Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
  • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
  • H04N3/16—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by deflecting electron beam in cathode-ray tube, e.g. scanning corrections
  • H04N3/18—Generation of supply voltages, in combination with electron beam deflecting
  • H04N3/19—Arrangements or assemblies in supply circuits for the purpose of withstanding high voltages
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
  • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
  • H04N3/16—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by deflecting electron beam in cathode-ray tube, e.g. scanning corrections
  • H04N3/20—Prevention of damage to cathode-ray tubes in the event of failure of scanning

Definitions

• the present invention is related to a method and a device for preventing a high voltage circuit from generating excessive high voltage.
• CRTs emit visible light by striking phosphors on the faceplate with electrons and transferring the electron' s kinetic energy to light, heat, and other forms of energy, e.g., X-radiation.
• the frequency spectrum of photon emission is a property of the phosphor material .
• the probability of emission of a photon of X-ray frequency depends on the accelerating potential (anode voltage) and the number of electrons striking the phosphor in a unit of time (“anode current" or "beam current”) .
• the perceived light output is a function of the amount of beam current and high voltage power.
• the high voltage operating point must be lower than desired to ensure the protection circuit will always trip at acceptable levels, but will not activate in normal operation, or during transients, such as channel change.
• Each model of CRT has an individual maximum acceleration voltage and beam current that corresponds to a maximum allowable X-radiation emission.
• the anode current for "normal operation” is adjusted to always be below a maximum, worst case current, ensuring the legal regulation regarding the maximum allowable X-radiation emission is not violated. Since, at any possible operating point, and under any possible fault condition, no television or computer display instrument is allowed to emit X- radiation in excess of published limits, many television receivers and computer displays using CRTs contain "X-ray protection circuits", or XRPs .
• the curve (1) for maximum allowable acceleration voltage for a television receiver model is illustrated as a function of the beam current .
• the television receiver has a high voltage circuit tolerance of 2.5kV and an X-ray protection circuit tolerance of 2.3kV is illustrated.
• Curves 2, 3 and 4 show the nominal, upper and lower trip voltages of the XRP circuit, respectively, and curves 5, 6 and 7 show the nominal, upper and lower voltages of the high voltage transformer, respectively, resulting from the component tolerances.
• the nominal operating high voltage is set approximately 9.5kV below the maximum value.
• the tolerance in the high voltage circuit may be reduced by selection of precision components. High voltage tolerance may be nearly eliminated by measuring the high voltage and providing a feedback loop to regulate the high voltage.
• XRP X-ray photoelectron spectroscopy
• One type of XRP causes the television picture to become "not viewable" when a fault is detected.
• One method to achieve this is to force the horizontal scan frequency high, resulting in a picture that "rolls".
• the disadvantage of this method is that the television receiver continues to operate with the fault present .
• Another, more recent type of XRP interrupts the horizontal deflection.
• the High Voltage transformer is an integral part of the deflection yoke scan current
• turning off the horizontal deflection may result in ceasing generation of the high voltage, which is the accelerating potential for the electron beam, as mentioned above.
• the video and color processing, audio, sync separator, and timing signals for the horizontal and vertical deflection are commonly contained in an Integrated Circuit, or chipset.
• Such so-called “One-Chips” often have an "X-Ray Protection” pin, which, when activated, removes the drive to the horizontal deflection. While stopping the horizontal deflection has the advantage of removing the source of the electrical field that allows acceleration of the electron beam, it may be difficult to implement, in practice. Because of the interest in larger receivers and monitors, and more light output, the horizontal scan circuitry is required to operate under a wide range of load conditions. One way to drive the horizontal scan more efficiently is to provide feedback regarding the load to the horizontal drive section. This "proportional drive” concept increases the base drive to the horizontal output switch when the load current is increased. The horizontal scan circuit, however, is a resonant circuit, by nature, and may continue to try to oscillate, even at very low drive levels. If no distinct "X-Ray protection” that stops the horizontal deflection is incorporated, it may, in the event of a fault, be difficult to remove the horizontal drive completely.
• XRP circuits monitor an "image" of the anode voltage.
• an additional winding on the high voltage transformer generates this image, which follows, by virtue of magnetic coupling, the high voltage at the anode of the CRT at a fixed ratio determined by the number of windings.
• the additional or "X-Ray Protection” winding voltage may be rectified and compared to a reference to determine whether or not a fault has occurred. If the "XRP voltage" is below a reference level, the television instrument is assumed to be in normal operation.
• the X-ray protection circuit must cause the instrument to cease "normal operation".
• One method to compensate for XRP circuit tolerances mentioned above is to add a variable resistor, or potentiometer, to adjust either the reference voltage to the XRP circuit, or the "image voltage" generated in the additional winding.
• the scan supply may be increased until the target high voltage for XRP circuit activation is reached.
• the potentiometer is then adjusted until the XRP output changes its state, indicating a fault has occurred.
• using potentiometers may cause many problems. As a mechanical device, it is subject to contamination, vibration, thermal expansion and contraction, and aging. Often, to reduce the chance the alignment will be changed adhesives or protective cases are used.
• An "open loop" method of reducing the high voltage tolerance during production alignment is to adjust the feedback of the power supply, which energizes the primary winding of the high voltage, until the desired target value of high voltage is obtained.
• This alignment method may increase the tolerance in any other secondary supplies for other circuits.
• CTR display X-ray protection device and method which overcomes the problems of large tolerances, avoids the susceptibility to environmental influences and aging, allows for simple alignment and adjustment during manufacturing and ensures safe cut-off of high voltages generating X-radiation.
• a high voltage protection circuit comprising a high voltage generator; a memory containing a representation of a reference value; means for providing a sensed signal representing the output of the high voltage circuit; means for comparing the sensed signal with the reference signal to detect a fault situation, wherein the means for developing a signal representing the output high voltage is programmable.
• the invention suggests a method for shutting down a high voltage circuit supplying a display device comprising a cathode ray tube, a horizontal scanning apparatus, a high voltage generator and a power supply for the high voltage generator, wherein the method comprises the following steps : a) providing a fault indication signal, b) switching off the power supply of the high voltage generator and c) continuing to operate the horizontal scanning apparatus until an essentially complete de-energization of the high voltage generator.
• the inventive shut down method allows a controlled de- energization of the device.
• Fig.l shows the operating point tolerances of the high voltage generator and the X-ray protection circuit for an exemplary high voltage circuit built according the state of the art, along with the maximum allowable acceleration voltage for an exemplary model of CRT,
• Fig.2 shows a block diagram of a display incorporating a CRT and the high voltage circuit according to the invention
• Fig.3 shows a detailed view of a portion of the inventive circuit shown in Fig.2
• Fig. 2 shows in a simplified schematic diagram a TV receiver or a computer monitor having a CRT.
• a controller 1 is controlling a horizontal oscillator 2 for generating a drive signal for the horizontal scanning switch 3.
• Horizontal scanning switch 3 is connected to one end of a primary winding 4 of a high voltage transformer 6.
• the other end of the primary winding 4 is connected to a scan power supply 7.
• a high voltage is generated in the secondary winding 8 of high voltage transformer 6.
• the high voltage is connected to the cathode ray tube (CRT) 9 in order to supply an accelerating potential for the electron beam issued by the anode electrode of the CRT (not shown) .
• CTR cathode ray tube
• the electron beam passes through a magnetic field, generated by a yoke 11 and controlled by the horizontal switch 3, and is thereby deflected in a raster scanning way.
• Yoke 11 is connected to a retrace capacitor 12 at one end, and at the other end is connected to the horizontal scanning switch 3.
• a voltage detecting circuit 14 is connected to a tertiary winding 16 of the transformer 6 and a signal divider 17, which presents at its output a signal that is fed to one input of a signal comparator 18.
• a reference signal 19 is fed to a second input of comparator 18.
• the output signal of comparator 18 is input to a self-biasing latching switch 21.
• the high voltage transformer 6 generates at its tertiary winding 16 a high voltage proportional to the ratio of the secondary and tertiary winding. Therefore, by detecting the voltage across the tertiary winding 16, information about the high voltage at the secondary winding 8 is derived.
• the reference signal is compared to the signal representing the high voltage at the tertiary winding 16 of high voltage transformer 6. On exceeding the reference value, the signal comparator's output changes its state, thus actuating the self-biasing latching switch 21.
• the self-biasing latching switch 21 is in a first point connected to an on-off control line 22 to the power supply and immediately inhibits operation of the power supply by applying a latched signal to the control line accordingly.
• the horizontal oscillator 2 for generating a drive signal for the horizontal scanning switch 3 keeps actuating the switch 3 and thereby discharges the energy stored in the power supply 7 and the high voltage from the secondary winding 8 of transformer 6 and the associated components.
• a second connection 23 issues a latched signal to power fail detect circuit 24, signaling a fault condition.
• the controller 1 periodically polls the status of the power fail detect circuit via bus connection 26 and, on detecting a fault condition, after a determined time inhibits the operation of the horizontal scanning switch 3 by controlling the means 2 for generating a drive signal accordingly. In the sequence following to an XRP failure, controller 1 removes the power to the self-biasing latching switch, allowing the switch to reset, and resets all other components and power supplies for a restart.
• controller 1 may inhibit further operation of the display device.
• controller 1 resets the power supplies and other components in the circuit and causes the power on-off control line 22 to go low, thus removing the self- biasing current from the latching switch 21.
• the controller 1 manipulates the signal provided by the divider 17 to the comparator 18.
• the controller 1 reads via a bus line 27 control data associated with an operating mode from a memory 28.
• a memory 28 multiple instances of a set of reference values are stored in different locations, often referred to as pages, shown in the drawing as P1...P5 of memory 28.
• the pages may be located in different physical areas in the memory 28.
• the controller 1 transfers the control data via a bus line 29 to a digital-to-analog-converter 31.
• the analog output signal of the DAC 31 controls a current sink 32, which determines in cooperation with a loss element 33 the level of the input signal of the divider 17. In this way, different switching levels of the comparator are selectable even though the reference signal remains unchanged.
• Fig. 3 shows a part of a preferred embodiment of the inventive circuit from Fig. 2 in a zoomed view.
• comparator 18 issues a signal having a voltage sufficient to forward-bias the base-emitter diode of transistor 211 and establishing a conducting path from the collector electrode to the emitter electrode of transistor 211. Thereby, a current path is established allowing a control current to forward-bias transistor 212. This, in turn, establishes a current flow from the emitter electrode to the collector electrode of transistor 212, drawing a current from the on-off control line 22 from the power supply 7 and thereby inhibiting the power supply.
• Controller 1 cyclic polls the state of the power fail detect circuit 24, and after controlled de- energizing the high voltage from the secondary winding 8 of the high voltage transformer 6, inhibits the horizontal scanning switch 3 by accordingly controlling drive signal generator 2.
• the power on-off line 22 may be used to drive the voltage control signal 27, e.g., from DAC 28, low, as indicated by the dashed line in Figs. 2 and 3, thus disabling the power supply 7.
• a checksum algorithm is applied onto the data. In the case of an isolated, random failure, the checksum algorithm is guaranteed to always detect a minimum of one fault. Depending on the nature of multiple faults, the algorithm will detect multiple faults as well.
• the storage device may contain all zeros or all ones due to a fault for the entire storage device or due to failure to program the device initially.
• the checksum algorithm will always generate a checksum of a different value than each of the individual alignments. Therefore, a fault will be detected if all alignment locations contain the same value as the checksum. This characteristic of the alignment will guarantee that devices that were never programmed or devices that fail such that the same value (typically zero or one) is stored in every location will be detected and no X-Rays will be emitted. Additional measures are taken to ensure the integrity of the alignment values.
• the alignment locations once written, are read-only, preventing tampering with the locations.
• the alignment values are not stored in contiguous locations. This benefits error detection by ensuring that if the storage device fails for only a block of memory, that either the alignment data or the checksum integrity is maintained, and that the fault would appear to be a random, isolated one that is easily detected by the algorithm. Finally, knowledge of the range limits for the alignment data allows each individual alignment to be verified prior to use. Therefore, even if multiple faults have occurred in such a way that the calculated checksum equals the stored checksum, a fault will still be detected because the content of the individual alignment location is not valid.
• DAC-output value block is stored at five locations in the memory 28, using five different pages.
• a read access for a single block has to always be done twice and the value is only valid if both reads return the same values without error.
• a block has the following structure:
• the 6 bit value is stored four times in the block at different bit positions. Each time, the remaining two bits are filled with a parity bit. A block is defined corrupt if one or more parity bits are wrong or if the four decoded DAC values are not all identical.

Landscapes

• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Details Of Television Scanning (AREA)
• Protection Of Static Devices (AREA)
• Dc-Dc Converters (AREA)
• Emergency Protection Circuit Devices (AREA)
• Measurement Of Current Or Voltage (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (3)

Family

ID=28685899

Family Applications (1)

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• 2002
  • 2002-04-24 EP EP02009136A patent/EP1357738A1/en not_active Withdrawn
• 2003
  • 2003-03-31 KR KR10-2003-0020091A patent/KR20030084595A/ko not_active Withdrawn
  • 2003-04-12 AU AU2003222810A patent/AU2003222810A1/en not_active Abandoned
  • 2003-04-12 WO PCT/EP2003/003821 patent/WO2003092024A2/en not_active Ceased
  • 2003-04-12 CN CNA03809276XA patent/CN1650612A/zh active Pending
  • 2003-04-21 MX MXPA03003441A patent/MXPA03003441A/es active IP Right Grant
  • 2003-04-23 US US10/421,505 patent/US7239493B2/en not_active Expired - Fee Related
  • 2003-04-24 CN CNB031232566A patent/CN1284352C/zh not_active Expired - Fee Related
  • 2003-04-24 JP JP2003119623A patent/JP2004007615A/ja not_active Withdrawn

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