Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1999-08-26
2001-09-25
Anderson, Bruce (Department: 2881)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S414000, C313S415000, C313S409000
Reexamination Certificate
active
06294865
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a display device having a cathode ray tube comprising an in-line electron gun for generating three in-line electron beams in a neck of the cathode ray tube, the in-line electron gun comprising a main lens part having three apertures for passing the three electron beams, and a deflection unit, the display device having means to supply an anode voltage to an electrode of the main lens and having a cathodoluminescent phosphor screen provided on a viewing panel of the cathode ray tube.
Display devices of the type mentioned in the first paragraph are used, for instance, in computer monitors and television apparatuses.
Display devices of the type mentioned in the first paragraph are known and on the market.
In operation, such display devices consume power. The operating power adds to the total cost of an apparatus, but apart from the cost factor, the power consumption of in particular computer monitors is an issue of environmental concern. This has led, e.g., to the EPA “Energy Star” guidelines, which most likely will be gradually included in legislation as well. From June 1998 a new IEC standard 1000-3-2 will become effective which sets standard limits for harmonic currents injected into the public supply system for all applications having an active input power exceeding 75 Watt. Depending on the size, computer monitors have averagely an active input power of around 80-85 Watt. Therefore, it is important, from the point of view of environmental concern, to reduce the power consumption of such display devices.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a display device with a low power consumption, yet without substantially reducing the image quality, in particular the colour purity.
To this end, a display device in accordance with the invention is characterized in that, in operation, the anode voltage supplied to the electron gun lies in the range 16-22 kVolt and the product of the square root of the anode voltage (V
a
0.5
) and the electron beam pitch p in the main lens raised to the 3/2 power (p
3/2
), i.e. V
a
0.5
.p
3/2
, is greater than 50 kVolt
0.5
mm
3/2
.
The electron beam pitch is half the distance between the centres of the outer electron beams in the main lens of the gun. Conventional cathode ray tubes have an anode voltage of 25-30 kVolt. The power consumed by a display device having a cathode ray tube is reduced substantially by reducing the anode voltage. The energy dissipated in the deflection unit and the drive circuit for the deflection unit is roughly proportional to the anode voltage. Reducing the anode voltage reduces the energy consumption of the deflection unit, roughly in accordance with the anode voltage. Image quality is decreased, however, appreciably if the value of V
a
0.5
.p
3/2
is smaller than 50 kVolt
0.5
mm
3/2
. The influence of magnetic spot displacement due to the earth's magnetic field is roughly inversely proportional to V
a
0 5
.p
3/2
and at values below 50 kVolt
0.5
mm
3/2
the influence becomes appreciable, leading, in particular, to a reduction of the colour purity. The earth's magnetic field influences the paths of the electron beams such that the beams at least partly impinge on phosphors of the “wrong colour” thereby negatively influencing the colour rendition. This effect results in a loss of colour purity. Reduction of the anode voltage reduces the value for V
a
0 5
.p
3/2
and thus colour purity can be negatively influenced. In devices according to the invention this effect is, however, limited. In devices having a cathode ray tube having a black-matrix on the screen the influence could be reduced by increasing the dimensions of the black matrix. This, however, leads to a reduction of the luminance. The negative effects on colour purity are usually at an acceptable level for values higher than 50 kVolt
0.5
mm
3/2
. Preferably the value for V
a
0.5
.p
3/2
is somewhat larger, i.e. larger than 55 kVolt
0.5
mm
3/2
, because magnetic fields other than the earth's magnetic field may be present in and around the device. Preferably, the value of V
a
0.5
.p
3/2
is less than 80 kVolt
0.5
mm
3/2
. A further increase of the value has only a limited positive effect, but may result in an increase in the operating power. In embodiments of the present invention the cathode ray tube is provided with a black-matrix layer between the viewing panel and the phosphor screen, which black matrix has apertures for passing light generated by the phosphor screen, the apertures having a maximum dimension (e.g. width or length) below 125 micrometers in at least one direction. For such small apertures in the black matrix the limitation to the value of V
a
0.5
.p
3/2
is of particular importance. In embodiments of the invention the display device has means for applying oscillating currents having a frequency higher than 65 kHz to the deflection unit, the deflection unit having deflection coils comprising solid wires. At such high frequencies, Litz wire, i.e. a type of wire in which several small strands are used in one wire, was used. By virtue of the reduction of power dissipation in the deflection unit, the present invention has the advantage that solid wire, i.e. wire in which only a single conductive core is used, can be used at frequencies above 65 kHz, even above 70 kHz. Important costs savings are the result. In other embodiments, in which the aim is to further reduce power consumption, the deflection unit comprises coils wound from Litz wire.
REFERENCES:
patent: 3771002 (1973-11-01), Standaart
patent: 4528476 (1985-07-01), Alig
patent: 5909080 (1999-06-01), Uchida et al.
Anderson Bruce
U.S. Philips Corporation
Wells Nikita
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