Abstract:
A transformer that is capable of setting any characteristics of a detection voltage of a detection winding and accurately detecting an output voltage includes a bobbin, a magnetic core, a first input winding, an output winding, a second input winding, and a detection winding. The bobbin is tubular and includes a plurality of winding regions located at its outer portion. The magnetic core is inserted in the bobbin. The first input winding is wound in a first winding region. The output winding is wound in a second winding region adjacent to the first winding region. The second input winding is wound in a third winding region adjacent to the second winding region. The detection winding is wound in the vicinity of the first input winding. The first input winding and the second input winding have different numbers of turns and are connected in series in the same winding direction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a transformer including a detection winding arranged to detect an output voltage and to a transformer device including a transformer and a load circuit connected thereto. 
     2. Description of the Related Art 
     To apply a specific voltage to a load circuit connected downstream of a transformer, an output voltage of the transformer may be monitored to control the output voltage. One example of a monitoring method involves monitoring a detection voltage of a detection winding provided in the transformer in addition to input and output windings (see, for example, Japanese Examined Utility Model Registration Application Publication No. 6-9463). 
       FIGS. 1A and 1B  are an illustration for describing a first configuration example of a traditional transformer; wherein  FIG. 1A  illustrates a partial cross-sectional view, and  FIG. 1B  illustrates a circuit diagram. 
     The transformer is made up of a roll  200  and a not-illustrated magnetic core. The roll  200  is made up of a tubular bobbin  204  and windings  201  to  203 . The magnetic core is inserted in the tube of the bobbin  204 . The bobbin  204  has a plurality of collars formed on its outer surface. The windings  201  to  203  are wound in winding regions between the collars (hereinafter referred to as sections). Specifically, the input winding  201  and the detection winding  203  are wound in a section adjacent to a first end, and the output winding  202  is wound in the other sections. The detection winding  203  is wound in a section different from the sections for the output winding  202  in order to isolate itself from the output winding  202 . 
     In this transformer circuit configuration, the input winding  201  is connected between an input terminal  214  and a ground terminal  216 . The input terminal  214  is connected to an AC voltage source. The detection winding  203  is connected to a voltage detector through a detection terminal  217 . The output winding  202  is connected to a load circuit through an output terminal  215 . For this transformer, a detection voltage proportional to an output voltage is detected by the voltage detector. 
     For the transformer having the above configuration, an input winding may be disposed at each of two sides of an output winding and the input windings may be connected in parallel in order to acquire strong connection between the output and input windings. 
       FIGS. 2A and 2B  are illustrations for describing a second configuration example of a traditional transformer, wherein  FIG. 2A  illustrates a partial cross-sectional view, and  FIG. 2B  illustrates a circuit diagram. 
     The transformer is made up of a roll  300  and a not-illustrated magnetic core. The roll  300  is made up of a tubular bobbin  310  and windings  311  to  314 . The magnetic core is inserted in the tube of the bobbin  310 . The bobbin  310  has a plurality of collars formed on its outer surface. The windings  311  to  314  are wound in sections between the collars. The output winding  313  is wound in central sections, the first input winding  311  and the second input winding  312  are wound in sections adjacent to opposite ends, and the detection winding  314  is wound in the same section as that for the first input winding  311 . 
     In this transformer circuit configuration, the first input winding  311  and the second input winding  312  are connected in parallel between an input terminal  321  and a ground terminal  322 . The detection winding  314  is connected to a voltage detector through a detection terminal  323 . The output winding  313  is connected to a load circuit through an output terminal  324 . Also with this transformer, a voltage proportional to an output voltage according to the turns ratio between the output winding and the detection winding is detected by the voltage detector. 
     With the above transformer, for example, when the number of turns of the output winding is 1000, the number of turns of the detection winding is 10, and the output voltage is 1000 Vp-p, a detection voltage of 10 Vp-p is output to the detection winding. 
     For the above-described transformers, to acquire isolation, the output and input windings are spaced away from each other with the collar disposed between. Therefore, a leakage inductance between the both windings is large. Accordingly, if a capacitive load circuit that mainly has a capacitive component, such as a lamp or a photosensitive drum, is connected as the load circuit, the leakage inductance and the capacitive load circuit may be series resonant, depending on a condition, for example, such as a condition in which the frequency of an AC input voltage is close to a resonant frequency between the leakage inductance and the load capacity. If series resonance occurs, a leakage flux resulting from the leakage inductance increases. 
     A leakage flux is proportional to a series resonance current, and the series resonance current is proportional to a series resonance voltage occurring in a leakage inductance. The output voltage of the transformer increases by the amount corresponding to the series resonance voltage. Therefore, due to the series resonance, a resonance voltage proportional to the increase in the leakage flux occurs in the leakage inductance, and the output voltage of the transformer increases. 
     Due to series resonance, a detection voltage corresponding to a combined magnetic flux of a main magnetic flux and a leakage flux is output from a detection winding. FIGS.  3 A and  3 B are illustrations for describing a leakage flux occurring in a traditional transformer.  FIG. 3A  illustrates a transformer according to a first configuration example, and  FIG. 3B  illustrates a transformer according to a second configuration example. 
     For the transformer according to the first configuration example, a main magnetic flux  221  and a leakage flux  222  occur inside a magnetic core  220 . The leakage flux  222  links the main magnetic flux  221  in the opposite direction at a linkage surface  223  of the detection winding. Accordingly, the main magnetic flux  221  and the leakage flux  222  cancel each other. During series resonance, the leakage flux  222  increases largely, so the main magnetic flux  221  is largely cancelled by the amount corresponding to the increase in the leakage flux  222 , and the detection voltage reduces. Similarly, for the transformer according to the second configuration example, during series resonance, a main magnetic flux  321  is cancelled by the amount corresponding to an increase in a leakage flux  323  at a linkage surface  323 , and the detection voltage reduces. 
     As described above, when an output voltage and a detection voltage are changed by the effects of series resonance, the accuracy of detecting an output voltage using a detection winding deteriorates. 
       FIGS. 4A and 4B  are illustrations for describing changes in an output voltage and a detection voltage. 
     Here, results of experiments of applying an AC input voltage that has a constant magnitude with varying frequencies to a traditional transformer with an input winding-output winding-detection winding ratio of 1:180:1 and driving the transformer when a capacitive load circuit switches to 100 pF, 200 pF, or 300 pF are illustrated. 
       FIG. 4A  illustrates the transformer according to the first configuration example. The output voltage of this transformer tended to increase with an increase in frequency. In contrast, the detection voltage of this transformer tended to reduce or remain virtually unchanged with an increase in frequency. Therefore, a calculated ratio between the detection voltage and the output voltage changed with respect to a change in frequency in a non-linear fashion. 
       FIG. 4B  illustrates the transformer according to the second configuration example. In comparison with the transformer according to the first configuration example, the degree of each of the change in the output voltage and that in the detection voltage is smaller. However, similar to the transformer according to the first configuration example, the ratio between the detection voltage and the output voltage changed with respect to a change in frequency in a non-linear fashion. 
     As described above, for the traditional transformer, if the frequency varied, the accuracy of detecting the output voltage using the detection winding significantly deteriorated. This was more noticeable at larger capacitive values of the capacitive load circuit connected to the output winding. 
     SUMMARY OF THE INVENTION 
     Accordingly, preferred embodiments of the present invention provide a transformer and a transformer device that are capable of accurately detecting an output voltage. 
     A transformer according to a preferred embodiment tof the present invention includes a bobbin, a magnetic core, a first input winding, an output winding, a second input winding, and a detection winding. The bobbin is tubular and includes a plurality of winding regions located at its outer portion. The magnetic core is inserted in the bobbin. The first input winding is wound in a first winding region. The output winding is wound in a second winding region adjacent to the first winding region. The second input winding is wound in a third winding region adjacent to the second winding region. The detection winding is wound in the vicinity of the first input winding. The first input winding and the second input winding are connected in series in the same winding direction, and the number of turns of the first input winding is smaller than that of the second input winding. 
     With this configuration, a main magnetic flux, a first leakage flux resulting from a leakage inductance between the first input winding and the output winding, and a second leakage flux resulting from a leakage inductance between the second input winding and the output winding occur. 
     Because the first input winding and the second input winding are connected in series, substantially the same amount of current passes through both of the windings. However, the first input winding has a number of turns that is smaller than that of the second input winding, the AT (ampere-turn: the number of turns×current) of the first input winding is smaller than the AT of the second input winding, and the first leakage flux is smaller than the second leakage flux. 
     Magnetic lines of force of the first leakage flux that link the detection winding extend in the opposite direction to the main magnetic flux, whereas magnetic lines of force of the second leakage flux that link the detection winding extend in the same direction as the main magnetic flux. Thus, of a magnetic flux that links the detection winding, a component resulting from the first leakage flux is cancelled by that resulting from the second leakage flux, and the direction of the magnetic flux linking the detection winding is the same as the main magnetic flux. Accordingly, in accordance with the magnitude of the leakage flux, the detection voltage increases. Thus, even when the frequency varies and the output voltage changes, the detection voltage follows the leakage flux varying in proportion to the frequency and changes correspondingly, so the ratio between the output voltage and the detection voltage can be stabilized. 
     A transformer according to another preferred embodiment of the present invention includes a bobbin, a magnetic core, a first detection winding, an output winding, a second detection winding, and an input winding. The bobbin is tubular and includes a plurality of winding regions located at its outer portion. The magnetic core is inserted in a tube of the bobbin. The first detection winding is wound in a first winding region. The output winding is wound in a second winding region adjacent to the first winding region. The second detection winding is wound in a third winding region adjacent to the second winding region. The input winding is wound in the vicinity of the first detection winding. The first detection winding and the second detection winding are connected in series in the same winding direction, and the number of turns of the first detection winding is smaller than that of the second detection winding. 
     With this configuration, a leakage flux occurs resulting from a leakage inductance between the input winding and the output winding. Of this leakage flux, magnetic lines of force that link the first detection winding extend in the opposite direction to the magnetic flux, whereas magnetic lines of force that link the second detection winding extend in the same direction as the main magnetic flux. Thus, in accordance with the magnitude of the leakage flux, the magnetic flux linking the first detection winding reduces, and the magnetic flux linking the second detection winding increases. 
     Because the number of turns of the first detection winding is smaller than that of the second detection winding, the winding voltage occurring in the second detection winding is larger than that in the first detection winding. Therefore, the detection voltage, which is a combined voltage of respective winding voltages of the first and second detection windings connected in series, is largely affected by a winding voltage occurring in the second detection winding and easily increases in accordance with the magnitude of the leakage flux. Accordingly, even if the frequency varies and the output voltage changes, the detection voltage follows the leakage flux varying in proportion to the frequency and changes correspondingly, so the ratio between the output voltage and the detection voltage can be stabilized. 
     A transformer according to another preferred embodiment of the present invention has its input and output windings interchanged compared to the circuit configurations of the transformers according to the preferred embodiments described above. Because circuit configurations according to various preferred embodiments of the present invention have reversibility, even if the windings are interchanged in this way, similar advantages are obtainable. 
     A transformer device according to a preferred embodiment of the present invention may include any one of the above-described transformers, a capacitive load circuit connected to the output winding, an AC voltage source connected to the input winding, and a detector connected to the detection winding. 
     With a transformer and a transformer device according to any of the various preferred embodiments of the present invention, a detection voltage following a change in leakage flux is obtainable. Thus, the ratio between the output voltage and the detection voltage can be accurately stabilized and the output voltage can be detected. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are illustrations for describing a first configuration example of a traditional transformer. 
         FIGS. 2A and 2B  are illustrations for describing a second configuration example of a traditional transformer. 
         FIGS. 3A and 3B  are illustrations for describing a leakage flux of a traditional transformer. 
         FIGS. 4A and 4B  are illustrations for describing a relationship between an output voltage and a detection voltage of a traditional transformer. 
         FIGS. 5A and 5B  are illustrations for describing a configuration of a transformer according to a first preferred embodiment. 
         FIGS. 6A and 6B  are illustrations for describing a leakage flux of the transformer illustrated in  FIGS. 5A and 5B . 
         FIG. 7  is illustrations for describing a relationship between an output voltage and a detection voltage of the transformer illustrated in  FIGS. 5A and 5B . 
         FIGS. 8A and 8B  are illustrations for describing a configuration of a transformer according to a second preferred embodiment. 
         FIGS. 9A and 9B  are illustrations for describing a leakage flux of the transformer illustrated in  FIGS. 8A and 8B . 
         FIG. 10  is illustrations for describing a relationship between an output voltage and a detection voltage of the transformer illustrated in  FIGS. 8A and 8B . 
         FIGS. 11A and 11B  are illustrations for describing a circuit configuration in which the input and output windings of the transformer according to the first preferred embodiment are interchanged. 
         FIGS. 12A and 12B  are illustrations for describing a circuit configuration in which the input and output windings of the transformer according to the second preferred embodiment are interchanged. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A transformer according to a first preferred embodiment of the present invention is described below.  FIGS. 5A and 5B  are illustrations for describing the transformer according to this preferred embodiment of the present invention.  FIG. 5A  illustrates a partial cross-sectional view of the transformer, and  FIG. 5B  illustrates a circuit diagram of a transformer device that includes the transformer and a load circuit connected thereto. 
     The transformer preferably includes a roll  100  and a not-illustrated magnetic core. The roll  100  preferably includes a tubular bobbin  105  and windings  101  to  104 . The magnetic core is inserted in the tube of the bobbin  105 . The bobbin  105  includes a plurality of collars located on its outer surface. The sections between the collars are adjacent with the collars disposed therebetween, and the windings  101  to  104  are wound in the sections. Specifically, the input winding  101  and the detection winding  104  are wound in the section at a first end, the input winding  102  is wound in the section at a second end, and the output winding  103  is wound in the central sections. The detection winding  104  is disposed in the same section as that for the input winding  101  and lies in the vicinity of the input winding  101 . The detection winding  104  is wound outside of the input winding  101 . A configuration in which the detection winding is wound inside and the input winding is wound outside may be used. The detection winding  104  is wound in a section different from the sections for the output winding  103  in order to isolate itself from the output winding  103 . 
     The turns ratio between the input winding  101  and the input winding  102  can be determined depending on necessary frequency characteristics of the detection winding. Here, the turns ratio of the input winding  101  to the input winding  102  is set at 3 to 7, for example, so that the detection voltage of the detection winding  104  and the output voltage of the output winding  103  are constant independently of the frequency of the AC input voltage. 
     Next, a circuit configuration of a transformer device including that transformer and a load circuit connected thereto is described. A first end of the input winding  101  is connected to an input terminal  115 , and a second end thereof is connected to the input winding  102 . An end of the input winding  102  that is opposite to another end connected to the input winding  101  is connected to a ground through a ground terminal  118 . The input winding  101  and the output winding  102  are connected to each other such that their winding directions are the same. The input terminal  115  is connected to a not-illustrated AC voltage source. The detection winding  104  is connected to a voltage detector  119  through a detection terminal  114 . The output winding  103  is connected to a capacitive load circuit  117  through an output terminal  116 . 
     With that circuit configuration, due to the occurrence of series resonance, a first leakage flux from a first leakage inductance between the input winding  101  and the output winding  103  and a second leakage flux from a second leakage inductance between the input winding  102  and the output winding  103  increase. 
     Because the input winding  101  and the input winding  102  are connected in series, substantially the same amount of current passes through both of the windings, so the ratio of the AT (ampere-turn: the number of turns×current) of the input winding  101  to the AT of the input winding  102  is 3 to 7, which is the same as the turns ratio. Therefore, the leakage flux is separated such that the ratio between the first leakage flux occurring between the input winding  101  and the output winding  103  and the second leakage flux occurring between the input winding  102  and the output winding  103  is also approximately 3:7. 
       FIGS. 6A and 6B  are illustrations for describing a leakage flux of that transformer.  FIG. 6A  illustrates a simulation image of this transformer, and  FIG. 6B  illustrates directions of a magnetic flux in this simulation image. With this transformer, a main magnetic flux  111  and a leakage flux  112  occur inside a magnetic core  110 . The leakage flux  112  illustrated here is a combined magnetic flux of a first leakage flux and a second leakage flux. The direction of the combined magnetic flux that links the detection winding  104  is the same as that of the main magnetic flux. 
       FIG. 7  is illustrations for describing changes in an output voltage and in a detection voltage of the transformer according to the present preferred embodiment. 
     Here, results of experiments of applying an AC input voltage that has a constant magnitude with varying frequencies to a transformer with an input winding-output winding-detection winding ratio of 1:180:1 and driving the transformer when the capacitive load circuit switches to 100 pF, 200 pF, or 300 pF are illustrated. 
     The output voltage of that transformer tended to increase with an increase in frequency. The detection voltage also tended to increase with an increase in frequency. Therefore, it is revealed that, irrespective of differences in frequency or a capacitive load circuit, the ratio between the detection voltage and the output voltage is stable, and high detection accuracy can be maintained. 
     Here, an example in which the turns ratio between the first and second input windings is set such that the amount of change in the detection voltage is approximately equivalent to the amount of change in the output voltage has been illustrated. However, any amount of change in the detection voltage with respect to frequency change can be set in accordance with the turns ratio between the input windings, so the amount of change in the detection voltage can also be set larger or smaller than the amount of change in the output voltage. 
     Next, a transformer according to the second preferred embodiment is described.  FIGS. 8A and 8B  are illustrations for describing the transformer.  FIG. 8A  illustrates a partial cross-sectional view of the transformer, and  FIG. 8B  illustrates a circuit diagram of a transformer device that includes the transformer and a load circuit connected thereto. 
     The transformer is made up of a roll  150  and a not-illustrated magnetic core. The roll  150  preferably includes a tubular bobbin  155  and windings  151  to  154 . The magnetic core is inserted in the tube of the bobbin  155 . The bobbin  155  includes a plurality of collars located on its outer surface. The sections between the collars are adjacent with the collars disposed therebetween, and the windings  151  to  154  are wound in the sections. Specifically, the detection winding  152  is wound in the section at a first end, the input winding  151  and the detection winding  154  are wound in the section at a second end, and the output winding  153  is wound in the sections at the central sections. The input winding  151  is disposed in the same section as that for the detection winding  154  and lies in the vicinity of the detection winding  154 . The detection winding  154  is wound outside the input winding  151 . A configuration in which the detection winding is wound inside and the input winding is wound outside may be used. Each of the detection windings  154  and  152  is wound in a section different from the sections for the output winding  153  in order to isolate itself from the output winding  153 . 
     The turns ratio between the detection winding  154  and the detection winding  152  can be determined depending on necessary frequency characteristics of the detection windings. Here, the turns ratio of the detection winding  154  to the detection winding  152  is set at 3 to 7, for example, so that the detection voltage of the series circuit of the detection windings  152  and  154  and the output voltage of the output winding  153  are constant independent of the frequency of the AC input voltage. 
     The transformer according to the second preferred embodiment preferably has a configuration in which a leakage inductance between the input winding and the output winding is larger than that of the first preferred embodiment and series resonance with the capacitive load circuit can be used more easily. Therefore, this transformer may be preferably used in a load circuit that uses high voltage, such as an inverter for use in a liquid crystal display device. 
     Next, a circuit configuration of a transformer device including that transformer and a load circuit connected thereto is described. A first end of the input winding  151  is connected to an input terminal  165 , and a second thereof is connected to a ground through a ground terminal  168 . The input terminal  165  is connected to a not-illustrated AC voltage source. The detection windings  152  and  154  are connected in series, and their opposite ends are connected to a voltage detector  169  through a detection terminal  164 . The detection windings  152  and  154  are connected such that their winding directions are the same. The output winding  153  is connected to a capacitive load circuit  167  through an output terminal  166 . 
     With that circuit configuration, due to the occurrence of series resonance, a leakage flux from a leakage inductance between the input winding  151  and the output winding  153  increases. 
       FIGS. 9A and 9B  are illustrations for describing a leakage flux of that transformer.  FIG. 9A  illustrates a simulation image of the transformer, and  FIG. 9B  illustrates directions of a magnetic flux in this simulation image. With this transformer, a main magnetic flux  161  and leakage fluxes  162  and  163  occur inside a magnetic core  160 . 
     Of the leakage fluxes  162  and  163 , a component that links the detection winding  154  flows in the opposite direction to the main magnetic flux, whereas a component that links the detection winding  152  flows in the same direction as the main magnetic flux. Hence, due to the leakage fluxes, the detection voltage of the detection winding  152  is large, whereas in contrast the detection voltage of the detection winding  154  is small. If the turns ratio of the detection winding  152  to the detection winding  154  is increased, the detection voltage of the series circuit of the detection winding  154  and the detection winding  152  is increased. In contrast, if the turns ratio of the detection winding  152  is reduced, the detection voltage is reduced. Accordingly, due to the effects of the series resonance, with an increase in leakage flux, the detection voltage can be increased or reduced. 
       FIGS. 10A and 10B  are illustrations for describing changes in an output voltage and in a detection voltage of the transformer according to the present preferred embodiment. 
     Here, results of experiments of applying an AC input voltage that has a constant magnitude with varying frequencies to a transformer with an input winding-output winding-detection winding ratio of 1:180:1 and driving the transformer when the capacitive load circuit switches to 100 pF, 200 pF, or 300 pF are illustrated. 
     The output voltage of that transformer tended to increase with an increase in frequency. The detection voltage also tended to increase with an increase in frequency. Therefore, it is revealed that, irrespective of differences in frequency or a capacitive load circuit, the ratio between the detection voltage and the output voltage is stable, and high detection accuracy can be maintained. 
     Here, an example in which the turns ratio between the first and second detection windings is set such that the amount of change in the detection voltage is approximately equivalent to the amount of change in the output voltage has been illustrated. However, any amount of change in the detection voltage with respect to frequency change can be set in accordance with the turns ratio between the input windings, so the amount of change in the detection voltage can also be set larger or smaller than the amount of change in the output voltage. 
     As described above, with various preferred embodiments of the present invention, even if the input AC voltage varies and the output voltage changes, that output voltage can be accurately detected. 
     Even with a circuit configuration that uses an input winding as an output winding or uses an output winding as an input winding, both of the windings being illustrated above, preferred embodiments of the present invention can be suitably carried out. 
     Next, a circuit configuration example in which the input and output connections in the transformer according to each of the above-described preferred embodiments are interchanged such that the input winding is used as the output winding and the output winding is used as the input winding are described. 
       FIGS. 11A and 11B  are illustrates for describing a configuration example in which the input winding and the output winding in the transformer according to the first preferred embodiment are interchanged.  FIG. 11A  illustrates a partial cross-sectional view of the transformer, and  FIG. 11B  illustrates a circuit diagram of a transformer device that includes the transformer and a load circuit connected thereto. 
     The roll  100  of that transformer is preferably the same as the roll of the first preferred embodiment. The winding  101  wound together with the detection winding  104  in the section at the first end is used as not an input winding but an output winding. The winding  102  wound in the section at the second end is also used as not an input winding but an output winding. The winding  103  wound in the central sections is used as an output winding. A configuration in which the detection winding  104  is wound inside the winding  101  may be used. 
     The turns ratio between the winding  101  and the winding  102 , each of which is the output winding, can be set in accordance with necessary frequency characteristics of the detection winding. Here, the turns ratio of the winding  101  to the winding  102  is set at 3 to 7, for example, so that the detection voltage from the detection winding  104  and the output voltage from the windings  101  and  102  are constant independent of the frequency of the AC input voltage. 
     Next, a circuit configuration of a transformer device including that transformer and a load circuit connected thereto is described. A first end of the winding  103  is connected to a not-illustrated AC voltage source through the terminal  116 , and a second end thereof is connected to a ground. The winding  101  and the winding  102  are connected in series and connected to the capacitive load circuit  117  through the terminals  115  and  118 . The winding  101  and the winding  102  are connected such that their winding directions are the same. The detection winding  104  is connected to the voltage detector  119  through the detection terminal  114 . 
     With that circuit configuration, due to the occurrence of series resonance, a first leakage flux from a first leakage inductance between the winding  101  and the winding  103  and a second leakage flux from a second leakage inductance between the winding  102  and the winding  103  increase. 
     Because the winding  101  and the winding  102  are connected in series, substantially the same amount of current passes through both windings, so the ratio between the AT (ampere-turn: the number of turns×current) of the winding  101  and the AT of the winding  102  is 3:7, which is the same as the turns ratio. Therefore, the leakage flux is separated such that the ratio of the first leakage flux occurring between the winding  101  and the winding  103  to the second leakage flux occurring between the winding  102  and the winding  103  is also approximately 3 to 7. 
     Also with this transformer, irrespective of differences in frequency or a capacitive load circuit, the ratio between the detection voltage and the output voltage is stable, and high detection accuracy can be maintained. 
       FIGS. 12A and 12B  are illustrations for describing a configuration example in which the input winding and the output winding in the transformer according to the second preferred embodiment are interchanged.  FIG. 12A  illustrates a partial cross-sectional view of the transformer, and  FIG. 12B  illustrates a circuit diagram of a transformer device that includes the transformer and a load circuit connected thereto. 
     The roll  150  of that transformer is preferably the same as the roll of the second preferred embodiment. The winding  151  wound together with the detection winding  154  in the section at the first end is used as not an input winding but an output winding. The winding  153  wound in the central sections is used as not an input winding but an output winding. A configuration in which the detection winding  154  is wound inside the winding  151  may be used. 
     Next, a circuit configuration of a transformer device including that transformer and a load circuit connected thereto is described. A first end of the winding  153  is connected to a not-illustrated AC voltage source through the terminal  166 , and a second end thereof is connected to a ground. The winding  151  is connected to the capacitive load circuit  167  through the terminals  165  and  168 . 
     With this circuit configuration, due to the occurrence of series resonance, a leakage flux from a leakage inductance between the winding  151  and the winding  153  increases. Because of this, the detection voltage of the detection winding  152  is large, whereas, in contrast, the detection voltage of the detection winding  154  is small. If the turns ratio of the detection winding  152  to the detection winding  154  is increased, the detection voltage of the series circuit of the detection winding  154  and the detection winding  152  is increased. In contrast, if the turns ratio of the detection winding  152  is reduced, the detection voltage is reduced. Accordingly, with an increase in leakage flux due to the effects of the series resonance, the detection voltage can be increased or reduced. Thus, irrespective of differences in frequency or a capacitive load circuit, the ratio between the detection voltage and the output voltage is stable, and high detection accuracy can be maintained. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.