JP2000012215A - El drive circuit system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide constitution of EL drive circuit system lowering luminance of an EL element at night, and automatically adjusting the luminance according to the brightness even in the daytime. SOLUTION: This EL drive circuit system 300 is constituted by a converter 220, a CPU block 310 in the front step to the converter 220, and a bridge 211. The CPU block 310 is composed of a brightness sensor (311), a signal amplifier (312), an analog-to-digital converter (313) and a CPU (301), on the same circuit board by an ASIC, etc. The luminance of an EL element 205 is automatically adjusted so as to accommodate itself to the environment, by introducing output frequencies corresponding to a real time clock and the brightness sensor 311 from the CPU (301) to the oscillator 209 of the converter 220.

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 system having multiple functions.

[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. Dispersion type EL elements that can be formed to have a large thickness have become widespread. The EL element is a capacitive load as a load of a driving circuit, and needs a luminance of about 20 Cd / m ² depending on a mounted device.
In addition, in order to obtain further luminance while avoiding deterioration due to the DC component of the driving of the EL element, it is necessary to drive with an AC voltage of about 80 to 90 V with a single amplitude of about 300 Hz. Especially for in-vehicle AV
In some cases, a device requires a luminance of 200 Cd / m ² or more, which requires a high driving voltage.
In addition, a battery is used in the device, and therefore, a DC-AC converter is required to drive the EL element. As a conventional example of the DC-AC converter for driving the above-mentioned EL element, a product number SP4425 (US
A drive IC (hereinafter, referred to as drive circuit A) such as a product manufactured by Shipex Corporation.
Can be mentioned. Hereinafter, a problem of the composite function related to the driving circuit A will be described.

[0003]

FIG. 6 is a schematic diagram showing the configuration of the driving circuit A. FIG. 7 is a main block diagram of the drive circuit A configured on the circuit board. In the same 2,
The driving circuit A mainly includes a converter 22 surrounded by a dotted line.
0 and an H bridge 22 which is a drive circuit for driving the EL element
1 and 1. The converter 220 mainly includes an oscillator 209 and frequency dividers 210 and 211.
The bridge 221 mainly includes a driving switching transistor (hereinafter, switching transistor) 208, thyristors 202, 204, and EL driving bipolar transistors (hereinafter, transistors) 201, 203.
A DC input power supply (battery in this case) is connected to a power supply terminal 212 (V
DD), 206 (VDD), and 217 (VSS), and connected to the same power supply. The oscillator 209 is connected to frequency dividers 210 and 211 for appropriately dividing the oscillation frequency of the oscillator 209. , 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. An output terminal of an AND circuit 214 connected to the main switch 213 is connected to the base of the switching transistor 208, 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 to the collectors of the transistors 201 and 203 via thyristors 202 and 204 as a load capacitance, and further connected to the collectors of the transistors 201 and 203. Also,
AND circuits 215 and 216 connected to the main switch 213 are provided at the bases of the transistors 201 and 203.
Are connected respectively.

In FIG. 6, when a main switch 213 is closed by an instruction from a main board of a portable device, frequency dividers 210 and 2 for appropriately dividing the oscillation frequency of an oscillator 209 are provided.
The output of the AND circuit 214 is applied to the base of the switching transistor 208 via 11, 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 about the remaining 6% of the frequency, the switching transistor 208 is turned off. On the other hand,
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 transistor 201 or 203 is turned on. Rise, and the EL element 205 is alternately driven at a drive frequency of about 300 Hz to turn on the AND circuit 215 or 216 alternately, and converts electric energy to emit light.

In FIG. 7, an EL driving circuit 102 surrounded by a dotted line includes a converter 22 similar to the conventional example shown in FIG.
0 and the H bridge 221 and are formed on the circuit board 101. Connection terminals are provided at both ends of the circuit board 101. For example, a Vdd terminal 104, an Hon terminal 105 for receiving an external signal, a Vss terminal 106, capacitor terminals 110 and 111 on one end, and an EL element 205 on the other end. The connected EL1 terminal 107, EL2 terminal 108, and Vss terminal 109 are provided. The converter 220 is connected to the oscillator 20
9; frequency dividers 210 and 211;
Reference numeral 21 denotes a driving switching transistor (hereinafter, switching transistor) 20 similarly to the conventional example of FIG.
It is composed of eight thyristors 202 and 204 and EL driving bipolar transistors (hereinafter referred to as transistors) 201 and 203, but details are omitted to avoid duplication with the conventional example. DC input power (battery in this case) is Vdd of circuit board 101
The terminal 104 and the Vss terminal 106 are connected to each other. The Vdd terminal 104 and the Vss terminal 106 are connected to a power supply terminal 212 (VD
D) 217 (VSS), the inductor 207 is connected between the power supply terminal 212 (VDD) and the H bridge 221, and the oscillator 209 connected to the power supply divides the oscillation frequency of the oscillator 209 appropriately. The frequency dividers 210 and 211 are connected to the Hon terminal 105 which enables the lighting of the EL element according to an instruction from a main board (not shown) of the portable device. The EL1 terminal 107 and the EL2 terminal 1 of the circuit board 101
Between 08, the EL element 105 is connected as a load of the H bridge. Then, the capacitor 103 is connected to the capacitor terminals 110 and 111 of the oscillator 209 so that the oscillation frequency is determined.

[0006] In FIG. 6 and FIG.
The oscillator 103 is connected to the capacitor 103. When a DC power supply is connected to the Vdd terminal 104 and the Vss terminal 106 and an enable signal is applied to the Hon terminal 105, the EL element 205 turns on.

[0007] However, only the circuit configuration disclosed in Document A requires reduction of the luminance of the EL element at night, and automatic adjustment of the luminance according to the brightness even at daytime, for example. Can not do. On the other hand, conventionally, an EL drive circuit having a multi-function has been announced.
For example, product number SP4415 manufactured by Sipex, USA
Has a built-in clock function. In addition, US
The product number SP4460 manufactured by Company x includes a clock motor driver, the SP4501 includes a piezo buzzer driver, and the SP4441 includes a multifunction timer. However, an EL drive circuit system having a composite function rather than a multifunction provided in a comprehensive manner in accordance with the brightness of the EL element according to life time and light / dark environment has not been proposed. An object of the present invention is to eliminate the above-mentioned disadvantages and propose an EL drive circuit system having a composite function.

[0008]

According to the present invention, there is provided an EL driving circuit system comprising an H-bridge for driving a converter and an EL element. A CPU block is provided before the converter, and the CPU block is provided with a light / dark sensor, a signal amplifier, an A / D converter, and an output frequency variable according to the output of the light / dark sensor.
C to be introduced into the external synchronous oscillator of the converter of the drive circuit
And the CPU block is formed on the same circuit board.

According to a second aspect of the present invention, there is provided an EL driving circuit system, wherein the CPU block amplifies a signal of the output of the light / dark sensor and digitizes the output to at least one bit by an A / D converter. The output frequency previously encoded by the CPU is
The decoding is performed according to the output of the D converter, and the output frequency that is variable according to the brightness is transmitted.

According to a third aspect of the present invention, there is provided an EL driving circuit system according to the third aspect, wherein the CPU block changes an output frequency previously encoded in the CPU by a real-time clock signal sent from the CPU. The decoding is performed according to the real-time clock signal, and an output frequency that is variable according to the real-time clock signal is transmitted.

According to a fourth aspect of the present invention, there is provided an EL driving circuit system according to the fourth aspect, wherein the A / D converter of the CPU block has at least one bit and preferably four bits. Item 3. The EL drive circuit system according to item 2 or 3.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings, using the same reference numerals to avoid duplication with the conventional example. FIG. 1 is a configuration diagram of an EL drive circuit system according to the present invention. FIG. 2 is a basic configuration diagram of the CPU block of the present invention. FIG. 3 is a circuit configuration diagram of the CPU block of the present invention. FIG. 4 is an explanatory diagram of the amplified output of the light / dark sensor. FIG. 5 is an explanatory diagram of luminance corresponding to a real-time clock according to another invention. In FIGS. 1 and 2, EL
The drive circuit system 300 includes a converter 220, a CPU block 310 provided in front of the converter 220, and an H bridge 211 on the same circuit board such as an ASIC. The CPU block 310 includes the light / dark sensor 31.
1, signal amplifier 312, A / D converter 313, CP
U301, and is connected to the Vdd terminal 104 via Vdd 314 and to the Vss terminal 106 via VSS 315. The output of the light / dark sensor 311 is
Is input to the A / D converter 313 through the signal amplifier 3
Twelve analog outputs are digitized. CPU3 in advance
The output frequency encoded as 01 is decoded by the output of the A / D converter 313. The output frequency terminal 111 of the CPU 301 is connected to the capacitor terminal 110, and the enable signal terminal 302 is connected to the Hon terminal 105. The oscillator 209 of the present invention is of an external signal synchronization type, and the output frequency signal is supplied by the CPU 301. In general, the luminance of the EL element 205 is
It has been confirmed that the oscillation frequency increases when the oscillation frequency increases.

Referring to FIG. 3, in this embodiment of the CPU block 310, the light / dark sensor 311 is constituted by a phototransistor, the output of which is connected to a signal amplifier 312 connected to the emitter, and the output of which is connected to an A / D converter 313. CPU 30 according to the output of A / D converter 313
1 outputs an output frequency. The light / dark sensor 311 may be constituted by a photodiode, CdS, or the like.

3 and 4, an output voltage is generated when the light sensor 311 receives light that changes depending on the brightness of the environment, and the output voltage is amplified by the signal amplifier 312. The amplified signal, which is an analog signal, is digitized by the A / D converter 313 of at least 1 bit and up to about 4 bits. A / D converter 3
The number of bits of 13 is just one step of light and dark with 1 bit, but if it is a little more detailed, the brightness can be controlled by 1/16 with 4 bits. Even if the number of bits is further increased, a remarkable effect cannot be expected so much, which leads to an increase in cost. Therefore, the number of bits of the A / D converter 313 is desirably 1 or more and about 4. When the external light is bright as in the daytime, the brightness of the external light is detected by the light / dark sensor 311 and the output frequency from the CPU 301 is increased to raise the oscillation frequency of the oscillator 209 synchronized therewith, thereby increasing the luminance of the EL element 205. When the external light is dark, such as at night, the brightness of the external light is detected by a sensor, the output frequency from the CPU 301 is reduced, the oscillation frequency of the oscillator 209 synchronized therewith is reduced, and the luminance of the EL element 205 is reduced. To do.

In FIG. 5, the CPU 301 controls the real-time clock function to adjust the luminance of the EL element 205 necessary during the daytime or at night according to the living time.
In accordance with the real-time clock signal transmitted from the CPU 301 of the PU block 310, the output frequency previously encoded in the CPU 301 is decoded in accordance with the real-time clock signal, and an output frequency that is variable in accordance with the real-time clock signal is transmitted. For example, in summer, if a relatively high frequency is transmitted from 7:00 to 18 hours, the oscillation frequency of the oscillator 209 is increased and EL is increased.
The luminance of the element 205 can be increased. If a low frequency is sent from 18:00 to 7:00 the next morning, the oscillator 20
9, the luminance of the EL element 205 can be reduced. In the case of winter, the real-time clock should be set accordingly. As described above, an EL drive circuit system having a complex function can be configured by the real-time clock function and the output frequency variable function adapted to the light and dark of the environment. Note that, in FIG. 5, the brightness is displayed only by one step difference, but the A / D converter 31
Obviously, the brightness can be variously adjusted with the number of bits of three. It is also clear that the contents of the real-time clock may be finely divided on the time axis. Further, the use of the light-dark function and the real-time function together does not disturb the gist of the present invention.

[0016]

According to the present invention, an EL drive circuit system having an integrated cost function and an excellent cost / performance having an integrated function is provided by an ASIC or the like according to the brightness of the EL element in accordance with the life time and the light and dark environment. It can be easily configured, and the practical effect is remarkable.

[Brief description of the drawings]

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

FIG. 2 is a basic configuration diagram of a CPU block of the present invention.

FIG. 3 is a circuit configuration diagram of a CPU block of the present invention.

FIG. 4 is an explanatory diagram of an amplified output of a light / dark sensor.

FIG. 5 is an explanatory diagram of luminance corresponding to a real-time clock according to another invention.

FIG. 6 is a schematic configuration diagram illustrating a driving circuit A.

FIG. 7 is a main block diagram of a drive circuit A configured on a circuit board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Circuit board 102 EL drive circuit 103 Capacitance change detection capacitor 104, 212, 314 Vdd terminal 105 Hon terminal 106, 109, 217, 315 Vss terminal 107 EL1 terminal 108 EL2 terminal 110 Capacitor terminal 111 Output frequency terminal 205 EL element 207 Inductor element 209 Oscillator 210, 211 Divider 220 Converter 221 H-bridge 300 EL drive circuit system 301 CPU 302 Enable signal terminal 310 CPU block 311 Light / dark sensor 312 Signal amplifier 313 A / D converter

Claims (4)

[Claims] 1. An H driver for driving a converter and an EL element
In an EL drive circuit system composed of a bridge,
A CPU block is provided before the converter,
The U block is constituted by a light / dark sensor, a signal amplifier, an A / D converter, and a CPU for introducing an output frequency variable according to the output of the light / dark sensor to an external synchronous oscillator of the converter of the EL drive circuit. An EL drive circuit system, wherein the CPU block is formed on the same circuit board. 2. The CPU block amplifies an output of the light / dark sensor and amplifies at least one signal by an A / D converter.
2. An output frequency digitized to bits or more, an output frequency previously encoded in the CPU is decoded in accordance with an output of the A / D converter, and an output frequency which is variable in accordance with light and dark is transmitted. 3. The EL drive circuit system according to claim 1. 3. The CPU block, according to a real-time clock signal sent from a CPU, pre-stores the C
The EL drive circuit system according to claim 1, wherein an output frequency encoded in a PU is decoded according to the real-time clock signal, and an output frequency that is variable according to the real-time clock signal is transmitted. 4. The EL device according to claim 2, wherein the A / D converter of the CPU block has at least one bit or more preferably four bits.
Drive circuit system.