JP2011176981A - Inverter circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter circuit reducing effects due to the fluctuation of a load and the characteristic dispersion of components containing a wound type transformer and improving the conversion efficiency of a power. <P>SOLUTION: The inverter circuit lights a discharge tube by converting a DC power supplied from a DC power supply into an AC power and supplying the discharge tube with the AC power. The inverter circuit includes a winding type transformer with a primary side coil and a secondary side coil, and a capacitor adding a capacitance component for reducing the effects of stray capacitances generated on the discharge tube, a load wire, or a pattern on a printed board while being mounted in parallel with the discharge tube or the discharging tube and a tube-current detector. The inverter circuit further includes a switching element which is switched at an oscillation frequency minimizing the absolute value of a phase difference between a voltage generated in the secondary side coil and a current flowing through the secondary side coil. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an inverter circuit that supplies electric power obtained by converting direct current to alternating current to a load via a transformer.

  When performing electrical insulation, voltage step-up, and step-down, a method of driving the winding transformer by an inverter circuit and obtaining the output is useful. When downsizing equipment, a method of driving at a high frequency is used to obtain a conventional output from a small winding transformer.

  For example, as a means for visually transmitting information, a method using a liquid crystal panel is useful from the viewpoints of low cost, clearness, and space saving. In a medium-sized or larger liquid crystal panel, a cold cathode tube is exclusively used as a backlight light source, and it is turned on by an inverter circuit for the cold cathode tube (see, for example, Patent Document 1).

  In order to increase the infinite rotation of joints that involve power transmission, ease of installation and removal, waterproofing, and dustproofness, a system that mechanically contactlessly transmits power and signals by inductive coupling is useful. There is a non-contact power transmission device that performs non-contact power feeding (see, for example, Patent Document 2).

JP 2007-265897 A JP 2009-189197 A

  In the conventional inverter circuit for lighting a discharge tube, a collector resonance type Royer circuit that can reduce the number of components has been widely used.However, due to self-excited oscillation, the oscillation frequency varies due to variations in the characteristics of the components. It was difficult to operate in the vicinity of the set optimum operating frequency. The main part of the wire-wound transformer is a mechanical part rather than an electronic part, and its characteristics vary greatly at the manufacturing stage. Therefore, it is difficult to match the oscillation frequency by self-excited oscillation with the optimum operating frequency in the actual circuit.

  In addition, as a method of non-contact power transmission, a non-contact winding type transformer has been used, but the characteristics as a winding type transformer are large due to the gap length between two pot cores constituting the non-contact winding type transformer. Because of the change, it was difficult to efficiently transmit power.

  The present invention has been made in order to solve the above-described problems, and is an inverter circuit in which the power conversion efficiency is improved by reducing the influence due to the fluctuation of the load and the characteristic variation of the components including the winding type transformer. The purpose is to obtain.

  An inverter circuit according to the present invention includes a primary side coil and a secondary side coil in an inverter circuit that turns on the discharge tube by converting DC power supplied from a DC power source into AC power and then supplying the AC power to the discharge tube. A winding-type transformer, a capacitance component added to reduce the influence of stray capacitance generated on the discharge tube, the load wire or the pattern on the printed circuit board, and the discharge tube, or the discharge tube and the tube current detection circuit, A capacitor provided in parallel; and a switching element that is switched at an oscillation frequency such that an absolute value of a phase difference between a voltage generated in the secondary coil and a current flowing in the secondary coil is minimized. Prepare.

  In another inverter circuit according to the present invention, a primary side coil and a secondary side coil are provided in an inverter circuit that converts a DC power supplied from a DC power source into an AC power and then supplies it to a movable load in a contactless manner. A non-contact winding transformer having a capacitor, a capacitor added in order to suppress a voltage drop due to a leakage inductance generated in the non-contact winding transformer, and a capacitor provided in series or in parallel with the secondary coil; A switching element that is switched at an oscillation frequency such that the absolute value of the phase difference between the voltage generated in the secondary coil and the current flowing in the secondary coil is minimized.

  In the inverter circuit according to the present invention, even if the same winding type transformer is used, the output impedance of the winding type transformer can be made smaller than that of the conventional inverter circuit. Can be miniaturized. Furthermore, since the loss in the primary side coil and the secondary side coil can be suppressed, the heat generation of the wire-wound transformer is suppressed, and it is small and efficient, and further has versatility with respect to the discharge tube.

The non-contact power transmission apparatus of the present invention includes a non-contact winding transformer having a primary side coil and a secondary side coil, and a secondary side coil for suppressing a voltage drop due to leakage inductance generated in the non-contact winding transformer. Since a capacitor provided in series or in parallel and an oscillator that determines the oscillation frequency of the primary side so that the absolute value of the phase difference between the secondary side voltage and the secondary side current is minimized, the same is provided. Even if a non-contact winding type transformer is used, the output impedance of the winding type transformer can be made smaller than that of a conventional inverter circuit, so that a larger amount of power can be taken out and the winding type transformer can be miniaturized with the same power capacity.
In addition, the gap length between the two pot-type cores does not cause a reduction in power transmission efficiency, and the voltage drop due to the leakage inductance of the secondary coil can be suppressed, so that the loss can be suppressed. Transformer heat generation is suppressed, and it is small and efficient.

It is a block diagram showing the structure of the cold cathode tube lighting circuit which concerns on Embodiment 1 of this invention. It is a secondary side voltage waveform and a secondary side current waveform. It is a figure which shows the mode of the damped oscillation wave contained in a primary side voltage waveform. It is a mode of the primary side voltage waveform at the time of setting an oscillation frequency so that switching may be performed in the valley of a damped oscillation wave. It is a block diagram showing the structure of the non-contact electric power transmission apparatus which concerns on Embodiment 2 of this invention. It is a disassembled perspective view which shows the structure of a non-contact winding type | mold transformer. It is a block diagram showing the structure of the other non-contact electric power transmission apparatus which concerns on Embodiment 2 of this invention.

Hereinafter, preferred embodiments of an inverter circuit of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing the configuration of a cold cathode tube lighting circuit according to Embodiment 1 of the present invention.
The cold cathode tube lighting circuit according to Embodiment 1 of the present invention is a circuit for lighting a cold cathode tube 16 as a discharge tube, as shown in FIG. An inverter circuit 100 that converts DC power into AC power, a tube current detection circuit 17 that detects a tube current flowing through the cold cathode tube 16, and a tube voltage detection circuit that detects a tube voltage applied to both ends of the cold cathode tube 16. 15.

  The inverter circuit 100 includes a switching element 5 that is interrupted for dimming the direct current input from the DC power source 1, and switching elements 7, 8 that are interrupted to convert the direct current flowing through the switching element 5 into alternating current. 9, 10, winding transformer 11 to which AC power converted by switching elements 7, 8, 9, 10 is input, capacitor 14 interposed between winding transformer 11 and cold cathode tube 16, switching A gate driver 6 that controls the gates of the elements 7, 8, 9, and 10; a phase comparator 4 that outputs a phase difference between the tube current from the tube current detection circuit 17 and the tube voltage from the tube voltage detection circuit 15; 4 includes an oscillator 3 that oscillates a signal whose oscillation frequency is controlled so that the phase difference from 4 is minimized, and a dimming circuit 2 that intermittently switches the switching element 5.

The basic operation of the inverter circuit 100 of the present invention is that the DC power source 1 is set so that the effective value of the tube current detected by the tube current detection circuit 17 also serving as the secondary current waveform detection function is equal to a preset value. To control the voltage. In addition, like patent document 1 mentioned above, you may use the switching element 5 for light control functions, and an equivalent effect can be acquired.
In addition, a function may be provided that stops output or suppresses output power when the peak value of the tube voltage detected by the tube voltage detection circuit 15 also serving as a secondary voltage waveform detection function exceeds a preset value. good.

The phase difference between the tube voltage detected by the tube voltage detection circuit 15 and the tube current detected by the tube current detection circuit 17 is compared by the phase comparator 4, and the oscillation frequency at which the absolute value of this phase difference is minimized. The oscillator 3 oscillates the above signal. When a signal having such an oscillation frequency is input to the gate driver 6, an induction component due to leakage inductance of the secondary coil 13, a capacitance component due to the capacitor 14, a cold cathode tube 16, a load wire (not shown), and a printed circuit board The capacitance components due to the stray capacitance generated on the secondary side including the above pattern cancel each other, and the voltage drop due to the inductive component of the leakage inductance of the secondary side coil 13 is kept to a minimum. Accordingly, since the impedance of the secondary coil 13 is lowered, the output impedance of the winding transformer 11 can be reduced. That is, a larger amount of power can be extracted from the wound transformer 11.
The phase comparator 4 may be a PLL (Phased Locked Loop) for several tens of kHz, or an equivalent function can be realized by using a microcomputer or the like. As for the phase difference between the tube current and the tube voltage, as shown in FIG. 2, the phase difference between the AC waveforms is shown.

  The signal oscillated by the oscillator 3 is subjected to current amplification, voltage shift, or dead time generation processing by the gate driver 6, and then the gates of the switching elements 7, 8, 9, 10 constituting the inverter circuit 100 are processed. Be controlled. The dead time here refers to the switching of each on / off control so that an overcurrent due to a short-circuit current does not flow when the switching element 7 and the switching element 8 or the switching element 9 and the switching element 10 are simultaneously turned on. This refers to a period during which all the switching elements 7, 8, 9, 10 are off. In addition, the method described in Unexamined-Japanese-Patent No. 2008-289249 can also be used for control of the switching element by the gate driver 6.

  In the switching elements 7, 8, 9, and 10, the switching element 7 and the switching element 10 are simultaneously turned on, the switching element 8 and the switching element 9 are simultaneously turned on, and these are turned on in conflict with the above-described dead time. Turned off. In addition, although the full bridge type inverter was described as an example in FIG. 1, even if it is a half bridge type or a push pull type (center tap type), an equivalent effect is obtained.

  The primary side coil 12 of the wound transformer 11 is bi-directionally excited by an inverter constituted by the switching elements 7, 8, 9, and 10 to obtain a secondary side voltage and a secondary side current in the secondary side coil 13.

The secondary coil 13 is controlled so that the phase difference between the secondary voltage and the secondary current is minimized. Here, the oscillation frequency f when the phase difference between the secondary side voltage and the secondary side current is minimized is the leakage inductance L ₁ of the secondary side coil 13, the capacitance C _C due to the capacitor 14, the cold cathode tube 16, the load. wire, a pattern on the printed circuit board using a total sum C _S of the stray capacitance that occurs in early secondary from equation (1).

Usually, the cold cathode tubes 16, the sum C _S of stray capacitance load wires, resulting in the pattern on the printed board initially secondary side is about 20 pF. The drive frequency recommended by the manufacturer of the cold cathode tube 16 is 40 k to 70 kHz as an example.
Here, the case without the capacitor 14 provided with a capacitance component, values required in the leakage inductance _{L 1} of the secondary coil 13 is 792MH, a large value 258mH even in a 70kHz when the oscillation frequency 40kHz .
If in order to obtain this value as a leakage inductance L ₁ can lead to increased number of turns of the secondary coil 13, requiring physically large wound-11.
Further, even if an extremely thin enamel wire is used for the secondary coil 13, copper loss increases, so it is difficult to use a small winding transformer thermally. Further, as an adverse effect of using an extremely thin enameled wire, an increase in the defect rate due to the breaking of the enameled wire can be mentioned.

For the purpose of providing the inverter circuit 100 with versatility, by providing a capacitor 14 that can add a capacitance component several times larger than the stray capacitance, strays generated in structural components around the cold cathode tube 16 or load electric wires are provided. Capacitance variation can be reduced when viewed from the inverter circuit 100.
As an example, if the electrostatic capacity is provided a capacitor 14 of 50 pF, the value required for the leakage inductance _{L 1} of the secondary coil 13, 226MH when the oscillation frequency 40 kHz, and 74mH when the 70 kHz, the practical It can be a close value.

In general, in many cold cathode tube lighting circuits, the primary and secondary are not insulated, and the secondary side voltage and secondary side current can be easily fed back to the primary side.
Even in a cold-cathode tube lighting circuit in which the primary and secondary are insulated, it is common to feed back the secondary current to the primary for the purpose of keeping the tube current constant.

A winding transformer used for a general switching power supply has a high coupling coefficient (close to 1) and a small leakage inductance, so the phase difference between the primary side voltage and the secondary side voltage is almost equal, and the waveform is also primary and secondary. It has the same shape with a peak value corresponding to the winding ratio. Therefore, the primary side voltage can be used as an alternative to the secondary side voltage.
However, the winding transformer 11 used in the cold cathode tube lighting circuit has a very large winding ratio between the primary side coil 12 and the secondary side coil 13, and the leakage inductance of the secondary side coil 13 is also large. The phase and shape of the voltage and the secondary voltage are different.
However, since the phase difference between the primary side voltage and the secondary side voltage has a fixed relationship with respect to the oscillation frequency, the oscillation frequency is controlled so that the primary side voltage and the secondary side current maintain a constant phase difference. By doing so, the phase difference between the secondary voltage and the secondary current can be indirectly minimized.

In some cold-cathode tube lighting circuits, the secondary current (tube current) is open-loop controlled, but such a cold-cathode tube lighting circuit outputs an output due to the leakage inductance of the secondary coil 13 at the oscillation frequency. The output power is only limited by the impedance and the impedance of the cold cathode tube itself as a load, and the wound transformer 11 always operates at the maximum output.
In such a cold cathode tube lighting circuit using the winding transformer 11, the output current naturally varies depending on the characteristic variation of the winding transformer 11 and the state of the load, and the variation range is wide.
Further, the cold cathode fluorescent lamp has a reduced amount of effective mercury inside due to deterioration over time, and the impedance increases, so that the output current decreases with time.

Moreover, even if the same tube current is applied due to a decrease in the amount of effective mercury, the emission luminance is reduced. Therefore, in the cold cathode tube lighting circuit operating in an open loop, the reduction in luminance is promoted by the above two synergistic effects. Is done. Therefore, the lifetime as a liquid crystal panel product is also short.
The structure of the components around the cold cathode tube, especially the product casing and the wiring of the electric current wire, also changes the stray capacitance of the load and changes the phase difference between the secondary voltage and the secondary current. As a result, the output impedance of the wound transformer varies.
Therefore, when using an open-loop cold-cathode tube lighting circuit, it is necessary to design the cold-cathode tube lighting circuit based on the structure of the entire panel product. That is, a dedicated cold cathode tube lighting circuit is required for the liquid crystal panel product, and the cost of the cold cathode tube lighting circuit is high for a small lot product.
In addition, since the cold cathode tube lighting circuit is a dedicated product, the versatility is poor, and it is difficult to divert the cold cathode tube lighting circuit to other liquid crystal panel products.

  The present invention solves the above problem by using a winding transformer 11 having a sufficient output current and feeding back the output current. In order to provide a margin for the output current, as described above, it is possible to extract more power from the winding transformer 11 of the same size by minimizing the phase difference between the secondary side voltage and the secondary side current. In addition, since the amount of heat generated by the winding transformer 11 can be suppressed, a winding transformer 11 having the same shape as the winding transformer 11 operating in an open loop or a smaller size can be used.

The cold-cathode tube lighting circuit obtained by the present invention can easily have versatility with respect to the cold-cathode tube. As long as the lighting start voltage and the maximum value of the output current can be cleared, the wound transformer 11 can be shared, and if the output current is the same as the output connector, the cold cathode tube lighting circuit can be shared.
The lighting start voltage is also stored in the primary side leakage inductance by loose coupling between the primary side coil 12 and the secondary side coil 13 of the wire-wound transformer 11 to some extent, that is, by reducing the coupling coefficient. The surge voltage generated when the energy is released and the damped vibration wave generated in the primary coil 12 to be described later are effectively used to generate a surge voltage higher than the voltage determined by the winding ratio between the primary coil 12 and the secondary coil 13. It can be obtained on the secondary side.

The surge voltage that is generally harmful can be effectively used in the cold cathode tube lighting circuit. However, the value of the surge voltage generated on the secondary side becomes smaller as the value of the capacitor 14 for adding the capacitance component provided in parallel to the cold cathode tube 16 becomes larger. However, in the panel product state in an actual use environment, a metal reflector is provided around the cold cathode tube 16 and is usually connected to the same potential as the low voltage side of the wound transformer 11.
Therefore, the lighting start voltage is often much smaller than the value described in the manufacturer's catalog due to the proximity conductor effect generated between the cold cathode fluorescent lamp and the reflector.

  On the other hand, paying attention to the waveform of the primary side voltage generated in the primary side coil 12, almost no residual magnetic flux is observed in the winding type transformer 11 due to bidirectional excitation of the winding type transformer 11. In such a state, a damped oscillation wave is generated between the primary inductance of the primary coil 12 and the stray capacitance of the switching elements 7, 8, 9, 10 and the primary circuit. This damped oscillatory wave includes an inductive component L mainly including the primary inductance of the wound transformer 11 in the primary circuit, a capacitance component C due to a parasitic capacitance mainly including a capacitor, an electric wire or printed circuit board pattern, and each element. This occurs when the pure resistance R due to the above satisfies the relationship of the expression (2).

In many cases, the primary circuit of the cold cathode tube lighting circuit satisfies the condition of Expression (2). An example of the damped oscillation wave seen in the primary side voltage is shown in FIG.
The vibration frequency of the damped vibration wave is determined mainly by the primary inductance of the primary coil 12 and the stray capacitance of the switching elements 7, 8, 9, 10 and the primary circuit. Since these values have small variations compared to the corresponding elements constituting the secondary circuit, even if they are adjusted by an actual machine, the difference for each individual is small.

Further, since the oscillation frequency of the signal from the oscillator 3 and the oscillation frequency of the damped oscillation wave are irrelevant, the oscillation frequency is set so that switching is performed at the valley of the damped oscillation wave. The state of the primary side voltage in this case is shown in FIG. The primary voltage does not have a pure square wave, but a waveform in which a damped oscillation wave is superimposed on a square wave. Further, the dead time described above is provided at each switching.
FIG. 4 shows an example in which switching is performed in the first valley caused by the damped vibration wave, but switching may be performed in the second and subsequent valleys as an example. As a result, the switching loss due to the voltage and current product during switching of the switching elements 7, 8, 9, and 10 and the iron loss due to the primary coil 12 can be reduced.

  Depending on the relationship between the oscillation frequency of the signal from the oscillator 3 and the oscillation frequency of the damped oscillation wave, the number of valleys to be switched is set. The beat of ceramic capacitors, choke coils, winding type transformers, etc. used in the primary circuit It is desirable to perform switching at the first valley in consideration of sound suppression and noise reduction due to damped vibration waves.

  Since the winding type transformer 11 used in the cold cathode tube lighting circuit generates a high voltage, it is strongly influenced by the capacitance component between the primary side coil 12 and the secondary side coil 13 and has a high withstand voltage between the enamel wires. In order to ensure, it is common to wind the primary side coil 12 and the secondary side coil 13 in the separate area | region provided in the bobbin, and the bobbin is also made into such a structure. When the enamel wire used for the secondary side coil 13 is determined by the secondary side current capacity and the operating temperature range, the maximum number of turns of the secondary side coil 13 is determined by the bobbin. At this time, a gap is provided in the core so that the leakage inductance of the secondary coil 13 falls within the expected value.

  For the primary side coil 12, when the number of turns is increased, the effective value of the primary side current (excitation current) is reduced, but the peak value of the voltage obtained on the secondary side is reduced. As described above, the peak value of the voltage obtained on the secondary side is not less than the value determined by the winding ratio between the primary side coil 12 and the secondary side coil 13, but the primary side coil 12 and the secondary side coil 13. The part that depends on the winding ratio is also large. The number of turns of the primary coil 12 is such that the voltage of the DC power supply 1 or the output voltage of the switching element 5 is input to the inverter circuit 100 when the cold cathode tube 16 is turned on without the dimming function being activated. Set to a value smaller than the minimum voltage. Here, if the voltage of the DC power supply 1 or the output voltage of the switching element 5 is smaller than necessary, the switching loss of the DC power supply 1 and the switching element 5 increases, but the DC power supply voltage range of the inverter circuit 100 can be widened. Furthermore, since the number of turns of the primary coil 12 also affects the vibration frequency of the damped vibration wave generated in the primary voltage, it is determined in consideration of these.

  The value of the capacitor 14 to which the capacitance component is added is determined so that the secondary side circuit satisfies the relationship of Expression (1) at the oscillation frequency set as described above.

The inverter circuit 100 constituting the cold cathode tube lighting circuit of the present invention includes a winding transformer 11 having a primary side coil 12 and a secondary side coil 13, a cold cathode tube 16, load electric wires, patterns on a printed circuit board, In order to reduce the influence of stray capacitance generated in the capacitor, the capacitor 14 provided in parallel with the cold cathode tube 16 and the tube current detection circuit 17, and the absolute value of the phase difference between the secondary side voltage and the secondary side current are minimized. Since the oscillator 3 that determines the oscillation frequency of the primary side and the switching elements 7, 8, 9, and 10 that are switched at the valley of the waveform of the primary side voltage are provided, the same winding type transformer is used. However, the output impedance of the winding transformer 11 can be made smaller than that of the conventional inverter circuit, and a larger amount of power can be taken out. Further, the wire-wound transformer 11 can be downsized if the power capacity is the same.
Moreover, since the loss in the primary side coil 12 and the secondary side coil 13 can be suppressed, the heat generation of the wire-wound transformer 11 is suppressed, and it is small and efficient, and can be used for any cold cathode tube 16.

Embodiment 2. FIG.
FIG. 5 is a block diagram showing the configuration of the non-contact power transmission apparatus according to Embodiment 2 of the present invention.
As shown in FIG. 5, the non-contact power transmission apparatus according to Embodiment 2 of the present invention includes a fixed unit 101, a movable unit 102 that is rotatably supported around an axis fixed to the fixed unit 101, Consists of The fixed unit 101 includes a DC power source 20, an inverter circuit 200 that converts DC power input from the DC power source 20 into AC power, a primary coil 29 of a non-contact winding transformer 28 to which AC power is input, Is provided. The movable unit 102 includes a secondary coil 30 that is electromagnetically coupled to the primary coil 29 of the non-contact winding transformer 28, a load 34 to which AC power is applied from the secondary coil 30 via the capacitor 31, and a load. A load current detection circuit 33 that detects a load current flowing through the load 34, and a load voltage detection circuit 32 that detects a load voltage applied to the load 34.

FIG. 6 is an exploded perspective view showing the configuration of the non-contact winding transformer 28 of the non-contact power transmission apparatus according to Embodiment 2 of the present invention.
As shown in FIG. 6, the non-contact winding type transformer 28 has a circular pot core so that it can cope with a case where the movable unit 102 such as a car steering, a rotary monitoring camera, and a robot joint rotates. It is used. The movable side pot core 151 on the movable unit 102 side and the fixed side pot core 157 on the fixed unit 101 side have the same center line as the center line 150 of the movable unit 102. It is fixed to.
The movable pot core 151 and the fixed pot core 157 are fixed so as to be separated by a predetermined distance so as to be mechanically non-contact.

  The movable side bobbin 152 and the fixed side bobbin 156 are housed and configured inside the movable side pot core 151 and the fixed side pot core 157, respectively. The fixed side bobbin 156 is formed by winding the primary side coil 29, and the movable side bobbin 152 is formed by winding the secondary side coil 30. The details of the non-contact winding type transformer 28 are described in Patent Document 2.

The basic operation of the non-contact power transmission apparatus according to the second embodiment of the present invention is that the DC power supply to the inverter circuit 200 is set so that the load voltage detected by the load voltage detection circuit 32 is equal to a preset value. 20 voltage is controlled. As a method for transmitting the detection signals of the load voltage detection circuit 32 and the load current detection circuit 33 to the primary side in a non-contact manner, the signal transmission circuit 35 by optical coupling is shown in FIG. 5, but inductive coupling or capacitive coupling is shown. However, the same effect can be obtained.
Also, a function may be provided to stop the output when the peak value of the load current detected by the load current detection circuit 33 exceeds a set value.

The phase difference between the secondary voltage detected by the load voltage detection circuit 32 and the secondary current detected by the load current detection circuit 33 is compared by the phase comparator 22, and the absolute value of these phase differences is minimized. Thus, the oscillation frequency of the signal oscillated from the oscillator 21 is varied.
When the absolute value of the phase difference is minimized, the inductive component of the leakage inductance of the secondary coil 30 and the capacitive component added by the capacitor 31 and the capacitive component due to stray capacitance generated on the secondary side such as the load 34 are mutually connected. The voltage drops due to the inductive component of the leakage inductance of the secondary coil 30 are kept to a minimum.
Accordingly, since the impedance of the secondary coil 30 is lowered, the output impedance of the non-contact winding transformer 28 can be reduced. That is, more electric power can be extracted from the non-contact winding type transformer 28.
Note that a PLL for several tens of kHz may be used as the phase comparator 22, or a microcomputer may be used.

  A signal oscillated by the oscillator 21 is input to the switching elements 24, 25, 26, and 27 constituting the inverter circuit 200 after being subjected to current amplification, voltage shift, or dead time generation processing by the gate driver 23. . The dead time here means that all switching elements 24, 27 and 27, or 25 and 26 are turned on at the same time so that overcurrent due to a short circuit current does not flow. This refers to the period during which 25, 26, and 27 are off. The gate driver 23 can use the method described in Japanese Patent Application Laid-Open No. 2008-289249.

In the switching elements 24, 25, 26, and 27, the switching element 24 and the switching element 27 are turned on at the same time, and the switching element 25 and the switching element 26 are turned on at the same time. Turned off.
FIG. 5 describes a full-bridge type inverter as an example of the inverter circuit 200. However, the inverter circuit 200 may be a half-bridge type, a push-pull type (center tap type), a flyback type, or a forward type. Also has the same effect.

In the non-contact power transmission device using the non-contact winding transformer 28, the leakage inductance of the primary coil 29 and the secondary coil 30 is very large due to the structure of the non-contact winding transformer 28. Reduces efficiency and increases surge voltage. In the forward type, the regenerative power to the primary circuit increases, and the loss in the regenerative circuit increases.
However, when the gap between the two pot cores constituting the non-contact winding type transformer 28 as shown in FIG. 6 is a fixed value and the leakage inductance of the primary side coil 29 and the secondary side coil 30 is not so large, switching is performed. Since the number of components constituting the inverter circuit 200 including elements can be reduced, a flyback type or a forward type may be useful.

  The primary coil 29 of the non-contact winding type transformer 28 is bi-directionally or unidirectionally excited by the inverter circuit 200 configured by the switching elements 24, 25, 26, 27, etc. Output is output. Compared to bidirectional excitation, the use efficiency of the non-contact winding transformer 28 is reduced in the case of unidirectional excitation, and therefore the non-contact winding transformer 28 becomes larger even when the same power is handled.

  The secondary coil 30 is controlled so that the phase difference between the secondary voltage waveform and the secondary current waveform is minimized. In FIG. 5, the capacitor 31 for adding a capacitance component is provided in series (current resonance type) with respect to the load 34. However, even if the capacitor 31 is provided in parallel (voltage resonance type) with respect to the load 34, both parallel and series are provided. (Resonant pole type) may be provided.

  When the number of turns of the primary side coil 52 is equal to or larger than the number of turns of the secondary side coil 53, the primary side voltage and the secondary side current as shown in FIG. In some cases, the transmission efficiency can be improved by comparing the secondary current with the phase comparator 42 and determining the oscillation frequency with the oscillator 41 so that the absolute value of these phase differences is minimized.

  As shown in FIG. 7, another non-contact power transmission apparatus according to Embodiment 2 of the present invention includes a fixed unit 103 and a movable unit 104 that is rotatably supported around an axis fixed to the fixed unit 103. And. The fixed unit 103 includes a DC power source 40, an inverter circuit 300 that converts DC power input from the DC power source 40 into AC power, and a non-contact winding transformer 51 through which AC power flows from the inverter circuit 300 via a capacitor 48. Primary side coil 52, primary side current detection circuit 50 that detects a primary side current flowing through primary side coil 52, and primary side that detects a primary side voltage applied to primary side coil 52. And a voltage detection circuit 49. The movable unit 104 includes a secondary coil 53 that is electromagnetically coupled to the primary coil 52 of the non-contact winding transformer 51, and a load 54 to which AC power is applied from the secondary coil 53.

  A signal oscillated by the oscillator 41 is input to the switching elements 44, 45, 46, and 47 constituting the inverter circuit 300 after being subjected to current amplification, voltage shift, or dead time generation processing by the gate driver 43. . The dead time here means that all switching elements 44, 47, 47, or 45, 46 are turned on at the same time so that no overcurrent due to a short-circuit current flows, This refers to the period during which 45, 46, and 47 are off. The gate driver 43 can also use the method described in Japanese Patent Application Laid-Open No. 2008-289249.

  The switching elements 44, 45, 46, and 47 are turned on simultaneously with the switching element 44 and the switching element 47, and simultaneously turned on with the switching element 45 and the switching element 46. Turned off.

  The non-contact power transmission apparatus according to the present invention includes a non-contact winding transformer 28 having a primary side coil 29 and a secondary side coil 30, and 2 in order to suppress a voltage drop due to leakage inductance generated in the non-contact winding type transformer 28. A capacitor 31 provided in series or in parallel with the secondary coil 30 and an oscillator 21 for determining the primary oscillation frequency so that the absolute value of the phase difference between the secondary voltage and the secondary current is minimized; Therefore, even if the same non-contact winding transformer is used, the output impedance of the non-contact winding transformer 28 can be made smaller than that of the conventional inverter circuit, so that larger electric power can be taken out.

Further, if the power capacity is the same, the non-contact winding type transformer 28 can be reduced in size, and the gap length between the two pot type cores does not cause a reduction in power transmission efficiency.
Moreover, since the voltage drop due to the leakage inductance of the secondary coil can be suppressed and the loss can be suppressed, the heat generation of the wire-wound transformer can be suppressed, and it is small and efficient.

  1, 20, 40 DC power supply, 2 dimming circuit, 3, 21, 41 oscillator, 4, 22, 42 phase comparator, 5, 7, 8, 9, 10, 24, 25, 26, 27, 44, 45 , 46, 47 Switching element, 6, 23, 43 Gate driver, 11 Winding transformer, 12, 29, 52 Primary coil, 13, 30, 53 Secondary coil, 14, 31, 48 Capacitor, 15 tube voltage Detection circuit, 16 Cold cathode tube, 17 tube current detection circuit, 28, 51 Non-contact winding type transformer, 32 Load voltage detection circuit, 33 Load current detection circuit, 34, 54 Load (LOAD), 35 Signal transmission circuit, 49 1 Secondary side voltage detection circuit, 50 Primary side current detection circuit, 100, 200, 300 Inverter circuit, 101, 103 Fixed unit, 102, 104 Movable unit, 150 Medium Line 151 movable pot core, 152 movable bobbin, 156 stationary bobbin, 157 fixed side pot core.

Claims (3)

In the inverter circuit for lighting the discharge tube by converting the DC power supplied from the DC power source into AC power and then supplying the discharge tube,
A winding transformer having a primary coil and a secondary coil;
A capacitor is added to reduce the influence of stray capacitance generated on the pattern on the discharge tube, load wire or printed circuit board, and the discharge tube, or a capacitor provided in parallel with the discharge tube and the tube current detection circuit, ,
A switching element that is switched at an oscillation frequency such that an absolute value of a phase difference between a voltage generated in the secondary coil and a current flowing in the secondary coil is minimized;
An inverter circuit comprising:   2. The inverter circuit according to claim 1, wherein the switching element is switched at a trough related to a damped oscillation wave of a voltage applied to the primary coil. In an inverter circuit for supplying contactless power to a movable load after converting DC power supplied from a DC power supply into AC power,
A non-contact winding transformer having a primary coil and a secondary coil;
A capacitor that is added in series or in parallel to the secondary coil and that adds a capacitance component to suppress a voltage drop due to leakage inductance generated in the non-contact winding transformer;
A switching element that is switched at an oscillation frequency such that an absolute value of a phase difference between a voltage generated in the secondary coil and a current flowing in the secondary coil is minimized;
An inverter circuit comprising:

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