Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
1999-11-16
2002-02-05
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021010
Reexamination Certificate
active
06344983
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to transformers for increasing a voltage output. In particular, the invention is related to a circuit for regulating the output of a flyback transformer.
Generally, a transformer includes at least a pair of spaced-apart, turned coils of conducting wire. The coils are spaced so that the magnetic flux generated by the inductance of one coil may be coupled with the other coil. This mutual inductance transfers energy between the input, or “primary” coil and the coupled, or “secondary” coil. Multiple primary and secondary stages having differing coil windings may be linked to generate voltages or currents of differing magnitude, impedance levels or phase angles.
Flyback transformers are typically used in consumer electronics, radio transmission and automotive applications to develop increased voltages based on lower primary voltages fed to the primary coil. In automotive applications, in particular, a regulated voltage of approximately 5 volts DC is required to be produced from a variable input voltage.
In some transformer applications, the input voltage on the primary coil will vary and therefore tend to produce subsequent variations in the output voltage. This situation arises, for example, in automotive applications where power supplied by an exposed wet-cell battery may fluctuate depending on temperature, load and the age of the battery. In these situations, there are various circuits that may be utilized to regulate the output voltage of the transformer by controlling input into the primary. One example of such a regulator circuit is a pulse-width modulation circuit, wherein power to the primary may be switched on and off or otherwise modified according to a feedback signal taken from the primary or the secondary side of the transformer circuit, the battery voltage or the output current. This type of circuit requires generally continuous sensing of output voltage and current in order to be effective, and involves various sensing circuits which make the overall circuitry more complex. Other methods of controlling the secondary side output have included sensing the current in the primary and having a constant, regulated off time in the circuit to control output, or, in the alternative, a voltage sensing circuit in which a control loop (like that used in a pulse-width modulation circuit) is used to stabilize the output voltage based on the input voltage to the transformer.
SUMMARY OF THE INVENTION
According to the present invention, the circuit provided can control a flyback transformer power supply without utilizing complicated circuits, components or periodic sensing techniques. The circuit can control the transformer by removing the battery from the primary winding and thus preventing the generation of excessively high voltages in the secondary stage.
In one aspect of the present invention, a regulation circuit for a transformer is provided. The circuit includes at least a primary stage in association with a primary coil of a transformer and a secondary stage in association with a secondary coil of the transformer. Switching means is circuited to control the primary stage and a comparing means is provided in communication with the switching means. The comparing means compares voltage in the secondary stage with at least one voltage within the primary stage. The comparing means operates to open and close the switching means in accordance with these voltages to maintain a desired output voltage.
In another aspect of the invention, a regulating circuit for a flyback transformer is provided. The circuit includes at least a primary stage and a secondary stage. Switching means are provided within the primary stage to control power supplied to the primary stage as an input voltage. Primary voltage detection means are also provided to detect a voltage of the primary stage of the transformer, and secondary voltage detection means are also provided in communication with the secondary stage for detecting an output voltage at the secondary stage of the transformer. Primary current detection means are also provided to detect current in the primary. The circuit also includes comparing means in communication with the switching means. The comparing means compares the values read by the primary and secondary detection means, and operates to open the switching means when the voltage of the primary stage exceeds the input voltage or the primary current detected exceeds a desired value.
The invention may also be embodied in a method of regulating a transformer having at least a primary stage circuit and a secondary stage circuit. The method includes the steps of determining a voltage at the primary stage circuit, determining a voltage at the input of the primary stage circuit, and comparing the voltages in a comparing means. The primary stage circuit may be opened to stop current flowing through the circuit when the voltage of the primary stage circuit exceeds the input voltage. Furthermore, the primary stage circuit is also opened if the current detected in the primary exceeds a desired value, or if the voltage in the secondary exceeds a desired value.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. The invention, together with further objects and attendant advantages, will best be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings.
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Anolick Simon B.
Labudda Kenneth D.
May Steven A.
Motorola Inc.
Nguyen Matthew
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