Driving circuit having voltage detecting circuit and liquid crystal display using same

An exemplary liquid crystal display (LCD) (20) includes: a gate driving integrated circuit (IC) (22) for scanning an LCD panel (24) of the LCD; a data driving IC (23) for providing a plurality of gradation voltages to the LCD panel; a primary control circuit board (21) configured for providing the operation voltage to the data driving IC; and a flexible printed circuit board (25) connected between the LCD panel and the primary control circuit board. The data driving IC includes a voltage detecting circuit (230), which detects an operation voltage applied to the gate driving IC and is configured to provide an all-scanning signal to the gate driving IC.

FIELD OF THE INVENTION

The present invention relates a driving circuit having a voltage detecting circuit for eliminating residual image and a liquid crystal display (LCD) using the same.

GENERAL BACKGROUND

An LCD has the advantages of portability, low power consumption, and low radiation, and has been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras and the like. Furthermore, the LCD is considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions.

Usually, an LCD needs an external power supply for providing operating power. When the LCD operates, much electric charge is stored therein. When the LCD is powered off, electric charge stored therein is not discharged quickly. This makes the voltage at the external power supply connection drop slowly. As a result, a gate driving circuit and a data driving circuit that drive the LCD operate incorrectly, thereby producing a residual image on the LCD.

FIG. 4is a schematic circuit diagram of a typical LCD. The LCD10includes an LCD panel14and a driving circuit (not labeled). The driving circuit includes a gate driving integrated circuit (IC)12, a data driving IC13, a primary control circuit board11, and a flexible printed circuit board (FPCB)15. The gate driving IC12and the data driving IC13are respectively formed on two adjacent sides of the LCD panel14by chip on glass (COG) technology. The FPCB15is connected between the LCD panel14and the primary control circuit board11. The gate driving IC12scans the LCD panel14. The data driving IC13provides a plurality of gradation voltages to the LCD panel14when the LCD panel14is scanned.

The primary control circuit board11includes a driving control circuit111, a power supply circuit112and a voltage detecting circuit113. The power supply circuit112directly provides an operation voltage (not labeled) to the driving control circuit111, and respectively provides two operation voltages V2, V1to the gate driving IC12and the data driving IC13via the FPCB15.

The voltage detecting circuit113generates an all-scanning signal “Xon” when the operation voltage V2falls below a predetermined threshold voltage. Then, the voltage detecting circuit113transmits the all-scanning signal “Xon” to the gate driving IC12through a conducting lead (not labelled) configured on the FPCB15. As the gate driving IC12receives the all-scanning signal “Xon”, the gate driving IC turns on all of TFTs (thin film transistors) of the LCD panel14. Thus the electric charge stored in the TFTs can be discharged quickly. As a result, the residual image on the LCD10does not appear when the LCD10is power off.

However, because the primary control circuit board11includes the voltage detecting circuit113, the volume occupied by the primary control circuit board11is large. Furthermore, because the voltage detecting circuit113is configured on the primary control circuit board11, the FPCB15needs a special conducting lead formed thereon for transmitting the all-scanning signal “Xon” from the voltage detecting circuit113to the gate driving IC12.

What is needed, therefore, is a driving circuit of an LCD that can overcome the above-described deficiencies.

SUMMARY

An exemplary driving circuit of an LCD includes a gate driving IC for scanning an LCD panel of the LCD; a data driving IC for providing a plurality of gradation voltages to the LCD panel; a primary control circuit board configured for providing the operation voltage to the data driving IC; and a flexible printed circuit board connected between the LCD panel and the primary control circuit board. The data driving IC includes a voltage detecting circuit. The voltage detecting circuit is configured for detecting an operation voltage applied to the gate driving IC and providing an all-scanning signal to the gate driving IC.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1is a schematic circuit diagram of an LCD according to a preferred embodiment of the present invention. The LCD20includes an LCD panel24and a driving circuit (not labeled). The driving circuit includes a gate driving IC22, a data driving IC23, a primary control circuit board21, and an FPCB25. The gate driving IC22and the data driving IC23are respectively formed on two adjacent sides of the LCD panel24by chip on glass (COG) technology. The FPCB25is connected between the LCD panel24and the primary control circuit board21. The gate driving IC22scans the LCD panel24. The data driving IC23provides a plurality of gradation voltages to the LCD panel24when the LCD panel24is scanned.

The primary control circuit board21includes a driving control circuit211and a power supply circuit212. The power supply circuit212directly provides an operation voltage to the driving control circuit211, and respectively provides operation voltages V2, V1to the gate driving IC22and the data driving IC23via the FPCB25.

The LCD panel24includes a conducting lead (not labeled) thereon formed by semiconductor technology. The conducting lead is configured between the gate driving circuit22and the data driving circuit23for electrically connecting the gate driving circuit22and the data driving circuit23.

The data driving circuit23includes a voltage detecting circuit230integrated therein. The voltage detecting circuit230generates an all-scanning signal “Xon” when the operation voltage V1falls below a predetermined threshold voltage. Then, the voltage detecting circuit230transmits the all-scanning signal “Xon” to the gate driving IC22through the conducting lead. The gate driving IC22turns on all of TFTs of the LCD panel24when the gate driving IC22receives the all-scanning signal from the voltage detecting circuit230. Thus the electric charge stored in the TFTs can be discharged quickly. As a result, a residual image on the LCD20does not appear when the LCD20is power off.

Referring to theFIG. 2, the voltage detecting circuit230includes an input terminal “IN” for receiving the operation voltage V1, an output terminal “OUT” connected to the conducting lead for providing the all-scanning signal “Xon” to the gate driving IC22, a first comparator241, a second comparator251, a first negative-positive-negative (NPN) bipolar transistor271, a second NPN bipolar transistor281, a first constant current power circuit242, a second constant current power circuit252, a constant voltage diode261, and a plurality of resistors231,232,233,234,235.

The resistors231,232are connected in series between the input terminal “IN” and ground. The first constant current circuit242and the constant voltage diode261are also connected in series between the input terminal “IN” and ground. A joint node between the resistors231,232is connected to an inverting input of the first comparator241. A joint node between the first constant current circuit242and the constant voltage diode261provides a constant reference voltage to a noninverting input of the first comparator241. An output of the first comparator241is connected to a base electrode “b” of the first NPN bipolar transistor271via the resistor233. An emitter electrode “e” of the first NPN bipolar transistor271is connected to ground. A collector electrode “c” of the first NPN bipolar transistor271is connected to the input terminal “IN” via the resistor234and the second constant current power circuit252in series. The collector electrode “c” of the first NPN bipolar transistor271is connected to an inverting input of the second comparator251via the resistor234. A noninverting input of the second comparator251is connected to the output terminal “OUT”. An output of the second comparator251is connected to a base electrode “b” of the second NPN bipolar transistor281via the resistor235. An emitter electrode “e” of the second NPN bipolar transistor281is connected to ground. A collector electrode “c” of the second NPN bipolar transistor281is connected to the output terminal “OUT”.

FIG. 3is an abbreviated timing chart illustrating operation of the voltage detecting circuit230. Vin represents the voltage wave provided to the input terminal “IN”. Vth represents a predetermined threshold voltage lower than a maximum voltage provided to the input terminal “IN”. Vout represents an output voltage wave of the output terminal “OUT”. Va represents a voltage wave output from the output of the first comparator241.

The operation of the voltage detecting circuit230is as follows. Normally, a constant operation voltage, such as the voltage V1, is applied to the input terminal “IN” from the power supply circuit212. Because the constant reference voltage is set to be lower than a division voltage provided from the joint node between the resistors231,232, a voltage of the noninverting input of the first comparator241is lower than that of the inverting input of the first comparator241. The first comparator241outputs a lower voltage to the base electrode “b” of the first NPN bipolar transistor271via the resistor233. Thus, the first NPN bipolar transistor271turns off. The constant operation voltage, such as the voltage V1, is provided to the inverting input of the second comparator251via the second constant current circuit252. Then the second comparator251outputs a low voltage to the base electrode “b” of the second NPN bipolar transistor281via the resistor235. The second bipolar transistor281turns off. Thus the output terminal “OUT” of the voltage detecting circuit230outputs a high voltage to the gate driving IC22through the conducting lead.

When the LCD is turned off, the voltage V1falls below a threshold voltage Vth. Thus the voltage of the noninverting input of the first comparator241is higher than that of the inverting input of the first comparator241. Then, the first comparator241outputs a high voltage to the base electrode “b” of the first NPN bipolar transistor271. The first NPN bipolar transistor271turns on. The inverting input of the second comparator251is connected to ground via the activated first NPN bipolar transistor271. Then, the second comparator251outputs a high voltage to the base electrode “b” of the second NPN bipolar transistor281. The second NPN bipolar transistor281turns on. Thus the output terminal “OUT” is connected to ground via the activated second NPN bipolar transistor281. Therefore, the output terminal “OUT” outputs a zero volt voltage as an all-scanning signal “Xon” to the gate driving circuit22through the conducting lead.

In summary, because the voltage detecting circuit230is integrated in the data driving IC23, the primary control circuit board21need not generate an all-scanning signal “Xon” and provide the all-scanning signal “Xon” to the gate driving IC22through the FPCB25. Thus the configuration of the FPCB25and the primary control circuit board21is simple.

In an alternative embodiment of the present invention, the voltage detecting circuit230can be integrated in the gate driving IC22for detecting an operation voltage applied thereon. When the operation voltage applied to the gate driving IC22falls below a predetermined threshold voltage, the gate driving IC22performs a function of turning on all the TFTs of the LCD.