Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1998-04-16
2001-03-13
Ham, Seungsook (Department: 2878)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S411000
Reexamination Certificate
active
06201359
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a high-voltage generator which includes a high-voltage unit for generating an output DC high voltage, and a voltage generating unit for generating at least one further, lower DC high voltage, the voltage generating unit receiving a DC voltage from the high-voltage unit, and including an adjustment unit for adjusting the further DC high voltage in a voltage range between a lower and an upper limit voltage.
2. Description of the Related Art
A high-voltage generator of this kind is known from U.S. Pat. No. 4,788,591. Therein, an output DC high voltage for feeding the anode of a picture tube is generated by means of a diode split transformer. Via an adjustment unit with two potentiometers, two voltages are generated so as to focus the electrons in the picture tube. The potentiometers are used to adjust these voltages in a range between a lower and an upper limit voltage which generally amount to 20% and 29%, respectively, of the output DC voltage in the case of a picture tube. One of the series-connected potentiometers is connected to a connection point of the high-voltage unit which carries a DC voltage. The base of the second potentiometer is connected to a DC voltage potential of 210 V which generally serves as a reference potential in a picture tube.
The dimensions and cost of a voltage generating unit in which adjustable DC high voltages are generated, for example, for the focusing of electrons in a tube, notably a picture tube, are determined essentially by the required electric strength and by the power loss of the adjustment unit which includes two potentiometers in the known device. In the case of a picture tube in which the output DC high voltage amounts to, for example, 25 kV so that the lower and the upper limit voltage amount to approximately 5 kV and 7.25 kV, respectively, the adjustment unit must have a high electric strength. In the known device, in which two series-connected potentiometers are arranged between a high-voltage potential of the high-voltage unit and a low-voltage potential which acts as a reference potential, the potentiometers must have a high electric strength, leading to high power losses, high costs and large dimensions of the potentiometers.
SUMMARY OF THE INVENTION
Therefore, it is an object of the invention to improve a high-voltage generator of the kind set forth, notably to provide a high-voltage generator which is inexpensive, has small dimensions and a high efficiency.
On the basis of a high-voltage generator of the kind set forth, this object is achieved in that there are provided means for supplying the adjustment unit with a DC voltage of between 100% and 200% of the upper limit voltage at one connection point, and with a DC voltage of between 50% and 100% of the lower limit voltage at a further connection point, said supplying means including at least one connection to a DC voltage point of the high-voltage unit which carries a DC voltage of between 50% of the lower limit voltage and 200% of the upper limit voltage.
The invention is based on the recognition of the fact that the adjustment unit need not necessarily be connected to a connection point carrying a low-voltage potential (for example, ground) which serves as a reference potential. In comparison with the known device, the adjustment unit in the device according to the invention may have a significantly lower electric strength since a significantly smaller voltage difference exists across the adjustment unit. The high-voltage generating unit also has a low impedance, so that variations of the DC high voltages, caused by variations of current values, are as small as possible. When the DC high voltages are used to focus the electrons in a picture tube, extremely stable focusing will thus be achieved. The closer the DC voltage at one connection point is to 100% of the upper limit voltage and the closer the DC voltage at the other connection point is to 100% of the lower limit voltage, the lower the electric strength of the adjustment unit may be, and the more advantageous the invention will be.
In a further embodiment of the high-voltage generator according to the invention, the connection point is connected to a DC voltage point of the high-voltage unit which carries a DC voltage of between 100% and 200% of the upper limit voltage, the further connection point being connected to a further DC voltage point of the high-voltage unit which carries a DC voltage of between 50% and 100% of the lower limit voltage. Using simple means, it is thus achieved that a small voltage difference occurs across the adjustment unit. In conformity with the number of amplifier stages of the high-voltage unit, suitable DC voltage points of the high-voltage unit can be selected for connection of the adjustment unit.
The high-voltage generator, in an embodiment, includes a transformer with a first secondary winding for generating the input voltage of the high-voltage unit, the transformer having a second secondary winding with a downstream rectifier circuit, the output connections of the rectifier circuit being connected to a respective one of the connection points of the adjustment unit, one of the connection points of the adjustment unit being connected to a DC voltage point of the high-voltage unit which carries a DC voltage of between 50% and 100% of the lower limit voltage, or between 100% and 200% of the upper limit voltage. This embodiment is particularly attractive for use when the high-voltage unit is suitable for supplying a DC voltage which corresponds as accurately as possible to the upper or the lower limit voltage, but not a further DC voltage which corresponds to the other limit voltage. The latter is then generated by way of the secondary winding of the transformer, so that only the maximum required voltage difference exists across the adjustment unit.
An alternative embodiment is characterized in that the high-voltage generator includes a transformer having a first secondary winding for generating the input voltage of the high-voltage unit, that the transformer includes a second secondary winding, that downstream from a first connection point and a central connection point of the secondary winding, there is connected a first rectifier circuit having a first output connection connected to a first connection point of the adjustment unit, and a second output connection connected to a DC voltage point of the high-voltage unit which carries a DC voltage which lies within the adjusting range, and that downstream from a second connection point and the central connection point of the secondary winding, there is connected a second rectifier circuit having a first output connection connected to the second connection point of the adjustment unit, and a second output connection connected to the same DC voltage point of the high-voltage unit. This embodiment is particularly advantageous when the high-voltage unit is suitable to derive a DC voltage which lies within the adjusting range, but not suitable to derive DC voltages which are exactly equal to the lower or the upper limit voltage. In this embodiment, two voltage potentials are derived from the DC voltage which lies within the adjusting range and is derived from the high-voltage unit, said voltage potentials corresponding to the upper and the lower limit voltage, so that once more, only the maximum required voltage difference is present across the adjustment unit.
A further embodiment of the invention is characterized in that one of the connection points of the adjustment unit is connected to a DC voltage point of the high-voltage unit which carries a DC voltage of between 50% and 100% of the lower limit voltage, or between 100% and 200% of the upper limit voltage, and that the supplying means includes a voltage multiplier circuit, notably a high-voltage cascade multiplier circuit, for generating a DC voltage from the input voltage of the high-voltage unit in order to feed the adjustment unit at the other connection point. This solution is particularly appropriate in
Goodman Edward W.
Ham Seungsook
Lee Shun
U.S. Philips Corporation
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