Electric lamp and discharge devices: systems – Cathode ray tube circuits – Power supply from deflection circuit source
Reexamination Certificate
1999-04-14
2001-09-11
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Power supply from deflection circuit source
C315S399000
Reexamination Certificate
active
06288504
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply for applying a high voltage and a deflection current to a cathode ray tube (CRT), etc.
2. Description of the Related Art
A high-voltage generation circuit using a flyback transformer has been employed in a power supply for a CRT. The high-voltage generation circuit using the flyback transformer supplies the anode voltage to an anode of the CRT and a deflection current to a deflection yoke of the CRT. A power supply enabling these two roles by a single flyback transformer is referred to as a deflection current/high voltage integration type power supply.
Conventionally, CRT displays for computers are required to display a highly precise image. Therefore, a deflection current/high voltage separation type power supply including a circuit part for generating a deflection current and a circuit part for generating a high voltage separately has been generally used. However, there arises a demand for a deflection current/high voltage integration type power supply for CRT displays for computers because of cost reduction and miniaturization requirements.
Such a deflection current/high voltage integration type power supply device controls the high voltage by feedback. However, the deflection current is affected and fluctuates due to the control for stabilization of the high voltage when the high voltage load changes. In general, the horizontal amplitude of the screen is proportional to I
DY
/(V
II
), where I
DY
is the deflection current and V
II
is the high voltage (anode voltage) to be output from the flyback transformer. Thus, the amplitude of the screen fluctuates according to the change in brightness of the screen.
To solve this problem, a power supply of a so-called diode modulator circuit system has been proposed. In this power supply, the high voltage is stabilized by controlling the primary input voltage (+B) of the flyback transformer and the deflection current is controlled by the bias to a transistor provided in a flow path of the deflection current.
However, in the power supply device of the diode modulator circuit system, there is a problem that a switch element for controlling the voltage +B mentioned above and an element for controlling the deflection current are also required in addition to a main switch element to connect/disconnect the primary current in the flyback transformer, and the number of total elements becomes large, and the circuit becomes complex. Further, there is a problem in that the responsiveness in stabilization of the high output voltage and stabilization of the deflection current deteriorate because smoothing circuits are interposed at the +B control part and the deflection current control part.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a deflection current/high voltage integration type power supply capable of stabilizing the high voltage and stabilizing the deflection current with excellent response without increasing the number of switch elements.
The deflection current/high voltage integration type power supply according to the invention comprises a flyback transformer having a primary winding and a secondary winding; a series circuit comprising a deflection coil and a first capacitor, connected in series to the primary winding of the flyback transformer; a resonance capacitor connected in parallel to the series circuit of the deflection coil and the first capacitor; a first switching element, connected in parallel with the series circuit of the deflection coil and the first capacitor, to be turned on/turned off by a drive signal or a signal synchronous to said drive signal so that a high voltage is generated at the secondary winding of the flyback transformer and a deflection current flows in the deflection coil; a parallel connection circuit comprising a second switching element and a second capacitor, connected in series to the primary winding of the flyback transformer; and a switching control means to control a deflection current flowing in the deflection coil and a high voltage generated at the secondary winding of the flyback transformer by controlling the on-timing and the off-timing of the second switching element in approximate synchronism with the drive signal.
According to the present invention, both the deflection current and the high voltage at the secondary winding of the flyback transformer can be independently controlled by the on-timing/off-timing of the second switching element to control the primary input voltage (+B) of the flyback transformer, and the number of elements is not increased, or the responsiveness in controlling the high output voltage and the deflection current is not degraded because no smoothing circuit is connected to the +B control part or the deflection current control part.
Thus, both the deflection current and the high voltage can be simultaneously stabilized by respectively detecting the deflection current and the high output voltage to control the on-timing and the off-timing of the second switching element in the stabilizing direction.
The switching loss can be reduced by providing the second switching element as a MOS-FET, and providing the second capacitor as a separate component is unnecessary or its capacity can be reduced because the parasitic capacity of the MOS-FET can be utilized.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.
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Patent Abstracts of Japan—Appln. No. 03245004 dated Aug. 30, 1991 “Horizontal Deflecting High Voltage Generation Circuit”.
Patent Abstracts of Japan—Appln. No. 06086045 dated Mar. 31, 1994 “Horizontal Deflection High Voltage Generation Circuit”.
Imamura Nobuaki
Takahashi Haruo
Dinh Trinh Do
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Wong Don
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