the voltage of the pulse signal V7 output from the dimming signal generation circuit 401 and the reference voltage Vref3 may be added, and the difference between the sum and the output voltage V11 of the current detection circuit 402 may be output. .

Next, a seventh embodiment of the present invention will be described.

FIG. 15 is a block diagram showing an electric circuit of the piezoelectric transformer driving device according to the seventh embodiment.
The seventh embodiment corresponds to claims 11 and 15 of the present invention.

In the figure, the same components as those in the above-described sixth embodiment are denoted by the same reference numerals, and description thereof is omitted. The difference between the seventh embodiment and the sixth embodiment is that the temperature of the FETs (Q1, Q2) of the output circuit 102 or the temperature in the vicinity thereof is detected, and the detected temperature becomes equal to or higher than a predetermined temperature. A temperature detection circuit 406 for outputting a temperature abnormality signal V13 when the temperature abnormality signal V13
, A PWM control circuit 303 ′ that stops operation when a temperature abnormality occurs.

The temperature detection circuit 406 is composed of, for example, a temperature sensor such as a thermistor, a comparator, and the like. The temperature sensor is fixed in close contact with the FETs (Q1, Q2), or is disposed in the vicinity thereof.

According to the above configuration, the input power of the piezoelectric transformer 104 increases due to a load abnormality or the like, and the FET (Q1,
When the heat generation of Q2) increases and the temperature of the FET (Q1, Q2) or its vicinity becomes equal to or higher than a predetermined temperature, the driving of the piezoelectric transformer 104 is stopped.
The destruction and accident of 04 are prevented.

[0146] The piezoelectric transformer 104 is a device that has a property of decreasing the efficiency at high temperatures and may cause thermal runaway. However, since the piezoelectric transformer 104 is a vibrating body, it is difficult to directly detect the temperature of the piezoelectric transformer 104.

As described above, the FETs (Q 1, Q 1) of the output circuit 102 having a correlation with the input power of the piezoelectric transformer 104.
By detecting the temperature of 2), the protection operation at the time of abnormal temperature can be performed.

In the first to seventh embodiments, the piezoelectric transformer driving device of the present invention is applied to the discharge lamp lighting device for lighting the discharge lamp 105. However, the present invention is not limited to this.

The configurations of the first to seventh embodiments are specific examples of the present invention, and the present invention is not limited to only these configurations.

For example, in the above-described embodiment, the output circuit 1
02 is a half-bridge type configured by FETs (Q1, Q2), but may be an output circuit of a full-bridge configuration. Further, an auxiliary boosting transformer may be used for the output circuit 102. The output circuit 102 is connected to one FET.
And a choke coil or a transformer. Further, a chopper circuit may be provided on the input side, and the input voltage level of the piezoelectric transformer 104 may be controlled to be constant by PWM control of the chopper circuit. Further, a method may be employed in which the duty of the half bridge section of the output circuit 102 is fixed to 50%.

[0151]

As described above, according to the piezoelectric transformer driving device of the first aspect of the present invention, the resonance current is reduced, and the loss generated by the resonance current can be reduced.

According to the piezoelectric transformer driving device of the second aspect, in addition to the above effects, the resonance frequency is 4.5% to 16% higher than the natural resonance frequency of the piezoelectric transformer.
Since the setting is made lower, the boosting effect of the inductor is reduced, and the variation of the input capacitance of the piezoelectric transformer and the influence of the input capacitance and the inductance change due to the temperature change are reduced.

According to the piezoelectric transformer driving device of the third aspect, in addition to the above effects, the resonance frequency is set so as to be 15% or more higher than the natural resonance frequency of the piezoelectric transformer. The step-up effect of the inductor is reduced, and variations in the input capacitance of the piezoelectric transformer and the effects of changes in the input capacitance and inductance due to temperature changes are reduced.

Further, according to the piezoelectric transformer driving device of the fourth aspect, in addition to the above effects, the generation of harmonic components is reduced, so that the conversion efficiency in the piezoelectric transformer can be improved.

According to the piezoelectric transformer driving device of the fifth aspect, in addition to the above effects, when a field effect transistor is used as the switching element, compared with a case where only a parasitic diode of the field effect transistor is used. Thus, the loss can be reduced.

According to the piezoelectric transformer driving device of the sixth aspect, in addition to the above effects, the input voltage level to the piezoelectric transformer is maintained at a constant value based on the voltage level detected by the voltage detecting means. Therefore, output voltage fluctuation of the piezoelectric transformer can be reduced.

According to the piezoelectric transformer driving device of claim 7, in addition to the above-mentioned effects, it is possible to control a constant current that can be changed to a load connected to the output side of the piezoelectric transformer. Accordingly, when a fluorescent tube or a discharge lamp is used as the load, a change in the brightness of the fluorescent tube or the discharge lamp can be suppressed even if the input voltage of the piezoelectric transformer changes.

According to the piezoelectric transformer driving device of the eighth aspect, in addition to the above effects, the amplitude of the input AC voltage of the piezoelectric transformer can be stabilized, and the DC voltage applied to the input voltage waveform of the piezoelectric transformer can be stabilized. Even when components are superimposed, the AC voltage level input to the piezoelectric transformer can be maintained at a constant level.

According to the piezoelectric transformer driving device of the ninth aspect, in addition to the above-described effects, the driving frequency of the piezoelectric transformer is changed in response to a change in the pulse width of the pulse signal. When a fluorescent tube or a discharge lamp is used as the load of the piezoelectric transformer, the efficiency when the output current is reduced can be improved by changing the pulse width of the pulse signal.

According to the piezoelectric transformer driving device of the tenth aspect, in addition to the above effects, when the pulse signal is changed and the output current of the piezoelectric transformer is reduced, the average value of the detected voltage decreases. However, since the protection means detects the load opening and the output short circuit on the output side of the piezoelectric transformer based on the pulse signal, the detection signal, and the reference signal, malfunction can be prevented.

According to the piezoelectric transformer driving device of the eleventh aspect, in addition to the above effects, the rising waveform of the switching element in the ON state period becomes gentle, and the low-frequency growling sound generated from the piezoelectric transformer is reduced. In addition to reducing the stress, the stress generated in the piezoelectric transformer can be reduced, and the reliability can be improved.

According to the piezoelectric transformer driving device of the twelfth aspect, in addition to the above effects, the response speed of the voltage level control feedback loop is set faster than the response speed of the frequency control feedback loop. When the output voltage or the output current of the piezoelectric transformer is changed using the level control loop, the influence on the frequency control loop can be reduced.

According to the piezoelectric transformer driving device of the thirteenth aspect, in addition to the above-described effects, even if the piezoelectric transformer is a vibrator and it is difficult to directly detect the temperature, the switching element or its switching element can be used. The protection operation at the time of abnormal temperature can be performed by detecting the temperature in the vicinity.

According to the piezoelectric transformer driving device of the present invention, the response speed of the voltage level control feedback loop is set faster than the response speed of the frequency control feedback loop. Thus, when the output voltage or the output current of the piezoelectric transformer is changed, the influence on the frequency control feedback loop can be reduced.

According to the piezoelectric transformer driving device of the fifteenth aspect, even if the output current of the piezoelectric transformer is reduced,
Since the protection means detects a load open and an output short circuit on the output side of the piezoelectric transformer based on the pulse signal, the detection signal, and the reference signal, malfunction can be prevented.

Further, according to the piezoelectric transformer driving device of the present invention, the driving frequency of the piezoelectric transformer is changed in accordance with the change of the pulse width of the pulse signal for changing the output current of the piezoelectric transformer. Further, when a fluorescent tube or a discharge lamp is used as the load of the piezoelectric transformer, the efficiency when the output current is reduced by changing the pulse width of the pulse signal can be improved.

According to the piezoelectric transformer driving device of the present invention, even if the piezoelectric transformer is a vibrating body and it is difficult to directly detect the temperature, the temperature of the switching element or the vicinity thereof is detected. The protection operation at abnormal temperature can be performed.

Further, according to the discharge lamp lighting device of the eighteenth aspect, the effect exhibited by the piezoelectric transformer driving device can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an electric circuit of a piezoelectric transformer driving device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an electric circuit of a conventional piezoelectric transformer driving device.

FIG. 3 is a block diagram showing an electric circuit of a conventional piezoelectric transformer driving device.

FIG. 4 is a diagram showing measured values of a detuning degree and a conversion efficiency of the piezoelectric transformer driving device according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing an equivalent circuit of an electric circuit of the piezoelectric transformer driving device according to the first embodiment of the present invention.

FIG. 6 is a block diagram showing an electric circuit of a piezoelectric transformer driving device according to a second embodiment of the present invention.

FIG. 7 is a diagram showing signal waveforms of main parts according to a second embodiment of the present invention.

8 is a diagram illustrating frequency components obtained by performing a Fourier transform on the input voltage waveform of the piezoelectric transformer illustrated in FIG. 7;

FIG. 9 is a diagram showing signal waveforms of main parts in a conventional piezoelectric transformer driving device.

FIG. 10 is a diagram illustrating frequency components obtained by Fourier transforming the input voltage waveform of the piezoelectric transformer shown in FIG. 9;

FIG. 11 is a block diagram showing an electric circuit of a piezoelectric transformer driving device according to a third embodiment of the present invention.

FIG. 12 is a block diagram showing an electric circuit of a piezoelectric transformer driving device according to a fourth embodiment of the present invention.

FIG. 13 is a block diagram showing an electric circuit of a piezoelectric transformer driving device according to a fifth embodiment of the present invention.

FIG. 14 is a block diagram showing an electric circuit of a piezoelectric transformer driving device according to a sixth embodiment of the present invention.

FIG. 15 is a block diagram showing an electric circuit of a piezoelectric transformer driving device according to a seventh embodiment of the present invention.

[Explanation of symbols]

101: control circuit, 102: output circuit, 103: sinusoidal filter, 104: piezoelectric transformer, 105: discharge lamp, 1
06: voltage detection circuit, 107: error amplification circuit, 301,
301 'VCO, 302 operation control circuit, 303, 3
03 ': PWM control circuit; 401: dimming signal generation circuit;
402: current detection circuit, 403: error amplification circuit, 404
.. LPF, 405 error amplifier circuit, 406 temperature detection circuit.

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[Procedure amendment]

[Submission date] November 12, 1999 (1999.11.
12)

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

According to the piezoelectric transformer driving apparatus, the piezoelectric transformer is driven at frequency load current value that is different from the frequency at which the maximum, a piezoelectric transformer natural resonant frequency of the series resonant frequency of the series resonant circuit Also, the frequency is set to one of the high frequency band and the low frequency band, and the frequency band is higher in efficiency than the efficiency at the natural resonance frequency, and is separated from the drive frequency. Loss can be reduced.
When the series resonance frequency is close to the driving frequency,
The boosting effect of the inductor has the effect of increasing the input voltage of the piezoelectric transformer, making it more susceptible to variations in the input capacitance of the piezoelectric transformer and changes in temperature. The boost effect of the inductor is reduced,
Variations in the input capacitance of the piezoelectric transformer and the effects of changes in input capacitance and inductance due to temperature changes are reduced.

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Claims (18)

[Claims] 1. A switching means comprising first and second switching elements connected in series between an input DC power supply and a ground potential section and driven alternately, and said first and second switching elements are connected to each other. A piezoelectric transformer driving device comprising: drive control means for alternately on / off driving control; and an inductor connected between a connection point of the first switching element and the second switching element and an input terminal of the piezoelectric transformer. The resonance frequency of the series resonance circuit including the inductor and the input capacitance of the piezoelectric transformer is one of a higher frequency band and a lower frequency band than the natural resonance frequency of the piezoelectric transformer, and at the natural resonance frequency. A piezoelectric transformer driving device, wherein the frequency band is set to a higher frequency band than the efficiency. 2. A resonance frequency of a series resonance circuit including the inductor and an input capacitance of a piezoelectric transformer is set in a frequency band of 4.5% to 16% lower than a natural resonance frequency of the piezoelectric transformer. The piezoelectric transformer driving device according to claim 1, wherein: 3. The resonance frequency of a series resonance circuit including the inductor and the input capacitance of the piezoelectric transformer is set to be higher than the natural resonance frequency of the piezoelectric transformer by 10% or more. The piezoelectric transformer driving device according to claim 1. 4. A control signal for switching an on / off state is input as the first and second switching elements,
A switching element that sets an on-state period and an off-state period in accordance with the pulse width of the control signal; and wherein the drive control unit controls the on-state of each of the first and second switching elements for one cycle. The pulse width control is performed so that the periods are equalized.
The piezoelectric transformer driving device as described in the above. 5. A field effect transistor is used as the first and second switching elements, and between a connection point between the first switching element and the second switching element and an input DC power supply, and between the connection point and ground. A low-loss diode connected in parallel with each of the switching elements and having a forward direction set in a direction opposite to a conduction direction of the switching elements connected in parallel with each other between the potentials; Item 6. The piezoelectric transformer driving device according to item 4. 6. A voltage detecting means for detecting and feeding back an input voltage level of the piezoelectric transformer, and a predetermined constant input voltage level of the piezoelectric transformer based on the voltage level detected by the voltage detecting means. 5. The piezoelectric transformer driving device according to claim 4, further comprising input voltage level control means for controlling the voltage to a value. 7. A voltage detecting means for detecting and feeding back an input voltage level of the piezoelectric transformer, generating a pulse signal at a repetition frequency in a range of 80 Hz to 300 Hz, and detecting a pulse width per cycle of the pulse signal. A pulse generating means for controlling a duty ratio; and a signal superimposing means for superimposing a pulse signal output from the pulse generating means on a voltage detected by the voltage detecting means and outputting the same. An on-state period per cycle of the repetition frequency of each of the first and second switching elements is set such that a voltage level output from the signal superimposing means substantially matches a predetermined voltage level set in advance. The piezoelectric transformer driving device according to claim 4, further comprising an on-period control unit. 8. The voltage detecting means includes means for detecting only an AC component of an input voltage level of the piezoelectric transformer and feeding back the voltage, and the input voltage level controlling means includes an AC voltage detected by the voltage detecting means. 8. The piezoelectric transformer driving device according to claim 7, further comprising means for changing an on-state period of each of the first and second switching elements based on a voltage level of the component. 9. A current detecting means for detecting a current value flowing to a load connected to an output side of the piezoelectric transformer, a pulse signal output from the pulse generating means, and a detection signal output from the output current detecting unit. 8. The piezoelectric transformer driving device according to claim 7, further comprising a frequency control feedback loop having frequency control means for changing a driving frequency of the piezoelectric transformer based on a predetermined reference signal set in advance. 10. An output current detection means for detecting an output current of the piezoelectric transformer and feeding back a detection signal corresponding to the output current value; a pulse signal output from the pulse generation means; Protection means for detecting a load release and an output short circuit on the piezoelectric transformer output side and stopping or limiting the driving of the piezoelectric transformer based on the output detection signal and a predetermined reference signal set in advance. The piezoelectric transformer driving device according to claim 7, wherein: 11. The piezoelectric device according to claim 7, wherein said pulse generating means includes an operational amplifier having a low processing speed at a final output stage of said pulse signal, and outputs said pulse signal from said operational amplifier. Transformer drive. 12. An output current detecting means for detecting a current flowing to a load connected to an output side of the piezoelectric transformer, a current / voltage converting means for converting the detected load current into a voltage and outputting the voltage, Frequency control means for comparing the voltage level output from the voltage conversion means with a reference voltage level, and changing the drive frequency of the piezoelectric transformer based on the comparison result and the frequency characteristic curve of the step-up ratio of the piezoelectric transformer. A frequency control feedback loop, voltage detection means for detecting an input voltage level of the piezoelectric transformer, and the piezoelectric transformer input terminal such that the input voltage level becomes substantially constant based on the detection result of the voltage detection means. And a voltage level control feedback loop having an energization time control means for controlling an energization time per cycle to the power supply. The response speed of changing loop, the piezoelectric transformer driving apparatus according to claim 1, characterized in that it is set slower than the response speed of the voltage level control feedback loop. 13. A temperature detecting means for detecting the temperature of the switching element or its vicinity, and a drive stop for stopping the driving of the piezoelectric transformer when a temperature detected by the temperature detecting means exceeds a predetermined threshold temperature. 2. The piezoelectric transformer driving device according to claim 1, further comprising means. 14. A current flowing in a load connected to an output side of a piezoelectric transformer is detected, the detected load current is converted into a voltage, and the voltage level is compared with a reference voltage level. A frequency control feedback loop having frequency control means for changing a driving frequency of the piezoelectric transformer based on a frequency characteristic curve of a step-up ratio of the piezoelectric transformer, and detecting an input voltage level of the piezoelectric transformer to connect to the piezoelectric transformer input terminal. In a piezoelectric transformer driving device having a voltage level control feedback loop for controlling an energization time per cycle, a response speed of the frequency control feedback loop is set to be lower than a response speed of the voltage level control feedback loop. A piezoelectric transformer driving device, characterized in that: 15. A pulse generating means for generating a pulse signal of a predetermined frequency for setting a voltage application time per one cycle of a dimming frequency to a piezoelectric transformer by a pulse width, and a pulse width for changing a pulse width of the pulse signal A piezoelectric transformer driving device comprising: a variable unit; and a voltage applying unit that applies a voltage to an input side of the piezoelectric transformer at a predetermined cycle based on the pulse signal. Output current detection means for feeding back a detection signal corresponding to a value, a pulse signal output from the pulse generation means, a detection signal output from the output current detection unit, and a predetermined reference signal set in advance. Protection means for detecting opening of the load and output short-circuit on the output side of the piezoelectric transformer and stopping or limiting the driving of the piezoelectric transformer. Piezoelectric transformer driving apparatus characterized by a. 16. A current detecting means for detecting a current value flowing to a load connected to an output side of a piezoelectric transformer, and a detection result of the current value detecting means is compared with a reference value to change a driving frequency of the piezoelectric transformer. A frequency control feedback loop having frequency control means for causing a voltage to be applied to the piezoelectric transformer, a pulse generation means for generating a pulse signal for setting a voltage application time per cycle of a dimming frequency by a pulse width, and a pulse of the pulse signal A piezoelectric transformer driving device comprising: a pulse width variable unit that changes a width; and a voltage application unit that applies a voltage to the input side of the piezoelectric transformer at a predetermined cycle based on the pulse signal. A piezoelectric transformer driving device comprising a mixing means for mixing the pulse signal with a signal. 17. A piezoelectric transformer driving device for applying a DC voltage intermittently by a switching element to an input side of a piezoelectric transformer, wherein a temperature detecting means for detecting a temperature of the switching element or a temperature near the switching element is provided. A driving means for stopping driving of the piezoelectric transformer when the temperature exceeds a predetermined temperature. 18. A discharge lamp lighting device using the piezoelectric transformer driving device according to any one of claims 1 to 17.