JPH0720439A - Liquid crystal driving device - Google Patents

Abstract

PURPOSE:To enable the liquid crystal driving device, which supplies or cuts off an AC-converted signal and electric power as the base of a voltage impressed to liquid crystal at timing that never deteriorates a liquid crystal display unit, to securely operate with simple constitution when the power source is turned ON and OFF. CONSTITUTION:When the power source is turned ON, a reset circuit 22 resets the reset state of a CPU 11 and a liquid crystal display controller 21 at a time T1 after the output voltage V of a 1st power source 13 for logic exceeds a 1st threshold value Vs1 which is lower than its stationary output voltage Vo and within the operation guarantee voltage range of a liquid crystal display controller 21 to send out a regular AC-converted signal and a display data signal to the liquid crystal display unit 10, and a switch control circuit 28 connects a switch circuit 27 at a time T2. set longer than the T1, after the output voltage V exceeds a 2nd threshold value Vs2 set between Vo and Vs1 to supply the output of a 2nd power source 14 to the liquid crystal display unit 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a liquid crystal display,
Inputs an alternating signal to invert the polarity of the display data signal and the voltage applied to the liquid crystal at the display point, and also supplies the power supply for driving the logic circuit in the liquid crystal display and the power supply that is the basis of the voltage applied to the liquid crystal In addition, the present invention relates to a liquid crystal drive device for displaying characters and images on a liquid crystal display.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays used as display units in various electronic devices receive a display data signal input together with a screen scanning signal from a liquid crystal display controller, and scan the screen horizontally and vertically. However, a voltage is sequentially applied to the liquid crystal at the display point corresponding to this display data to display characters and images in dots.

In order to prevent a chemical change in the liquid crystal at each display point, the polarity is inverted in synchronism with a screen scanning signal (for example, a frame synchronization signal) so that the average becomes zero. The general liquid crystal display is internally provided with a logic circuit for screen scanning and a logic circuit for applying an alternating voltage to the liquid crystal at each display point.

Therefore, in order to drive such a liquid crystal display device, a liquid crystal display controller and a first power source for driving the above-mentioned circuits in the liquid crystal display device (usually, a voltage of 5V for a logic circuit is used). In addition to the (power supply), a second power supply (for example, a power supply having a voltage of 12V) that is the basis of the voltage applied to the liquid crystal cell is required.

In this type of liquid crystal display, however, the second power source is supplied in the state where the signal (AC signal) for inverting the polarity of the voltage applied to the liquid crystal at the display point is not input. Then, the liquid crystal portion is driven by direct current, so the power supply timing must be controlled so that such a state does not occur.

That is, when the power is turned on, the first power supply for driving the logic circuit is first supplied to the liquid crystal display controller and the liquid crystal display, and the normal AC signal is sent to the liquid crystal display. It is necessary to prevent the direct current drive of the liquid crystal by supplying the second power supply after turning off the power supply and stopping the supply of the second power supply when the power supply is cut off.

In order to perform such timing control, conventionally, the power supply itself of the first power supply device and the second power supply device (usually a switching power supply) for the logic circuit is turned on or started up. When the power is turned on, a timing shift is provided in the lowering operation, or a switch circuit is provided between the output of the second power supply device and the liquid crystal display, and this switch is turned on and off by the CPU (that is, software). A method of preventing direct current driving of the liquid crystal during cutting or cutting has been taken.

[0008]

However, as described above, in the case of directly controlling the start-up operation between the two power supply devices, the change in the input of the commercial power supply due to the on / off of the power switch must be directly detected. In addition, the first power supply of 5 V, which is generally used as a common power supply for driving other logic circuits, has a voltage of 12 V.
Since it outputs a very large current compared to the second power source of Volt, for example, when the power switch is turned off,
In order to delay the fall of the first power supply more than the fall of the second power supply, the output of the first power supply must be charged in an extremely large-capacity capacitor, and the cost is high. The structure becomes large-scale. In addition, when a large-capacity capacitor is used for charging in this way, it is necessary to take a long time to charge it in order to reduce the inrush current when the power is turned on. There was also a problem that was very slow.

On the other hand, in the method of turning on / off the second power source and the liquid crystal display by software, the switch circuit is turned on / off at an abnormal timing when the CPU goes out of control, and a DC voltage is applied to the liquid crystal. There is a risk that it will be done and there is a problem of lack of reliability.

Further, in any of the methods, there is a problem that the circuit and the program are complicated in order to prevent the liquid crystal from being driven by the direct current when the power supply is interrupted.

It is an object of the present invention to solve this problem and to provide a liquid crystal driving device which can supply an alternating signal and a power source with a simple structure and at a certain timing that does not deteriorate the liquid crystal display.

[0012]

In order to solve the above-mentioned problems, a liquid crystal driving device of the present invention is a logic for applying a voltage whose polarity is inverted to a liquid crystal at a display point corresponding to an input display data signal. With respect to a liquid crystal display having a circuit inside, while inputting the display data signal and an alternating signal for inverting the polarity of the voltage applied to the liquid crystal at the display point, the logic circuit in the liquid crystal display is connected. A liquid crystal driving device for driving the liquid crystal display by supplying a first power source of a steady output voltage V ₀ for driving and a second power source which is a basis of the applied voltage, wherein the power source is the first power source. The liquid crystal display controller, which receives the supply and outputs the normal display data signal and the alternating signal to the liquid crystal display after the reset state is released, has a voltage comparator and a timer circuit. Compares the output voltage V of the first threshold value Vs1 and the first power supply which is set lower than the steady output voltage V ₀ within the guaranteed operating voltage range of the controller,
The output voltage V of the first power supply is the first threshold value Vs
When the output voltage V of the first power source is 1 or less or after the output voltage V of the first power source exceeds the first threshold value Vs1 until a predetermined time T1 elapses, the liquid crystal display controller is set to the reset state and the predetermined time T1 is set. When the output voltage V of the first power source exceeds the first threshold value Vs1 after the passage of, a reset circuit for canceling the reset state of the liquid crystal display controller, the output of the second power source and the liquid crystal A switch circuit for connecting or disconnecting the display, a voltage comparator, and a timer circuit, and the first threshold Vs
A second threshold value Vs2 set higher than 1 and lower than the steady output voltage V _0, and the output voltage V of the first power supply.
And when the output voltage V of the first power supply is less than or equal to the second threshold Vs2 or after the output voltage V of the first power supply exceeds the second threshold Vs2. The switch circuit is turned off until a predetermined time T2 set longer than the predetermined time T1 elapses, and after the elapse of the predetermined time T2, the output voltage V of the first power supply is changed to the second threshold value. And a switch control circuit for bringing the switch circuit into a connected state when Vs2 is exceeded.

[0013]

With this configuration, in the liquid crystal drive device of the present invention, the output voltage V of the first power supply is the same as when the power is turned on.
If the voltage rises from zero volts, this output voltage V
Since the liquid crystal display controller is reset by the reset circuit while the threshold value Vs1 is not exceeded, the normal AC signal for inverting the polarity of the voltage applied to the liquid crystal at the display point is output to the liquid crystal display. The output of the second power supply is not supplied to the liquid crystal display because the switch circuit is also in the disconnected state. When the predetermined time T1 elapses after the output voltage V of the first power supply exceeds the first threshold value Vs1,
The reset circuit releases the reset state of the liquid crystal display controller and sends a regular AC signal to the liquid crystal display. Further, when the output voltage V of the first power supply further rises and exceeds the second threshold value Vs2, the switch circuit becomes the connection state after a predetermined time T2 longer than T1 has elapsed from the timing, and the second power supply Output is supplied to the liquid crystal display.

Further, when the output voltage V of the first power supply drops from the steady output voltage V ₀ to the second threshold value Vs2 or less when the power supply is cut off, the switch circuit is cut off to the liquid crystal display. Supply of the second power source is stopped. Further, the output voltage V of the first power supply drops and the first threshold Vs1
In the following cases, the liquid crystal display controller is reset and the input of the regular AC signal to the liquid crystal display is stopped.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a dot matrix type liquid crystal display 1
0, the CPU 11, and the power switch 12 are provided in an electronic device having a first power source 13 and a second power source 14 that output a steady output voltage of 5 volts and a 12-volt power source, respectively. 1 shows a configuration of a liquid crystal drive device 20 of one embodiment.

A plurality of liquid crystal displays 10 (for example, 640 ×
Display signals such as a frame signal FS, a vertical synchronizing signal VS, and a horizontal synchronizing signal HS for receiving a screen scanning signal and an AC signal together with the display data signal. While changing the display position in order, it operates so as to apply a voltage to the liquid crystal at the display point (independent liquid crystal cell or liquid crystal at the electrode intersection) corresponding to this display data, and displays characters and figures on the screen. Let

The liquid crystal display 10 has a logic circuit for scanning the position of the display point and a polarity of an applied voltage applied to the liquid crystal at the display point, for example, every half cycle of the frame signal FS. A logic circuit and the like are provided inside, and a power supply (5 volt power supply for logic circuit) for driving each of these circuits and a power supply (for example, 12 volt) which is the basis of the positive and negative voltages applied to the liquid crystal. It receives the supply of and operates. The liquid crystal display 10 also incorporates a switching power supply for converting an external 12-volt power supply into positive and negative voltages.

A liquid crystal driving device 20 for driving the liquid crystal display 10 is supplied with a first power source 13, and receives the frame signal FS, the vertical synchronizing signal VS, and the horizontal synchronizing signal H.
A liquid crystal display controller 21 is provided which sends out S and display data signals of a plurality of bits to the liquid crystal display 10. The liquid crystal display controller 21 operates by receiving power supply from the first power supply 13, and when the reset terminal becomes low level, the internal circuit (counter or the like) is hardware reset, and the CPU 11 operates after the reset is released. When the mode is initialized, the signals are properly transmitted at regular timing according to the set mode, and in the reset state, the signals cannot be correctly transmitted. This controller is a well-known one that is integrated into one chip by an integrated circuit.

Liquid crystal display controller 21 and CPU 1
1 is reset by the output of the reset circuit 22. The reset circuit 22 includes reset integrated circuits 23 and 2
It is composed of two resistors R1 and R2 and a capacitor C1. The two resistors R1 and R2 divide the output voltage V of the first power supply 13 by its resistance ratio, and the divided voltage Va = V · R2 / (R1 + R2) is supplied to the reset integrated circuit 23. It has been entered.

The reset integrated circuit 23 is, for example, as shown in FIG.
, The voltage comparator 24, the timer circuit 25
And AND circuit 26, and the rising output of the voltage comparator 24 when the input voltage Va exceeds the reference voltage Vr activates the retrigger type timer circuit 25, and the timer output is timed T1 proportional to the capacitor C1. Only low level, this timer output and voltage comparator 2
4 is output from the AND circuit 26.

The resistance values of the two resistors R1 and R2 are
When the input voltage Va becomes equal to the reference voltage Vr, the voltage (first threshold value) Vs1 applied to both ends is lower than the steady output voltage V ₀ of the first power source 13 and the liquid crystal display controller 21 operates. So that it is within the guaranteed operating voltage range,
It is predetermined and the capacitance of the capacitor C1 is determined such that the timer time T1 thereof is longer than the time required for the output voltage of the first power supply to completely reach the steady output voltage V ₀ from Vs1. There is.

Therefore, when the power is turned on, the first power source 13
Output voltage V rises from zero volt as shown in FIG. 3A, and the first threshold value Vs1 = Vr.multidot.
At time t1 when (R1 + R2) / R2 is exceeded (when Va exceeds Vr), the output of the voltage comparator 24 is as shown in FIG.
As shown in (b) of FIG. 3, the output of the timer circuit 25 rises to a high level in synchronization with this rising, and
It falls to a low level like. Then, when the output of the timer circuit 25 returns to the high level at the time of t2 when T1 time has elapsed from the time of t1, the output of the AND circuit 26 rises to the high level as shown in FIG. Then, when the output voltage V of the power supply becomes Vs1 or less (Va is Vr or less) at the time of t3 due to the power shutdown, the output of the voltage comparator 24 becomes low level, and the output of the AND circuit 26 also returns to low level.

On the other hand, the output of the second power source 14 is supplied to the liquid crystal display 1 via the switch circuit 27 as shown in FIG.
It is supplied to 0. For example, as shown in FIG. 5, the switch circuit 27 includes two transistors TR1 and TR2 and resistors R3 to R5. When a voltage higher than a predetermined value is input to the resistor R4 and the control transistor TR1 is turned on. , Switching transistor TR2
Is turned on, and the output of the second power supply 14 and the liquid crystal display 10 are connected.

This switch circuit 27 is turned on and off as shown in FIG.
As shown in, the switch control circuit 28 is constituted by the reset integrated circuit 23, the resistors R6 and R7, and the capacitor C2, similarly to the reset circuit 22.

The operation of the switch control circuit 28 is exactly the same as that of the reset circuit 22, but the resistance values of the resistors R6 and R7 are when the input voltage Vb of the reset integrated circuit 23 becomes equal to the reference voltage Vr. Applied voltage V
It is predetermined that s2 (second threshold value) is between the steady output voltage V ₀ of the first power supply 13 and the first threshold value Vs1.

That is, the switch control circuit 28 has the first
Of the output voltage V of the power supply 13 of the second threshold Vs2 = Vr
When (R6 + R7) / R7 or less or when the output voltage V exceeds Vs2 and before T2 time elapses, a low level voltage is output to the switch circuit 27, and after T2 time elapses, the output voltage V is Vs2. If it exceeds, the high level voltage is sent to the switch circuit 27. The capacity of the capacitor C2 becomes longer than the time obtained by adding the time T3 and the time T1 required for the CPU 11 to initialize the setting data in the liquid crystal display controller 21 at least after the reset is released. Is decided.

Therefore, in this liquid crystal drive device 20,
When the power is turned on, the output voltage V of the first power supply 13 rises to V
The reset state of the liquid crystal display controller 21 (and the CPU 11) is released after T1 time from the timing when s1 is reached, and the output voltage of the first power supply 13 is further increased to V
The output of the second power supply 14 is supplied to the liquid crystal display 10 after T2 time from the timing when s2 is reached.

Next, based on FIG. 5, this liquid crystal drive device 2
The operation of 0 will be described. First, when the power switch 12 is turned on, the first and second power supplies 13 and 14 are activated, and the output voltages of the first and second power supplies 13 and 14 rise from zero volt with a predetermined time constant.

After the power switch 12 is turned on at t0, the output voltage V of the first power supply 13 exceeds Vs1 at t1 and further exceeds Vs2 at t2 as shown in FIG. Assuming that the voltage V ₀ is reached, the output of the reset circuit 22 becomes high level at t3 when T1 time has elapsed from t1 as shown in (b) of FIG.
The reset state of the PU 11 and the liquid crystal display controller 21 is released.

By releasing this reset, the CPU 11
Starts a program operation from an initial address of a ROM (not shown) and initializes setting data to the liquid crystal display controller 21 together with initialization of other circuits (not shown).

The liquid crystal display controller 21 receives the initial setting during the time T3 after the internal circuit is hardware reset while the time T1 has elapsed, and is controlled at a regular timing from the time t4. The signal FS ((c) in the figure), the vertical synchronizing signal VS, and the horizontal synchronizing signal HS are sent to the liquid crystal display 10 together with the display data signal DS.

The liquid crystal display 10 receives the power supply from the first power supply 13 and each signal from the liquid crystal display controller 21, and applies a voltage to the liquid crystal at the display point corresponding to the screen scanning and the display data. Works. However, at this time, since the time T2 has not elapsed from the time t2, the second power source 14 is not supplied to the liquid crystal display 10, and no voltage is applied to the liquid crystal of the liquid crystal display 10. , Is not displayed.

The output voltage V of the first power supply 13 is V
At time t5 when T2 time has passed after s2 is exceeded, the output of the switch control circuit 28 becomes high level as shown in FIG. Therefore, the output of the second power supply 14 is supplied to the liquid crystal display 10, and from this point of time, a voltage whose polarity is inverted every half cycle of the frame signal FS is applied to the liquid crystal cell corresponding to the display data, so that the screen is displayed. A display corresponding to the display data is made.

Further, the power switch 12 is turned off at t6, the output voltage V of the first power supply 13 drops, and t7
When the voltage falls below the voltage Vs2, the output of the switch control circuit 28 immediately changes to the low level, so the switch circuit 2
7 is turned off. Further, when the output voltage of the first power supply 13 falls below Vs1 at t8, the reset circuit 2
The output of 2 also changes to low level.

As described above, in the liquid crystal drive device 20,
The voltage that is the basis of the applied voltage when the alternating current signal (frame signal FS) for alternating the voltage applied to the liquid crystal is not supplied to the liquid crystal display 10 at the time of turning on and off the power supply. Since the (second power supply 14) is not applied, the liquid crystal is not chemically changed and destroyed.

Further, such a state is maintained even when the output voltage of the first power source 13 is temporarily lowered due to a momentary interruption as shown in FIG. That is, when the output voltage V of the power supply instantaneously drops to between Vs2 and Vs1 as shown in FIG. 6A, it exceeds Vs2 again from t9 when the output voltage V becomes Vs2 or less ( The output (d) of the switch control circuit 28 goes to the low level and the supply of the second power supply 14 during that period is stopped only until t11 when the time T2 has elapsed, and the resetting is performed during this period. The output (b) of the circuit 22 remains at the high level,
Since Vs1 is within the operation guarantee voltage range in which the liquid crystal display controller 21 operates normally, the frame signal (c) from the liquid crystal display controller 21 is also supplied to the liquid crystal display 10.
Therefore, no direct current is applied to the liquid crystal since it is continuously transmitted to the liquid crystal.

Further, when the output voltage V of the first power supply 13 instantaneously drops from the steady output voltage V ₀ to Vs1 or less, the operation is exactly the same as when the power is turned on as shown in FIG. In this case, the liquid crystal is also protected.

Further, when the power is turned on, even if the power-off operation or momentary power-off occurs before the output voltage V of the first power supply 13 has completely reached V ₀ , the normal frame signal is always displayed on the liquid crystal display. Since the switch circuit 27 is turned on after the switch circuit 27 is turned on and the sending of the frame signal is stopped after the switch circuit 27 is turned off, the liquid crystal is not driven by direct current.

In this embodiment, the reset circuit 22
And the switch control circuit 28 to the reset integrated circuit 23.
However, it is also possible to use individual circuits such as the voltage comparator 24 and the timer circuit 25 shown in FIG.

Further, the switch circuit 27 may have any structure as long as it can connect and disconnect the liquid crystal display and the second power source, and not only the semiconductor type shown in FIG. A formula relay or the like may be used.

In the above embodiment, the timer time T2 of the switch control circuit 28 is set to the timer time T1 of the reset circuit 21 plus the time T3 for initial setting of the liquid crystal display controller 21. , This time T3
However, when the output voltage V of the power supply is shorter than the time required to rise from Vs1 to Vs2, or the initial state of the liquid crystal display controller 21 is fixed in advance, the liquid crystal display 10 displays the frame signal or the like immediately after the reset is released. If a liquid crystal display controller that sends the
If 2 is set to T1 or more, no direct current is applied to the liquid crystal.

[0042]

As described above, in the liquid crystal drive device of the present invention, the output voltage V of the first power supply is set to be lower than the steady output voltage V _{0 and} within the operation guarantee voltage range of the liquid crystal display controller. When the predetermined time T1 has passed since the first threshold value Vs1 was exceeded, the reset of the liquid crystal display controller is released, and while the output voltage V of the first power supply is lower than Vs1 or the predetermined time after exceeding Vs1. Until T1 elapses, the reset circuit that puts the liquid crystal display controller in the reset state and the output voltage V of the first power supply is Vs.
Is provided between the liquid crystal display and the second power supply when a predetermined time T2 longer than T1 has passed after the second threshold Vs2 set between 1 and the steady output voltage V ₀ was exceeded. The switch circuit connected to the first power source is connected, and the output voltage of the first power supply is lower than Vs2 or exceeds Vs2 for a predetermined time T.
A switch control circuit for disconnecting the switch circuit is provided until 2 has elapsed, and a normal AC signal is generated by the difference between the threshold value of the reset circuit and the switch control circuit and the timer time. The second power source is supplied or shut off while being supplied to the.

Therefore, as compared with the conventional method of directly controlling the rise and fall times of the power source itself, the configuration can be extremely simple and inexpensive, and the start-up operation of the entire apparatus can be prevented from being delayed.

Further, even if the CPU runs out of control or the power is momentarily cut off, the liquid crystal is not destroyed and the liquid crystal can be driven reliably with a simple structure.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a main part of one embodiment.

FIG. 3 is a timing chart for explaining an operation of a main part of one embodiment.

FIG. 4 is a circuit diagram showing a specific example of a main part of one embodiment.

FIG. 5 is a timing chart for explaining the overall operation of one embodiment.

FIG. 6 is a timing diagram when the power is cut off instantaneously.

[Explanation of symbols]

 10 Liquid Crystal Display 11 CPU 12 Switch 13 First Power Supply 14 Second Power Supply 20 Liquid Crystal Driving Device 21 Liquid Crystal Display Controller 22 Reset Circuit 23 Reset Integrated Circuit 27 Switch Circuit 28 Switch Control Circuit

Claims (1)

[Claims] 1. The display data signal and the display point for a liquid crystal display device having a logic circuit for applying a voltage of which polarity is inverted to the liquid crystal of the display point corresponding to an input display data signal. A first power source of a steady output voltage V ₀ for driving a logic circuit in the liquid crystal display and a base of the applied voltage, while inputting an alternating signal for inverting the polarity of the applied voltage to the liquid crystal. In the liquid crystal drive device for driving the liquid crystal display device by supplying the second power source, the power source is supplied by the first power source, and the normal display data signal and the AC signal are supplied after the reset state is released. a liquid crystal display controller for outputting to the liquid crystal display device includes a voltage comparator and a timer circuit, the steady output voltage set lower than V ₀ within the guaranteed operating voltage range of the liquid crystal display controller It has been first compared with the threshold Vs1 of the output voltage V of the first power supply, the output voltage V of the first power supply
Is less than or equal to the first threshold Vs1 or the first
The liquid crystal display controller is in a reset state until the output voltage V of the power source exceeds the first threshold value Vs1 and the predetermined time T1 elapses, and the first power source is supplied after the predetermined time T1 elapses. A reset circuit for canceling the reset state of the liquid crystal display controller when the output voltage V of the second threshold voltage Vs1 exceeds the first threshold value Vs1, and the output of the second power source and the liquid crystal display are connected or A switch circuit for disconnecting, a voltage comparator and a timer circuit, and the first threshold value V
A second threshold value Vs2 set higher than s1 and lower than the steady output voltage V ₀ is compared with the output voltage V of the first power supply, and the output voltage V of the first power supply is compared with the second threshold value Vs2.
When the output voltage V of the first power source exceeds the second threshold value Vs2 until a predetermined time T2 set longer than the predetermined time T1 elapses. Is a switch control circuit that disconnects the switch circuit and, when the output voltage V of the first power supply exceeds the second threshold value Vs2 after the elapse of the predetermined time T2, switches the switch circuit to the connection state. A liquid crystal driving device comprising: