Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
1999-10-28
2001-02-06
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
Reexamination Certificate
active
06185113
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to transformers, and more particularly to a winding structure for a transformer. The present invention is suitable, for example, for a transformer for use with self-excited (or self-oscillating) switching converters, such as a ringing chalk converter (RCC).
An RCC is known as a typical on/off switching regulator. The switching regulator is a circuit that efficiently regulates a power flow by controlling a time ratio between switching on and off in transistor(s). The on/off type means that a rectifier diode turns off while a switching transistor turns on in a switching regulator. The on/off type transistor stores energy in transformer's primary winding while the transistor turns on, and releases the stored energy to an output side (i.e., a load) via a rectifier diode from transformer's secondary winding while the transformer turns off. The on/off switching regulator is divided into two types; a separately excited type that is activated by an external oscillator, and a self-excited type that switches without an aid of an external oscillator. The latter type is generally referred to as an RCC.
The RCC needs to determine an oscillation frequency and time ratio in order to stabilize an output voltage, and therefore design a transformer considering various parameters including inductance values for primary and secondary windings. Experimentally speaking, an actual transformer that is designed in accordance with conventional theoretic equations would not completely conform to these equations. As a consequence, an attempt to obtain a desired output voltage using a transformer that is designed in accordance with the theoretic equations would cause a transistor to flow infinite collector current Ic over its rated road in a split second due to the excessive low oscillation frequency, possibly breaking down the transistor (while this phenomenon is known as “magnetic saturation”). The actually used transformer used to form an air gap having a gap length of a necessary distance in order to reduce the inductance down to a necessary value by lowering core's effective magnetic permeability. The air gap means core's gap formed at a center pole.
However, the air gap portion has no core connection, and thus causes a leakage magnetic field. The leakage magnetic field might generate, when crossing with a winding, heat in the winding. In particular, a winding having a high turn density (i.e., cohesive turning) has the increased number of turns that cross with the leakage magnetic field, and generates a large amount of heat. The heat increasing the temperature in the power source unit lowers components' reliability, and causing a problem, such as shortening a life of an electrolysis capacitor or another component. The winding generally uses an enamel line that has an upper limit on heatproof temperature, and heat that exceeds the upper limit would disadvantageously break the isolative coat and cause rare short.
SUMMARY OF THE INVENTION
Therefore, it is an exemplified general object of the present invention to provide a novel and useful transformer and switching regulator in which the above disadvantages are eliminated.
Another exemplified and more specific object of the present invention is to provide a transformer and switching regulator that improves reliability of a power-supply unit component and prevents winding's breakdown by preventing the temperature rise in the winding caused by the leakage magnetic field.
In order to achieve the above objects, a transformer of one aspect of the present invention comprises a core having an air gap, and a winding wound around the core, a turn density of the winding being made least on the air gap.
A core for use with a transformer of one aspect of the present invention comprises a first core member, and a second core member coupled to the first core member, an air gap formed between the first and second core member being offset from a center of the core.
A switching regulator of one aspect of the present invention comprises a switch, a transformer, connected to the switch, which comprises a core having an air gap, and a winding wound around the core, a turn density of the winding being made least on the air gap, and a rectifier connected to the transformer.
A transformer manufacturing method of one aspect of the present invention comprises the steps of forming a core having an air gap by connecting first and second core member to each other, connecting said core to a bobbin, and forming a winding on said bobbin so that a turn density becomes least on the air gap.
A transformer of the present invention has the least turn density on the air gap where the leakage magnetic field becomes the largest, and thus has the minimum calorific value resulted from the leakage magnetic field. The switching regulator having this transformer has the same effects. The manufacturing method of the transformer of one aspect of the present invention facilitates manufacturing of a transformer. The core of one aspect of the present invention facilitates manufacturing of a transformer by forming an air gap at the edge of the core.
Other objects and further features of the present invention will become readily apparent from the following description of the embodiments with reference to accompanying drawings.
REFERENCES:
patent: 4757433 (1988-07-01), Santelmann, Jr.
patent: 6043994 (2000-03-01), Keller
Muta Tokio
Sato Yuichi
Shimada Kazuo
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Riley Shawn
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