Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-04-27
2001-09-11
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S025000, C363S133000
Reexamination Certificate
active
06288913
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a power supply for providing high voltage power from a low voltage source. The present invention can be manufactured so as to have a thin profile (less than 0.25 inch in width) and therefore is particularly well-suited for use as a power supply for a flat screen CRT (cathode ray tube).
Although the general concept of providing power conversion is known, the recently developed technology of flat screen CRTs has presented a greater need for power conversion circuitry capable of providing high voltage power from a low voltage source (e.g., 8,000 volts from a 5 volt source). In order to maximize the compactness of such flat screen CRTs, it is important that their power supplies also be compact. Further, in the highly competitive market for consumer electronics, it is important that the power supply be constructed at the lowest cost possible and therefore in a manner which permits automated manufacturing.
As is generally known by those skilled in the art, zero voltage switching of switches in electrical circuitry has been used to reduce the losses associated with opening and closing the switches. Thus, the switches have been operated in such a manner as to improve the efficiency of the electrical circuitry which incorporates the switches.
To increase the output power of conventional power supplies, two or more converters, including two or more transformers, two or more constant current sources and associated circuitry for each transformer, can be connected together. Alternatively, a power supply with increased output power has been provided by incorporating a larger transformer design. Thus, an increase in output power necessitates a much larger power supply design because of the increased number of components and/or a large transformer. The cost of manufacture is therefore increased and possibility of automated construction becomes limited. Moreover, if two or more converters are connected together to obtain an increased maximum output power, the multiple converters will often detrimentally interact with one another so that one or more of the transformer cores saturates.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide a power supply device capable of providing high voltage power from a low voltage source.
Another object of the present invention is to provide such a power supply device using components which facilitate automated manufacturing of the power supply device.
Another object of the present invention is to provide a power supply device having a high power output which can be manufactured to provide a thin overall profile of no more than 0.25 inches in width.
Another object of the present invention is to provide a power supply device having a high output-to-input voltage ratio (e.g., at least 500 times), compact size, and a relatively steady output voltage which remains within a close range of (e.g., at least within 10% or less) a desired voltage level, even if the load on the power supply varies significantly.
Another object of the present invention is to provide a power supply device including a resonant oscillator which is capable of maintaining a cycle to cycle flux balance of the transformer of the resonant oscillator and thus a cycle to cycle energy balance of the transformer. Due to the maintenance of the energy balance of the resonant oscillator's capacitive and inductive elements, the present invention allows multiple transformers to be connected together to form the resonant oscillator to thereby increase the maximum output power capability of the power supply device relative to a resonant oscillator having only a single transformer. The maximum output power capability thus increases as the number of connected transformers increases.
Another object of the present invention is to operate multiple transformers of a resonant oscillator at the natural resonant frequency of the equivalent inductive and capacitive elements forming the individual transformers so that the transformer cores can be prevented from saturating. Any detrimental interaction between the transformers is thus eliminated. The power supply of the present invention is therefore capable of providing power conversion in a highly efficient manner.
Another object of the present invention is to provide a power supply device in which multiple transformers of a resonant oscillator are connected directly in parallel to increase the output power capability with a lower number of components than what is conventionally required. Accordingly, the costs for constructing the power supply is relatively low since the same transformer design is used in the power supply device and the construction can be implemented by an automated process.
A power supply device according to the present invention therefore includes a current regulator, a resonant oscillator and a zero voltage level detector. The current regulator is connectable to a low voltage source (e.g., a 5 volt battery) and is arranged to provide a constant amount of current regardless of the changing load that is imposed on it.
The resonant oscillator preferably includes a first transformer, with its associated distributed capacitance and inductance, switches coupled to the primary winding and a switch driver for opening and closing the switches. The resonant oscillator receives a signal from the current regulator and transfers energy in a resonant fashion at the natural resonant frequency of its capacitive and inductive elements. The transfer is provided from the source to the capacitive and inductive elements of the transformer and to the load connected to the power supply.
The zero voltage level detector detects when the voltage level of a signal output from the current regulator reaches a zero level. In response to such a detection, the zero voltage level detector outputs an enable signal which triggers the switch driver to open and close the switches of the resonant oscillator so that a cycle to cycle energy energy balancebalance of the transformer of the resonant oscillator is maintained. That is, the resonance of the resonant oscillator is maintained through the operation of the zero voltage level detector to achieve a cycle to cycle balance of energy between the magnetic and capacitive elements of the resonant oscillator.
According to a preferred exemplary embodiment, the switches of the resonant oscillator are connected to opposite ends of the primary winding of the resonant oscillator and the current regulator is connected to a center tap of the primary winding. The switch driver receives the enable signal from the zero voltage level detector when the voltage level of the signal output from the current regulator reaches a zero level and opens and closes the switches in a push-pull mode in response to receiving the enable signal.
According to a preferred exemplary embodiment, the resonant oscillator can further include a second transformer which is connected in parallel to the primary winding of the first transformer. Through these two transformers, the output power capability of the power supply device can be increased (at least double) relative to a power supply device having only a single transformer. The transformers can be operated in a resonant mode at the natural resonant frequency of the combined capacitive and inductive elements of the individual transformers so that the transformer cores can be prevented from saturating and thus achieve a high conversion efficiency. More than two transformers can be connected together to further increase the maximum output power capability of the power supply device.
Another object of the present invention is to provide a power supply device having a multiplier which is connected to a secondary winding of the transformer. The multiplier is arranged so as to provide an output signal which has a DC voltage level which is significantly higher than the source voltage level. Preferably, the multiplier includes an assembly of interconnected capacitors and diodes to provide voltage multiplication.
Preferab
Berhane Adolf Deneke
Pillsbury & Winthrop LLP
Rantec Power Systems Inc.
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