JP3461647B2 - Drive device for piezoelectric transformer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of a piezoelectric transformer used for generating a high voltage for lighting a discharge lamp in a lighting device for a cold cathode discharge lamp used as a backlight of a liquid crystal display device, for example. It relates to the device.

[0002]

2. Description of the Related Art Conventionally, it is known that a piezoelectric transformer can be used to generate a high voltage for lighting a cold cathode discharge lamp used as a backlight of a liquid crystal display device, for example, Nikkei Electronics magazine No. 1994.11.1.7. , Pp. 147, and is well known.

Further, as a driving method of the piezoelectric transformer, a separately-excited method as disclosed in the above-mentioned literature or a driving method by a self-excited method is well known. Briefly describing the separately excited method disclosed in the above-mentioned document, the oscillation frequency of the voltage controlled oscillator is first set by turning on the power source, and the piezoelectric transformer is driven based on the output signal of the set frequency. Is fed back to the integrator through the operational amplifier, and the oscillation frequency of the voltage controlled oscillator is controlled so that the output current of the integrator has a set value.

The self-excited system is generally constructed such that an amplifier drives a piezoelectric transformer and a signal indicating the state of the piezoelectric transformer is positively fed back to an input terminal of the amplifier, that is, a power source is used. After being turned on, a steady oscillation drive state is reached after a certain period of time during which oscillation is gradually grown by the amplifier and the feedback circuit.

[0005]

However, the resonance frequency of the piezoelectric transformer has a temperature characteristic, and therefore, when the piezoelectric transformer is driven by the separate excitation method, in order to compensate the temperature characteristic, for example, the frequency is changed by the above voltage. It is necessary to adopt a configuration in which the output current is stabilized by the voltage-controlled oscillator, which has the disadvantage that the configuration becomes complicated.

On the other hand, when oscillating by the self-excited method,
Even if the resonance frequency changes due to temperature, the drive frequency automatically follows and a stable output is obtained, so the circuit configuration can be simplified compared to the case of driving by the above-mentioned external excitation method, There is a disadvantage that it is necessary to use a lossy amplifier such as a class A amplifier.

The present invention provides a piezoelectric transformer drive device capable of driving a piezoelectric transformer with a simple circuit configuration without using a voltage-controlled oscillator or a class A amplifier which easily causes loss, which has such a complicated circuit configuration. The purpose is to do.

[0008]

In order to solve this problem, the present invention provides a driving method of the piezoelectric transformer in response to the output state of the piezoelectric transformer, which is a separately excited method set when the power is turned on. Second method including at least self-excited method
The piezoelectric transformer driving device is configured by changing the method.

As a result, the piezoelectric transformer can be used without using a voltage controlled oscillator or a class A amplifier which easily causes a loss.
With a simple circuit configuration, it can be driven reliably even immediately after the power is turned on.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a method of separately exciting a piezoelectric transformer at the time of starting, and then self-exciting.
It is a drive device driven by a formula, the output of the drive device
Equipped with a current detector that detects the output current of the piezoelectric transformer,
Connect the time constant circuit after differentiating the signal from the current detector
The peak value of the waveform shaping circuit is the trigger level of the self-excited oscillator.
If the external excitation method at startup is
The piezoelectric transformer driving device is configured to switch to the excitation system operation , and the piezoelectric transformer has a simple circuit configuration without using a voltage-controlled oscillator or a class A amplifier that easily causes loss, and immediately after power-on. It has an effect that it can be driven reliably.

[0011]

[0012]

According to a second aspect of the present invention, there is provided a drive circuit which is connected between a power source and a piezoelectric transformer to supply a drive voltage to the piezoelectric transformer, and the piezoelectric circuit which controls the operation of the drive circuit. A square wave oscillator circuit that generates a first one-sided wave output that controls the drive operation of the transformer, a differentiation circuit and a time constant circuit that form an output having a waveform having a phase difference with respect to the output current waveform of the piezoelectric transformer , Differentiation circuit and
And the output level is triggered by the output of the time constant circuit
And a waveform shaping circuit that outputs a second square wave output ,
The output terminal of the waveform shaping circuit is connected to the feedback input section of the square wave transmission circuit so that the second square wave output is input in parallel to the feedback input of the square wave transmission circuit, and the square wave is also connected. The oscillator circuit is a piezoelectric transformer driving device configured to preferentially output the second square wave output when the waveform shaping circuit outputs the second square wave output. The circuit has a simple circuit configuration without using a controlled oscillator or a class A amplifier that easily causes a loss, and can reliably drive even immediately after power-on.

The invention according to claim 3 of the present invention is a claim
In the waveform shaping circuit of the piezoelectric transformer driving device described in 2 ,
The time constant circuit is configured to include a variable resistor , and in addition to the function of the invention described in claim 2 described above, it has the function of variably adjusting the output current of the piezoelectric transformer. According to a fourth aspect of the present invention, the square wave transmission circuit of the piezoelectric transformer driving device according to the second aspect is provided with frequency adjusting means in the feedback section, whereby the output current of the piezoelectric transformer is made variable. In addition to the function of the invention described in claim 2 , the output current of the piezoelectric transformer can be variably adjusted.

The invention according to claim 5 of the present invention is
The square wave oscillator circuit of the piezoelectric transformer driving apparatus according to 2, provided with a non-linear circuit against voltage feedback unit, thereby is obtained by stabilizing the piezoelectric transformer output current, claim 2 described above In addition to the function of the invention described in (1), it has a function of stabilizing the output current of the piezoelectric transformer.

The invention according to claim 6 of the present invention is
The square wave transmission circuit of the piezoelectric transformer driving device described in 2 to 5 is constituted by an astable multivibrator, and has the same operation as that of the invention described in claims 2 to 5 . Embodiments of the present invention will be described below with reference to FIGS. 1 to 5.

(Embodiment 1) FIG. 1 is an electric circuit diagram showing Embodiment 1 of the present invention. The voltage for driving the piezoelectric transformer 1 by being applied to the primary side 1a of the piezoelectric transformer 1 is an inductor. 2 and a power source 23, which is generated by the drive circuit 4 formed by the transistor 6 which is a switching element, and specifically, a voltage having a waveform as shown in FIG. By being applied, the energy stored in the inductor 5 while the transistor 6 is ON is released by resonance with the electrostatic capacitance on the primary side of the piezoelectric transformer 1 when the transistor 6 is OFF. By doing so, Fig. 2 (B)
The voltage has a waveform like this.

By applying the voltage as described above to the primary side of the piezoelectric transformer 1, the piezoelectric transformer 1 undergoes mechanical resonance vibration to generate a substantially perfect high voltage of a sine wave on the secondary side 1b.
An output current is passed through the load 2, for example, a cold cathode fluorescent discharge lamp. In FIG. 1, a portion 7 surrounded by a dotted line shows a square wave oscillator circuit which is an astable multivibrator including inverters 8 and 9, resistors 10 and 11, a variable resistor 12 and a capacitor 13, and a portion 14 is a variable wave oscillator. A phase conversion circuit for changing the phase of the terminal voltage of the resistor 3 which is a state detecting means for detecting the output current of the piezoelectric transformer 1 and which includes the resistor 15 and the capacitor 16 is shown. 18, a resistor 19, 20 and a capacitor 21, and the terminal voltage of the resistor 20 is converted into an input threshold voltage of the inverter 18 to convert the output voltage of the phase conversion circuit 14 into a square wave at the zero cross point. 2 shows a waveform shaping circuit. In addition, one end of the inverter 18 is connected to the square wave oscillation circuit 7 through a coupling means, for example, a capacitor 22.

Next, the operation immediately after the power source 23 is turned on will be described. When the power supply 23 is turned on, the square wave oscillator circuit 7 includes a capacitor 13, a resistor 10, a variable resistor 12, and a resistor 1.
1, the operation of the drive circuit 4 is controlled by oscillating at a frequency determined by the constant of the capacitor 22, and the primary side 1a of the piezoelectric transformer 1 is controlled.
Is driven by the voltage as shown in FIG.

That is, since the piezoelectric transformer 1 is driven by the separate excitation method, the amplitude of mechanical vibration of the piezoelectric transformer 1 temporarily increases, and accordingly, the current flowing through the load 2 and the terminal voltage of the resistor 3 increase. Go. When the load 2 is a cold cathode fluorescent discharge lamp, the rising characteristic of the terminal voltage of the resistor 3 becomes more gradual.

The terminal voltage of the resistor 3 is advanced to the phase adjusted by the variable resistor 15 and the capacitor 16 of the phase conversion circuit 14 and input to the inverter 18 of the waveform shaping circuit 17, but the terminal voltage of the resistor 3 is The inverter 18 does not operate until it reaches an appropriate size, and the waveform of the voltage applied to the input terminal of the inverter 9 of the square wave oscillation circuit 7 in such a state is t0 when the power is turned on and the inverter 9 is turned on. The input threshold voltage of 1 is shown as Vth in FIG. 3 (A).

The rising portion of this waveform is blunt because the capacitor 22 is connected to the ground in the inverter 9 or the power supply. When the output current of the piezoelectric transformer 1 starts to flow due to the drive by the above-described separate excitation method, and the terminal voltage of the resistor 3 becomes an appropriate magnitude at time t1, the inverter 18 starts operating and applies a square wave voltage to the output terminal. After the output, the input voltage of the inverter 9 of the square wave oscillation circuit 7 is changed at this time t1.

That is, as shown in FIG. 3A, the voltage rises sharply at time t1 and then the voltage decreases due to the time constants of the capacitor 13 , the resistors 10 and 11 and the variable resistor 12 from the time t1. , At time t2 when the input threshold voltage is not reached yet, the inverter 18
Is inverted, and thereafter, the voltage waveform formed based on the similar operation is repeatedly supplied as the input voltage of the inverter 9.

As described above, since the time constant of the capacitor 13 and the resistor 10 and the like no longer acts on the input terminal of the inverter 9, the square wave oscillator circuit 7 drives the piezoelectric transformer 1 up to that point. The circuit that functions as the oscillation circuit that controls the operation of the above shifts to a transmission circuit that only transmits the output of the inverter 18 as a drive signal to the gate of the transistor 6.

In such a state, since the transistor 6 functions as an inverter, a positive feedback is applied to the primary side 1a of the piezoelectric transformer 1 in combination with the inverter 18, that is, the piezoelectric transformer 1 after the time t1 described above.
Will be driven by the so-called self-excited method. The magnitude of the output of the piezoelectric transformer 1 is the largest when driven at the resonance frequency, and becomes smaller as the frequency becomes higher than the resonance frequency. However, in the first embodiment, the variable resistor 15 is used.
The operating timing of the inverter 18, that is, the frequency of the drive signal transmitted to the drive circuit 4 via the square wave oscillating circuit 7 can be controlled by adjusting the output voltage. The current flowing through is set appropriately.

Further, when the capacitance value of the capacitor 22 which is the coupling means between the inverter 18 and the square wave oscillation circuit 7 in the first embodiment shown in FIG. 1 is reduced, the input voltage waveform of the inverter 9 becomes as shown in FIG. Like When the output current of the piezoelectric transformer 1 starts to flow due to the drive by the separate excitation method after the power is turned on at the time point t0 and the terminal voltage of the resistor 3 becomes an appropriate value at the time point t3, the inverter 18 performs the inverting operation at the time point t3. , At this time t3, the inverter 9
The input voltage of 1 is increased by v in the figure by the capacitor 22, then decreases and reaches the threshold voltage at time t4, and the output of the inverter 9 is inverted to the low level.

From time t4, the normal oscillation operation is performed depending on the period of the current flowing through the capacitor 22, and the output voltage of the inverter 18 is inverted at time t5. Note that FIG.
From time t4 to time t5 in (B), there is a phase difference,
In the first embodiment, it cooperates with the phase difference set by the phase conversion circuit 14 so that the output phase of the piezoelectric transformer 1 becomes approximately 90 degrees.

If the resistance value of the variable resistor 15 of the phase conversion circuit 14 is increased, the phase difference approaches 90 degrees, and if it is decreased, the phase difference becomes smaller than 90 degrees. Therefore, by adjusting the variable resistor 15, the piezoelectric transformer is adjusted. 1 can be controlled, and the load current flowing through the load 2 can be finely adjusted. (Embodiment 2) FIG. 4 is an electric circuit diagram (A) showing Embodiment 2 of the present invention and an operation characteristic diagram (B) for explaining the features thereof, which is apparent from FIG. 4 (A). As described above, the second embodiment is different from the square wave oscillator circuit 7 according to the first embodiment shown in FIG. 1 in that the resistor 24 and the Zener diode 2 are provided.
It has a configuration in which 5, 26 are added.

Therefore, in the second embodiment, the square wave oscillating circuit 7 operates so that its oscillation frequency becomes higher as the power supply voltage becomes higher. As a result, FIG. 4 is an operation characteristic diagram showing load-current change characteristics with respect to fluctuations in the power supply voltage in the first embodiment shown in FIG. 1 and the second embodiment shown in FIG. As is clear from FIG. 4 (B), since the oscillation frequency is fixed, the power supply voltage is higher than that of the first embodiment, which has a characteristic that the load current increases as the power supply voltage increases. Therefore, the ratio of increase of the load current with respect to increase of is reduced.

The fact that the rate of increase of the load current with respect to the rise of the power supply voltage can be made small means that the change of the load current with respect to the change of the power supply voltage can be made small. For example, when a cold cathode fluorescent discharge lamp is used as the load. ,
The fluctuation of the tube current with respect to the fluctuation of the power supply voltage can be reduced, and specifically, the fluctuation of the brightness of the cold cathode fluorescent discharge lamp can be suppressed without using a complicated and expensive constant voltage configuration. You can expect an effect.

(Third Embodiment) FIG. 5 is an electric circuit diagram showing a third embodiment of the present invention. In the first embodiment of the present invention shown in FIG. 1, three inverters are used, but in the third embodiment, five inverters are used. When the output circuit of the piezoelectric transformer 1 is accidentally opened, the vibration amplitude and the output voltage of the piezoelectric transformer become extremely large, which may cause inconvenience such as destruction of the piezoelectric transformer 1. Is to prevent this.

That is, FIG. 5 shows an inverter 27 for the square wave oscillator circuit 7 in the first embodiment shown in FIG.
28, capacitors 29 and 30, resistors 31 and 32, diodes 33 and 34, and a power supply 35 are added.
In FIG. 5, the capacitor 29 is configured to be charged by the power source 35 via the resistor 31, and when the charging voltage of the capacitor 29 reaches the threshold voltage of the inverter 28, the inverter 28 outputs a low level, As a result, the input terminal of the inverter 9 of the square wave oscillator circuit 7 is fixed at a low level, and the piezoelectric transformer 1 is no longer driven at this point.

On the other hand, when the output of the inverter 18 is applied to the inverter 27 via the capacitor 30 and the resistor 32, the inverter 27 will perform an inverting operation according to the output cycle of the inverter 18 , and its output will be low. When the voltage is set to the level, the charged electric charge of the capacitor 29 is discharged through the diode 34. Therefore,
When the piezoelectric transformer 1 is normally driven, the inverter 1 is fed back by the output state of the piezoelectric transformer 1.
Since the inverting operation output of No. 8 is applied to the inverter 27, the charging voltage of the capacitor 29 does not rise and the inverter 28 operates and the piezoelectric transformer 1 is not driven. On the other hand, the output of the piezoelectric transformer 1 does not occur. When the circuit is opened, its output state is not fed back, so that the output of the inverting operation output of the inverter 18 is stopped, and as a result, the capacitor 29 is continuously charged, as described above. Moreover, the operation of the inverter 28 prevents the piezoelectric transformer 1 from being driven.

For example, in FIG. 5, by setting the time constant of the capacitor 29 and the resistor 31 to about 0.5 seconds, the inverter is driven when the piezoelectric transformer 1 is driven.
18 high-level output within 30 seconds capacitor 30
If it is not supplied to the inverter 27 via the, the input terminal of the inverter 9 of the square wave oscillation circuit 7 can be fixed to the low level by the operation of the inverter 28.
This can prevent undesired driving of the piezoelectric transformer 1.

Since this state continues until the power supply 23 is opened, the piezoelectric transformer is not destroyed.

[0036]

According to the piezoelectric transformer driving apparatus of the present invention, the piezoelectric transformer driving method is at least self-excited in response to the output state of the piezoelectric transformer, from the first method, which is the separate excitation method set when the power is turned on. It is configured by changing to the second method including the method. Therefore, without using a voltage controlled oscillator or a class A amplifier that easily causes loss,
It has an effect that it can be driven reliably with a simple circuit configuration even immediately after the power is turned on.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a first embodiment of a piezoelectric transformer driving device of the present invention.

FIG. 2A is a voltage waveform diagram applied to the base of the transistor 6 of the first embodiment, and FIG. 2B is a voltage waveform diagram applied to the primary side of the piezoelectric transformer 1 of the first embodiment.

FIG. 3A is an input voltage waveform diagram of the inverter 9 in the first embodiment. FIG. 3B is an input voltage waveform diagram of the inverter 9 in the first embodiment.

FIG. 4A is an electric circuit diagram showing a piezoelectric transformer driving device according to a second embodiment of the invention, and FIG. 4B is an operation characteristic diagram for explaining the features of the second embodiment.

FIG. 5 is an electric circuit diagram showing a third embodiment of the piezoelectric transformer driving device of the present invention.

[Explanation of symbols]

1 Piezoelectric transformer 2 load 3 resistance 4 drive circuit 5 inductor 6 transistors 7 Square wave oscillator 8 inverter 9 inverter 10 resistance 11 resistance 12 variable resistance 13 capacitors 14 Phase conversion circuit 15 Variable resistance 16 capacitors 17 Wave shaping circuit 18 Inverter 19 resistance 20 resistance 21 capacitor 22 Capacitor 23 Power 24 resistance 25 Zener diode 26 Zener diode 27 inverter 28 Inverter 29 capacitors 30 capacitors 31 resistance 32 resistance 33 diode 34 diode 35 power supply

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 5/10 H01L 41/107

Claims (6)

(57) [Claims] 1. A piezoelectric transformer is separately excited when starting up.
A drive device driven by a rear self-exciting method,
The current output detects the output current of the piezoelectric transformer
The time constant after the signal from the current detector is differentiated
The peak value of the waveform shaping circuit connected to the circuit is
If the trigger level is exceeded, other excitation at startup
Piezoelectric transformer switching from self-excited operation to self-excited operation
apparatus. 2. A connection between a power supply and a piezoelectric transformer
A drive circuit for supplying a drive voltage to the piezoelectric transformer
And the operation of the drive circuit to control the piezoelectric transformer
Square wave generator that produces a first-sided wave output that controls drive operation
Phase difference between the output current waveform of the transmission circuit and the piezoelectric transformer
Differentiating circuit and time constant forming an output having a certain waveform
Trigger on the output of the circuit and the differentiation circuit and the time constant circuit
Output a second square wave output whose output level is switched.
A waveform shaping circuit, and the output terminal of the waveform shaping circuit
The second square wave output is fed to the feedback input of the square wave oscillator circuit.
Force is input in parallel to the feedback input of the square wave oscillator circuit.
And the square wave transmission circuit,
When the waveform shaping circuit outputs the second square wave output
The second square wave output is configured to be output preferentially.
And a piezoelectric transformer drive device. 3. The time constant circuit in the waveform shaping circuit is variable
Adjusting the value of the variable resistor, which is configured to include a resistor
The oscillation frequency is changed by the
The piezoelectric transformer according to claim 2, wherein the
Drive. 4. The square-wave oscillator circuit comprises a frequency feedback circuit.
Adjusting means is provided so that the output current of the piezoelectric transformer
The drive device for the piezoelectric transformer according to claim 2, wherein
Place 5. The square-wave oscillator circuit uses a voltage for the feedback section.
A non-linear circuit is provided for the piezoelectric transformer.
The piezoelectric transformer according to claim 2, wherein the output current of the device is stabilized.
Su. 6. The square-wave oscillator circuit is an astable multi-by circuit.
A piezoelectric transformer according to any one of claims 2 to 5, which is a blater.
Drive circuit.