JP3042166B2 - Power supply circuit and display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly to a power supply circuit of a liquid crystal display device.

[0002]

2. Description of the Related Art Generally, driving a liquid crystal panel of a liquid crystal display device requires a plurality of voltages. A conventional voltage power supply circuit for generating this voltage will be described with reference to FIG. FIG. 2 shows a configuration of a conventional power supply circuit. To drive the liquid crystal panel, generally, there are six levels of voltages, for example, voltage V0-voltage V1 = voltage V1-voltage V2 = voltage V3-voltage V4 = voltage V4-voltage V5 (= V). V0−voltage V5 = n · V
(N is a positive number, usually about 10). In FIG. 2, reference numeral 21 denotes a voltage dividing circuit formed by connecting five resistors R1 to R5 in series, and the resistors R1, R2, R4, and R5 have the same resistance value R.
R3 has a resistance value (n-4) R. Then, a voltage V0 and a voltage V5 are applied to both ends of the voltage dividing circuit 21, that is, above the resistor R1 and below the resistor R5 in the figure, respectively.
Voltages V1, V2, V3, and V4 are generated between the resistors R1 and R2, R2 and R3, R3 and R4, and R4 and R5, respectively. A circuit 12 outputs the voltages V1, V2, V3, and V4 generated by the voltage dividing circuit 21 with reduced impedance. This circuit 12 generally includes a voltage follower circuit 0P by an operational amplifier circuit as shown in the figure.
1 to OP4 and this voltage follower circuit 0P1 to OP
4 and capacitors C1 to C4 connected between the voltages V0 and V5. Note that large-capacity electrolytic capacitors and tantalum capacitors are generally used for the capacitors C1 to C4.

[0003] With the above configuration, the impedance is reduced and the voltages V0 to V5 are supplied to the liquid crystal panel.

[0004]

However, in the conventional power supply circuit, for example, any one of the resistors R1, R2, R4, and R5 constituting the voltage dividing circuit 21 in FIG. 2 is damaged or the connection is broken. Then, the voltages V1 to V4 become equal to the voltages V0 or V5, respectively. For example, if the resistor R2 breaks, the voltage V1 becomes equal to the voltage V0, and the voltages V2 to V4 become equal to the voltage V5. Then, when the capacitor C2 is not damaged, only the voltage V is applied, but the voltage nV is applied.

[0005] Therefore, when the capacitors C1 to C4 have only a withstand voltage corresponding to the voltage of V, there is a danger of heat generation caused by dielectric breakdown of the capacitors. Further, when a capacitor having a withstand voltage corresponding to the voltage of nV is used, there is a problem that the shape of the capacitor becomes large.

The present invention has been made in view of such a problem, and a constant voltage diode is connected in parallel to each of the resistors constituting the voltage dividing circuit, so that even if one resistor is damaged, the voltage is applied to the capacitor. The purpose of the present invention is to provide a display device with high safety and an electronic device equipped with the display device with high security by minimizing the increase in the voltage of the display device. is there.

[0007]

A power supply circuit according to the present invention comprises: a voltage dividing circuit having a plurality of resistors connected between two different potentials; and a plurality of operational amplifier circuits connected to the voltage dividing circuit. In a power supply circuit that supplies the potential or the output of the operational amplifier circuit, a capacitor is connected between the potential and the output of the operational amplifier circuit or between the outputs of the operational amplifier circuit. A constant voltage diode is connected in parallel to at least one of the resistors.

The display device of the present invention comprises a liquid crystal panel, a voltage dividing circuit having a plurality of resistors connected between two different potentials, and a plurality of operational amplifier circuits connected to the voltage dividing circuit. And a power supply circuit for supplying the potential or the output of the operational amplifier circuit to the liquid crystal panel, between the potential and the output of the operational amplifier circuit or between the output of the operational amplifier circuit. Is connected to a capacitor, and a constant voltage diode is connected in parallel to at least one of the resistors.

[0009]

[0010]

[Embodiment 1] A driving method using a power supply circuit of the present invention will be described in more detail with reference to embodiments. Now, taking the case of driving a liquid crystal panel of a liquid crystal display device as an example, six levels of voltages required to drive the liquid crystal panel, voltage V0-voltage V1 = voltage V1-voltage V2 = voltage V3-voltage V4 = voltage V4 A case is considered in which the voltages V0 to V5 having a relationship of voltage V5 (= V) and voltage V0−voltage V5 = n · V (n is a positive number, usually about 10) are generated.

FIG. 1 is a diagram showing a configuration of a power supply circuit.

In FIG. 1, reference numeral 11 denotes a voltage dividing circuit which is formed by connecting five resistors R1 to R5 in series.
1, R2, R4, and R5 have the same resistance value R, and R3 has a resistance value (n-4) R. A voltage V0 and a voltage V5 are applied to both ends of the voltage dividing circuit 21, that is, above the resistor R1 and below the resistor R5 in the figure, and the resistors R1 and R5 are applied.
2, voltages V1, V2, V3, and V4 are divided between R2 and R3, R3 and R4, and R4 and R5, respectively.

Reference numeral 12 denotes a voltage V generated by the voltage dividing circuit 21.
1, V2, V3, and V4 are output with reduced impedance. This circuit 12 generally includes a voltage follower circuit 0P1 using an operational amplifier circuit as shown in the figure.
To OP4 and this voltage follower circuit 0P1 to OP4
, And capacitors C1 to C4 connected between the voltages V0 and V5.

Reference numerals 13 to 16 denote constant voltage diodes which are connected in parallel to the resistors R1, R2, R4 and R5, respectively, so as to be reverse biased. And the constant voltage diode 1
Nos. 3 to 16 have a Zener voltage slightly higher than V.

With the above configuration, the resistor R
Even if any one of R1, R2, R4 and R5 is broken or disconnected, a very large voltage is not applied to the capacitors C1 to C4.

That is, the constant voltage diodes 13 to 16 having a zener voltage slightly higher than V are connected to the respective resistors R1 and R2.
Since the resistors R1, R2, R4, and R5 other than the resistor R3 are damaged in the case where the resistors R1, R2, and R5 are connected in parallel to R2 and R5, only a zener voltage slightly higher than V is applied to the capacitor. If the resistor R3 is damaged, the voltages V1 and V2 are equal to the voltage V0, and the voltages V3 and V4 are equal to the voltage V0.
Therefore, no voltage is applied to the capacitors C1 to C4. Here, when the resistor is not damaged, the voltage applied to the constant voltage diodes 13 to 16 becomes equal to or lower than the zener voltage and becomes insulated, so that the power supply circuit is not affected.

Therefore, the withstand voltage of the capacitor may be set slightly higher than the normally applied voltage V in preparation for the damage of the resistor. Note that the probability that each resistor and the corresponding constant voltage diode will be damaged at the same time is the product of the probability that the resistor will be damaged and the probability that the constant voltage diode will be damaged, and is extremely small.

As a result, it is possible to prevent an overvoltage from being applied to the capacitor without increasing the withstand voltage of the capacitor so much that danger such as flames is eliminated.

As described above, a constant voltage diode is connected in parallel to each of the resistors constituting the voltage dividing circuit, thereby minimizing an increase in the voltage applied to the capacitor even if one resistor is damaged. It can improve the safety of the power supply circuit.

[Second Embodiment] The use of the power supply circuit of the first embodiment can improve the safety of a display device. Note that the use of the power supply circuit according to the first embodiment in a display device can be easily embodied, and a detailed description thereof will be omitted.

[Embodiment 3] Improving the safety of electronic equipment by using the display apparatus of Embodiment 2 using the power supply circuit of Embodiment 1 in an electronic device requiring a display function, such as a personal computer or a word processor. Can be done.

[0022]

As described above, by connecting a constant voltage diode in parallel to each of the resistors constituting the voltage dividing circuit, even if one resistor is damaged, an increase in the voltage applied to the capacitor can be minimized. The safety of the power supply circuit is improved, and the withstand voltage of the capacitor is not required to be larger than necessary, so that the power supply circuit can be reduced in size and weight. And by using this power supply circuit as a power supply of the display device, the safety of the display device is improved,
As a result, the safety of an electronic device incorporating the display device is improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a power supply circuit according to a first embodiment.

FIG. 2 is a diagram illustrating a configuration of a power supply circuit according to the related art.

[Explanation of symbols]

 11 is a voltage dividing circuit 12 is a circuit for outputting a voltage with lowered impedance R1 to 5 are resistors OP1 to 4 are operational amplifier circuits C1 to 4 are capacitors V0 to 5 are voltages

Continuation of the front page (51) Int.Cl. ⁷ identification code FI H02H 7/20 G06F 1/00 330A (58) Investigation field (Int.Cl. ⁷ , DB name) G05F 1/10 G02F 1/133 520 G06F 1/26 G09G 3/18 H02H 7/20

Claims (2)

(57) [Claims] 1. A voltage dividing circuit having a plurality of resistors connected between two different potentials, and a plurality of operational amplifier circuits connected to the voltage dividing circuit, wherein the potential or the operational amplifier In a power supply circuit for supplying an output of a circuit, a capacitor is connected between the potential and an output of the operational amplifier circuit or between outputs of the operational amplifier circuit, and at least one of the resistors has a constant value. A power supply circuit characterized in that voltage diodes are connected in parallel. 2. A liquid crystal panel, comprising: a voltage dividing circuit having a plurality of resistors connected between two different potentials; and a plurality of operational amplifier circuits connected to the voltage dividing circuit. Alternatively, in a display device having a power supply circuit for supplying an output of the operational amplifier circuit to the liquid crystal panel, a capacitor is connected between the potential and an output of the operational amplifier circuit or between outputs of the operational amplifier circuit. A display device, wherein a constant voltage diode is connected in parallel to at least one of the resistors.