WO2006137607A1

WO2006137607A1 - Adaptive coupling circuits using multi resonance tanks

Info

Publication number: WO2006137607A1
Application number: PCT/KR2005/001930
Authority: WO
Inventors: Doohwan Lee
Original assignee: Leetronix Co., Ltd.
Priority date: 2005-06-22
Filing date: 2005-06-22
Publication date: 2006-12-28

Abstract

Disclosed herein is a power transmission coupling circuit using a high frequency inverter for stabilized operation of a severely varied load. The primary winding of a matching transformer is used as a path of a serial resonance circuit. The secondary winding of the matching transformer, which is coupled to the primary winding of the matching transformer according to magnetic field coupling, constructs a path of a serial or parallel resonance circuit. Accordingly, an output variation of the load caused by a variation in a power supply voltage is reduced and resonant frequency selection factors of the resonance circuits are controlled without having a separate protection circuit or control circuit even when the impedance of the load, a rated voltage and rate current are abruptly varied, to thereby stably drive the load. The coupling circuit can save power and stabilize its operation. Furthermore, the size and weight of the coupling circuit can be reduced.

Description

ADAPTIVE COUPLING CIRCUITS USING MULTI RESONANCE TANKS

Technical Field

[1] The present invention relates to a power transmission coupling circuit of a high- efficiency high-frequency electronic power supply device, which stably operates a load even when the characteristic of the load is severely varied. Background Art

[2] A conventional electronic power supply device has a problem of deterioration of power efficiency due to defective control and switching loss. A high-frequency electronic power supply device transforms a commercial voltage into a driving voltage of several KHz using an inverter. When the high-frequency electronic power supply device uses pulse width modulation of forced switching, a loss is increased in proportion to a frequency and electromagnetic fault occurs to result in no improvement of the performance of the device.

[3] Korean Patent Laid-Open Publication. No. 10-2001-0113187 discloses a technique relating to a circuit for driving an LCD backlight inverter, which can regulate an input line of the inverter and minimize unbalance of output currents of lamps caused by a variation in characteristic of each circuit component. This circuit includes a class-E power amplifier for maximizing power efficiency, a pulse width modulator, an error amplifier and an insulation sensor. Two lamps are serially connected such that the inverter driving the two loads solves a problem caused by unbalance of output currents of the two loads, and the insulation sensor is connected between the lamps. Furthermore, the two lamps are constructed of the same current loop such that the two lamp currents become identical to each other, and the lamp currents are controlled using an output signal obtained by the insulation sensor to obtain a constant voltage and current even when an input voltage is varied in a wide range. In this manner, the circuit drives the LCD backlight. However, this circuit uses incomplete resonance in a power circuit that transmits maximum power in the case of full resonance because it employs pulse width modulation that increases/decreases the width of a driving pulse with a signal fed back from the output terminal. Accordingly, reactive power is increased when a load, that is, impedance, is abruptly varied and thus unnecessary power is emitted as heat. Furthermore, there are limitations in load adaptability of the circuit due to the response speed of a feedback circuit.

[4] Korean Patent Laid-Open Publication. No. 10-1998-0011571 discloses a cold cathode ray tube driving inverter circuit. This circuit includes a controller receiving an input voltage, a switch serially connected to the controller and controlled by the controller, a resonator serially connected to the output of the switch to resonate, a voltage transformer for inducing the output voltage of the resonator from the primary side to the secondary side thereof, and an output part controlled and operated using the voltage induced by the voltage transformer as an input signal. However, this circuit proposes only simple impedance matching and feedback control based on a load having impedance within a predetermined range. Thus, the inverter is destroyed when the load is abruptly changed or has a trouble.

[5] Korean Patent Laid-Open Publication. No. 10-2000-0060883 discloses a system for restricting an over- voltage of an inverter-driven motor, which includes an inverter that converts a commercial AC power having a fixed voltage and a fixed frequency into a DC power and then converts the DC power into an AC power having a variable voltage and a variable frequency, and a variable speed motor driven by the AC power provided by the inverter. The system further includes an over- voltage restricting unit connected to the output terminal of the inverter to restrict an over- voltage that can be generated at the input terminal of the motor due to impedance matching at the output terminal of the inverter. However, this system connects an impedance circuit having the same value as the characteristic impedance of a line to the output terminal of the inverter to make reflection coefficient at the output terminal of the inverter zero such that voltage reflection at the output terminal of the inverter is eliminated to restrict the over- voltage at the input terminal of the motor. Accordingly, the impedance circuit connected to the output terminal of the inverter should be designed based on characteristic of a load. In addition, when the impedance characteristic of the load is abruptly changed over a wide range, the impedance circuit having the same value as the characteristic impedance of the line consumes energy to result in heat radiation. Furthermore, the impedance circuit connected to the output terminal of the inverter is destroyed when the load is abruptly varied or has a trouble. To meet this, a large-size impedance circuit having the same capacity as that of the load is required.

[6] Korean Patent Laid-Open Publication. No. 10-1996-0039621 (U.S. Patent No.

5,495,209) discloses a switched- inverter modulator for use in driving a magnetron and a microwave tube. A synchronized pulse generator provides pulse width timing and synchronized amplitude commands to a high- voltage switch power supply while an output voltage pulse signal is directly supplied to a continuous wave magnetron oscillator, for example. The power supply is separated from a power resistor in order to block dissolution of magnetron arc reflections. The switched inverter modulator is capable of varying pulse widths, pulse repetition frequencies, and amplitude output. However, the switched inverter modulator also proposes only simple impedance matching and feedback control based on the magnetron having impedance in a pre- determined range, and thus it cannot cope with an abrupt variation or a trouble in a load.

[7] U.S. Patent No. 5,053,682 discloses a microwave discharge light source which rectifies a high-frequency AC generated by a high-frequency inverter using a waveform of alternating pulses obtained by rectifying a commercial voltage as a power supply voltage, applies the rectified AC to a magnetron, and turns on an electrodeless discharge bulb using a microwave generated from the magnetron. The microwave discharge light source includes a high-frequency component suppressing unit coupled across the output terminal of a part that rectifying the magnetron high-frequency AC to suppress a high-frequency component of the microwave power applied to the electrodeless discharge bulb. However, this device cannot cope with an abrupt variation or a trouble in a load because it also has the magnetron.

[8] U.S. Patent No. 4,222,098 discloses a base drive of a parallel inverter system. In this system, a positive feedback current derived from the total current from all of the modules of the inverter system is applied to the base drive of each of the power transistors of all modules, to thereby provide all modules protection against open or short circuit faults occurring in any of the modules. However, this system also cannot handle an abrupt variation or a trouble in a load because it proposes only feedback control.

[9] Korean Patent No. 10-1998-0077020 discloses a circuit for driving an induction lamp for use in fire equipment using a circuit of driving a fluorescent lamp having no ballast. The induction lamp driving circuit includes a power supply, a rectifier, a charging/discharging part, a charging/discharging sensor, a power switch, a received signal switch, an oscillator and a lighting part. The circuit pre-heats the fluorescent lamp with an AC voltage induced to the secondary side of an oscillating transformer to facilitate electron emission in the fluorescent lamp. However, this circuit also proposes only simple impedance matching and feedback control based on a load that is constructed of a fluorescent lamp filament and has impedance in a predetermined range. Thus, an inverter can be destroyed when the load is abruptly varied or has a trouble.

Disclosure of Invention Technical Problem

[10] Accordingly, the present invention is directed to an adaptive coupling circuit that substantially obviate one or more problems due to limitations and disadvantages of the related art.

[11] An object of the present invention is to provide an adaptive coupling circuit that uses the primary winding of a matching transformer as a path of a serial resonance circuit and uses the secondary winding of the matching transformer, which is coupled to the primary winding of the matching transformer according to magnetic field coupling, as a path of a serial or parallel resonance circuit to determine matching characteristic by a part or all of resonant frequency selection factors of the serial resonance circuit and the parallel resonance circuit, thereby reducing an output variation of a load, caused by a variation in a power supply voltage, and stably driving the load without having a separate protection circuit or control circuit even when characteristics of the load, that is, impedance, rated voltage and rate current, are abruptly changed. Technical Solution

[12] To accomplish the object, according to one aspect of the present invention, there is provided an adaptive coupling circuit including an inverter having a switching frequency f , which converts a commercial AC voltage into a DC voltage and converts the DC voltage into a high frequency AC voltage, in which one terminal of the primary winding L of a matching transformer 22 is coupled to a node at which condensers C and C for distributing a high frequency square wave voltage from the inverter are coupled to each other and the other terminal of the primary winding L of the matching transformer 22 is coupled to a node at which switching elements of the inverter are coupled to each other to construct a first serial resonance circuit, and the secondary winding L of the matching transformer 22 is serially connected to a resistor R , a coil L , a condenser C , and a load to construct a second serial resonance circuit.

3 6

[13] The primary winding L and the secondary winding L of the matching transformer

22 are electrically insulated from each other and connected to each other according to magnetic filed coupling.

[14] The resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit are determined by the inductance of the primary winding L of the matching transformer 22 constructing the first serial resonance circuit and the capacitance values of the condensers C and C .

[15] The resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second serial resonance circuit are determined by the inductance of the second winding L of the matching transformer 22 constructing the second serial resonance circuit, the inductance of the coil L and the capacitance value of the condenser C .

6

[16] Matching characteristic is determined by a part or all of the switching frequency f of the inverter, the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit, and the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second serial resonance circuit. [17] According to another aspect of the present invention, there is also provided an adaptive coupling circuit including an inverter having a switching frequency f , which converts a commercial AC voltage into a DC voltage and converts the DC voltage into a high frequency AC voltage, in which one terminal of the primary winding L of a matching transformer 22 is coupled to a node at which condensers C and C for distributing a high frequency square wave voltage from the inverter are coupled to each other and the other terminal of the primary winding L of the matching transformer 22 is coupled to a node at which switching elements of the inverter are coupled to each other to construct a first serial resonance circuit, and the secondary winding L of the

2 matching transformer 22 is connected in parallel with a resistor R , a coil L , a condenser C , and a load to construct a second parallel resonance circuit. [18] The primary winding L and the secondary winding L of the matching transformer

22 are electrically insulated from each other and connected to each other according to magnetic filed coupling. [19] The resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit are determined by the inductance of the primary winding L of the matching transformer 22 constructing the first serial resonance circuit and the capacitance values of the condensers C and C . [20] The resonant frequency f P , frequency bandwidth BW p and frequency selection factor Q of the second parallel resonance circuit are determined by the inductance of

P the second winding L of the matching transformer 22 constructing the second parallel resonance circuit, the inductance of the coil L and the capacitance value of the

4 condenser C .

7

[21] Matching characteristic is determined by a part or all of the switching frequency f of the inverter, the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit, and the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second parallel

P P resonance circuit.

Advantageous Effects

[22] As described above, the present invention provides an adaptive coupling circuit including an inverter having a switching frequency f , which converts a commercial AC voltage into a DC voltage and converts the DC voltage into a high frequency AC voltage. In the coupling circuit, one terminal of the primary winding L of the matching transformer 22 is coupled to a node at which the condensers C and C for distributing a high frequency square wave voltage from the inverter are coupled to each other and the other terminal of the primary winding L of the matching transformer 22 is coupled to a node at which the switching elements of the inverter are coupled to each other to construct the first serial resonance circuit. The secondary winding L of the matching transformer 22 is serially connected to the resistor R , the coil L , the condenser C , and the load to construct the second serial resonance circuit.

3 6

[23] The primary winding L and the secondary winding L of the matching transformer

[24] The resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit are determined by the inductance of the primary winding L of the matching transformer 22 constructing the first serial resonance circuit and the capacitance values of the condensers C and C . [25] The resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second serial resonance circuit are determined by the inductance of the second winding L of the matching transformer 22 constructing the second serial resonance circuit, the inductance of the coil L and the capacitance value of the condenser C 6.

[26] Matching characteristic is determined by a part or all of the switching frequency f of the inverter, the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit, and the resonant frequency f 2S , frequency bandwidth BW and frequency selection factor Q of the second serial resonance circuit.

[27] Furthermore, the present invention provides an adaptive coupling circuit including an inverter having a switching frequency f , which converts a commercial AC voltage into a DC voltage and converts the DC voltage into a high frequency AC voltage. In the coupling circuit, one terminal of the primary winding L of the matching transformer 22 is coupled to a node at which the condensers C and C for distributing a high frequency square wave voltage from the inverter are coupled to each other and the other terminal of the primary winding L of the matching transformer 22 is coupled to a node at which the switching elements of the inverter are coupled to each other to construct a first serial resonance circuit. The secondary winding L of the matching transformer 22 is connected in parallel with the resistor R , the coil L , the condenser C

3 4

, and the load to construct a second parallel resonance circuit.

[28] The primary winding L and the secondary winding L of the matching transformer

[29] The resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit are determined by the inductance of the primary winding L of the matching transformer 22 constructing the first serial resonance circuit and the capacitance values of the condensers C and C . [30] The resonant frequency f , frequency bandwidth BW and frequency selection

P p factor Q of the second parallel resonance circuit are determined by the inductance of

P the second winding L of the matching transformer 22 constructing the second parallel resonance circuit, the inductance of the coil L and the capacitance value of the condenser C .

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[31] Matching characteristic is determined by a part or all of the switching frequency f of the inverter, the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit, and the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second parallel

P P resonance circuit. [32] Accordingly, the adaptive coupling circuit according to the present invention can save power and stabilize the operation thereof. Furthermore, the size and weight of the coupling circuit can be reduced.

Brief Description of the Drawings [33] The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: [34] FIG. 1 illustrates a conventional R-L-C serial circuit;

[35] FIG. 2 illustrates a characteristic curve showing the relationship between the frequency and reactance of a serial resonance circuit; [36] FIG. 3 illustrates a characteristic curve showing the relationship between the frequency and the total impedance of the serial resonance circuit; [37] FIG. 4 illustrates a characteristic curve showing the relationship between the frequency and current of the serial resonance circuit; [38] FIG. 5 illustrates conventional R-L-C parallel circuits;

[39] FIG. 6 illustrates a characteristic curve showing the relationship between the frequency and impedance of a parallel resonance circuit; [40] FIG. 7 is a circuit diagram of a coupling circuit according to a first embodiment of the present invention; [41] FIG. 8 illustrates equivalent circuits of the coupling circuit according to the first embodiment of the present invention; [42] FIG. 9 illustrates a characteristic curve showing the relationship between the frequency and current of the coupling circuit according to the first embodiment of the present invention; [43] FIG. 10 is a circuit diagram of a coupling circuit according to a second embodiment of the present invention; and [44] FIG. 11 illustrates a characteristic curve showing the relationship between the frequency and current of the coupling circuit according to the second embodiment of the present invention.

Best Mode for Carrying Out the Invention

[45] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[46] A conventional R-L-C serial resonance circuit shown in FIG. 1 includes an inductive element L, a capacitive element C, a resistor of a power supply, an internal resistor of an inductor, and an additional resistor (R=R s +R 1+R d ). The total impedance of the R-L-C resonance circuit at a certain frequency is as follows. [47] MathFigure 1

Z_T ⁼R+jX _L-jX_c ⁼R+j(X _L-X_c ⁾

[48] Here, X is reactance according to a coil and X is reactance according to a condenser C. A resonance condition is that a reactance component in the total impedance is zero, X equals X , and a resonant frequency is

1

[49] Since Z is a minimum value under the resonance condition, the current flowing through the circuit has the same phase as that of an input voltage and a maximum current flows through the circuit.

[50] MathFigure 2

R L O R

[51] The voltages respectively applied to the condenser and the coil have the same level but different phases having a difference of 180 because the current flowing through the condenser is identical to the current flowing through the coil under the resonance condition.

[52] MathFigure 3

V₁=(I Z O)(X_x 19O)=IX₁ Z 90 V_C=(I L 0)(X_cZ 90)=ZX_c-90

[53] A frequency selection factor Q of the serial resonance circuit is defined as a ratio of reactive power of the coil or the condenser to a mean power of the resistors in resonance and represents a stored power (power moved from one reactive element to another reactive element) in comparison to a consumed power. [54] MathFigure 4

[55] The relationship between the total impedance and frequency of the serial R-L-C circuit, shown in FIG. 2, can be represented as follows. [56] MathFigure 5

[57] where Z (f) is a function of frequency and means the total impedance.

[58] FIG. 3 illustrates the total impedance Z (f). Here, a resonance condition is the intersection of two curves, that is, the point at which X =X . The circuit is capacitive (X >X ) at a frequency lower than f but inductive (X >X ) at a frequency higher than the resonant frequency. The minimum impedance is generated at the resonant frequency and corresponds to the resistor R.

[59] FIG. 4 is a characteristic curve showing the relationship between a current I=E/Z and frequency for an applied voltage E. The curve represents frequencies corresponding to 0.707 of the maximum current as f and f , which are called band

Sl S2 frequencies, cutoff frequencies or half-power frequencies. The frequency range between the two frequencies is considered as the bandwidth (BW) of the resonance circuit. The power at the half-power frequencies corresponds to a half of the power obtained at the resonant frequency. [60] MathFigure 6

[61] or

[62] MathFigure 7

[63] If the inductance and capacitance values are fixed and the resistance value is decreased, the bandwidth is reduced and selectivity is increased. If the resistance value is fixed and the ratio of the inductance value to the capacitance value (L/C) is increased, the bandwidth is decreased and selectivity is increased. Accordingly, Q becomes smaller according to Equation 4 when R is larger than X . Therefore, the circuit has a larger bandwidth and smaller selectivity when Q is decreased but has smaller bandwidth and larger selectivity when Q is increased.

[64] An R-L-C parallel resonance circuit in consideration of an internal resistor R of a coil, which is serially connected to the coil, has a basic form including an internal resistor R of a current source, as shown in FIG. 5(a). Here, R =(R +X )/R , X =(R

S P 1 L 1 LP 1

+X )/X , R=R HR , and R is varied with frequency. Accordingly, the total

L L S P P admittance Y of the R-L-C parallel resonance circuit shown in FIG. 5(b) is represented by Equation 8 and the total impedance according to the frequency has a characteristic curve shown in FIG. 6. [65] MathFigure 8

1 1 I _x

JX JV _c JV _Lp

[66] When a power factor is 1, 1 /X =1 /X and a parallel resonant frequency f is represented as follows. [67] MathFigure 9

[68] The frequency selection factor Q of the parallel resonance circuit is determined by

P the ratio of an effective power to a reactive power and represented as follows. [69] MathFigure 10

[70] When there is an ideal current source (R =ooΩ) or R is sufficiently larger than R ,

. Thus, the frequency selection factor Q of the parallel resonance circuit can be

P represented as follows. [71] MathFigure 11

X∑

[72] A parallel resonant frequency bandwidth is determined based on the parallel resonant frequency or the frequency selection factor as follows. [73] MathFigure 12

[75] FIG. 7 is a circuit diagram of a coupling circuit according to a first embodiment of the present invention. The coupling circuit includes a zero voltage switching resonant inverter, a first serial resonance circuit and a second serial resonance circuit. Referring to FIG. 7, a voltage source (2E) 21 is obtained by filtering and smoothing a commercial AC voltage using a line filter and a high power factor smoothing circuit. Condensers C and C divide the input voltage (2E) 21 to use it as a voltage source. One terminal of the primary winding L of a matching transformer 22 is coupled to a node at which the condensers C and C , which distribute a high-frequency square wave voltage of the inverter, are connected to each other, and the other terminal of the primary winding L of the matching transformer 22 is coupled to a node at which switching elements of the inverter are connected to each other, to construct the first serial resonance circuit.

[76] The switching elements that switch at a high frequency f use MOSFETs S and S , and diodes D and D are reversely coupled in parallel with the MOSFETs and bidi- rectionally operated. Condensers C and C coupled in parallel with the diodes D and D are resonant condensers that resonate only at switching moments to make a zero voltage switching condition. The MOSFETs S and S construct a half-bridge structure and are alternately turned on and off. The MOSFETs S and S perform their switching operations when the voltage across each of them is zero, and power transmitted to a load can be controlled in response to a ratio of an ON period to one switching period. The high-frequency square wave voltage that has passed through a snubber circuit constructed of a resistor R and the condenser C is applied to the primary winding L of the matching transformer 22 such that an alternating current I flows to generate a resonant frequency f in the first serial resonance circuit according to the condensers C

1 and C 2.

[77] The secondary winding L of the matching transformer 22 is serially connected to a resistor R , a coil L , a condenser C and the load, to construct the second serial

2 3 6 resonance circuit having a resonant frequency f . Here, the primary winding L and the secondary winding L of the matching transformer 22 are electrically insulated from each other and connected to each other according to magnetic field coupling. The matching transformer transmits a voltage I X applied to the primary winding L of the first serial resonance circuit to the secondary winding L of the second serial resonance circuit according to mutual inductance and a magnetic field coupling coefficient. [78] FIG. 8(a) roughly shows the inverter circuit and the first serial resonance circuit, which can be represented by an equivalent circuit including a voltage source E , a leq resistor R including the internal resistor of the inverter and the winding resistor of an leq inductor, a condenser C , and the inductor L , as shown in FIG. 8(c). FIG. 8(b) leq leq shows the second serial resonance circuit, which can be represented by an equivalent circuit including a voltage source E , a resistor R including a magnetic resistor and

2eq 2eq winding resistor of an inductor, a condenser C , and the inductor L , as shown in

2eq 2eq

FIG. 8(d). FIG. 9 is a characteristic curve showing the relationship between the current and frequency of each of the first and second serial resonance circuits shown in FIGS. 8(c) and 8(d). Referring to FIG. 9, the frequency selection factor Q is increased and the frequency bandwidth BW is decreased as L eq /C eq is increased. In addition, and the quantity of current is reduced as L eq /C eq is increased at a predetermined inverter switching frequency f .

[79] When the inverter switching frequency f of power transmitted to the second serial resonance circuit according to the resonance frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit, which are determined by the inductance of the primary winding L of the matching transformer 22 constructing the first serial resonance circuit and the capacitance values of the condensers C and C , is identical to the resonant frequency f of the second serial

1 2 ^{n J} 2S resonance circuit, resonance occurs such that the phases of voltage and current applied to the circuit become identical to each other. This minimizes the impedance of the second serial resonance circuit and thus a maximum current flows through the second serial resonance circuit. In addition, there is no reactive power caused by the condensers and coils and the total reactive power becomes identical to the mean power consumed by resistance components, and thus the power factor of the second serial resonance circuit becomes 1. Furthermore, when the inverter switching frequency f is different from the resonant frequency f of the second serial resonance circuit, the impedance Z (f ) of the second serial resonance circuit is increased to reduce the

T2 2S current I flowing through the load. Accordingly, the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second serial resonance circuit are determined by the inductance of the second winding L of the matching transformer 22 constructing the second serial resonance circuit, the inductance of the coil L , the resistance value of the resistor R , and the capacitance values of the condensers C and C , and thus the current I flowing through the load can be controlled.

[80] As described above, the characteristic of the coupling circuit including the first and second serial resonance circuits can be easily determined by a part of all of the inverter switching frequency f , the resonance frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit, and the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second serial resonance circuit. Mode for the Invention

[81] FIG. 10 is a circuit diagram of a coupling circuit according to a second embodiment of the present invention. The coupling circuit includes a zero voltage switching resonant inverter, first and second serial resonance circuits. Referring to FIG. 10, a voltage source (2E) 21 is obtained by filtering and smoothing a commercial AC voltage using a line filter and a high power factor smoothing circuit. Condensers C and C divide the input voltage (2E) 21 to use it as a voltage source. One terminal of the primary winding L of a matching transformer 22 is coupled to a node at which the condensers C and C , which distribute a high-frequency square wave voltage of the inverter, are connected to each other, and the other terminal of the primary winding L of the matching transformer 22 is coupled to a node at which switching elements of the inverter are connected to each other, to construct the first serial resonance circuit. The high-frequency square wave voltage from the zero voltage switching inverter is applied to the primary winding L of the matching transformer 22 such that an alternating current I flows to generate a resonant frequency f in the first serial resonance circuit according to the condensers C and C .

[82] The secondary winding L of the matching transformer 22 is connected in parallel with a resistor R , a coil L , a condenser C and a load, to construct the second parallel resonance circuit having a resonant frequency f . Here, the primary winding L and the secondary winding L of the matching transformer 22 are electrically insulated from each other and connected to each other according to magnetic field coupling. The matching transformer transmits a voltage I X applied to the primary winding L of the first serial resonance circuit to the secondary winding L of the second parallel resonance circuit according to mutual inductance and a magnetic field coupling coefficient.

[83] FIG. 11 is a characteristic curve showing the relationship between the voltage and frequency of each of the first serial resonance circuit shown in FIG. 8(c) and the R-L-C parallel resonance circuit shown in FIG. 8(d). The voltage characteristic curves of FIG. 11 are similar to the current characteristic curves shown in FIG. 9. The effect of R , L

1 P and C on the total impedance Z in the parallel resonance circuit is very similar to the effect on the current characteristic curve of the serial resonance circuit. Referring to FIG. 11, the frequency selection factor Q is increased and the frequency bandwidth

P

BW is decreased as L /C is increased. In addition, the quantity of current is reduced as

P P

L /C is increased at a predetermined inverter switching frequency f . Furthermore, the

P 0 voltage applied to the parallel resonance circuit has the same form as the total impedance Z because the current I of the current source is constant at Z or any

T T frequency value.

[84] When the inverter switching frequency f of power transmitted to the second parallel resonance circuit according to the resonance frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit, which are determined by the inductance of the primary winding L of the matching transformer 22 constructing the first serial resonance circuit and the capacitance values of the condensers C and C is identical to the resonant frequency f of the second

1 2 ^ ^J P parallel resonance circuit, resonance occurs such that the phases of voltage and current applied to the circuit become identical to each other. This minimizes the impedance of the second parallel resonance circuit and thus a maximum voltage is applied to the second parallel resonance circuit. When the inverter switching frequency f is different from the resonant frequency f of the second parallel resonance circuit, the impedance of the second parallel resonance circuit is decreased to reduce the voltage V applied to

P the parallel resonance circuit. Accordingly, the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second parallel resonance

P P circuit are determined by the inductance of the second winding L of the matching transformer 22 constructing the second parallel resonance circuit, the inductance of the coil L , the resistance value of the resistor R and the capacitance value of the condensers C , and thus the voltage V applied to the load can be controlled.

1 P

[85] As described above, the characteristic of the coupling circuit including the first serial resonance circuit and the second parallel resonance circuit can be easily determined by a part of all of the inverter switching frequency f , the resonance frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit, and the resonant frequency f , frequency bandwidth BW and

P p frequency selection factor Q of the second parallel resonance circuit.

P

Claims

[1] An adaptive coupling circuit including an inverter having a switching frequency f

, which converts a commercial AC voltage into a DC voltage and converts the DC voltage into a high frequency AC voltage, wherein one terminal of the primary winding L i of a matching transformer 22 is coupled to a node at which condensers C and C for distributing a high frequency square wave voltage from the inverter are coupled to each other and the other terminal of the primary winding L of the matching transformer 22 is coupled to a node at which switching elements of the inverter are coupled to each other to construct a first serial resonance circuit, and the secondary winding L of the matching transformer 22 is serially connected to a resistor R , a coil L , a condenser C , and a load to construct a second serial resonance circuit.

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[2] The adaptive coupling circuit as claimed in claim 1, wherein the primary winding

L and the secondary winding L of the matching transformer 22 are electrically insulated from each other and connected to each other according to magnetic filed coupling.

[3] The adaptive coupling circuit as claimed in claim 1, wherein the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit are determined by the inductance of the primary winding L of the matching transformer 22 constructing the first serial resonance circuit and the capacitance values of the condensers C and C .

[4] The adaptive coupling circuit as claimed in claim 1, wherein the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second serial resonance circuit are determined by the inductance of the second winding L of the matching transformer 22 constructing the second serial resonance circuit, the inductance of the coil L and the capacitance value of the condenser C 6.

[5] The adaptive coupling circuit as claimed in claim 1, wherein matching characteristic is determined by a part or all of the switching frequency f of the inverter, the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit, and the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second serial resonance circuit.

[6] An adaptive coupling circuit including an inverter having a switching frequency f

, which converts a commercial AC voltage into a DC voltage and converts the DC voltage into a high frequency AC voltage, wherein one terminal of the primary winding L of a matching transformer 22 is coupled to a node at which condensers C and C for distributing a high frequency square wave voltage from the inverter are coupled to each other and the other terminal of the primary winding L of the matching transformer 22 is coupled to a node at which switching elements of the inverter are coupled to each other to construct a first serial resonance circuit, and the secondary winding L of the matching transformer 22 is connected in parallel with a resistor R , a coil L , a condenser C , and a load to construct a second parallel resonance circuit.

[7] The adaptive coupling circuit as claimed in claim 6, wherein the primary winding

[8] The adaptive coupling circuit as claimed in claim 6, wherein the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit are determined by the inductance of the primary winding L of the matching transformer 22 constructing the first serial resonance circuit and the capacitance values of the condensers C and C .

[9] The adaptive coupling circuit as claimed in claim 6, wherein the resonant frequency f P , frequency bandwidth BWp and frequency selection factor Q p of the second parallel resonance circuit are determined by the inductance of the second winding L of the matching transformer 22 constructing the second parallel resonance circuit, the inductance of the coil L and the capacitance value of the condenser C .

7

[10] The adaptive coupling circuit as claimed in claim 6, wherein matching characteristic is determined by a part or all of the switching frequency f of the inverter, the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the first serial resonance circuit, and the resonant frequency f , frequency bandwidth BW and frequency selection factor Q of the second

P p p parallel resonance circuit.