Electric lamp and discharge devices: systems – With cathode or cathode heater supply circuit – Pulsating or a.c. supply to the cathode or heater circuit
Reexamination Certificate
1999-03-19
2001-07-24
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
With cathode or cathode heater supply circuit
Pulsating or a.c. supply to the cathode or heater circuit
C315S291000, C363S021030, C363S098000, C219S716000
Reexamination Certificate
active
06265830
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to power supplies and, more particularly, to a power supply and method for controlling the filament voltage in a magnetron.
BACKGROUND OF THE INVENTION
In lamp heating and curing applications, a magnetron is used to provide microwave radiation to a lamp source, such as an electrodeless ultraviolet (UV) lamp used in the curing of adhesives, sealants or coatings in industrial applications. When the plasma of the lamp is sufficiently excited by the microwave radiation from the magnetron, the lamp illuminates to provide the necessary light wavelength and intensity for the particular heating or curing process.
Known magnetrons typically require one or more power supplies to be coupled to the magnetron for supplying the necessary anode DC current and filament voltage to the magnetron. The filament current of the magnet-on can be relatively high, such as 20 A or more depending on the operating specifications of the magnetron, so a filament transformer that supplies current to the filament is typically mounted at or near the magnetron to eliminate or at least reduce voltage drop in the interconnecting wires.
When the filament transformer is mounted remotely from the magnetron as may be required in certain applications, various approaches have been developed to compensate for the voltage drop in the interconnecting wires to provide the necessary filament voltage at the magnetron. In one approach, the output voltage of the filament transformer is increased at the terminals of the magnetron to compensate for the voltage drop in the interconnecting wires. The input voltage of the filament transformer is then trimmed by a series resistor or a tap associated with the filament transformer to provide the correct filament voltage for a given anode current or operating mode of the magnetron. Another approach is to phase control the voltage output of the filament transformer until the correct filament voltage is obtained.
However, in each of these known approaches, the filament transformer output voltage must be “calibrated” for each lamp heating or curing application to compensate for the voltage drop in the interconnecting wires. Moreover, these known approaches are not immune to variations in line input voltage to the filament transformer. That is, a proper setting or “calibration” of the filament transformer output voltage for one input line voltage will be adversely affected by a change in the input line voltage.
Thus, there is a need for a power supply that may be conveniently mounted remotely from a magnetron without requiring calibration for each lamp heating or curing application. There is also a need for a power supply in a lamp heating or curing system that is generally immune to voltage drops in the wires interconnecting the power supply to the magnetron. There is yet also a need for a lamp heating or curing system power supply that is generally immune to variations in the input line voltage to the power supply.
SUMMARY OF THE INVENTION
The present invention overcomes the foregoing and other shortcomings and drawbacks of power supplies and methods heretofore known for regulating the filament voltage in a magnetron. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
The power supply and method of the present invention are particularly adapted to supply a regulated filament current to a magnetron. When the magnetron is operating, the resistance of the magnetron filament is constant as the temperature of the filament is maintained constant according to the specifications of the magnetron supplier. By supplying the proper or regulated filament current to the magnetron for a given anode current or operating mode of the magnetron, the proper filament voltage is assured for that specific anode current or magnetron operating mode, regardless of variations in the resistance in the interconnecting wires or in the input voltages to the power supply.
The power supply includes a switching device adapted to be coupled to an AC voltage source and having a variable conduction angle. The switching device may be a triac, pair of silicon controlled rectifiers (SCRs) or equivalent device that has a variable conduction angle. A filament transformer has a primary that is adapted to be coupled to the AC voltage source through the switching device. The filament transformer has a secondary coupled to the magnetron filament for supplying filament current to the magnetron that is related to the conduction angle of the switching device.
A current sensor is coupled to the filament transformer primary for sensing current in the primary that is proportional to the filament current. A control is coupled to the filament transformer primary and responsive to the current sensor for selectively varying the conduction angle of the switching device to regulate the filament current supplied to the magnetron. By regulating the filament current, the proper filament voltage is assured regardless of variations in the resistance in the interconnecting wires or in the input voltages to the power supply.
In one embodiment of the present invention, the control includes a microcontroller coupled to the switching device and responsive to the current sensor for varying the conduction angle of the switching device coupled to the filament transformer. By varying the conduction angle of the switching device, the filament current supplied to the magnetron by the filament transformer is regulated to thereby provide the proper filament voltage.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.
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patent: 4620078 (1986-10-01), Smith
patent: 4700113 (1987-10-01), Stupp et al.
patent: 4900909 (1990-02-01), Suenage et al.
patent: 4928040 (1990-05-01), Uesaki
patent: 5082998 (1992-01-01), Yoshioka
patent: 5224027 (1993-06-01), Kyong-keun
patent: 5571439 (1996-11-01), Daley et al.
patent: 5642268 (1997-06-01), Pratt et al.
Loctite,Light Cure Technology, Brochure, undated.
Bretmersky Carl A.
Schmitkons James W.
Lee Wilson
Nordson Corporation
Wong Don
Wood Herron & Evans LLP
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