Patent Publication Number: US-7224354-B2

Title: Apparatus and method for generating high-voltage regulation signal in a display

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of Korean Patent Application No. 2002-78717, filed on Dec. 11, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a regulation circuit for a Color Display Tube (CDT), and, more particularly, to an apparatus and method for generating a high-voltage regulation signal capable of protecting components in a regulation circuit. 
   2. Description of the Related Art 
   Images on a bright area of a display screen sometimes appear as being expanded, and images on a dark area of the display screen sometimes appear as being contracted. This situation occurs because of a poor high-voltage regulation. Generally, image displays include a regulation circuit for controlling such a high-voltage regulation which has a direct influence on picture quality. 
     FIG. 1  is a block diagram of a regulation circuit used in a conventional Color Display Tube (CDT). The regulation circuit comprises an oscillation circuit  100 , a Pulse Width Modulation (PWM) generator  110 , a switching unit  120 , a transformer  130 , an error detector  140 , and a feedback unit  150 . 
   The oscillation circuit  100  generates an oscillation clock pulse. The PWM generator  110  generates and outputs a PWM control signal for controlling a high-voltage regulation using the oscillation clock pulse. The switching unit  120  outputs a signal switched according to the PWM control signal output from the PWM generator  110 . 
   The transformer  130  generates and outputs a high-voltage regulation signal at a secondary side, using an output signal from the switching unit  120  as a primary-side voltage. The transformer  130  supplies the high-voltage regulation signal via a secondary-side output to the CDT, and simultaneously supplies a feedback voltage, proportional to the high-voltage regulation signal, to the PWM generator  110  via the feedback unit  150 . 
   The error detector  140  detects an error using the signal output from the switching unit  120 . When an error is detected, the error detector  140  notifies the PWM generator  110  of the error to enable the PWM generator  110  to stop outputting the PWM signal. 
   However, in the conventional regulation circuit, an error is detected after an excessive current due to the error already flows to the switching unit  120 , and then the voltage signal input to the switching unit  120  is controlled. Therefore, components constituting the switching unit  120  can be damaged due to the excessive current. Such a damage of the switching unit adversely affects the control of the regulation voltage, thereby resulting in deterioration of picture quality of the CDT. Furthermore, the components constituting the switching unit  120  must be frequently replaced, resulting in an increase in cost of the whole system. 
   SUMMARY OF THE INVENTION 
   The present invention provides an apparatus and method for generating a high-voltage regulation signal that protects a switching device, in order to stabilize a regulation voltage of a display and achieve a reduction in costs thereof. 
   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. 
   According to an aspect of the present invention, there is provided an apparatus to generate a high-voltage regulation signal to control regulation of a display, the apparatus comprising: a pulse generator to generate a pulse; a reference signal generator to generate a reference signal with a desired duty ratio using the pulse generated from the pulse generator; and a high-voltage signal generator to generate a switching signal with a duty ratio controlled by the reference signal, according to the pulse from the pulse generator and a feedback regulation output voltage, and to generate a high-voltage regulation signal according to the switching signal, wherein the feedback regulation output voltage is based upon the the high-voltage regulation signal. 
   The pulse generator may generate a square wave pulse to synchronize a frequency of a regulation output voltage signal with a horizontal frequency of the display to which a regulation voltage is supplied. 
   The high-voltage signal generator may comprise: a Pulse-Width Modulation (PWM) generator to generate a PWM control signal according to the pulse from the pulse generator and the feedback regulation output voltage; a switching unit to generate a primary induction voltage switched according to the PWM control signal; a transformer to generate a secondary induction voltage proportional to the primary induction voltage; and a feedback unit to generate the feedback regulation output voltage based upon the secondary induction voltage to the PWM generator. 
   The reference signal generator may generate the reference signal on the basis of a regulation voltage specification of the display and a maximum current tolerance of the switching unit. 
   According to another aspect of the present invention, there is provided an apparatus to generate a high-voltage regulation signal to control regulation of a display, the apparatus comprising: a pulse generator to generate a pulse; a PWM generator to generate a PWM signal to control the regulation using the pulse generated from the pulse generator; a switching unit to output a primary induction voltage switched according to the PWM signal; a transformer to output a secondary regulation voltage proportional to the primary induction voltage; and a reference signal generator to generate a reference signal having a desired duty ratio using the pulse from the pulse generator and supply the reference signal to the PWM generator, wherein the PWM generator stops outputting the PWM signal in response to a duty ratio of the PWM signal being above the duty ratio of the reference signal. 
   The pulse generator may generate a square wave signal to synchronize a frequency of the secondary regulation voltage signal with a horizontal frequency of the display to which the secondary regulation voltage is supplied. 
   The reference signal may be set in consideration of a regulation voltage specification of the display and a maximum current tolerance of the switching unit. 
   According to still another aspect of the present invention, there is provided a method of generating a high-voltage regulation signal in a display, the method comprising: setting a reference signal with a desired duty ratio; generating a PWM signal to control regulation of the display; comparing the PWM signal to the reference signal; stopping outputting the PWM signal in response to a duty ratio of the PWM signal being above a duty ratio of the reference signal; and generating a high-voltage signal switched by the PWM signal. 
   The reference signal may be set in consideration of a regulation voltage specification of the display and a maximum current tolerance of a switching unit that generates the high-voltage signal switched by the PWM signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a block diagram of a regulation circuit used in a conventional CDT; 
       FIG. 2  is a block diagram of an embodiment of an apparatus for generating a high-voltage regulation signal, according to the present invention; and 
       FIG. 3  shows a flow chart illustrating a method of generating a high-voltage regulation voltage, according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   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. 
     FIG. 2  is a block diagram of an apparatus generating a high-voltage regulation signal, according to an embodiment of the present invention. 
   The high-voltage regulation signal generation apparatus controlling regulation of a display comprises a pulse generator  200 , a reference signal generator  210 , and a high-voltage signal generator  220 . 
   The pulse generator  200  generates a square wave pulse to synchronize a frequency of a regulation output voltage signal with a horizontal frequency of a display such as a CDT, to which a regulation voltage is supplied. 
   The reference signal generator  210  generates a reference signal with a desired duty ratio using a pulse generated from the pulse generator  200 . The reference signal has a duty ratio by which a maximum pulse width of the reference signal does not apply a load to a switching device, in consideration of a maximum current tolerance of the switching component included in the high-voltage signal generator  220 , while maximally satisfying the regulation voltage specification of the display. 
   The high-voltage signal generator  220  generates a switching signal with a duty ratio controlled by the reference signal, according to an output pulse from the pulse generator  200  and a feedback regulation output voltage, and generates a high-voltage regulation signal according to the switching signal. The high-voltage signal generator  220  includes a Pulse-Width Modulation (PWM) generator  221  which generates a PWM control signal according to the pulse from the pulse generator  200  and the feedback regulation output voltage, a switching unit  222  which generates a primary induction voltage switched according to the PWM control signal, a transformer  223  which generates a secondary induction voltage having a desired multiplied value in proportion to the primary induction voltage, and a feedback unit  224  which transfers information related to the secondary induction voltage to the PWM generator  221 . 
   The PWM generator  221  compares the duty ratio of the generated PWM signal with the duty ratio of the reference signal generated from the reference signal generator  210 , and stops outputting the PWM signal when the duty ratio of the PWM signal is above the duty ratio of the reference signal, thereby preventing an excessive current from flowing to the switching unit  22 . 
     FIG. 3  shows a flow chart illustrating a method of generating a high-voltage regulation voltage, according to the present invention. 
   Referring to  FIG. 2 , first, a reference signal is set as a pulse signal with a desired duty ratio in operation  300 . The reference signal may have a desired duty ratio by which a maximum pulse width of the reference signal does not apply a load to the switching device, in consideration of a maximum current tolerance of the switching component constituting the switching unit  222  of  FIG. 2 , while maximally satisfying the regulation voltage specification of the display. Such a duty ratio of the reference signal will be determined by the designer of the circuit. 
   Then, a PWM signal to control regulation of the display is generated in operation  310 . The PWM signal is created using a feedback regulation output voltage and a square wave pulse for synchronizing a frequency of a regulation output voltage signal with a horizontal frequency of a display such as a CDT, to which a regulation voltage is supplied. 
   Thereafter, the PWM signal is compared to the reference signal in operation  320 . When the duty ratio of the PWM signal is above the duty ratio of the reference signal, the output of the PWM signal is interrupted in operation  330 . The output of PWM signal begins again when the next PWM signal period starts. 
   Then, a high-voltage signal switched according to the PWM output signal is generated in operation  340 . A primary induction voltage switched by the PWM output signal is first generated, and a secondary induction voltage having a desired divided value proportional to the primary induction voltage is generated as a high-voltage regulation voltage. The generated high-voltage regulation voltage is output to the display. Also, high-voltage regulation information related to the high-voltage regulation voltage is sent back to the PWM generator  221 , so that it can be provided when a new PWM signal is generated. 
   As described above, according to the present invention, an apparatus for generating a regulation voltage for a display can prevent a switching component from being damaged, stabilize a regulation voltage, and contribute to a reduction in the costs of the display, by restricting a duty ratio of a regulation control voltage in advance. 
   Although a few embodiments of the present invention have been shown and described, it would 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.