Abstract:
A CRT (Cathode Ray Tube) display device, and method, having a FBT (Fly Back Transformer) with a conductive coil, and a step-up circuit supplying a predetermined power to the FBT The CRT includes a high voltage sensor sensing a voltage applied to the step-up circuit and a controller receiving the voltage outputted from the FBT and controlling an input voltage of the step-up circuit to be dropped when the received voltage from the FBT is higher than a predetermined dangerous voltage. With this configuration, the present invention provides the CRT display device that decreases an input voltage of a step-up circuit to operate normally and to prevent elements of the step-up circuit from being destroyed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Patent Application No. 2003-44899, filed Jul. 3, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a Cathode Ray Tube (CRT) display device, and method. More particularly, the present invention relates to a CRT display, with a step-up circuit, and method for the same.  
         [0004]     2. Description of the Related Art  
         [0005]     In general, a Fly Back Transformer (FBT) of a CRT display outputs up to 26 kV. Generally, there are two types of high voltage regulation circuits available to stably supply high voltage. One circuit is a separable regulating circuit, separately regulating a high voltage and a deflection coil (Deflection Yoke, DY), and the other circuit is an integrated regulating circuit, regulating the high voltage and the deflection coil together.  
         [0006]      FIG. 1  is an integrated regulating circuit of a conventional CRT display.  
         [0007]     As illustrated in  FIG. 1 , the integrated regulating circuit includes a FBT  110 , a horizontal deflection coil  120 , a deflection signal controller  130 , and a step-up circuit  140 .  
         [0008]     The FBT  110  has a primary conductive coil  111  and a secondary conductive coil  112 . The secondary conductive coil  112  has a comparatively greater turn ratio than the primary conductive coil  111 , and increases the voltage applied to the primary conductive coil  111 . The voltage at the secondary conductive coil  112  is then supplied to a cathode of the CRT.  
         [0009]     The horizontal deflection coil  120  is combined with an end of the primary conduction coil  111  of the FBT. By having a ramped current, the horizontal deflection coil  120  deflects an electron beam, generated by an electron gun, so that the electron beam is caused to scan across a display tube of the CRT, from corner to corner.  
         [0010]     The deflection signal controller  130  includes a transistor Q 3 , pull-up resistors R 1  and R 2 , and a damper-diode D 2 . The damper-diode D 2 , typically embodied by a silicon diode, is used to constrain a free oscillation generated after a flyback period of the ramped current waveform of the horizontal deflection coil  120 . The transistor Q 3  uses a BJT (Bipolar Junction Transistor) and switches on and off the voltage applied to the horizontal deflection coil  120 , responding to a control signal applied to a base terminal thereof.  
         [0011]     A primary purpose of the deflection signal controller  130  is to drive the horizontal deflection coil  120 . The horizontal deflection coil  120  has to be correctly charged to a proper current level to enable a scanning of the electron beam to proceed from left to right on the screen. A control of the current strength, in the horizontal deflection coil  120 , controls the deflection of the horizontal deflection coil  120  and enables the scanning to proceed horizontally. The horizontal deflection coil  120  generates a magnetic field and causes the electron beam to be deflected by applying a magnetic force to the electron beam. Horizontal-size (H-size) and horizontal-linearity (H-linearity), respectively, control the degree of deflection and the speed of the deflection. The step-up circuit  140  supplies power to the horizontal deflection coil  120 , to enable a continuous deflection operation.  
         [0012]     The step-up circuit  140  may include a BJT (Bipolar Junction Transistor) Q 1 , a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) Q 2 , a diode D 1 , pull-up resistors R 3  and R 4 , a capacitor C 1 , and an inductor L 1 .  
         [0013]     A signal generated according to a PWM (Pulse Width Modulation) signal, applied to the BJT Q 1 , is sequentially applied to a gate terminal of the MOSFET Q 2 , as a control signal switching the MOSFET Q 2 . The PWM signal applied to the BJT Q 1  is a waveform designed to alternate between a zero duty level and a half duty level. When the MOSFET Q 2  is in an off state, that is, when the PWM signal inputted to the BJT Q 1  is in the zero duty level, the capacitor C 1  is charged with a voltage applied to a drain terminal of the MOSFET Q 2 . On the other hand, when the PWM signal is in the half duty level, the voltage charging the capacitor C 1  is increased by an electromotive force stored in the inductor L 1 . When the voltage (Vcc) applied to the drain terminal of the MOSFET Q 2  is 50V, a voltage of the capacitor C 1  is 50V if the PWM signal is in the zero duty level, but the voltage of the capacitor C 1  increases to 160V or 180V if the PWM signal is in the half duty level.  
         [0014]     A main role of the pull-up resistor R 3  is to inform an IC (integrated circuit), controlling the deflection, that the MOSFET Q 2  is in an on-state. When current is flowing through the pull-up resistor R 3 , during the on-state of MOSFET Q 2 , the voltage at Bsense is increased. Thus, the deflection controlling IC senses the voltage at Bsense and controls the same to be a high voltage by changing the on/off state of the MOSFET Q 2 .  
         [0015]     The step-up circuit  140 , focusing on the MOSFET Q 2 , is efficient for controlling the high voltage. The voltage at the capacitor C 1  is flexibly changed based on a frequency varying from 31 kHz to 70 kHz, for example, as well as a maxmum/minmum load amount, of the electron beam, thereby compositively changing the high voltage.  
         [0016]     The magnetic force applied to the inductor L 1  is dependent on the length of the on-duty state of MOSFET Q 2 , e.g., the magnetic force will increase as the length of the on-duty state increases. Thus, the voltage in the capacitor C 1  can be changed by the MOSFET Q 2  being in the on-duty state. The voltage in the capacitor C 1  is conducted to the primary coil  111  of the FBT  110  and supplied to the horizontal deflection coil  120 .  
         [0017]     Such a CRT device is widely used in TV picture tubes, computer monitors, and the like. A relay is also used to control a system of the above CRT devices, though the relay may be harmful to the system because of a chattering noise, a time delay, and so on.  
         [0018]     Referring to  FIG. 1 , the conventional CRT display devices have several problems, such as the horizontal deflection signal controller  130  suddenly stopping because of an error from the relay, being an inefficient system environment, and potentially causing the PWM signal of the step-up circuit  140  to be continuously applied. Consequently, the electromotive force stored in the inductor C 1  may continuously increase, and the current flowing through the MOSFET Q 2  may rise to a dangerous level, such that the MOSFET Q 2  may actually be destroyed.  
       SUMMARY OF THE INVENTION  
       [0019]     Accordingly, it is an aspect of the present invention to provide a CRT (Cathode Ray Tube) display device, and method, that decreases an input voltage of a step-up circuit, to perform regular scanning operations and to prevent elements of the step-up circuit from being destroyed.  
         [0020]     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
         [0021]     To accomplish the above and/or other aspects and advantages, embodiments of the present invention provide a Cathode Ray Tube (CRT) display, including a Fly Back Transformer (FBT) with a conductive coil, a step-up circuit supplying a predetermined power to the FBT, a high voltage sensor sensing a voltage output from the step-up circuit, and a controller receiving the sensed voltage and controlling an input voltage of the step-up circuit to be dropped when the sensed voltage is higher than a predetermined dangerous voltage.  
         [0022]     The CRT display may further include a deflection signal output applied a predetermined deflection voltage from the step-up circuit and a deflection signal controller controlling an application of the applied deflection voltage from the step-up circuit to the deflection signal output, wherein the controller drops the input voltage applied to the step-up circuit when the step-up circuit continuously supplies power to the FBT without the deflection signal controller controlling application of the applied deflection voltage to the deflection signal output.  
         [0023]     Further, the controller may controls the CRT display to be operated in a Display Power Management Signaling (DPMS) mode when the sensed voltage is higher than the dangerous voltage, to drop the input voltage applied to the step-up circuit. In addition, the controller may output a predetermined control signal to the deflection signal controller to enable the deflection signal controller to control the deflection voltage applied to the deflection signal output, thereby dropping the input voltage to the step-up circuit, when the sensed voltage is higher than the dangerous voltage.  
         [0024]     To accomplish the above and/or still another aspect and advantage, embodiments of the present invention provide a method of controlling a Cathode Ray Tube (CRT) display, including sensing a voltage output from a step-up circuit of a Fly Back Transformer (FBT), and controlling an input voltage of the step-up circuit to be dropped when the sensed voltage is higher than a predetermined voltage.  
         [0025]     The method may further include applying a deflection voltage from the step-up circuit to a deflection signal output to control an electron beam deflection of the CRT, wherein the input voltage applied to the step-up circuit is dropped when the step-up circuit continuously supplies power to the FBT without a use, by the deflection signal output, of the deflection voltage from the step-up circuit being controlling by a deflection signal controller, controlling the deflection signal output.  
         [0026]     Further, the CRT display to be operated in a Display Power Management Signaling (DPMS) mode when the sensed voltage of the output of the step-up circuit is higher than the predetermined voltage, to drop the input voltage applied to the step-up circuit. In addition, a deflection signal controller may control usage, by a deflection signal output, of a deflection voltage, from the step-up circuit, by dropping the input voltage to the step-up circuit, when the sensed voltage of the output of the step-up circuit is higher than the predetermined voltage. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompany drawings of which:  
         [0028]      FIG. 1  illustrates a circuit diagram of an integrated regulating circuit of a conventional CRT (Cathode Ray Tube) display;  
         [0029]      FIG. 2  is a block diagram of a CRT display, according to an embodiment of the present invention;  
         [0030]      FIG. 3  is a block diagram of a CRT display, having an integral regulation circuit, according to another embodiment of the present invention; and  
         [0031]      FIG. 4  illustrates a circuit diagram of the CRT display, according to still another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.  
         [0033]      FIG. 2  is a block diagram of a CRT (Cathode Ray Tube) display, according to an embodiment of the present invention.  
         [0034]     As illustrated in  FIG. 2 , the CRT display device comprises a FBT (Fly Back Transformer)  10 , a step-up circuit  20 , a high voltage sensor  30 , and a controller  60 .  
         [0035]     The FBT  10  increases an input voltage to a high output voltage, and outputs the high output voltage to an anode (not shown), a focus grid, and a control grid (not shown) of the CRT display.  
         [0036]     The step-up circuit  20  amplifies a predetermined input voltage, so as to output an amplified voltage to a primary coil of the FBT  10 . The high voltage sensor  30  senses the amplified input voltage output by a transistor of the step-up circuit  20  and outputs the sensed input voltage to the controller  60 .  
         [0037]     The controller  60  applies a switching voltage signal to the transistor of the step-up circuit  20  so as to control the voltage level output from the step-up circuit  20 . Also, the controller  60  receives a predetermined voltage from the high voltage sensor  30  and controls the input voltage of the step-up circuit  20  to be dropped if the predetermined voltage is higher than a predetermined dangerous voltage. The controller  60  can also control the CRT display device to be operated in a power saving mode of Display Power Management Signaling (DPMS), and can maintain the switching signal applied to the transistor of the step-up circuit  20  to be in an off state.  
         [0038]     The high voltage sensor  30  senses the voltage output from the step-up circuit  20  and outputs the sensed voltage to the controller  60 . Then the controller  60  determines whether the sensed voltage is higher than a normal voltage, e.g., due to a malfunctioning of the CRT display, so as to control the dropping of the input voltage to the step-up circuit  20 .  
         [0039]     The high voltage sensor  30  may directly sense the input voltage of the step-up circuit  20  and may measure voltages formed in other nodes, so as to output the sensed voltages to the controller  60 . Controller  60  compares the sensed voltages to predetermined dangerous voltages, to detect a malfunction of the CRT.  
         [0040]     Further, the high voltage sensor  30  may sense the voltage output from the FBT  10  or applied to the FBT  10  from the step-up circuit  20  and output the sensed voltage to the controller  60 .  
         [0041]      FIG. 3  is a block diagram of a CRT having an integrated high voltage regulating circuit, according to another embodiment of the present invention.  
         [0042]     As illustrated in  FIG. 3 , the integrated high voltage regulating circuit can have a similar configuration as the CRT illustrated in  FIG. 2 , except that a deflection circuit  35  has been added in the present embodiment.  
         [0043]     The deflection circuit  35  includes a deflection signal output  40  and a deflection signal controller  50 .  
         [0044]     The deflection signal output  40  receives a sawtooth shaped current signal from the step-up circuit  20  and outputs a deflection signal, deflecting the electron beam from the electron gun (not shown). Such a deflection signal deflects a flow of electrons to control the scanning of the electron beam across the screen of the CRT.  
         [0045]     The deflection signal controller  50  controls the flow of current supplied by the step-up circuit  20  to the deflection signal output  40 , thereby controlling the amount of deflection of the electron beam, as well as the variation of the deflection.  
         [0046]     As an example of a potential malfunction of the CRT system, if the deflection signal controller  50  stops operating while the step-up circuit  20  is continuously operating, then a predetermined high voltage will likely be supplied to the Fly Back Transformer (FBT) and the deflection signal output  40 . In that case, the controller  60  senses the malfunction and properly drops the input voltage of the step-up circuit  20 . In this manner, the controller  60  controls the deflection signal controller  50  to be operated normally, thereby dropping the input voltage of the step-up circuit  20 .  
         [0047]      FIG. 4  illustrates a circuit diagram of a CRT display, according to another embodiment of the present invention.  
         [0048]     As illustrated in  FIG. 4 , the CRT display may include a the Fly Back Transformer (FBT)  10 , the step-up circuit  20 , the high voltage sensor  30 , the deflection signal output  40 , and the deflection signal controller  50 , and a controller  60 .  
         [0049]     The FBT  10  has a primary conductive coil  11  and a secondary conductive coil  12 , and transfers a high voltage to the secondary coil  12 , which is being coupled, with a high turn ratio, to the primary conductive coil  11 . The voltage output by the secondary conductive coil  12  is applied to the anode of the CRT display.  
         [0050]     The step-up circuit  20  may include a BJT Q 4 , a MOSFET Q 5 , a diode D 22 , pull-up resistors R 24  and R 25 , a capacitor C 23 , and an inductor L 21 .  
         [0051]     A signal generated according to a PWM signal applied to the BJT Q 4  is sequentially applied to a gate terminal of the MOSFET Q 5  as a control signal switching the MOSFET Q 5 . The PWM signal applied to the BJT Q 4  is a waveform designed to alternate between a zero duty level and a half duty level. When the MOSFET Q 5  is in an off state, that is, when the PWM signal applied to the BJT Q 4  is in the zero duty level, the capacitor C 23  is charged with a voltage applied to a drain terminal of the MOSFET Q 5 . On the other hand, when the PWM signal is in the half duty level, the voltage charging the capacitor C 23  is increased by an electromotive force stored in the inductor L 21 . For example, when the voltage applied to the drain terminal of the MOSFET Q 5  is 50V, a voltage of the capacitor C 23  is 50V if the PWM signal is in the zero duty level, but the voltage of the capacitor C 23  increases to 160V or 180V, for example, if the PWM signal is at the half duty level.  
         [0052]     A main role of the pull-up resistor R 25  is to inform a deflection control integrated circuit (IC), which may be embodied in controller  60 , and which controls the deflection, that the MOSFET Q 5  is in an on-state. If current is flowing through the pull-up resistor R 25  during the on-state of MOSFET Q 5 , the voltage at Bsense increases. Thus the deflection control IC senses the voltage at Bsense and controls it to be a high voltage by changing the on/off state of the MOSFET Q 5 .  
         [0053]     The step-up circuit  20 , focusing on the MOSFET Q 5 , is efficient for controlling the high voltage. The voltage in the capacitor C 23  is flexibly changed, corresponding to a frequency varying from 31 kHz to 70 kHz, for example, and a maxmum/minmum load amount of the electron beam, thereby changing the high voltage.  
         [0054]     A longer on-duty state of the MOSFET Q 5  results in increasing magnetic force conducted in the inductor L 21 . Thus, the voltage in the capacitor C 23  can be changed by the on-duty state of the MOSFET Q 5 . The voltage in the capacitor C 23  is transferred to the primary coil  11  of the FBT  10  and supplied to a deflection coil  41 .  
         [0055]     The high voltage sensor  30  may include a conductive coil  31 , a diode D 32 , a resistor R 33 , and a capacitor C 34 .  
         [0056]     The conductive coil  31  is coupled by a comparatively small turn ratio to the secondary conductive coil  12  of the FBT  10 . The voltage applied to the secondary coil  12  is thereby dropped and applied to the conductive coil  31  at a lower voltage, based on the turn ratio.  
         [0057]     The diode D 32  prevents the current from flowing backward. The resistor R 33  and the capacitor C 34  make up a Low Pass Filter (LPF) for removing a ripple from a voltage stored in the conductive coil  31  and outputting the ripple-removed voltage to a microcomputer  61 .  
         [0058]     The deflection signal output  40  may include the deflection coil  41 . A magnetic field generated by the sawtooth shaped current flowing through the deflection coil  41  deflects an electric charge of the electron beam, enabling the scanning of the electron beam across the CRT screen.  
         [0059]     The deflection signal controller  50  may also include a BJT Q 6 , pull up resistors R 51  and R 52 , and a damper diode D 53 .  
         [0060]     The BJT Q 6  receives a predetermined switching signal in a base terminal and the damper diode D 53  prevents the sawtooth shaped current from oscillating during the flyback period.  
         [0061]     The deflection signal controller  50  controls the voltage or the current applied to the deflection signal output  40 . The current flowing through the deflection coil  41  flows to a ground terminal connected with an emitter of the BJT Q 6  when the BJT Q 6  is on.  
         [0062]     The controller  60  includes the microcomputer  61 , and the microcomputer  61  includes a high voltage sensor port P 1 , receiving the high voltage from the high voltage sensor  30 , and an output terminal outputting switching signals controlling the transistors Q 4  and Q 6  of the step-up circuit  20  and the deflection signal controller  50 , respectively.  
         [0063]     If the switching signal is not applied to the transistor Q 6 , of the deflection signal controller  50 , from the microcomputer  61  because the system is malfunctioning in the relay, and the like, an electromotive force of the inductor L 21  will increase by a predetermined amount responding to an operation of the step-up circuit  20 . Such electromotive force causes the voltage of the capacitor C 23  to increase, resulting in the high voltage being applied to the primary conductive coil  11  of the FBT  10 , such that the secondary conductive coil  12 , and the conductive coil  31  of the high voltage sensor  30 , generate higher voltages than normal. This phenomenon may occur because the switching signal from microcomputer  61  stops being output to the deflection signal controller  50 , causing energy supplied to the step-up circuit  20  to be accumulated in the inductor L 21 , which does not dissipate through the ground terminal connected with the transistor Q 6 .  
         [0064]     Accordingly, the high voltage sensor  30  then outputs an abnormally high voltage signal, induced in the conductive coil  31  through the LPF, to the high voltage sensor port P 1  of the microcomputer  61 . The microcomputer  61  thereby detects the malfunctioning of the system when the voltage at the high voltage sensor port P 1  is higher than a predetermined dangerous voltage, and, accordingly, stops outputting the control signal switching the step-up circuit  20 , thereby turning transistor Q 4  off, for example.  
         [0065]     As described above, the controller  60  also enables the display device to be operated in DPMS (Display Power Management Signaling) mode, and supplies the switching signal to the transistor Q 6  of the deflection signal controller  50 , enabling the transistor Q 6  to remain in the on state during a predetermined period, and also applies a normal switching signal when the voltage sensed in the high voltage sensor  30  drops below a predetermined voltage.  
         [0066]     Although a few embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.