JP2000060136A - Piezoelectric inverter circuit and on-duty correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct deviations from the optimum value of on-duty at frequency ripple of voltage applied to a piezoelectric transformer caused by input voltage change or dimming operation, etc. SOLUTION: Correction of on-duty is performed by providing a frequency controller 10a, which controls the frequency of the voltage applied to a piezoelectric transformer, with an on-duty resistor 12, which performs the correction to the ripple of input voltage by adding a voltage value which is proportional to the input voltage thereby correcting the reference value, and a dimming on duty switching circuit 13, which corrects the reference value by switching a voltage dividing resistor for correcting the reference value through switching of the voltage dividing resistor for creating a reference value by the existence of dimming operation, and controlling the frequency with the corrected reference value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric inverter circuit using a piezoelectric transformer for lighting a fluorescent tube, and more particularly to a piezoelectric inverter in which the frequency control of the voltage applied to the piezoelectric transformer at the time of input voltage change or light control operation is improved. The present invention relates to a circuit and an on-duty correction method.

[0002]

2. Description of the Related Art A piezoelectric inverter circuit is a circuit for controlling the lighting of a fluorescent tube. In order to keep the brightness of the fluorescent tube constant, the piezoelectric inverter circuit controls the frequency of a voltage applied to a piezoelectric transformer. Is going.

A conventional piezoelectric inverter circuit using a piezoelectric transformer will be described. FIG. 4 shows a conventional piezoelectric inverter circuit. This piezoelectric inverter circuit includes a fluorescent tube 30
Control unit 10 that controls the frequency of the signal supplied to the piezoelectric transformer 20 in order to keep the tube current flowing through the piezoelectric transformer 20 constant.
, A piezoelectric transformer 20 as a booster, and a piezoelectric transformer 2
A fluorescent tube 30 illuminated with an output of 0, and a fluorescent tube 3
It comprises a tube current sensing unit 40 that detects a current flowing through 0 and supplies a difference from a reference value to the frequency control unit 10, and a dimming control unit 50.

In a conventional piezoelectric inverter circuit having such a configuration, when an input voltage is supplied, Q1 and L1
A signal of the frequency set by the frequency control unit 10 is generated. A4 is the resonance waveform. When this signal is applied to the piezoelectric transformer 20, the piezoelectric transformer 20 boosts the signal and outputs a high-voltage sine wave signal (B4). This output is applied to the fluorescent tube 30, and the fluorescent tube 30 is turned on. At this time, the tube current flowing through the fluorescent tube 30 is detected by the tube current sensing unit 40. At normal times, when the dimming control is off, the tube current sensing unit 40
Tube current is detected by resistors R3 and R4 connected between GND, and diode D1, capacitor C1, resistors R5 and R5 are detected.
The voltage is converted into a voltage via the rectifier circuit composed of the rectifier circuit 6 and input to the negative terminal of the operational amplifier 41. The output of the frequency control unit 10 is divided by the resistors R1 and R2 to the + terminal of the operational amplifier 41 and input as a reference value. Operational amplifier 41,
The difference between the tube current value and the reference value is output to the frequency control unit 10 via the resistors R7 and R8. The frequency control unit 10 receiving this difference controls the frequency of the voltage applied to the piezoelectric transformer so that the tube current becomes constant.

In the light control operation, when the light control is turned on, the transistor Q2 of the light control unit 50 is turned on and the resistor R4 is bypassed. The tube current is detected by a resistor R3 connected between the fluorescent tube 30 and GND, and a diode D1, a capacitor C1, and a resistor R3 are connected.
The voltage is converted to a voltage via a rectifier circuit composed of R5 and R6, and input to a negative terminal of the operational amplifier 41. This difference is calculated, and when the frequency control is performed by the frequency control unit 10 according to the difference, the tube current flowing through the fluorescent tube 30 decreases.

Next, the frequency control unit 10 will be described in detail. FIG. 5 is a circuit diagram of a conventional frequency control unit 10b. The frequency control unit 10b includes an operational amplifier 11 and a resistor R
9, R10, R11 and a variable resistor VR1. The output of the operational amplifier 11 is divided by the resistor R11, the resistor R10, and the variable resistor VR1, and the output of the operational amplifier 41 for calculating the difference between the reference value and the tube current value of the tube current sensing unit 40 via the resistor R11. Output to the + terminal as a reference value.

A description will be given of frequency control performed for a change in input voltage. FIG. 6 is a characteristic diagram of the input voltage-tube current of the piezoelectric inverter circuit. As shown in FIG.
The frequency control unit 10b controls the frequency of the voltage applied to the piezoelectric transformer so that the tube current becomes constant when the input voltage fluctuates. A method for controlling this frequency will be described. FIG. 7 is a transformer frequency characteristic diagram of the piezoelectric transformer 20. The piezoelectric transformer 20 has a characteristic that if the frequency falls within a certain frequency range (162 to 164 KHz in FIG. 6), as the frequency decreases, the transformer current increases accordingly. In the frequency control unit 10b, control is performed to lower the output frequency in accordance with the decrease in the input voltage and increase the transformer current value. FIG. 8 shows a change in a resonance waveform applied to the piezoelectric transformer due to a difference in input voltage. Each input voltage is
(A) is 5.3 V, (b) is 7.2 V, and (c) is 8.6.
V.

The frequency control unit 10b accompanies a change in the input voltage.
The on-duty is optimally adjusted by the variable resistor VR1 to adjust the resonance waveform to be optimal.

[0009]

However, in the conventional piezoelectric inverter circuit, the optimal adjustment of the on-duty is performed only by the variable resistor VR1 of the frequency control unit 10b. For this reason, when the adjustment voltage changes due to a change in the input voltage, the on-duty deviates from the optimum value, and the resonance waveform is disturbed, resulting in a problem that the efficiency is deteriorated. For example, in FIG. 8, when the input voltage in (a) is 5.3 V, the overshoot is large, and when the input voltage in (c) is 8.6 V, biting occurs. In such a state, the loss current increases and the efficiency also deteriorates.

Further, the on-duty is adjusted to be optimal when the dimming control is off (Hi). Therefore, the dimming control is turned on (L
ow), there is a problem that the resonance waveform at the frequency applied to the piezoelectric transformer controlled to match the tube current in this case deviates from the optimum value. As an example, FIG. 9 shows a resonance waveform at the time of dimming operation of a conventional piezoelectric inverter circuit. Compared to the case where the dimming control is off (Hi) in FIG. 9A, the resonance waveform when the dimming control is on (Low) in FIG. 9B has a bite. In such a state, the loss current increases and the efficiency also deteriorates. For this reason, when the dimming control is turned on, the tube current of the fluorescent tube 30 decreases and the luminance also decreases, but the power consumption does not decrease so much because the loss current increases.

The present invention has been made in view of the above points, and in particular, a piezoelectric inverter circuit which corrects the on-duty when the frequency applied to the piezoelectric transformer changes in frequency due to an input voltage change or dimming operation, and the like. An object of the present invention is to provide an on-duty correction method.

[0012]

According to the present invention, in order to solve the above problems, a piezoelectric inverter circuit for controlling a frequency of a voltage applied to a piezoelectric transformer in accordance with a difference between a tube current value flowing through a fluorescent tube and a reference value. A piezoelectric inverter circuit provided with input voltage change on-duty correction means for correcting the on-duty of the voltage applied to the piezoelectric transformer according to the input voltage value when the input voltage changes. You. The piezoelectric inverter circuit having such a configuration is capable of reducing the deviation from the optimum value of the on-duty that occurs in the resonance waveform due to the fluctuation of the input voltage or the frequency fluctuation of the voltage applied to the piezoelectric transformer due to dimming operation or the like. By performing the correction using the change on-duty correction means, the on-duty is optimally operated.

Further, an on-duty for correcting an on-duty of a voltage applied to a piezoelectric transformer of a piezoelectric inverter circuit for controlling a frequency of a voltage applied to the piezoelectric transformer according to a difference between a tube current value flowing through the fluorescent tube and a reference value. The correction method includes a step of correcting the on-duty according to an input voltage value when the input voltage changes, and a step of controlling a frequency of a voltage applied to the piezoelectric transformer according to the correction. A correction method is provided.

According to the on-duty correction method of such a procedure, the on-duty deviation in the resonance waveform from the optimum value due to the fluctuation of the input voltage or the frequency fluctuation of the voltage applied to the piezoelectric transformer due to the dimming operation or the like occurs. , A correction value is calculated with an input voltage value corresponding to the input voltage, and this is reflected in, for example, a reference value to control the frequency of the voltage applied to the piezoelectric transformer, thereby operating the on-duty optimally.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a frequency control unit 10a of a piezoelectric inverter circuit according to one embodiment of the present invention. Frequency control unit 10a of this piezoelectric inverter circuit
Is the frequency control unit 1 of the piezoelectric inverter circuit shown in FIG.
0 is incorporated. The frequency control unit 10 is connected to the tube current sensing unit 40 and the transistor Q1 that turns on and off at the frequency output from the frequency control unit 10. The input voltage is Q
According to 1 and L1, the signal is supplied to the piezoelectric transformer 20 as a signal of the resonance waveform (A4) of the frequency set by the frequency control unit 10. The piezoelectric transformer 20 converts this input into a high-voltage sine wave (B4) and applies the output to the fluorescent tube 30.
Thereby, the fluorescent tube 30 is turned on. The tube current of the fluorescent tube 30 is detected by the tube current sensing unit 40. When the dimming control is off, the tube current sensing unit 40 supplies the tube current to the resistors R3 and R3 connected between the fluorescent tube 30 and GND.
4 to detect. When the dimming control is on, the transistor Q2 of the dimming control unit 50 is turned on, the resistor R4 is bypassed, and the tube current is reduced to the fluorescent tube 30-G.
It is detected by a resistor R3 connected between ND. The detected tube current is converted into a voltage via a rectifier circuit including a diode D1, a capacitor C1, and resistors R5 and R6, and is input to a negative terminal of the operational amplifier 41. Operational amplifier 4
The output of the frequency control unit 10 is connected to the + terminal of R1 and R1.
2 and input as a reference value. The difference between the tube current value and the reference value is output to the frequency control unit 10 via the operational amplifier 41 and the resistors R7 and R8.

Returning to FIG. 1, the description will be continued. Frequency control unit 10
a is an operational amplifier 11 for generating a reference value signal, and a resistor R
9, a circuit comprising R10, R11 and a variable resistor VR1, an on-duty input correction resistor 12 for correcting a change in input voltage, and a dimming on-duty switching circuit 13 for correcting a dimming operation. Yes,
The reference value for adjusting the tube current is corrected and output to the operational amplifier 41+ terminal of the tube current sensing unit 40.

The output of the operational amplifier 11 is a resistor R11,
The voltage is divided by the resistor R10 and the variable resistor VR1,
11 and the operational amplifier 41 of the tube current sensing unit 40
Is output as a reference value to the + terminal. By changing the resistance value of the variable resistor VR1, the on-duty can be optimally adjusted according to the change in the input voltage. However, the resistance value is rarely changed after the initial adjustment.

The on-duty input correction resistor 12 is connected from the input voltage line to the output of the operational amplifier 11 by a resistor R12. Dimming on-duty switching circuit 1
Reference numeral 3 denotes a transistor Q3 that is turned on and off in response to the on / off of the dimming control signal, and a resistor R13 provided in parallel with Q3, and is connected in series with the resistor R10 and the variable resistor VR1. When the dimming control signal is turned on, the resistor R13 is bypassed.
Current flows through In this manner, the resistance division value for the output of the operational amplifier 11 is switched by turning on / off the dimming control, and the reference value output to the tube current sensing unit 40 is switched accordingly.

The operation of the piezoelectric inverter circuit having the frequency control unit 10a having such a configuration when the input voltage fluctuates and the method of correcting the on-duty will be described. The frequency control unit 10a controls the frequency of the voltage applied to the piezoelectric transformer so that the tube current becomes constant when the input voltage changes. Since the piezoelectric transformer has a characteristic that the transformer current increases as the frequency decreases, the frequency control unit 10a increases the output frequency when the input voltage increases and outputs the frequency when the input voltage decreases. Lower.

The reference value generated by the frequency control unit 10a is set so that a voltage proportional to the input voltage becomes a reference value by an on-duty input correction resistor 12 connected from the input voltage line to the output of the operational amplifier 11 by a resistor R12. Added and corrected. Therefore, when the input voltage increases, the reference value also increases by the correction amount proportional to the input voltage, and when the input voltage decreases, the reference value also decreases by the correction amount proportional to the input voltage.

[0021] In this manner, with respect to the fluctuation of the input voltage,
By correcting the reference value with a value proportional to the input voltage,
The deviation of the resonance waveform from the optimum value is corrected. The effect of the correction by the on-duty input correction resistor 12 will be described with an actual example. FIG. 2 shows a resonance waveform when the input voltage changes in the piezoelectric inverter circuit according to one embodiment of the present invention. FIG.
FIG. 8A shows the case where the input voltage is 5.3 V. Compared with FIG. 8A in which the correction is not performed, the overshoot is smaller. FIG. 2C shows the case where the input voltage is 8.6 V. Compared with FIG. 8C in which the correction is not performed, the biting amount is reduced. Thus, the on-duty input correction resistor 12
When the correction is performed on the reference value, the effect of reducing the overshoot of the resonance waveform and reducing the biting amount is obtained as compared with the case where the correction is not performed.

Next, the operation at the time of the light control operation and the method of correcting the on-duty will be described with reference to FIG. The on-duty of the resonance waveform is adjusted in normal times, that is, when the dimming control is off (Hi). When the dimming control is turned on (Low), the fluorescent tube 30-GND detecting the tube current of the tube current sensing unit 40
The resistance connected to the tube switches from R4 and R3 to only R3, and the detected tube current value fluctuates. The operation of the frequency control unit 10a in response to this will be described with reference to FIG. When the dimming control is turned on, the transistor Q3 of the dimming on-duty switching circuit 13 is also turned on, and the resistor R13 is bypassed. For this reason, the resistance voltage division value of the output section of the operational amplifier 11 is switched, and the reference value is switched in accordance therewith, which is a value suitable for dimming control off.

The effect of correction by the dimming on-duty switching circuit will be described in an actual example. FIG. 3 shows a resonance waveform at the time of dimming operation of the piezoelectric inverter circuit according to one embodiment of the present invention. FIG. 3A shows a state in which the dimming control is off (Hi), and FIG. 3B shows a state in which the dimming control is on (L).
ow). FIG. 3B shows a comparison with FIG. 9B showing the dimming control ON state in which the correction is not performed.
Then, the biting phenomenon is suppressed. in this way,
When the reference value is corrected by the dimming on-duty switching circuit 13, the overshoot of the resonance waveform is reduced and the biting amount is reduced as compared with the case where the correction is not performed. Can be As the biting amount is reduced, the loss current is reduced and the power consumption is reduced. That is, the efficiency can be improved. In an actual test, the efficiency was improved by 15% compared with the conventional case.

[0024]

As described above, in the piezoelectric inverter circuit of the present invention, when the frequency of the voltage applied to the piezoelectric transformer fluctuates due to the change of the input voltage and the dimming operation, the input voltage change on-duty correction means. Then, if necessary, for example, by providing a dimming operation on-duty correcting means, the deviation from the optimal value of the on-duty of the resonance waveform is corrected, and the on-duty is operated optimally. As a result, the loss current is reduced, and the efficiency can be improved. Also, abnormal oscillation due to collapse of the resonance waveform can be prevented.

In the on-duty correction method according to the present invention, the procedure of correcting the on-duty in accordance with the input voltage value when the input voltage changes, and, if necessary, for example, determining whether or not dimming is performed during the dimming operation. The frequency of the voltage applied to the piezoelectric transformer is controlled so that the on-duty of the resonance waveform is optimized by the procedure for correcting the on-duty accordingly. As a result, the loss current is reduced, and the efficiency can be improved. Also, abnormal oscillation due to collapse of the resonance waveform can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a frequency control unit of a piezoelectric inverter circuit according to an embodiment of the present invention.

FIG. 2 is a resonance waveform when the input voltage changes in the piezoelectric inverter circuit according to one embodiment of the present invention.

FIG. 3 is a resonance waveform at the time of dimming operation of the piezoelectric inverter circuit according to one embodiment of the present invention.

FIG. 4 is a circuit diagram of a piezoelectric inverter circuit.

FIG. 5 is a circuit diagram of a frequency control unit of a conventional piezoelectric inverter circuit.

FIG. 6 is a characteristic diagram of input voltage-tube current of the piezoelectric inverter circuit.

FIG. 7 is a transformer frequency characteristic diagram of the piezoelectric inverter circuit.

FIG. 8 is a resonance waveform of the conventional piezoelectric inverter circuit when the input voltage changes.

FIG. 9 is a resonance waveform at the time of dimming operation of the conventional piezoelectric inverter circuit.

[Explanation of symbols]

10: frequency control unit, 10a: frequency control unit of the present invention,
10b: Conventional frequency control unit, 12: On-duty input correction resistor, 13: Dimming on-duty switching circuit,
20: piezoelectric transformer, 30: fluorescent tube, 40: tube current sensing unit, 50: dimming control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H05B 41/38 H01L 41/08 A F term (Reference) 3K072 AA01 AC20 BA03 BC07 EB05 EB07 GA01 GB03 GC04 HA06 HA10 HB03 3K098 CC56 DD22 DD37 DD43 EE14 EE32 FF04 FF14 GG10 5H007 AA07 BB03 CA01 CB07 CB09 CC32 DA03 DB03 DC02 5H730 AA14 AA15 AS11 BB13 DD02 DD21 EE48 FD31 FG05 FG25

Claims (8)

[Claims] 1. A piezoelectric inverter circuit for controlling a frequency of a voltage applied to a piezoelectric transformer according to a difference between a tube current value flowing through a fluorescent tube and a reference value. A piezoelectric inverter circuit comprising input voltage change on-duty correction means for correcting on-duty of an applied voltage. 2. The piezoelectric device according to claim 1, wherein the piezoelectric inverter circuit further includes a dimming operation on-duty correction unit that corrects the on-duty according to the presence or absence of dimming during the dimming operation. Inverter circuit. 3. The piezoelectric inverter circuit according to claim 1, wherein said input voltage change on-duty correction means is an on-duty input correction resistor for adding a voltage value proportional to an input voltage to said reference value. 4. The piezoelectric inverter according to claim 2, wherein the dimming operation on-duty correction means is a dimming on-duty switching circuit that switches a resistance value that generates the reference value depending on the presence or absence of a dimming operation. circuit. 5. An on-duty for correcting an on-duty of a voltage applied to a piezoelectric transformer of a piezoelectric inverter circuit for controlling a frequency of a voltage applied to the piezoelectric transformer according to a difference between a tube current value flowing through the fluorescent tube and a reference value. The on-duty method, comprising: a step of correcting the on-duty according to an input voltage value when an input voltage changes, and a step of controlling a frequency of a voltage applied to the piezoelectric transformer according to the correction. Correction method. 6. The on-duty correction method according to claim 5, wherein said on-duty correction method further includes a step of correcting said on-duty in accordance with the presence or absence of dimming during a dimming operation. 7. The on-duty correction method according to claim 5, wherein the on-duty correction procedure when the input voltage changes is a step of adding a voltage value proportional to the input voltage to the reference value. 8. The on-duty correction method according to claim 6, wherein the dimming operation on-duty correction procedure is a step of switching a resistance value for generating the reference value according to the presence or absence of a dimming operation.