JP5769641B2 - Power circuit device for induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker, and more particularly to a frequency variable power supply circuit device that supplies a high-frequency current to a heating coil of an induction heating cooker.

  Induction heating cookers such as so-called IH cooking heaters and IH rice cookers directly cause the bottom plate of the cooking pan to flow directly through the induction heating coil and eddy current to the bottom plate of the cooking pan to generate Joule heat. It is for heating. Many methods for controlling the “heating power (effective value of electric power by high-frequency current flowing in the induction heating coil)” of the induction heating cooker have been proposed. For example, in the induction heating cooker described in Patent Document 1, an induction heating cooker that adjusts the heating power by controlling the switching frequency of an inverter that supplies a high-frequency current to the induction heating coil has been proposed.

  For example, a half-bridge inverter includes a pair of switching elements connected in series with each other. A heating coil and a resonance capacitor disposed between an intermediate terminal between these switching elements and a ground potential have a predetermined switching frequency. A high-frequency current having At this time, the electric power generated by the high-frequency current flowing in the heating coil is obtained by making the ON period in which each switching element is ON constant and increasing / decreasing the OFF period (duty ratio) in OFF state, that is, by controlling the switching frequency. The effective value is controlled, and the Joule heat (thermal power) generated in the cooking pan is adjusted. More specifically, the higher the switching frequency, the longer the off period with respect to the on period, and the smaller the effective power value due to the high-frequency current (the thermal power becomes weaker). On the other hand, the lower the switching frequency, the shorter the off period relative to the on period, and the larger the effective power value due to the high-frequency current (the thermal power becomes stronger).

By the way, in a switching element used in an inverter, a transitional current normally flows when an off state is switched to an on state and from an on state to an off state, and switching loss (switching loss) is inevitably generated. A conduction loss proportional to the square of the amount of current flowing through the switching element in the on state or the conduction resistance occurs.
Therefore, in an inverter that achieves a desired thermal power (effective power value due to a high-frequency current) by controlling the switching frequency while keeping the ON period in the ON state constant, the higher the switching frequency, the greater the number of ON / OFF times that are repeated. Therefore, the switching loss is substantially increased compared to the conduction loss (the switching loss becomes dominant), and the conduction resistance increases as the switching frequency is lower. Therefore, the conduction loss is more significant than the switching loss. (Conduction loss is dominant).

JP 2011-1555022 A

  Conventionally, in an inverter of a variable frequency induction heating cooker in which the ON period during which the switching element is in an ON state is constant, the switching frequency is controlled, and the heating power is adjusted, the switching loss is particularly high when the switching frequency is high. While suppressing, it has been required to reduce the overall energy loss by suppressing conduction loss when the switching frequency is low. In order to meet these demands, inverters using switching elements such as SiC (silicon carbide) semiconductor elements having high-speed switching characteristics and low switching loss have been proposed. However, such high-speed switching elements are expensive and low-cost. It was a hindrance.

  Accordingly, the present invention has been made to solve the above-described problems, and has an extremely simple and inexpensive circuit configuration, reduces switching loss when the switching frequency is high, and conducts when the switching frequency is low. It aims at providing the power supply circuit apparatus of the induction heating cooking appliance which can suppress loss.

A power supply circuit device for an induction heating cooker having a heating coil according to the present invention includes first and second rectifier circuits for converting an AC voltage into a DC voltage, and a high frequency from the DC voltage from the first rectifier circuit. A transformer including first and second switching elements connected in series with each other for generating a current, a primary winding wound on the same axis, and first and second secondary windings. Coupling inhibiting means disposed between the first and second secondary windings, and rectifying and smoothing the voltage generated in the first and second secondary windings, First and second secondary side rectifying / smoothing circuits for generating first and second DC power sources including two voltages, and intermittently cutting off the DC voltage from the second rectifying circuit to A transformer control circuit for supplying to the primary winding; A feedback circuit that controls the transformer control circuit so that the second voltage is constant by adjusting an interval at which a second voltage is supplied to the primary winding of the transformer; A switching element drive connected to both ends of one DC power source and supplying a voltage for turning on the first and second switching elements to the first and second switching elements based on the first voltage A circuit and a control signal having a variable switching frequency are supplied to the switching element driving circuit, and the switching frequency of the control signal is controlled to thereby provide a reference potential between the first and second switching elements. A switching control circuit for controlling an effective power value due to a high-frequency current flowing in the heating coil provided, and both ends of the second DC power source. Current adjusting means for changing a current value together with a desired power effective value due to a high-frequency current flowing in the heating coil, and the first and second secondary windings of the transformer have a desired power effective value. The larger the current is, the larger the current supplied from the second DC power supply increases, and the first voltage increases.

  According to the present invention, the power supply circuit device of the variable frequency induction heating cooker that controls the heating frequency by controlling the switching frequency has a very simple and inexpensive configuration including a transformer, a feedback circuit, and a transformer control circuit. As the thermal power (switching frequency) increases or decreases, switching loss or conduction loss that causes more substantial energy loss can be efficiently reduced.

It is a block diagram which shows the circuit structure of the power circuit device of Embodiment 1 which concerns on this invention. It is a graph which shows the relationship between a thermal power and a switching frequency. It is a graph which shows the relationship between switching frequency and switching loss, and the relationship between switching frequency and conduction | electrical_connection loss. (A) is a graph showing an AC voltage waveform from a commercial power supply, (b) a DC voltage waveform from a transformer rectifier circuit, and (c) a graph showing an intermittently interrupted DC voltage waveform from a transformer control circuit. . 2 is a cross-sectional view of an exemplary transformer according to Embodiment 1. FIG. It is a graph which shows the relationship between the electric current which flows into a thermal-power display means, and the voltage of a secondary side winding. It is a graph which shows the relationship between a switching frequency and the voltage of a secondary side winding. It is a graph which shows the relationship between the electric current which flows into a secondary side coil | winding, and a voltage. It is a block diagram which shows the 1st and 2nd drive circuit which comprises an inverter. FIG. 6 is a block diagram illustrating a circuit configuration of a power supply circuit device according to a second embodiment. 5 is a cross-sectional view of a transformer according to Embodiment 2. FIG. FIG. 6 is a block diagram showing first and second drive circuits that constitute an inverter according to a second embodiment.

Embodiment 1 FIG.
Embodiments of a power supply circuit device for an induction heating cooker according to the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a block diagram illustrating a circuit configuration of the power supply circuit device 1 according to the first embodiment. The power supply circuit device 1 generally includes a power supply unit 10 and a transformer circuit unit 30 surrounded by a broken line, a switching control circuit 50, and a thermal power display unit (current adjustment unit) 60.

The power supply unit 10 includes a power rectifier circuit (first rectifier circuit) 12, an inverter 14 surrounded by a one-dot chain line, and an LCR induction heating unit 6. The power supply rectifier circuit 12 rectifies the AC voltage from the two-phase or three-phase commercial power supply 5 into a DC voltage. The inverter 14 includes a pair of (first and second) voltage-driven switching elements 16 and 18 connected in series with each other, and a pair of (first and second) drive circuits that drive the switching elements 16 and 18. 20 and 22. In the inverter 14, each drive circuit 20, 22 receives a control signal from the switching control circuit 50, drives each switching element 16, 18, and generates a high-frequency current from a DC voltage from the power supply rectifier circuit 12. is there. The LCR induction heating unit 6 includes a heating coil 7 connected between the intermediate terminal 9 between the switching elements 16 and 18 and a reference potential (ground potential, GND _A ), and a resonance capacitor connected in series to the heating coil 7. 8, the high frequency magnetic field is formed by the high frequency current supplied from the inverter 14, and the cooking pot is heated by generating an Joule heat by flowing an eddy current through the bottom plate of the cooking pot.

  The switching elements 16 and 18 of the inverter 14 keep the ON period in the ON state constant, and control the switching frequency f, whereby the effective power value P (hereinafter referred to as “thermal power” for convenience) due to the high-frequency current flowing in the heating coil 7. ), That is, the amount of Joule heat generated in the cooking pan is controlled. FIG. 2 is a graph showing the relationship between the thermal power P and the switching frequency f. The switching control circuit 50 controls the drive circuits 20 and 22 by selecting the switching frequency f corresponding to the thermal power P set or desired by the user. Specifically, the switching control circuit 50 reduces the thermal power P of the LCR induction heating unit 6 by lowering the switching frequency f to increase the thermal power and increasing the switching frequency f to decrease the thermal power. To be adjusted.

  FIG. 3 is a graph showing the relationship between the switching frequency f and the switching loss (solid line) and the relationship between the switching frequency f and the conduction loss (broken line). As described above in the section of the background art, the higher the switching frequency f, the more the switching loss increases compared to the conduction loss. The lower the switching frequency f, the more dominant the conduction loss than the switching loss. It becomes.

  Note that the circuit configuration of the above-described power supply unit 10 is not limited to this, and may employ a full-bridge inverter, and may have any type known to those skilled in the art. Therefore, further detailed description is omitted.

  Next, the transformer circuit unit 30 according to the present invention will be described. The transformer circuit unit 30 includes a transformer rectifier circuit (second rectifier circuit) 32 that rectifies an AC voltage (FIG. 4A) from the commercial power supply 5 into a DC voltage (FIG. 4B), a transformer 40, A transformer control circuit 34 that intermittently cuts off the DC voltage from the transformer rectifier circuit 32 (FIG. 4C) and supplies the primary voltage to the primary winding of the transformer 40. That is, the transformer control circuit 34 can control the input energy to the transformer 40 by adjusting the interval τ at which the DC voltage shown in FIG.

Transformer 40 constituting the transformer circuit 30, as shown in FIG. 1 includes a primary winding _{P 1,} 3 single secondary winding _{S A,} S B, and _{S C.} The secondary winding _{S A, S B, S C,} respectively, the rectifier diodes 38A, 38B, series to 38C, the smoothing capacitor 39A, 39B, are connected in parallel to 39C, the voltage _V A which is smoothed to a DC, V _B, and supplies the _{V C.}

The secondary side winding S _A (first secondary side winding) of the transformer 40 according to the first embodiment will be described in detail later, but the ON voltage (voltage V _A ) of the switching elements 16 and 18 of the inverter 14 is set. To give.

The secondary winding S _B of the transformer 40 via a constant-voltage generating circuit 37 such as a series regulator, and supplies the driving voltage (voltage V _B) to the switching control circuit 50 (FIG. 1).

The secondary winding S _C (second secondary winding) of the transformer 40 has a thermal power display means 60 (FIG. 1) such as an LED lamp array whose lighting number increases or decreases according to the thermal power P, or the thermal power P. The drive voltage (voltage V _C ) of the current adjusting means whose current value is increased or decreased in response to is given.
According to the present invention, the secondary winding S _C is connected to the feedback circuit 36, and the feedback circuit 36 has a constant driving voltage (voltage V _C ) applied to the thermal power display means or current adjustment means 60. It is configured to control the transformer control circuit 34 so as to be maintained.

A specific configuration of the transformer 40 will be described with reference to FIG. FIG. 5 is a cross-sectional view of an exemplary transformer 40 according to the first embodiment. The transformer 40 of FIG. 5 is configured as a so-called coil bobbin type transformer, and is coaxially centered on a core 42 with a first primary winding P ₁ a, secondary windings S _A , S _B , S _C , and the second primary winding P _{1 b} is successively wound. First and second primary winding _P 1 a, _{P 1} b is connected in series with each other, the secondary winding _{S A,} S B, electrically insulated from the _{S C,} magnetic It is formed so that it may couple | bond with. That split primary winding _P 1 a, _{P 1} b is the secondary winding _{S A,} S B, by sandwiching the _{S C,} the magnetic field energy arising from the primary winding of the transformer 40 It is intended to efficiently transmit to the secondary winding and reduce energy loss due to magnetic field leakage.

The transformer control circuit 34 intermittently supplies the DC voltage rectified by the transformer rectifier circuit 32 to the primary windings P ₁ a and P ₁ b at a predetermined time interval τ, and the feedback circuit 36 adjusts the time interval tau, in which the voltage V _C of the secondary winding S _C controls the transformer rectifier circuit 32 to be maintained at a constant value. For example, when the voltage V _C is smaller than a predetermined reference set value, the transformer control circuit 34 increases the time τ during which the voltage is applied to the primary windings P ₁ a and P ₁ b and is larger than the reference set value. the primary winding P _{1 a} when, by reducing the time τ for applying a voltage to P 1 _b, the DC voltage V _C is controlled to a constant value.

6 shows the current I _C flowing through the thermal power display means or current adjusting means 60, the voltage V _{A of the} secondary winding S _A (first secondary winding) of the transformer 40, and the secondary winding S. is a graph showing the relationship between the voltage V _C of _{C (the} second secondary winding). In FIG. 6, the voltage V _C of the secondary winding S _C is maintained at a constant value, when the current value of the thermal power display means or current regulating means 60 drive voltage V _C is applied is increased, this Current I _C (not shown) and output energy flowing to the secondary side winding P ₁ are increased, and the input energy to the primary side winding P ₁ is also increased. Accordingly, the voltage V _A across the secondary side winding S _A is increased. It increases with current _{I C.}

The slope of the voltage V _A in FIG. 6 becomes larger when the coupling between the secondary windings S _A and S _C is poor. The secondary winding S _A, binding of S _C is the secondary winding S _A, defined by the position relation of S _C, the distance between the windings is poor farther. As described with reference to FIG. 5, the secondary windings S _A and S _C are wound around another secondary winding S _B, and thus the distances S _A and S between the secondary windings. _C is far away. That is, since the transformer 40 according to the present invention is configured so that the coupling between the secondary windings S _A and S _C is poor, the voltage across the secondary winding S _A is shown in FIG. V _A increases with current I _C.

Transformer 40 according to the present invention, between the secondary winding S _A and the secondary winding S _C, winding the secondary winding S _B Alternative supplies a drive voltage V _B to the switching control circuit 50 Turn the secondary side winding S _A and the secondary side winding S _C away from each other and intentionally design the secondary side windings S _A and S _{C so that} the coupling between them becomes worse. The voltage V _A across the winding S _A is configured to increase with the current I _C (FIG. 6). In other words, the transformer 40 according to the present invention is provided with coupling inhibition means (secondary winding S _B ) that inhibits the magnetic coupling relationship between the secondary windings S _A and S _C. voltage V _a of the next winding S _a is configured so as to increase with the current I _C. Binding inhibition means, the secondary winding S _A, may be a secondary winding S _B which are wound between the S _C, may simply a spacer member (not shown).

As described above, the thermal power display means or the current adjustment means 60 simply increases or decreases the current value according to the thermal power P, and the relationship between the switching frequency f and the thermal power P is as shown in the graph of FIG. Therefore, the relationship shown in FIG. 7 is established between the switching frequency f and the voltages V _A and V _C of the secondary windings S _A and S _C. Further in other words, when the thermal power P is constant, since the input energy from the voltage V _C and the primary winding P ₁ is constant, the output energy of the secondary winding S _A becomes constant, secondary current I _a flowing to the side winding S _C, as shown in FIG. 8, increases or decreases according to the variation of the voltage V _a.

A specific configuration of the inverter 14 according to the first embodiment will be described with reference to FIG. FIG. 9 is a block diagram showing the first and second drive circuits 20 and 22 constituting the inverter 14. The first drive circuit 20 includes a bootstrap diode 23 and a charging resistor 24 connected in series to a voltage V _A from the secondary winding S _A (first secondary winding) of the transformer 40. A bootstrap capacitor 25 connected in parallel to each other, and driving circuit switches (hereinafter simply referred to as “switches”) 26A and 26B are provided. The first drive circuit 20 includes a first switching element 16 having a control terminal (gate terminal) connected to the intermediate terminals of the switches 26A and 26B via resistors.

On the other hand, the second driving circuit 22 via directly connected to the drive circuit switch 28A to the voltage V _A from the secondary winding S _A of transformer 40, and 28B, the resistor in between the terminal connection And a second switching element 18 having a control terminal (gate terminal). The intermediate terminal 9 between the first and second switching elements 16 and 18 is connected to the heating coil 7 (LCR induction heating unit 6, FIG. 1). The reference potential GND _A for the voltage _{V A} is the through the intermediate terminal 9, a reference potential (source terminal in the case of MOSFET, in the case of IGBT emitter terminal) of the second switching element 28B is connected to .

In the operation of the inverter 14 according to the first embodiment, the high-frequency current can be supplied to the heating coil 7 by alternately turning on and off the voltage-driven first and second switching elements 16 and 18. In order to turn on the first switching element 16, the switch 26A is turned on and the switch 26B is turned off, so that the control terminal (gate terminal) of the first switching element 16 and the intermediate terminal 9 are connected. Conduct. At this time, a voltage _VA equivalent to both ends of the bootstrap capacitor 25 is applied between the control terminal (gate terminal) of the first switching element 16 and the intermediate terminal 9 (source terminal or emitter terminal). The parasitic capacitance Q between the control terminal and the intermediate terminal 9 needs to be charged. Incidentally current I _A flowing to the secondary winding S _A is proportional to the product of the parasitic capacitances Q and the switching frequency _{f (I A αQ × f)} .

Here thermal P (switching frequency f), the voltage of the secondary winding _{S A V A} and the current _{I A} flowing therethrough, as well as switching loss (switching loss) of the switching elements 16, 18, and conduction loss (conduction loss) Think about the relationship. As described above, the smaller the heating power P is (the higher the switching frequency f is), the switching caused by the transient current flowing in the first and second switching elements 16 and 18 during the transition between the off state and the on state. loss, substantially greater than the conduction losses proportional to the square or the conduction resistance of the switching elements 16, 18 of the current I _a. That is, when the thermal power P is small, the switching loss is dominant, and when the thermal power P is large, the conduction loss is dominant.
In general, a voltage-driven switching element has a feature that the higher the voltage applied between the control terminal and the intermediate terminal, the lower the conduction loss, and the lower the voltage, the lower the switching loss. In a typical case, the voltage applied between the control terminal and the intermediate terminal should be reduced, and when conduction loss is dominant, the voltage applied between the control terminal and the intermediate terminal should be increased. Is required.

Therefore the induction heating cooker of the power supply circuit device 1 according to the present invention, in order to reduce energy losses to be more dominant, to maintain the voltage V _C of the second secondary winding S _C to a constant value In addition, coupling inhibiting means for inhibiting the magnetic coupling relationship between the secondary windings S _A and S _C (for example, the secondary winding S _B provided between the secondary windings S _A and S _C ). Or a spacer). That is, according to the present invention, when thermal power P is small, the thermal power display means or current regulating means 60 so that the voltage V _A across the first secondary winding S _A is reduced by adjusting the I _C (FIG. 7), the switching frequency f is higher for current I _a increases (FIG. 8), can be reduced greater switching loss relatively. Additionally, according to the present invention, when thermal power P is large, the thermal power display means or current regulating means 60 so that the voltage V _A of the secondary winding S _A becomes greater adjusts the I _C (Fig. 7) in addition, the switching frequency f is low because current I _a decreases (Fig. 8), the conduction loss to be relatively conspicuous can be substantially suppressed.

In other words, the power supply circuit device 1 according to the present invention has a transformer circuit unit 30 having a very simple and inexpensive configuration, and thus causes more substantial energy loss as the thermal power P or the switching frequency f increases or decreases. The switching loss or conduction loss is effectively reduced. Note the voltage V _B across the secondary winding S _B of the transformer 40 is, similarly to the voltage V _A of the first secondary winding, increases and decreases depending on the current value of the thermal power P or current regulating means 60 However, since it is connected to the constant voltage generation circuit (FIG. 1) 37, the voltage V _D applied to the switching control circuit 50 does not depend on the thermal power P.

Embodiment 2. FIG.
A second embodiment of the power supply circuit device for an induction heating cooker according to the present invention will be described in detail below with reference to FIGS. The power supply circuit device 2 of the second embodiment has the same configuration as that of the power supply circuit device 1 of the first embodiment except that the circuit configuration of the inverter 14 and the components of the transformer 40 are different. Description is omitted.

FIG. 10 is a block diagram illustrating a circuit configuration of the power supply circuit device 2 according to the second embodiment. Circuit device 2 of the second embodiment has the transformer 40 and the primary winding _{P 1,} 4 single secondary winding _{S A1, S A2, S B} , and _{S C,} the embodiments 1 Compared to the power supply circuit device 1, a (third) secondary winding S _A2 is added. In the power supply circuit device 2 according to the second embodiment, the switching elements 16 and 18 of the inverter 14 are applied with the voltages V _A1 and V _{A2 that} are smoothed to the direct current from the secondary windings S _A1 and S _A2 . .

FIG. 11 is a cross-sectional view of the transformer 40 according to the second embodiment. A transformer 40 shown in FIG. 11 is similarly configured as a coil bobbin type transformer, and coaxially with a core 42 as a center, the first primary winding P ₁ a and the secondary windings S _A1 , S _A2 , S _{B 1} , S _C , and the second primary winding P ₁ b are wound sequentially. First and second primary winding _P 1 a, _{P 1} b are connected in series to each other, the secondary winding _{S A1, S A2, S B} , and _{S C} is electrically insulated, It is formed so as to be magnetically coupled.

Transformer 40 according to the second embodiment, as in the first embodiment, between the secondary winding S _A1, S _A2 and secondary winding S _C, as the binding inhibiting means, drive the switching control circuit 50 by winding the separate secondary winding S _B supplies a voltage V _B (or the spacer member is provided), with each other by separating the secondary winding S _A1, S _A2 and the secondary winding S _C By intentionally making the coupling relationship between the secondary windings S _A1 and S _A2 and the secondary winding S _C inconsistent, the voltages V _A1 and V across the secondary windings S _A1 and S _{A2 A2} is configured to increase with current I _C.

FIG. 12 is a block diagram showing the first and second drive circuits 20 and 22 constituting the inverter 14 according to the second embodiment. The first drive circuit 20 of the second embodiment is directly connected to the secondary side winding S _A1 (first secondary side winding) of the transformer 40, and the boot described in the first embodiment. Does not have strap diode or bootstrap capacitor. Similarly, the second drive circuit 22 is directly connected to the secondary winding S _A2 (first secondary winding) of the transformer 40.

  In the power supply circuit device 2 according to the second embodiment, it is necessary to add the secondary winding of the transformer 40. However, the circuit configuration of the first drive circuit 20 can be simplified, and is the same as in the first embodiment. The effect of can be realized. That is, the power supply circuit device 2 according to the second embodiment has a transformer circuit unit 30 having a very simple and inexpensive configuration, which causes more substantial energy loss as the thermal power P or the switching frequency f increases or decreases. Thus, the switching loss or conduction loss can be reduced efficiently.

1,2. 4. power supply circuit device; Commercial power supply, 6. 6. LCR induction heating unit, Heating coil, 8. 8. resonant capacitor, Intermediate terminal, 10. Power supply unit, 12. 13. power supply rectifier circuit (first rectifier circuit); Inverters 16, 18. Voltage-driven switching element 20, 22. Drive circuit, 23. Bootstrap diode, 24. Charging resistance, 25. Bootstrap capacitor, 26, 28. Drive circuit switch, 30. Transformer circuit section, 32. Rectifier circuit for transformer, 34. Transformer control circuit, 36. Feedback, 37. Constant voltage generating circuit, 38. Rectifier diode, 39. Smoothing capacitor, 40. Transformer, 42. Core, 50. Switching control circuit, 60. Thermal power display means (current adjustment means), P ₁ , primary winding, S _A , S _B , S _C. Secondary winding.

Claims (5)

In a power supply circuit device (1) for an induction heating cooker having a heating coil (7),
First and second rectifier circuits (12, 32) for converting an AC voltage into a DC voltage;
An inverter (14) having first and second switching elements (16, 18) connected in series to generate a high-frequency current from a DC voltage from the first rectifier circuit (12);
_A transformer (40) including a primary winding (P ₁ ) wound coaxially and first and second secondary windings (S _A , S _C );
_A coupling inhibiting means disposed between the first and second secondary windings (S _A , S _C );
_A voltage generated in the first and second secondary windings (S _A , S _C ) is rectified and smoothed, and includes first and second voltages (V _A , V _C ). First and second secondary side rectifying and smoothing circuits (38, 39) for generating a DC power source;
A transformer control circuit (34) that intermittently cuts off the DC voltage from the second rectifier circuit (32) and supplies the DC voltage to the primary winding ( P ₁ ) of the transformer (40);
By the second voltage _{(V C)} to adjust the spacing (tau) supplied to said primary winding _{(P 1)} of the transformer (40), said second voltage _{(V C)} is A feedback circuit (36) for controlling the transformer control circuit (34) to be constant;
The first is connected to both ends of a DC power source, the first and second of the first to turn on the switching element (16, 18) of the voltage (V _A) said first and second switching elements Switching element drive circuits (20, 22) to be supplied to (16, 18);
By supplying a control signal having a variable switching frequency (f) to the switching element driving circuit (20, 22) and controlling the switching frequency (f) of the control signal, the first and second switching operations are performed. A switching control circuit (50) for controlling an effective power value (P) by a high-frequency current flowing in the heating coil (7) provided between the elements (16, 18) and a reference potential (GND);
Current adjusting means (60) connected to both ends of the second DC power source and for changing a current value (I _C ) together with a desired power effective value (P) by a high-frequency current flowing in the heating coil (7). ,
The first and second secondary windings (S _A , S _C ) of the transformer (40) are supplied with a current (2) supplied from the second DC power source as the desired effective power value (P) increases. I _C ) is increased, and the first voltage (V _A ) is increased. The transformer (40) has a third secondary winding ( S _A2 ),
The coupling inhibiting means is disposed between the second and third secondary windings (S _C , S _A2 ),
The power supply circuit device rectifies and smoothes a voltage generated in the third secondary winding ( S _A2 ) to generate a third DC power source including a third voltage ( V _A2 ). A secondary rectifying / smoothing circuit (38, 39);
The first, second, and third DC power sources of the transformer (40) are configured such that the third voltage ( V _A2 ) increases as the desired effective power value (P) increases. The power supply circuit device according to claim 1. The power supply circuit device according to claim 1 or 2 , wherein the current adjusting means (60) includes a light emitting element array exhibiting a desired power effective value (P). As the desired effective power value (P) is larger, the switching control circuit (50) lowers the switching frequency (f) of the control signal, and the current adjusting means (60) reduces the current (I _C ) flowing therethrough. by increasing, reducing the conduction loss of the first voltage across the first secondary winding (S _a) (V _a) increase, the first and second switching elements (16, 18) And
The smaller the desired effective value (P), the higher the switching control circuit (50) increases the switching frequency (f) of the control signal, and the current adjusting means (60) causes the current (I _C ) flowing therethrough. by reducing, the first to reduce the first voltage across the secondary winding (S _a) (V _a), the switching of the first and second switching elements (16, 18) power circuit arrangement according to any one of claims 1-3, characterized in that to reduce the loss. First voltage (V _A 5 is configured to decrease as the switching frequency (f) of the control signal increases.

Images