JPS61122630A - Liquid crystal driving circuit - Google Patents

Abstract

PURPOSE:To improve the responsiveness of a liquid crystal at a low temperature by making a voltage at ending the application lower than that at starting the application, in a liquid crystal driving circuit for driving the liquid crystal by applying a comparatively high driving voltage, when starting the application of the driving voltage to the liquid crystal. CONSTITUTION:In a liquid crystal driving device for driving liquid crystal by applying a comparatively high driving voltage V1 to the liquid crystal, when starting the application of the driving voltage to the liquid crystal, a controlling circuit for making a voltage V2 of the time when ending the application of the driving voltage to the liquid crystal lower than the voltage V1 of the time when starting the application of the driving voltage is provided. In such a state, when a signal from a control terminal becomes '0' in order to set the liquid crystal to an off-state, an output of an AND gate 11 goes to '0', and the output of an inverter 9 goes to '0'. Accordingly, switching circuits 6, 7 go to an on- state, and the liquid crystal goes to an off-state. In such a case, the applied voltage V2 of the liquid crystal is a comparatively low voltage, therefore, the fall characteristic of the liquid crystal can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a liquid crystal drive circuit that drives a liquid crystal by applying a drive voltage to the liquid crystal.

(Prior Art) In a conventional liquid crystal drive circuit, the drive voltage for driving the liquid crystal is kept constant.

(Problem to be solved by the invention) However, the response speed of liquid crystals slows down when the temperature becomes low, so when used to display numbers such as a speedometer in a car, there will be discrepancies in the response between each segment, resulting in incorrect display. The problem arises that the To prevent this, some devices shorten the response time by applying a high voltage to the rise of the liquid crystal, but as the voltage is increased, the fall time becomes longer, so do not increase the voltage too high. There is a problem in that it is not possible to effectively take measures against low temperatures (see Figure 5). In addition, there are devices that install a heater near the liquid crystal and operate the heater when the temperature is low to improve the responsiveness of the liquid crystal, but this requires extra configuration such as a heater and a heater drive circuit, so it is costly. There is a problem that the cost is high.

The present invention has been made in view of the above problem, and is designed to improve the responsiveness of liquid crystal at low temperatures by modifying the circuit without using a heater or the like.

(Means for Solving the Problems) In order to achieve the above-mentioned technical problem, the present invention provides a liquid crystal drive circuit that drives the liquid crystal by applying a relatively high drive voltage to the liquid crystal when starting to apply a drive voltage to the liquid crystal. The invention is characterized in that a control circuit is provided that makes the voltage at the end of application of the drive voltage to the liquid crystal lower than the voltage at the start of application of the drive voltage.

(Function) According to the above configuration, when the drive voltage application to the liquid crystal starts, a relatively high voltage is applied to the liquid crystal to improve the rising responsiveness of the liquid crystal, and when the drive voltage application to the liquid crystal ends, the voltage is applied to the liquid crystal at the time when the voltage application starts. By applying a voltage lower than the voltage of , the falling response of the liquid crystal is improved.

(Effects of the Invention) Therefore, according to the present invention, the rise and fall of the liquid crystal at low temperatures is zero due to the circuit design.
This has the excellent effect of improving responsiveness.

(Example) The present invention will be described below with reference to embodiments shown in the drawings.

FIG. 1 is an electrical circuit diagram showing one embodiment.

In Fig. 1, 1 is an oscillation circuit, which is composed of an astable multivibrator using an inverter, and as shown in Fig. 2, the duty ratio is 1/2 and the peak value is V+(
For example, an oscillation signal of 7V) is generated. Reference numerals 2 to 7 are switch circuits, which conduct between input and output when a "1" signal is input to the CIN terminal.

The output terminal of the switch circuit 24.6 is connected to the segment terminal of the liquid crystal via a resistor and a diode, and the output terminal of the switch circuit 3, 5.7 is connected to the common terminal of the liquid crystal via a resistor and a diode. There is. When a voltage is applied between the segment terminal and the common terminal, the liquid crystal turns on.

Reference numeral 8 denotes a monostable multi-pipe rake, which, when a lighting signal of "1" is input from an external control terminal, generates a signal of "1" from the Q terminal for a predetermined period of time from the rising point of the lighting signal. 9
．． 10 is an inverter, and 11 is an AND gate. 12
, 13, 14, and 15 are non-invert buffers that output a voltage of V2 (for example, 5 V) with respect to the input voltage 1.

The operation of the above configuration will be explained with reference to the waveform diagram shown in FIG.

Now, when the signal from the control terminal is in the "O" state, the I-stable multivibrator 8 generates a "0" signal from its Q terminal and a "1" signal from its Q terminal. Also, since the signal from the control terminal is "0", the output of the AND gate 11 (Fig. 3 (C)) is "0", and the output of the inverter 9 (Fig. 3 (d)) is "1". Therefore, inverter 9
The switch circuit 6.7 is turned on by receiving a signal from the non-invert buffer 15 from the switch circuit 6.7.

Since the switch circuits 6 and 7 receive the same oscillation signal from the oscillation circuit 1 via the non-invert buffer 12, their output terminals output the same oscillation signal. Therefore, there is a gap between the segment terminal and the common terminal as shown in Fig. 3(e).
, (f), since signals of the same phase are applied, no voltage is applied between the terminals, and the liquid crystal is in the on state.

From this state, the liquid crystal should be turned on (when the signal from the control terminal (Fig. 3 (a)) becomes 1", the monostable multi-bi break is activated by the rising edge of that signal, and the Q
“1” from the terminal (Fig. 3(b)), “1” from the Q terminal
0” signal is generated.

Since the signal from the Q terminal of the monostable multi-bi break 8 is "0", the output of the AND circuit 11 is "O". Also, since the signal from the control terminal is "1", the output of the inverter 9 is "0". Therefore, upon receiving the "1" signal from the Q terminal of the monostable multipipe rake 8, the switch circuits 2 and 3 are turned on. 2. An oscillation signal is applied through a resistor and a diode, and an oscillation signal obtained by inverting the oscillation signal from the oscillation circuit 1 by an inverter 10 is applied to the common terminal through the switch circuit 3. a resistor and a diode. As a result, a voltage is applied between the segment terminal and the common terminal, turning one liquid crystal on.At this time, the peak value of the oscillation circuit applied to each terminal is 1, which is a relatively high voltage. The rise characteristics of liquid crystal can be improved.

After a predetermined time T has elapsed from this state, when the Q terminal output of the monostable multi-pie break 8 is inverted to 10'' and the Q terminal output is inverted to 1'', the output of the AND gate 11 becomes 1''. is applied to the switch circuit 4.5 via the non-invert buffer 14, and the switch circuit 4.5 is turned on.As a result, the oscillation signal from the oscillation circuit 1 via the non-invert buffer 12 is applied to the switch circuit 4.5. Circuit 4. An oscillation signal is applied to the segment terminal via a resistor and a diode, and an oscillation signal obtained by inverting the oscillation signal from the oscillation circuit 1 by an inverter 10 is applied to the common terminal via a non-invert buffer 13 and a switch circuit 5. A resistor and a diode. At this time, non-inverter
Due to the action of buffers 12 and 13, the segment terminals,
The peak value of the oscillation signal applied to the common terminal is ■2. Therefore, the voltage applied between the segment terminal and the common terminal decreases to 2 as shown in FIG. 3(g).

After that, the liquid crystal should be turned off (when the signal from the control terminal becomes "0", the output of the AND gate 11 becomes "0" and the output of the inverter 9 becomes "1". Therefore, the switch circuit 6. 7 is turned on, and as described above, the liquid crystal is turned off.

In this case, since the voltage applied to the liquid crystal up to that point was 2, which is a relatively low voltage, it is possible to improve the falling characteristics of the liquid crystal.

Table 1 shows the response characteristics when the applied voltage was changed with (I=7) and (2-5).

Note that the same effect can be achieved by using AND gates 16 to 21 as shown in FIG. 4 in place of the switch circuits 2 to 7 of the above embodiment.

Further, in a device where the on/off time of the liquid crystal by a signal from a control terminal is variable depending on various conditions, the voltage switching time between V and -V2 may be made variable.

Furthermore, the magnitude of the applied voltage at the end of application of the drive voltage may be changed depending on the magnitude of the applied voltage at the beginning of application of the drive voltage to the liquid crystal.

Furthermore, the drive voltage described above may be controlled to be changed only when the liquid crystal is at a low temperature, and the drive voltage may be kept constant at other times.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing oscillation waveforms from the oscillation circuit, FIG. 3 is a signal waveform diagram of each dish circuit shown in FIG. 1, and FIG. The figure is a main part electric circuit diagram showing another embodiment, and FIG. 5 is a characteristic diagram showing voltage vs. response speed. 1...Oscillation circuit, 2-7...Switch circuit, 8...
・Monostable multi-pie break, 12, 13. 14. 15
...Non-invert buffer.

Claims (1)

[Scope of Claims] In a liquid crystal drive circuit that drives the liquid crystal by applying a relatively high drive voltage to the liquid crystal at the start of application of a drive voltage to the liquid crystal, the voltage at the end of application of the drive voltage to the liquid crystal is defined as the drive voltage. A liquid crystal drive circuit characterized by being provided with a control circuit that lowers the voltage from the voltage at the start of application.