JPS6051718B2 - LCD driving method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving a liquid crystal, and more particularly to a method for applying a power supply voltage when dynamically driving a liquid crystal.

In general, regarding the characteristics of a liquid crystal display board, the effective value of the voltage applied when the contrast of the liquid crystal becomes 90% is defined as the saturation voltage Vsat, and the effective value of the voltage when the contrast becomes 10% is defined as the rise. Assuming that the voltage is Vth, the temperature dependence characteristics of the saturation voltage Vsat and the rising voltage Vth are as shown in FIG. 1, and as the temperature rises, the saturation voltage Vsat and the rising voltage Vth decrease.

Conventionally, when dynamically driving a liquid crystal display panel having the characteristics shown in FIG. 1 using the 113/Ias two-digit driving method as shown in FIG. The voltage VSL and the effective voltage VN,L applied between the electrodes in the non-selected state are constant with respect to temperature, and when the supply voltage is 3 volts, the value is defined as the effective value VRM, = () )"dt to the effective voltage V, L2
．． The effective voltage VNS is 235 volts and 0.999 volts.

When these values are shown in the graph of Figure 1, the rise voltage Vth of the liquid crystal becomes smaller than the effective voltage VNS in the non-selected state when the temperature exceeds 40°C, that is, no display is produced in the non-selected state. The liquid crystal that is supposed to be driven is driven, resulting in a thin display, resulting in crosstalk, and as the temperature rises, the saturation voltage Vsat of the liquid crystal becomes smaller than the effective voltage in the selected state, which reduces the contrast of the liquid crystal. is completely saturated, but as the temperature rises further, the effective voltage decreases.
. The present invention has been made in view of the above-mentioned points, and it is possible to obtain the optimum effective voltage for the liquid crystal display panel by changing the effective voltages in the selected state, VN, L and the effective voltages in the non-selected state, with respect to temperature. The present invention provides a method for driving a liquid crystal in which a voltage is applied and the power supply voltage is also switched at intervals such that no DC component remains in the liquid crystal.

The present invention will be described in detail below with reference to the drawings. FIG. 3 is a circuit diagram showing an embodiment of the present invention.

This embodiment shows the case where it is used in the 113/2-digit drive method, where 1 is the battery and 2 is the P-M which is the switching means.
OSFETl3 is “0n゛゛゜0 of P-MOSFET2
4 is a current limiting resistor R.
15 is a dividing means, which includes a capacitor C1 connected in parallel to the diodes D1 to D6 and diodes Dl and D2, a capacitor C2 connected in parallel to the diodes D1 to D4, and a capacitor C3 connected in parallel to the diodes D1 to D6.
It consists of The principle of the dividing means 5 is that when the P-MOSFET 2 becomes "0n", current flows through the diodes D1 to D6 and charges are accumulated in the capacitors Cl, C2, and C3, so that the diodes D1 to D6 all have substantially the same characteristics. Therefore, if the forward voltage of the diodes D1 to D6 is ■F, then V1=2VF..V2=4VF,.V3
=6*7, and the voltage * applied to the dividing means 5 is divided into three.

That is, V3, V2, Vl=V:213V:113■. These divided voltages are appropriately applied to the liquid crystal display panel to drive the liquid crystal. Also P-MOSFET
Even if becomes ``0f1'2, the capacitors Cl, C2, C3
The charges accumulated in the diodes D1 to D6 flow to the diodes D1 to D6, and the voltages 1, V2, and V3 at each terminal gradually decrease, and the liquid crystal is driven by the decreasing voltages V1, V2, and 3. At this time, for example, even if the current consumption of terminal voltage V2 is large and the voltage increases, the voltage between ■3 and ■2 will increase, so
The current flowing from the capacitor C3 to the diodes D5 and D6 increases, and part of the current charges the capacitor C2. Therefore, even when the terminal voltages Vl, V2, and V3 are decreasing, the ratio is kept constant. The characteristics of the forward voltage VF and forward current 1p of the diodes D1 to D6 described above depend on temperature, and an example thereof is shown in FIG.

This VF-1F characteristic diagram shows the forward voltage on the horizontal axis and the forward current on the vertical axis, and the temperature is 0℃, 25℃, 50℃, 7℃.
Each characteristic at 5°C is shown.

According to this characteristic diagram, it can be seen that if the forward current 1F is constant, the forward voltage VF decreases as the temperature increases. Similarly, the voltages (1), (2), and (3) divided by the diodes D1 to D6 having such characteristics decrease as the temperature rises. If the current temperature is 25°C and the forward current 1F is 10-5 [A], the forward voltage is ■.

is 0.36 [V]. Therefore, the voltage ■1 is ■1=2■
Since F, V1=0.72 [■], voltage V2 is V2=
4VF and V2 = 1.44 [■], V3 = 3 = 6VF and V3 = 2.16 [■]. P-MOSFET2 is “
Assuming that the voltage of battery 1 is supplied without becoming 0fr, the effective voltage ■SL applied in the selected state in the case of the drive waveform shown in Fig. 2 is ■SL (25°C) = 1.61 [ ■〕
Therefore, the effective voltages ■N and L applied to the non-selected state are ■
N, L (25°C) = 0.72 [■]. Also, if the forward voltage ■1 changes by △■ due to a change in temperature, then
Each voltage ■1, ■2, ■3 is V3−υ▼VVLΔ ▼ −
0▼1, and the voltage value changes depending on the temperature, but the voltage ratio is constant.

If the temperature is 50℃ and = 10-5 [A], then VF =
0.30CV], V1=0.60[V], V2=
1.20CV], V3=0.80[■]. Therefore, according to the waveform diagram shown in Figure 2, the effective voltage in the selected state is 5L (50°C) = 1.34 [V], and the effective voltages in the non-selected state, N and L, are N. ,L(50℃)=0.60
CV]. In other words, at 50°C, the effective voltage is 25°C.
This is a reduction of 83% compared to the case of . Then the third
The operation of the embodiment shown in the figure will be explained with reference to the waveform diagram in FIG.

The gate control circuit 3 sets the gate voltage Vc of the P-MOSFET 2 to the ゜"0゛ level at regular intervals, and only when the gate voltage ■c is at the "゜0゛ level, the battery 1
A voltage ①E is applied to the dividing means 5 via the resistor R4.

Gate voltage■. The period when is at the “0” level is 113
In the case of bias 2-digit drive, 11 of one period T of the drive waveform
4, and the interval is 312 of one cycle T of the drive waveform.
It has doubled. The reason for this, which will become clear later, is to cancel the DC component of the voltage applied to the liquid crystal. First, the gate voltage ■. When is at ゜゜0゛ level, P-MOSFE
When T2 becomes "0n", a constant current of 1 F flows through the diodes D1 to D6, and a voltage determined depending on the temperature at that time is generated at each terminal (1), V2, and V3. Next is the gate voltage ■. When becomes '4■i level, P-MOSFET2 becomes "0ff".
Therefore, the voltage VE of the battery 1 is cut off from being supplied to the dividing means 5, but as described above, current flows through the diodes D1 to D6 due to the charges accumulated in the capacitors Cl, C2, and C3, so that each terminal Vl , ■2, and V3 gradually decrease as shown in FIG. However, as mentioned above, the voltage ratio is always constant. After the period T1 has elapsed, the gate voltage ■ is increased again. When becomes “0゛ level, P-M
Since OSFET 2 becomes 0n and the voltage of battery 1 is supplied, current flows through diodes D1 to D6, charges are accumulated in capacitors Cl, C2, and C3, and each terminal Vl
, V2, and V3 are initial voltages. By repeating the above operation, each terminal voltage Vl, V2, V3 is
The waveform is as shown in the figure, and in this waveform, the waveform shown by a solid line shows the case when the temperature is 25°C, and the waveform shown by the broken line shows the case when the temperature is 50°C. When driving the liquid crystal using the voltage waveform obtained as described above,
As shown in the waveform of the selected state in Fig. 5, each terminal voltage V
Naturally, the drive waveform also repeats attenuation due to the repetition of attenuation of l, V2, and ■3, but since the attenuation period is 312 times one period T of the drive waveform, the In this period, the first half 312 and the second half 312 have the same waveform with opposite polarity, and during this period, the voltages cancel each other out and no DC component remains in the liquid crystal.

Therefore, the adverse effect on the life of the liquid crystal can be completely eliminated. FIG. 6 shows the temperature characteristics when the liquid crystal display panel is driven according to this embodiment, and shows the effective voltage (2) in the selected state as well as the saturation voltage Vsat and rising voltage (2) of the liquid crystal display panel. and the effective voltage (N) in the non-selected state decrease as the temperature increases. From this characteristic diagram, it is clear that crosstalk and unnecessary voltage application at high temperatures can be prevented. As described above, according to the present invention, the effective voltage applied is changed according to the temperature characteristics of the liquid crystal display panel, so that crosstalk can be prevented and the adverse effect on the life of the liquid crystal due to unnecessary voltage application can be prevented. . In addition, since battery voltage is supplied to the dividing means at regular intervals, battery power consumption is reduced and battery life is extended, and no direct current remains in the liquid crystal, preventing deterioration of the liquid crystal, which is highly effective. There is something that will happen. In addition, although the embodiment of the present invention has been described using the 113/(Ias two-digit driving method) method, the present invention is not limited to this method, and the effects of the present invention become more pronounced as the number of digits to be driven increases.

[Brief explanation of the drawing]

Figure 1 is a temperature characteristic diagram of the liquid crystal display panel and the effective voltage applied to it when driven by the conventional driving method.
The figure is a waveform diagram showing the conventional 113/kuias two-digit driving method, Figure 3 is a circuit diagram showing an embodiment of the present invention, and Figure 4 is a waveform diagram showing the 3-digit driving method.
5 is a waveform diagram showing the operation of the embodiment shown in FIG. 3, and FIG. 6 is a characteristic diagram of the diode used in the embodiment shown in FIG. FIG. 4 is a temperature characteristic diagram of the effective voltage applied to the liquid crystal display panel when the liquid crystal display panel is driven. 1...Battery, 2...P-MOSFETl3...Gate control circuit, 4...Current limiting resistor Rl5...Dividing means.

Claims (1)

[Claims] 1. In a liquid crystal driving method in which a power supply voltage is divided into a plurality of voltages and the divided voltages are selectively applied to electrodes of a liquid crystal display panel for dynamic driving, diodes are connected in series, the power supply voltage is divided by the plurality of diodes into a plurality of voltages whose voltage value changes depending on the temperature, and the plurality of divided voltages are applied to a capacitor connected to the diodes. By charging and holding the battery and selectively applying the plurality of held voltages to the electrodes of the liquid crystal display plate, the effective voltage between the electrodes of the dynamically driven liquid crystal display plate changes depending on the temperature. A liquid crystal driving method characterized by: 2. In a liquid crystal driving method in which the power supply voltage is divided into a plurality of parts and the divided voltages are selectively applied to the electrodes of the liquid crystal display panel for dynamic driving, a plurality of temperature-dependent diodes are connected in series. , when one period is defined as the period in which the waveform of the dynamic drive has opposite phases in the first half and the second half, Part 3
applying the power supply voltage to the plurality of diodes for a predetermined period with a cycle of /2, causing the diodes to generate a plurality of voltages whose voltage values change depending on temperature, and applying the voltages to the diodes. By charging and holding the connected capacitors and selectively applying the held voltages to the electrodes of the liquid crystal display plate, the effective voltage between the electrodes of the liquid crystal display plate that is dynamically driven increases with temperature. A liquid crystal driving method characterized by changing depending on.