JPH11224776A - El driver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the emission efficiency and to reduce the electromagnetic noise, and the deterioration of an element by connecting a load impedance including the EL element to a driving circuit consisting of two sets of serially connected electric field effect transistors, and connecting a control circuit in such a manner that a time difference is caused in the application of the gate voltage of the driving circuit to provide a resting period in the circuit of driving voltage. SOLUTION: The oscillating frequency of an oscillator 124 is properly divided through frequency dividers 125a-125f, and a current is carried to a first inductor 117 by the resulting frequency to store an electric energy. On the other hand, the output voltage of a one-shot multi-circuit 127 is applied to the AND circuits 128b, 128c of a gate voltage control circuit 131, and FET 113, 115 are ON/OFF. In a resting period determined by the design, FET 114, 116 are simultaneously laid in ON state, load terminals 132, 133 are short-circuited to form a closed circuit, and the electric energy stored in the load impedance including an EL element 118 is naturally released.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EL (electroluminescence) element serving as a backlight of a liquid crystal display device used for in-vehicle AV equipment and portable equipment such as PDAs, portable telephones, PHSs and pagers. The present invention relates to a driving circuit to be driven, and more particularly to a configuration of a driving circuit which functions with a low input power supply voltage.

[0002]

2. Description of the Related Art In-vehicle AV equipment and PD which is a portable equipment
A, a mobile phone, a PHS, a pager, and the like often use a light-transmitting liquid crystal display device to make the display easier to see, and in that case, a backlight is used on the back side of the liquid crystal display device. Fluorescent tubes and EL elements are sometimes used for the above-mentioned backlight, but recently, in order to respond to light, thin and short dimensions and strict cost requirements, about 0.5 mm or less manufactured by printing technology on film. Organic EL elements that can be formed to a large thickness have become widespread. The EL element comprises:
The load of the drive circuit is a capacitive load, and a luminance of about 20 Cd / m ² is necessary depending on the device to be mounted. Therefore, it is necessary to drive with an AC voltage of about 80 to 90 V of about 300 Hz. In particular, in-vehicle AV equipment may require a luminance of 200 Cd / m ² or more, which requires a high driving voltage. And, a battery is used in the device, and thus the EL device is used.
A DC-AC converter is required to drive the elements. As a conventional example of a DC-AC converter for driving the above-described EL element, a product number SP4428 (Si, USA)
pex) (hereinafter referred to as drive circuit A).

FIG. 10 is a schematic diagram showing the configuration of a drive circuit 200, in which a DC input power supply (battery in this case) is connected to power supply terminals 212 (VDD), 206 (VDD), and 217 (VSS). Oscillator 209 connected to the power supply includes frequency dividers 210 and 21 for appropriately dividing the oscillation frequency of oscillator 209.
1 and the frequency dividers 210 and 211 are connected to a main switch 213 for turning on and off the EL element according to an instruction from a main board (not shown) of the portable device. A main switch 213 is provided at the base of a driving switching transistor (hereinafter, switching transistor) 208.
Is connected to the output terminal of an AND circuit 214, and an inductor 207 formed by winding a magnet wire as a load of the switching transistor 208.
Is connected. The EL element 205 is connected as a load capacitance between the collector of the switching transistor 208 and the power supply, and at the same time, through the thyristors 202 and 204, an EL driving bipolar transistor (hereinafter, transistor).
An EL element 205 having a load capacitance is connected to the collectors of the EL driving transistors 201 and 203. The bases of the EL drive transistors 201 and 203 have AND circuits 215 and 216 connected to the main switch 213.
Are connected respectively.

In FIG. 10, when the main switch 213 is closed by an instruction from a main board of a portable device, a frequency divider 2 for appropriately dividing the oscillation frequency of an oscillator 209 is provided.
The output of the AND circuit 214 is applied to the base of the switching transistor 208 via the switches 10 and 211, and the switching transistor 208 is turned on. The ON period is several tens of kHz, which is driven at a duty of about 94%, and the inductor 207 stores electromagnetic energy. With the remaining duty of about 6% of the frequency, the switching transistor 208 is turned off, and the output of the AND circuit 215 or 216 is applied to the base according to the polarity of the voltage applied to the EL element 205, and the EL drive transistor 201 or 203 is turned on, the electric charge is accumulated in the EL element 205 and the voltage rises, and the EL element 205 is alternately driven at a driving frequency of about 300 Hz to convert electric energy and emit light.

FIG. 12 shows another example of the prior art.
L driver IC (Matsushita Electronics Co., Ltd., product number MIP80
5) is a main circuit diagram 280 (hereinafter referred to as Document B). Document B
The EL driver IC 280 is composed of two sets of field effect transistors (hereinafter, FETs) 282, 283 and 284, 285 connected in a complementary manner, has a drive circuit 281 for the EL element 286, and has FETs 282, 284 of the drive circuit 281.
Of the inductor 29 connected to the power supply 290
2 are connected. The oscillation circuit 288 is connected to the external signal terminal 29
1 and the FET 282 via the voltage control circuit 287,
285 and 284 and 283 are connected by so-called crossing. The load terminal of the EL element 286 is
2, 284 sources. In addition, inductor 2
92 is connected to the drain of FET 289 and
The gate of 89 is connected to the oscillation circuit 288.

The operation of the EL driver IC 280 shown in FIG. 12 can be described in exactly the same manner as in FIG. In FIG. 12, when a signal is applied to the external signal terminal 291 from the main board of the portable device, an output obtained by appropriately dividing the oscillation frequency of the oscillator 288 is applied to the gate of the switching FET 289, and
ET289 turns on. The cycle of turning on can be configured as a circuit by the user's design choice, and is several tens of kHz. When driven at a required duty, the inductor 292 stores electromagnetic energy. At the remaining duty of the frequency, the FET 289 is turned off, and the output of the voltage control circuit 287 is applied to the gate of each of the FETs according to the polarity of the voltage applied to the EL element 286, so that the FETs 282, 285 and 284, 283 The EL elements 286 are alternately turned on, and charges are accumulated in the EL elements 286 to increase the voltage. The EL elements 286 are alternately driven at a driving frequency of about several hundred Hz to convert electric energy and emit light.

[0007]

However, document A
And Document B have a common problem. This will be described in detail with reference to the voltage waveform of the applied voltage of the conventional EL element drive circuit shown in FIG. FIG. 11A shows the switching transistor 208 (FIG. 10) or the switching FE.
It is a pulse-like discharge voltage waveform 220 of T289 (FIG. 12). FIGS. 2B and 2C show the EL element 205 (FIG. 1).
0) or 286 (FIG. 12). FIG. 11D shows the AC composite voltage waveform 22 shown in FIGS.
3.

As can be seen from the composite voltage waveform 223 in FIG. 11D, the EL element 205 (FIG. 10) or 286
The AC voltage for driving (FIG. 12) changes rapidly in the regions 275a, 275a during the zero-crossing period in which the polarity is changed.
75b, which rapidly discharges the accumulated charge, causing electromagnetic noise, deteriorating drive efficiency, and deteriorating the EL element 205 (FIG. 10) or 286 (FIG. 12). . The present invention proposes a simple FET drive circuit configuration that eliminates the above-mentioned drawbacks, has good luminous efficiency, has low electromagnetic noise, and can reduce deterioration of EL elements.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. An oscillator connected to a DC power supply, a frequency divider for appropriately dividing the frequency of the oscillator, and a frequency of the frequency divider are provided. And a pair of complementary connected field effect transistors that are switched by the switching circuit and that are loaded with a load capacitance that is a first inductor element and an EL element (electroluminescence). And the driving circuit
EL that intermittently charges and accumulates the electromagnetic energy stored in the inductor element in the load capacitance, which is an EL element, and drives it positively or negatively to convert electric energy into light energy.
In the element drive circuit, a load impedance including the EL element is connected to a drive circuit including the two sets of serially connected field effect transistors, and a drive circuit including the two sets of serially connected field effect transistors is connected. A gate voltage control circuit is connected so as to cause a time difference in the application of the gate voltage, and an idle period is provided in the drive circuit of the drive voltage that drives positively and negatively.

According to another aspect of the present invention, an output of a pair of AND circuits having a common input and an input related to an oscillation frequency are used as a common input. The driving circuit is constituted by a pair of OR circuits, and is driven by connecting the gates of the driving circuit crosswise, and a pause period is provided in the driving circuit of the driving voltage for driving positively and negatively.

According to another aspect of the present invention, a load resistance of the drive circuit is connected to a load terminal of a leakage resistance in parallel with the EL element.

According to another aspect of the present invention, a second inductor element is connected to a load terminal of the drive circuit in series with the EL element as a load.

According to another aspect of the present invention, a primary winding of a winding transformer is connected to a load terminal of the drive circuit, and the EL element is connected in series with a secondary winding. It is characterized by the following.

According to another aspect of the present invention, a primary winding of a winding transformer is connected to a load terminal of a driving circuit, and the primary winding and the secondary winding of the winding transformer are connected. Are connected in series to the EL element.

Further, the present invention has been made to solve the above-mentioned problems. According to the present invention, there is provided a semiconductor device, comprising:
The device is characterized in that the waveform of the drive voltage is made continuous by self-discharge of the element.

According to another aspect of the present invention, there is provided a driving circuit which is driven by transient vibration of a combined load by a second inductor connected to the EL element as a load of the driving circuit during a pause of the driving circuit. It is characterized in that the voltage waveform is configured to be continuous.

Further, the present invention has been made to solve the above-mentioned problems. According to the present invention, a primary or secondary winding transformer connected to the EL element as a load of the driving circuit or a related element thereof is provided during a pause of the driving circuit. The present invention is characterized in that the waveform of the drive voltage is made continuous by the combined vibration of the combined load.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. To avoid duplication with the description of the conventional example, differences will be mainly described. FIG. 1 is a configuration diagram of a main circuit of the EL driver of the present invention. FIG. 2 is a circuit configuration diagram in which an EL element and a leakage resistor to a load terminal of a drive circuit according to the present invention are connected in parallel. FIG. 3 is a circuit diagram in which an EL element and a second inductor connected to a load terminal of a drive circuit according to the present invention are connected in series. FIG. 4 is a circuit configuration diagram in which a primary winding of a winding transformer is connected to a load terminal of a drive circuit according to the present invention, and the primary winding and the secondary winding are connected in series with an EL element. . FIG. 5 shows the connection of the primary winding of the winding transformer to the load terminal of the drive circuit according to the present invention,
FIG. 3 is a circuit configuration diagram in which elements are connected in series. FIG. 6 is a time chart of each part of the main circuit of the EL driver of the present invention. FIG. 7 is a waveform diagram of the AC drive voltage of the present invention. FIG. 8 is a drive voltage waveform diagram of the EL driver of the present invention. FIG. 9 is an explanatory diagram of characteristics of the EL driver of the present invention.

Referring to FIG. 1, the EL driver 100 of the present invention
Is a drive circuit 11 surrounded by a dotted line, which is composed of two sets of FETs 113, 114 and 115 and 116 which are complementarily connected on an inverter substrate 111 and drives an EL element 118.
2, a power supply 121 (VDD) and a power supply voltage of 122a.
(VDD), 122b (VSS) as one end 121 of the power supply.
The first inductor 117 connected to (VDD) is connected to the drains of the FETs 113 and 115 of the drive circuit 112 and the collector of the switching transistor 120.
The output of the oscillating circuit 124 passes through 125a indicating the frequency divider 1, 125b indicating the frequency divider 2,... 125f indicating the frequency divider 6, and then to the gate voltage control circuit 131 and the AND circuit 126 surrounded by a dotted line. The output of the AND circuit 128 a to which the output of the oscillation circuit 124 and the output of the one-shot multi-circuit 127 are input is connected to the switching transistor 120.
Connected to the base. The gate voltage control circuit 131
AND circuit 128b, AND circuit 128c, OR circuit 1
30a, an OR circuit 130b, and an inverter 129. The input of the AND circuit 128b is the signal of the control switch 123, the one-shot multi-circuit 12
7 and the output of the frequency divider 125f. The output of the AND circuit 128b is
5 gate. The input of the AND circuit 128c is composed of the signal of the control switch 123, the output of the one-shot multi-circuit 127, and the output of the frequency divider 125f. The output of the AND circuit 128b is
b and the gate of the FET 114. The inverter 129 connected to the one-shot multi-circuit 127
Is connected to the input side of the OR circuits 130a and 130b,
The outputs of the OR circuit 130a and the OR circuit 130b are connected to the gates of the FET 116 and the FET 114, respectively.
The load terminals 132, 1 are connected to the sources of the FETs 113, 115, respectively.
33, and the load terminals 132 and 133 are connected to EL.
Element 118 is connected.

As a load of the embodiment of the present invention, the EL element 118 is used as a load of a driving circuit. As shown in FIG.
8a and the leakage resistance 118 existing inside the EL element 118
b. Further, another resistor may be added in addition to the leakage resistor 118b as required in design.

As a load of another embodiment of the present invention, FIG. 3 shows that a load impedance including the EL element 118 is obtained by connecting an EL element 118 and a second inductor 119 in series. , 133.

FIG. 4 shows the primary winding 1 of the winding transformer 135.
In this embodiment, an EL element 118 is connected in series with 34a and 134b, and a primary winding 134a is connected to load terminals 132 and 133 of a drive circuit 112.

FIG. 5 shows the load impedance of another embodiment of the present invention.
In this embodiment, b is connected in series to the EL element 118 and its primary winding 134a is connected to the load terminals 132 and 133 of the drive circuit 112.

The operation of the EL driver of the present invention can be explained as follows. In FIG. 1, an external signal from a main board such as a portable device is received and a control switch 123 is received.
Is closed, the oscillation frequency of the oscillator 124 is appropriately divided via frequency dividers 125a, 125b,... 125f and the like, and the AND circuit 126, the one-shot multi-circuit 12
7. The voltage is applied to the base of the switching transistor 120 via the AND circuit 128a, and the switching transistor 120 is turned on. This ON period can be configured by a user's design choice.
The first inductor 117 is driven at the required duty cycle, and the first inductor 117 stores electromagnetic energy. At the remaining duty of the frequency, the switching transistor 120 is turned off, and the output of the gate voltage control circuit 131 is applied to the respective gates of the FETs according to the polarity of the voltage applied to the EL element 118, so that the FETs 113, 1
14, 115, and 116 are turned on alternately, the electromagnetic energy stored in the first inductor 117 is released, the electric charge is stored in the EL element 118, and the voltage rises. Are alternately driven at the drive frequency of, and convert electric energy to emit light.

The operation of the EL driver 100 of the present invention will be described in more detail with reference to FIG. The oscillation frequency of the oscillator 124 is appropriately divided by a frequency 136 through frequency dividers 125a, 125b,... 125f, etc., so that a current 137 flows through the first inductor 119 to store electromagnetic energy. On the other hand, the output voltage 138 of the one-shot multi-circuit 127 is output from the AND circuit 12 of the gate voltage control circuit 131.
8b and 128c to be applied to FET113, FET1
The ON and OFF operations of 15 are 139 and 140, respectively, and have an idle period 145 determined by design. That is, the half period 147 of the drive voltage of the drive circuit 112 has a pause period 145 shorter than the half period, and the drive circuit 112 is simultaneously turned on and the drive voltage is energized. Period 146. Similarly, FET 114,
The ON and OFF operations of the FET 116 are 141 and 142, respectively, and have an idle period 145 determined by design. That is, the half period 147 of the drive voltage of the drive circuit 112 has a pause period 145 shorter than the half period, and the drive circuit 112 is simultaneously turned on and the drive voltage is energized. Period 146. As a result, EL
Voltage waveforms applied to the element 118 are 143 and 144, respectively.
Becomes On the other hand, in the idle period 145, the FETs 114 and 116 of the drive circuit 112 are turned on 141 and 142, and the FETs 114 and 116 are always turned on at the same time. This is very important in the present invention. That is, even during the pause period 145, the load terminals 132 and 133 of the drive circuit 112 are short-circuited to form a closed circuit, and the electric energy stored in the load impedance including the EL element 118 can be naturally discharged. .

[0026]

Embodiment 1 In general, an EL element 118 is an equivalent circuit as shown in FIG.
In FIG. 2, the area of the EL element 118 is about 10 c
At m ² , the capacitance CEL 118a is about 10,000 pF, the leakage resistance REL 118b is about 300Ω, and the following value may be assumed as the time constant τ.

Τ = 0.7 × C _EL × R _EL = 0.7 × 10 ⁴
× 10 ^-12 × 3 × 10 ² = 2.1 μSec.

Therefore, if the pause period 145 is set to 10 μSec., The drive voltage 1 on one side in FIG.
43, 143a, and the other one side drive voltage 144, 1
As shown at 44a, the EL element 118 can naturally release the sufficiently stored electrical energy by self-discharge.

As shown in FIG. 7, in addition to the leakage resistor 118b, generally, a resistor is connected to the capacitor 118 of the EL element 118.
If the value of the quiescent period 145 and the value of the time constant 153a can be substantially matched by being connected in parallel with a, the pulse is discharged from the first inductor 117 in FIG. According to the applied voltage 150 (A), it becomes as follows. EL1 voltage (B) 151, EL2
The voltage for driving the EL element 118 by the voltage (C) 152 is a combined AC voltage waveform 153, which is a more continuous waveform.

In the load impedance including the EL elements shown in FIGS. 3 to 5, a resonance circuit is equivalently formed. In the idle period 145, as shown in FIG. Is obtained. Also in this case, in the idle period 145, the load terminals 132 and 133 of the drive circuit 112 are short-circuited to form a closed circuit, and the electric energy stored in the load impedance including the EL element 118 can be naturally discharged. The energy stored in the EL element 118 is
The sufficiently stored electrical energy is naturally released by the damping transient vibration 154a.

[0031]

Embodiment 2 In an embodiment of the EL driver 100 of the present invention, the load impedance circuit including the EL element is shown in FIG. 3, the first inductor in FIG. 1 is set to 100 μH, the second inductor is set to 1.7 mH, and the EL element is set to 1.7 mH. 8cm area of 118
^{2. The} experiment was performed with a capacitance of 8000 pF. As a result, as shown in FIG. 9, a luminance of 160 and a combined AC voltage of 161 were obtained, which was sufficiently effective.

In the description of the embodiments of the present invention, the EL element has been mainly described, but it is apparent that the present invention can be applied to a fluorescent tube.

In the embodiment of the present invention, the driving circuit is F
Although described as ET, it is apparent that a bipolar transistor or a bi-C / MOS type or the like can be arbitrarily selected.

[0034]

According to the present invention, the idle period is provided in the drive circuit of the EL element, and the load impedance circuit including the EL element becomes a closed circuit during the idle period, so that the combined AC voltage has a continuous waveform. Since the electric energy stored in the EL element is naturally released, the electromagnetic noise and E
Since the deterioration of the L element is small and the stored electric energy can be sufficiently used, the luminance of the EL element can be improved.

Further, according to the present invention, an EL driver can be realized with a simple circuit configuration, so that cost / performance is greatly improved.

Further, according to the present invention, since the configuration of the load impedance circuit including the EL element can be flexibly formed, the degree of freedom in design is large and the practical effect is remarkable.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an EL driver of the present invention.

FIG. 2 is a load equivalent circuit of the EL driver of the present invention.

FIG. 3 is a load impedance circuit of the EL driver of the present invention.

FIG. 4 is a load impedance circuit of the EL driver of the present invention.

FIG. 5 is a load impedance circuit of the EL element driver of the present invention.

FIG. 6 is a time chart of each part of the EL driver of the present invention.

FIG. 7 is a driving voltage waveform of the EL driver of the present invention.

FIG. 8 is another driving voltage waveform of the EL driver of the present invention.

FIG. 9 is an explanatory diagram of characteristics of the EL driver of the present invention.

FIG. 10 is a circuit configuration diagram of a conventional EL driver.

FIG. 11 is a driving voltage waveform of a conventional EL driver.

FIG. 12 is another EL driver circuit configuration diagram of the conventional example.

[Explanation of symbols]

 Reference Signs List 100 EL driver 111 Inverter substrate 112 Drive circuit 113, 114, 115, 116 FET 117 First inductor 118 EL element 118a EL element capacitance 118b EL element leakage resistance 119 Second inductor 120 Switching transistor 121, 122a Power supply (VDD) ) 122b Power supply (VSS) 123 Control switch 124 Oscillator 125a, 125b, ... 125f Divider 126, 128a, 128b, 128c AND circuit 129 Inverter 130a, 130b OR circuit 131 Gate voltage control circuit 132, 133 Load terminal 134a Primary winding Wire 134b secondary winding 135 winding transformer

Claims (9)

[Claims] 1. An oscillator to which a DC power supply is connected, a frequency divider for appropriately dividing the frequency of the oscillator, a switching circuit intermittently driven by the frequency of the frequency divider, and switching by the switching circuit. And a drive circuit composed of two sets of field-effect transistors connected in a complementary manner and loaded with a load capacitance which is an EL element (electroluminescence), and stored in the first inductor element. In the EL element driving circuit which intermittently charges and accumulates the stored electromagnetic energy in the load capacitance which is an EL element, drives it positively and negatively, and converts electric energy to light energy, the two sets of series connected in series. A load impedance including the EL element is connected to a drive circuit including a field-effect transistor, and a time lag is applied to application of a gate voltage of the drive circuit. An EL driver, wherein a gate voltage control circuit is connected so as to generate a driving voltage, and an idle period is provided in the driving circuit of the driving voltage for driving positively and negatively. 2. The driving circuit according to claim 1, wherein the gate voltage control circuit comprises a pair of OR circuits having a common input of an output of a pair of AND circuits having a common input and an input relating to the oscillation frequency. 2. The EL driver according to claim 1, wherein a gate of the circuit is connected in a crossover manner and driven, and a drive circuit of the drive voltage for driving positively and negatively is provided with an idle period. 3. The EL driver according to claim 1, wherein a leakage resistance in parallel with the EL element is connected as a load to a load terminal of the drive circuit. 4. The EL driver according to claim 1, wherein a second inductor element is connected as a load in series with the EL element to a load terminal of the drive circuit. 5. The device according to claim 1, wherein a primary winding of a winding transformer is connected to a load terminal of the drive circuit, and an EL element is connected in series with the secondary winding. EL driver. 6. A primary winding of a winding transformer is connected to a load terminal of the drive circuit, and the primary winding and the secondary winding of the winding transformer are connected in series to the EL element. The EL driver according to claim 1 or 2, wherein: 7. The driving circuit according to claim 1, wherein a waveform of a driving voltage is continuous by a self-discharge of said EL element during a quiescent period of said driving circuit. EL driver. 8. A configuration in which the drive voltage waveform is configured to be continuous due to transient vibration of a combined load by a second inductor connected to the EL element as a load of the drive circuit during a pause period of the drive circuit. The EL driver according to any one of claims 1 to 5, wherein: 9. A drive voltage caused by transient vibration of a primary or secondary of a winding transformer connected to the EL element or a combined load formed by engaging the primary and secondary windings as a load of the drive circuit during a pause of the drive circuit. The EL driver according to any one of claims 1 to 5, wherein the waveform is configured to be continuous.