JP2003207763A - Lcd driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LCD (liquid crystal display) driving circuit capable of making the contrast of an LCD optimum over a wide temperature range. <P>SOLUTION: This circuit is an LCD driving circuit which is provided with a feedback circuit 9 including a resistance voltage dividing circuit consisting of resistors 4, 5, 6 and the thermistor 7 connected in parallel with the resistor 6 and an LCD driving power source generating part 1 hanging an output voltage V0 to a direction compensating the output voltage of the feedback circuit 9, and moreover, the LCD driving circuit is provided with a temperature sensor 10 which is constituted by connecting resistors 11 to 15 in series between a power source V CC and the ground and by connecting a thermistor 16 in parallel with the resistor 11 and a voltage changeover part 20 which changes the output voltage of the feedback circuit 9 by changing over a plurality of voltage curves which are preliminarily set in accordance with a plurality of temperature ranges in response to the plurality of detected voltages of the temperature sensor part 10 and the driving circuit generates the output voltage V0 approximated to the optimum driving voltage characteristic of the LCD. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an LCD (Liquid Crystal).
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a Crystal Display), and more particularly to an LCD drive circuit that prevents a change in contrast due to a change in ambient temperature and prevents the visibility of a display screen from decreasing.

[0002]

2. Description of the Related Art Monochrome LCDs are used as display devices such as portable terminals and measuring devices which have relatively small display contents. Normally, in a monochrome LCD, when the surface temperature (ambient temperature) rises, the screen becomes black overall,
Since the background is black and the characters are displayed in black, the visibility of the display contents such as characters is significantly deteriorated. In this way, the reason why the screen becomes black as a whole is monochrome L
The component of CD has temperature dependency.

FIG. 6 shows a temperature-drive voltage characteristic of a monochrome LCD. The optimum driving voltage value changes logarithmically with respect to the change of the surface temperature (ambient temperature). Therefore, if you bring in a portable terminal that is in a proper display condition in the shade outdoors and bring it into a vehicle with insufficient cooling, the LCD drive voltage rises and the entire screen becomes a blackish display. May not be read. As a countermeasure against this, in general, a circuit that linearly changes the LCD drive voltage with respect to a change in ambient temperature is provided by utilizing the temperature characteristics of a thermistor.

FIG. 7 shows a conventional LCD drive circuit. The LCD drive circuit includes an LCD drive power supply generator 1 and a feedback circuit 9. The LCD drive power supply generation unit 1 generates a drive voltage to be applied to the LCD (not shown) based on the power supply Vcc applied to the power supply terminal 2, outputs it from the output terminal 8, and outputs it to the drive electrode of the LCD. To do. The LCD driving power generation unit 1 has a feedback terminal 3
Is provided, and a feedback circuit 9 is connected between the feedback terminal 3 and the output terminal 8. The feedback circuit 9 includes a resistor 4 connected between the feedback terminal 3 and the output terminal 8, a resistor 5 connected in series between the feedback terminal 3 and the ground (ground), a resistor 6, and a thermistor connected in parallel to the resistor 6. It is configured with 7.

At the feedback terminal 3, the output voltage of the LCD drive power supply generation unit 1 is VO, and the resistance value of the resistor 4 is R.
4, the resistance value of the resistor 5 is R5, and the combined resistance of the resistor 6 and the thermistor 7 is R67, the voltage V3 applied to the feedback terminal 3 is V3 = VO * (R5 + R67) / (R4 + R5 + R67). . Here, the thermistor 7 has a characteristic that the internal resistance decreases when the ambient temperature rises. Resistance 4, 5,
Assuming that 6 does not have temperature dependency, when the ambient temperature rises, the combined resistance R67 is reduced by the thermistor 7 and the terminal voltage V3 of the feedback terminal 3 is lowered, and accordingly, the output voltage VO is raised and the LCD drive voltage is increased. Is applied with a voltage commensurate with the temperature rise to compensate for the contrast.

However, in the LCD, when a backlight is used, the temperature of the LCD during operation becomes higher than the ambient temperature. In such a case, when the thermistor (other temperature sensor) measures not the LCD itself but the ambient temperature in which it is placed, the proper voltage is not applied to the LCD.

FIG. 8 shows a characteristic 81 of the optimum driving voltage of the LCD.
And the output voltage characteristic 82 of the LCD drive power generation unit. As shown in FIG. 8, when the output voltage characteristic 82 of the LCD drive circuit having the configuration of FIG. 7 is set to be optimal at 20 ° C., the deviation from the output voltage characteristic 82 becomes large at the low temperature end and the high temperature end, The contrast deteriorates at both low and high temperatures. As a solution to such a problem, there is, for example, Japanese Patent Laid-Open No. 2001-134237.

FIG. 9 shows the structure of another conventional drive circuit for an LCD. The drive circuit shown in FIG. 9 includes a power supply circuit 3 including a first power supply circuit 30A having a first temperature-voltage characteristic and a second power supply circuit 30B having a second temperature-voltage characteristic.
0, a voltage generation circuit 40, a liquid crystal drive circuit 50, a temperature detection unit 60, an electronic volume switch control unit 70, and an amplifier 80.

The power supply circuit 30 generates a reference voltage necessary for driving the liquid crystal. The voltage generation circuit 40 generates the voltage VLCD and the voltages V1 to V4 necessary for driving the liquid crystal based on the output from the power supply circuit 30. The oscillation circuit 90 oscillates and outputs the reference frequency, and the PWM clock generation circuit 70 generates a PWM (pulse width modulation) clock (GCP) based on the oscillation frequency from the oscillation circuit 90. LCD drive circuit 5
Reference numeral 0 indicates the wave height of the grayscale pulse from a PWM decoder (not shown) based on a polarity inversion signal or the like (not shown).
The voltage values VLCD, V1 to V4 from 0 or the ground voltage VGND are shifted and supplied to the electrodes of the LCD. The power supply circuit 30 includes a first power supply circuit 30A and a second power supply circuit 3
In addition to 0B, a temperature gradient selection circuit 36 that outputs a voltage according to a voltage characteristic having a desired temperature gradient based on the output voltage from these circuits is provided.

The first power supply circuit 30A outputs the voltage A which changes according to the temperature-voltage characteristic of the first temperature gradient (for example, -0.2% / ° C) shown in FIG. On the other hand, the second power supply circuit 30B outputs the voltage B that changes according to the temperature-voltage characteristic of the second temperature gradient (for example, -0.15% / ° C) shown in FIG. 7. Then, the temperature gradient selection circuit 36
Selects and outputs a voltage C having a desired temperature gradient between the first and second temperature gradient voltages A and B shown in FIG.

The first power supply circuit 30A uses the voltage from the constant voltage source 32A having the first temperature gradient characteristic as an amplifier 34A.
Amplify with and output. A resistor R1 is connected between the output line of the amplifier 34A and the ground. By connecting the middle of the resistor R1 to the negative terminal of the amplifier 34A,
A feedback resistor R1A is formed in the feedback path of the amplifier 34A. The second power supply circuit 30B amplifies the voltage from the constant voltage source 32B having the second temperature gradient characteristic by the amplifier 34B and outputs the amplified voltage. A resistor R2 is connected between the output line of the amplifier 34B and the ground. By connecting the middle of the resistor R2 to the negative terminal of the amplifier 34B, the amplifier 3
A feedback resistor R2A is formed in the feedback path of 4B. In addition,
The above-mentioned first and second temperature gradients are the same as the constant voltage sources 32A, 3A.
It is determined depending on the process characteristics of the MOS transistor forming 2B.

The temperature gradient selection circuit 36 includes an amplifier 34A,
A resistor R3 inserted and connected in the middle of a connecting line connecting the output lines of 34B, a switch SW1 connected to an arbitrary position in the middle of the resistor R3, and a temperature gradient selection register storing connection position information of the switch SW1. And 38. The power supply circuit 30A includes a feedback resistor R1A connected to the amplifier 34A and a temperature detection switch SW3, and the power supply circuit 30B includes a feedback resistor R2A connected to the amplifier 34B.
And a temperature detection switch SW4.

The temperature gradient selection register 38 is a programmable register, and the user can freely select the temperature gradient. However, when the liquid crystal panel 10 to be used is specified, the temperature gradient unique to the liquid crystal panel 10 is selected and is not changed thereafter. Here, it is assumed that the initial value has already been set in the temperature gradient selection register 38 and the output voltage from the power supply circuit 30 has the voltage characteristic C shown in FIG.

An amplifier 8 is provided after the temperature gradient selection circuit 36.
0 is connected, and a resistor R4 is connected between the output line of the amplifier 80 and the ground. This resistance R4
A feedback resistor R4A is formed in the feedback path of the amplifier 80 by connecting the intermediate position of the to the negative terminal of the amplifier 80. The first electronic volume switch SW2 is connected in the middle of the feedback resistor R4A of the amplifier 80, and the resistor selected by this electronic volume switch SW2 is represented as the resistor R4B in FIG. By making the value of the resistor R4B variable, the voltage characteristic C shown in FIG. 10 can be further corrected.

The voltage generation circuit 40 has a fourth amplifier 42 to which a voltage is input via the electronic volume switch SW2.
And a resistor R5 connected between its output line and ground
Have. The output voltage VCLD of the amplifier 42 is resistance-divided by the resistor R5 to generate the voltages V1 to V4.

As described above, in the configuration of FIG. 9, by controlling the first electronic volume switch SW2 in accordance with the ambient temperature, the voltage characteristic C shown in FIG. 10 is further corrected in accordance with the ambient temperature. For this purpose, the temperature detection unit 6 that detects the ambient temperature by utilizing the two types of temperature gradient characteristics shown in FIG.
It has 0. The temperature detection unit 60 includes an oscillator circuit 6
1, a counter 63, a comparator 64, and a temperature setting register 65. The oscillation output of the oscillation circuit 61 is divided by a frequency divider 62, the clock from the frequency divider 62 is counted by a counter 63, and the counter 63 is reset every predetermined count value. The comparator 64 compares the voltages from the temperature detection switch SW3 and the temperature detection switch SW4. When the output from the comparator 64 changes, the temperature setting register 65 outputs the data corresponding to the actual temperature based on the output of the counter 63.

The temperature detection switch SW3 or SW4 is
Each time the output from the counter 63 changes, the feedback resistor R2
The connection points are sequentially switched from one end of A and R3A toward the other end. For example, when the switch SW3 is fixed at the position of FIG. 10 and only the switch SW4 is switched, the voltage input to the comparator 64 is swept from the voltage V1 on the voltage characteristic B of FIG. 10 in the arrow direction a, Voltage V2 on voltage characteristic A (comparator 64 via temperature detection switch SW3
The voltage of the comparator 64 changes from "H" to "L" at the time when the voltage of the comparator 64 falls below the voltage (input voltage). At this time, if the voltage change amount is ΔV, this change amount ΔV becomes a value specific to the temperature t1. Therefore, the temperature setting register 65 is provided in the comparator 64.
The actual temperature t1 is output based on the count value of the counter 63 (corresponding to the amount of voltage change ΔV) when the output of 1 changes.

On the contrary, the actual temperature t2 is detected by the switch SW.
4 is fixed, the switch SW3 is switched, and sweeping is performed in the direction of arrow b in FIG. Voltage V on voltage characteristic A
The voltage swept from 3 is the voltage V during the sweep process.
Below 4, the output of the comparator 64 changes from "L" to "H", so that the actual temperature t2 is detected.

As described above, the temperature detecting section 60 can detect the actual temperature by utilizing the temperature gradient characteristic of the power supply circuit 30 itself. In this way, the power supply circuit 30 is provided with the constant voltage sources 30A and 30B having two kinds of temperature gradients, and the liquid crystal applied voltage is corrected based on the actual temperature detected by utilizing the two kinds of temperature gradients. , More accurate correction becomes possible.

Next, the operation of controlling the electronic volume switch SW2 based on the actual temperature thus detected will be described. To this end, an electronic volume switch control unit 70 is provided, and a correction value is preset in the electronic volume switch control unit 70 by the manufacturer of the liquid crystal panel. Electronic volume switch control unit 70
Is provided with a correction table 132, a register 73 similarly storing the control reference value of the electronic volume switch SW2 set by the liquid crystal panel manufacturer, and an adder 72 for adding and outputting the digital values of both.

FIG. 11 shows the temperature-dependent characteristics of the liquid crystal applied voltage VCLD obtained based on the output from the electronic volume switch SW2 controlled by the electronic volume switch controller 70. FIG. 11 shows that the liquid crystal voltage VCLD has temperature-dependent characteristics of different temperature gradients depending on the low temperature region Ta, the intermediate temperature region Tb, and the high temperature region Tc. The intermediate temperature range Tb is basically the temperature gradient selection switch SW based on the output from the temperature gradient selection register 38.
1 and the electronic volume switch SW2 based on the output from the register 73. Also, the low temperature region T
The a and the high temperature region Tb are set by the electronic volume switch SW2 controlled by the output from the correction table 71. The low temperature region Ta has a resistance R4B selected by the electronic volume switch SW2 as the temperature becomes lower.
Is set small (the contact of the switch SW2 is brought close to the output side of the amplifier 80). On the other hand, in the high temperature region Tc, the resistance value of the resistor R4B is set to be higher as the temperature becomes higher (the contact of the switch SW2 is brought closer to the ground GND side).

As described above, the liquid crystal application voltages VCLD, V1 to V4 having the temperature dependence peculiar to the LCD can be generated from the output voltage of the power supply circuit 30 having two kinds of temperature gradient characteristics.

[0023]

However, the conventional LCD
According to the drive circuit, in the configuration of FIG. 7, the characteristics of the ambient temperature-optimal drive voltage shown in FIG. 6 may be different as shown in FIG. 8 depending on the LCD, and a simple linear curve may not be able to follow. In this case, the temperature range that can be tracked must be specified and the constant must be determined.However, with such a method, in applications that require high temperature and low temperature, such as for business use and in-vehicle use, It becomes a factor that reduces the commercial value. Further, in order to recover this, a method of externally attaching a controller to monitor the temperature and switching the constant can be considered, but it is not practical because it is expensive, requires development man-hours, and costs development.

In the configuration of FIG. 9, the characteristics of the low temperature region Ta and the high temperature region Tb are uniquely determined by the temperature gradient characteristics of the two constant voltage sources 30A and 30B, and the low temperature end and high temperature shown in FIG. Although it is possible to correct one edge at a time, the entire range of the characteristic shown in FIG. 6 is corrected by a curve similar to this characteristic, and the LCD is displayed over a wide temperature range (close to the characteristic 81 in FIG. 8). The contrast of can't be optimized. Further, the configuration is extremely complicated, and although it can be applied to a display for a personal computer or the like, it is difficult to apply to a small device such as a mobile terminal such as a mobile phone or a PDA (Personal Digital Assistant) device.

Therefore, it is an object of the present invention to provide an LCD driving circuit capable of optimizing the LCD contrast over a wide temperature range.

[0026]

In order to achieve the above object, the present invention is designed to change a resistance voltage dividing circuit to which an output voltage for driving an LCD is applied and a combined resistance of some of the resistances. In an LCD drive circuit including a feedback circuit including a connected temperature detection element, and an LCD drive power supply generation unit that changes the output voltage in a direction to compensate for the change in the output voltage of the feedback circuit, the ambient temperature or the temperature of the LCD. A temperature sensor unit that outputs a plurality of detection voltages according to a plurality of temperature ranges of the ambient temperature or the temperature of the LCD by a second temperature detection element that detects the temperature, and is set in advance corresponding to the plurality of temperature ranges. A plurality of voltage curves that are switched based on the plurality of detected voltages of the temperature sensor unit to change the output characteristics of the feedback circuit. L, characterized in that it comprises a changing unit
A CD drive circuit is provided.

According to this structure, the ambient temperature or the LCD
Temperature is detected by the temperature sensor, the voltage change due to the temperature change is detected for each temperature range, and one of the plurality of voltage curves is selected by the voltage curve switching unit according to this voltage change, and the output of the feedback circuit is output. By changing the voltage characteristic, the output voltage of the feedback circuit is modified according to the change of the temperature (ambient temperature or LCD temperature) so as to guarantee the temperature of the output voltage of the LCD drive power generation unit, and this output voltage is input. The temperature of the output voltage of the LCD drive power generation unit is guaranteed. Therefore, L over a wide temperature range
It becomes possible to optimize the contrast of the CD.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of an LCD drive circuit of the present invention. The LCD drive circuit of the present invention is configured by adding a temperature sensor 10 and a voltage curve switching unit 20 to the LCD drive circuit of FIG. Temperature sensor 10
Is composed of resistors 11, 12, 13, 14, 15 connected in series between the power source Vcc and ground (GND), and a thermistor 16 connected in parallel with the resistor 11.
Further, the voltage curve switching unit 20 includes the voltage detection unit 21.
a, 21b, 21c, 21d, this voltage detection unit 21a-
An electronic switch 22a which is turned on / off by 21d,
22b, 22c, 22d, and electronic switches 22a-2
Resistors 23a, 23b, 23 connected to each of 2d
c, 23d. Voltage detector 21a
Is connected to the connection point c between the resistors 11 and 12, and the voltage detection unit 2
1b is connected to a connection point d between the resistors 12 and 13, the voltage detection unit 21c is connected to a connection point e between the resistors 13 and 14, and the voltage detection unit 21b is connected to a connection point f between the resistors 14 and 15. The input terminals of the electronic switches 22a to 22d are connected in parallel, and the output voltage VO is applied to this line.
The electronic switches 22a to 22d are all turned on when the ambient temperature is low, and are sequentially turned off as the ambient temperature rises. The output side ends of the resistors 23a to 23d are connected in parallel and are connected to the feedback terminal 3.

Each of the voltage detection units 21a to 21d is set to a different detection voltage, and when the voltage at the resistance division point by the resistors 13 to 15 reaches the set voltage value, the corresponding electronic switch (22a to 22d) is turned off. Become. By turning off the electronic switches 22a to 22d in stages,
Since the combined resistance value of the resistors 23a to 23d with respect to the resistance 4 changes, that is, the combined resistance between the output terminal 8 and the feedback terminal 3 changes, the voltage value applied to the feedback terminal 3 changes.

FIG. 2 shows temperature-resistance characteristics of the thermistor 16, FIG. 3 shows voltage curve characteristics of the voltage curve switching section 20, and FIG. 4 shows LCD drive power generation corresponding to the voltage curve characteristics of the voltage curve switching section 20. 4 shows changes in the output voltage characteristic of the part 1. Further, FIG. 5 shows a state in which the voltage curve characteristic of FIG. 4 is superimposed on the ambient temperature-optimal drive voltage characteristic of the LCD. 1 to 5, the LCD of the present invention will be described below.
The operation of the drive circuit will be described. Here, the case where the temperature changes from the lower side to the higher side will be described.

When the ambient temperature of the LCD is low, all the voltage detectors 21a to 21d are on. Therefore, the combined resistance of the resistors 23a to 23d is in the smallest state. If the ambient temperature of the LCD rises from this state,
The resistance value of the thermistor 16 decreases as shown in FIG. As a result, the combined resistance of the thermistor 16 and the resistor 11 becomes small, so that both the voltages at the connection points c to f become high. When the voltage at these connection points rises, the input voltage of the voltage detection units 21a to 21d also rises, but the voltage detection unit 21a first detects the voltage rise, and the others do not detect the voltage rise, so only the voltage detection unit 21a is detected. Turn off. When the voltage detector 21a is turned off, the resistor 23a is disconnected from the resistor voltage dividing circuit, and the combined resistance value of the resistor 4 and the resistors 23 (23a to 23d) increases by that amount. On the other hand, in the feedback circuit 9, the resistance value of the thermistor 7 decreases as the temperature rises,
The resistance value between the feedback terminal 3 and the ground decreases. The characteristics of the thermistor 7 are, for example,
In the state where the temperature is relatively low, the voltage applied to the feedback terminal 3 is insufficient with only the feedback circuit 9. On the other hand, when the switch 22a is turned off, the combined resistance value on the resistor 4 side is reduced, so that the voltage applied to the feedback terminal 3 is further reduced as compared with the case where the feedback circuit 9 is alone. As a result, the voltage applied to the feedback terminal 3 has the voltage curve characteristic of i in FIG. 3, and the output voltage VO of the LCD drive power generation unit 1 has the characteristics of FIGS. 4 and 5. Therefore, it is possible to obtain the output voltage VO that is close to the optimum drive voltage characteristic 81 of the LCD.

When the ambient temperature further rises, the voltage detector 21b detects the voltage rise due to the decrease in the resistance value of the thermistor 16 and turns off the electronic switch 22b. When the electronic switch 22b is turned off, the resistor 23b is disconnected from the resistance voltage dividing circuit, and the resistance value between the output terminal 8 and the feedback terminal 3 is increased by that amount, and as a result, the increase of the voltage applied to the feedback terminal 3 is prevented. After that, in the process of increasing the ambient temperature, the voltage detectors 21c → 21d are sequentially operated, and the electronic switches 22c → 22d are switched on and off in this order.

Referring to FIG. 5, the characteristic 8 of the thick line is shown.
1 shows a characteristic example of the optimum driving voltage, and the curve gradually becomes steeper as the temperature rises. For this reason,
With a single voltage curve setting up to around 20 ° C, characteristic 8
It can be seen that the temperature cannot be followed in the temperature regions at both ends of 1. However, in the present invention, the voltage detection unit 21a and the electronic switch 22 are
By combining a, the combined resistance value changes at a point of 20 ° C., so that the voltage curve in the low temperature region can be changed more sharply (points). Furthermore, it is possible to follow up to 40 ° C. by the voltage curve by the combination of the voltage detection unit 21b and the electronic switch 22b (point). Points after that and points
However, similarly, the combined resistance value is set to the electronic switches 23c and 23d.
The voltage curve can be switched by switching with, and it is possible to follow up to a high temperature region of 60 ° C.

[Other Embodiments] As a means for switching the voltage curve of FIG. 5, a voltage detector 21 and an electronic switch 2 are used.
In addition to the combination of 2, the ambient temperature is regularly monitored using a microcomputer with a built-in A / D converter, and when the temperature at which the voltage curve is switched is reached, the resistance value is switched by the output port, or the D / A converter By changing the output voltage by controlling the
It is also possible to change the feedback voltage. It is also possible for the operator to monitor the temperature and manually switch to switch the voltage curve.

Further, although the monochrome LCD is described in the above embodiment, the present invention can be applied to the LCD having the characteristics shown in FIG. 5 even in the color LCD.

Further, although the thermistors 7 and 16 are used as the temperature detecting elements in the above-mentioned embodiment, if the insertion positions are on the resistors 4 and 15 side, the temperature characteristics opposite to those of the thermistors such as posistors are obtained. A detection element can also be used. Further, instead of the thermistor, another temperature detecting element,
For example, it is possible to use a semiconductor device.

Further, although there are four types of voltage curves by the voltage curve switching unit 20, the number of connection points of the temperature sensor 10 is increased, and accordingly, the voltage detection unit 21 and the electronic switch 2 are connected.
By increasing the number 2 and the resistance 23, more voltage curves can be obtained, and more accurate temperature compensation becomes possible.

Further, the thermistor 16 of the temperature sensor 10
May detect the ambient temperature or the temperature of the LCD body. Similarly, the thermistor 7 may detect either the ambient temperature or the temperature of the main body of the LCD.

[0039]

As is clear from the above, the LC of the present invention
According to the D drive circuit, the ambient temperature or the temperature of the LCD is detected by the temperature sensor, the voltage change accompanying the temperature change is detected for each temperature range, and one of the plurality of voltage curves is subjected to the voltage change according to the voltage change. Since it is selected by the curve switching unit to change the output voltage characteristic of the feedback circuit,
The output voltage of the feedback circuit is modified according to the change of the temperature (ambient temperature or LCD temperature) so that the output voltage of the LCD drive power supply generation unit is temperature-guaranteed, and the output of the LCD drive power supply generation unit that receives this output voltage is input. Since the voltage is temperature-guaranteed, it becomes possible to optimize the contrast of the LCD over a wide temperature range.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an LCD drive circuit of the present invention.

FIG. 2 is a characteristic diagram showing temperature-resistance characteristics of the thermistor of FIG.

FIG. 3 is a characteristic diagram showing a voltage curve characteristic of a voltage curve switching unit in FIG.

FIG. 4 is an explanatory diagram showing a change in output voltage characteristic of the LCD drive power generation unit corresponding to the voltage curve characteristic of the voltage curve switching unit of FIG.

FIG. 5 is a characteristic diagram showing temperature compensation characteristics (temperature-LCD drive voltage characteristics) by the LCD drive circuit of the present invention.

FIG. 6 is a characteristic diagram showing an example of temperature-drive voltage characteristics of a monochrome LCD.

FIG. 7 is a circuit diagram showing a conventional LCD drive circuit.

FIG. 8 is an explanatory diagram showing a deviation between the characteristic of the optimum drive voltage of the LCD and the output voltage characteristic of the LCD drive power generation unit.

FIG. 9 is a circuit diagram showing a configuration of another conventional drive circuit for an LCD.

10 is a characteristic diagram showing respective temperature gradients of the first and second power supply circuits in the drive circuit of FIG.

11 is a characteristic diagram showing temperature dependence of a liquid crystal applied voltage obtained by the electronic volume of FIG.

[Explanation of symbols]

1 LCD drive power generation unit 2 power supply terminals 3 Feedback terminal 4, 5, 6 resistance 7 Thermistor 8 output terminals 10 Temperature sensor 11,12,13,14,15 Resistance 16 thermistor 20 Voltage curve switching unit 21a, 21b, 21c, 21d Voltage detector 22a, 22b, 22c, 22d Electronic switch 23a, 23b, 23c, 23d resistors

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/36 G09G 3/36 F term (reference) 2H093 NC01 NC24 NC27 NC47 NC50 NC57 ND05 5C006 AF46 AF51 AF53 AF54 BB11 BC03 BC11 BF14 BF15 BF22 BF23 BF24 BF25 BF38 FA19 FA54 5C080 AA10 BB05 DD03 DD20 EE28 JJ02 JJ03 JJ05

Claims (5)

[Claims] 1. A feedback circuit including a resistance voltage dividing circuit to which an output voltage for driving an LCD is applied, a feedback circuit including a temperature detection element connected so as to change a combined resistance of some of the resistors, and a feedback circuit of the feedback circuit. In an LCD drive circuit including an LCD drive power supply generation unit that changes the output voltage in a direction of compensating for a change in the output voltage, the ambient temperature or the LCD is detected by a second temperature detection element that detects the ambient temperature or the temperature of the LCD. A temperature sensor unit that outputs a plurality of detection voltages according to a plurality of temperature ranges of the temperature, and a plurality of voltage curves preset corresponding to the plurality of temperature ranges, the plurality of detection voltages of the temperature sensor unit. An LCD drive circuit, comprising: a voltage curve switching unit for switching based on, and changing an output characteristic of the feedback circuit. 2. The temperature sensor unit includes a plurality of resistors inserted in series between a power source and a ground, and one of the plurality of resistors on the power source side serves as the second temperature detecting element. 2. The LCD drive circuit according to claim 1, wherein said thermistors are connected in parallel. 3. The voltage curve switching unit is driven by a plurality of voltage detection units that operate when each of the plurality of detection voltages exceeds a predetermined value, and is driven by each of the plurality of voltage detection units, A plurality of output terminals of the LCD drive power supply generation unit or the input end of the feedback circuit are connected to one contact, and an input end of the feedback circuit or the output end of the LCD drive power supply generation unit is connected to the other contact. 2. The LCD drive circuit according to claim 1, further comprising: a second plurality of resistors that are inserted and connected in series to one or the other contacts of the plurality of electronic switches. 4. The LCD according to claim 1, wherein the plurality of electronic switches are sequentially turned off as the temperature rises to change a combined resistance of the second plurality of resistors.
Drive circuit. 5. The voltage curve switching unit includes an A / D conversion unit that converts an analog output voltage output from the temperature sensor unit into a digital signal, and the resistor based on the output of the A / D conversion unit. 2. The LCD drive circuit according to claim 1, further comprising a microcomputer that corrects an output characteristic of the feedback circuit by changing a combined resistance value of the resistors of the voltage dividing circuit.