JPH0246685A - Induction heating apparatus - Google Patents

Abstract

PURPOSE:To reduce loss of an induction heating apparatus by altenatively switching switching elements which are respectively connected across both terminals of an auto-transformer, the midpoint of whose windings being connected to a terminal of a power source, and the other terminal thereof to restrict a transistor current in about half. CONSTITUTION:An induction heating apparatus consists of a d.c. power source 21, an auto-transformer 25, the midpoint C of whose windings being connected to a terminal of the d.c. power source 21, a load circuit 32 connected to both terminals of the auto-transformer 25 and a controller 35 for altenatively switching switching elements 26 and 29 respectively connected across the both terminals of the auto-transformer 25 and the other terminal of the d.c. power source 21. When the switching elements 26 and 29 are altenatively switched, the d.c. power source 21 applies heating power, altenatively through the switching elements 26 and 29, since the terminal of the d.c. power source 21 is connected to the midpoint C of the auto-transformer 25. The currents of the switching elements 26 and 29 are thus restricted in about half compared to the conventional apparatus. Therefore, the switching elements 26 and 29 require less capacity to minimize heating to be loss.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an induction heating device used in an induction heating cooker or an induction heating type iron.

BACKGROUND OF THE INVENTION A circuit diagram of a conventional induction heating iron using this type of induction heating device is shown in FIG. In FIG. 6, reference numeral 1 denotes a DC power supply, which is composed of an AC power supply 2 and a rectifier 3. 4 is a smoothing capacitor for absorbing voltage ripples at a drive frequency of about 28 KHz, and at both ends of the smoothing capacitor 4 there is a switching element 6 composed of a transistor 6 and a diode 7, a transistor 9 and a diode 1o. A series circuit with switching element 8 is connected. A load circuit 11 is composed of a heating coil 12 and a resonant capacitor 13, and is connected in parallel with the switching element 8. 14 is a control unit that drives the transistors 6 and 9; 16 is an iron serving as a load that is inductively heated by the heating coil 12;

The operation in the above configuration will be explained. A case where the output of the AC power supply 2 is 1 oov and 60 Hz will be explained. The voltage vc across the smoothing capacitor 40 has a waveform shown in FIG. In addition, the output voltages vb1 and Vb2 of the control unit 14
As shown in FIG. 8(7) and (a), each has a dead time period Td that is alternately positive and both negative. Therefore, the transistors 6 and 8, which are turned on and off by the output voltages Vbt and vb2 of the control section 14, are turned on and off alternately. Therefore, the collector-emitter voltage VOX of the switching element 6 is as shown in FIG.
7). Due to the resonance of the load circuit 11, the current flow of the switching element 6 has a waveform approximately in the upper half of a sine wave, as shown in FIG. 9(1). switching element 60
If the on-period 1 is set to half the resonance period, the switching element 8 will be turned on just when I becomes 0,
Current flows from the load circuit 11 to the transistor 9. When the transistor 9 is kept on for a period T2, which is half of the resonance period, and then the transistor 6 is turned on again, the voltage vL applied to the load circuit 11 becomes as shown in FIG. 9 (fj), and the load circuit 11 has a An alternating current as shown in FIG. 9) flows, thereby inductively heating the iron 16 of the load. Note that the voltage and current values shown in (7) to (7) in Figure 9 are all when the input power is 12ooW, and the time scale is expanded around the peak of Va shown in Figure 7, that is, the part where VC = 141v. This is the waveform.

Problems to be Solved by the Invention However, in the conventional configuration, the current of the transistor becomes large, so the power loss of the transistor is large, and the emitters of transistor 6 and transistor 9 in the conventional technology are not at the same potential, which causes the drive The problem was that the circuit was complicated.

Let me explain a little more about the former issue. In the conventional technology, the peak value Ipeak of the collector current I of the switching element 6 and the output (rmg) T of the AC power supply 2 are
The relationship between in and input power Pin is as follows, P1n
==1200W, if Vin=100v, I
peak″=i53.3 μm, which is a large value, and therefore the transistors 6 and 9 have to be large in size, resulting in a problem of large heat generation.

The first purpose of the present invention is to solve these problems. By adding a simple and small component called a single-winding transformer, the current of the transistor can be suppressed to a fishing machine, thereby reducing and controlling the loss. The purpose is to eliminate the need for an insulating structure for the parts.

In addition, in the conventional configuration, the heating coil current is determined by the input power Pin s input voltage Win of the device, so the cross-sectional area of the copper wire of the heating coil, the number of turns, and the capacity of the resonant capacitor are fixed, resulting in heating. The problem was that there was no freedom in designing the applied voltage and supply current of the coil and resonant capacitor.

The second purpose of the present invention is to solve these problems, by adding a transformer, the current of the transistor is suppressed to a fishing machine, reducing loss, and eliminating the need for an insulating structure in the control section. It is also important to have flexibility in the design of the heating coil and resonant capacitor.

Means for Solving the Problems The technical means of the present invention for achieving the above object includes a DC power supply, an autotransformer whose midpoint is connected to one end of the DC power supply, and a transformer connected to both ends of the autotransformer. a load circuit;
The load circuit includes switching elements connected between both ends of the autotransformer and the other terminal of the DC power supply, and a control unit that alternately turns on and off each of the switching elements, and the load circuit includes a heating coil and a resonant capacitor connected in series. It is composed of circuits.

A second technical means includes a DC power supply, a transformer having a middle point of a primary winding connected to one end of the DC power supply, a load circuit connected to a secondary winding of the transformer, and a primary winding of the transformer. The load circuit includes switching elements connected between both ends of the wire and the other terminal of the DC power source, and a control for alternately turning on and off each of the switching elements, and the load circuit is composed of a series circuit of a heating coil and a resonant capacitor. It is something.

Effects According to the first technical means, one end of the DC power supply is connected to the midpoint of a small autotransformer with a simple structure.
When each switching element is turned on and off alternately, heating power is supplied from the DC power supply through the two switching elements alternately, so the current of the switching element becomes like a conventional fishing machine, making it smaller and generating less heat. Can be done. Furthermore, since the potentials of the emitters are the same, there is no need for an insulating structure for the control section.

Moreover, according to the second technical means, since one end of the DC power source is connected to the midpoint of the primary coil of the transformer, when each switching element is turned on and off alternately, two ends of the DC power source are connected.
Since the heating power is supplied through the two switching elements alternately, the current of the switching elements becomes a conventional fishing machine, making it compact and generating less heat. Furthermore, since the emitters of the two transistors are common, an insulating structure for the control section is not required. Furthermore, by adjusting the turns ratio between the primary and secondary coils of the transformer, degrees of freedom are created in the cross-sectional area of the heating coil's copper wire, the number of turns, and the value of the resonant capacitor. It is possible to keep the voltage below a certain value or to adjust the heating coil current and resonant capacitor ripple current, so that, for example, a switch can be installed in series with the heating coil to switch between multiple heating coils. The rating (voltage, current) of the switch can be matched when the switch is used.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an induction heating iron according to an embodiment of the present invention. In FIG. 1, 21 is a DC power supply, which is composed of an AC power supply 22 and a rectifier 23. 24 is a smoothing capacitor, 26 is an autotransformer, 26 is a switching element, which is composed of a transistor 27 and a diode 28, and the switching element 29 is also composed of a transistor 3o and a diode 31. 32 is a load circuit, which is composed of a series circuit of a heating coil 33 and a resonant capacitor 34.

36 is a control unit, and 36 is a load iron.

The operation in the above configuration will be explained. The functions of the DC power supply 21 and the smoothing capacitor 240 are similar to those of the conventional technique. FIG. 2 shows the waveform of the voltage VC of the smoothing capacitor 24. FIG. 3 shows the output voltage Vb1. of the control section 36. This is the waveform of Vb+. That is, the switching element 26 and the switching element 29 are turned on alternately.

FIG. 4 shows the waveforms of various parts when Va=141V, and (7) shows the applied voltage VC+X of the switching element 26,
(a) is the current Ic, ('7) is the applied voltage vL of the load circuit 32, ('7) is the current flow of the load circuit 32, and (3) is the waveform of the current flowing into the midpoint C of the autotransformer 26. It is.

When the transistor 27 is turned on by the control unit 36,
Since Vc141V is applied between c and C of the autotransformer 25, Vc is also applied between b and o due to the action of the autotransformer 26.
a occurs, and as a result, 'Vl, = -2 as shown in
It becomes 82V. Since vL is applied to the load circuit 32,
IL flows as shown in ) and returns to 0 again after time T1, which is half the resonance period. Next, when transistor 27 is turned off and transistor 3o is turned on, 141V is applied between c and b, so 141v is generated between a and C.
The OT2 period when VL=+282V is II.

The current is of the opposite sign for one period.

By repeating the above operations, the current IL flows through the load circuit 32 and heats the iron 36 serving as the load by induction. The voltage and current values shown in FIG. 4 are under the same conditions as in the conventional technology: <Vin=1ooV, Pirl"1200W. Because the input current is alternately supplied from the two switching elements. As shown in FIG. 4, the peak of IO is 26.7 μm, which is half that of the conventional technology.

, while the VOI is 282v, twice that of the conventional technology,
In general, power transistors generally have a breakdown voltage of 46 ov or more, so there is no problem, and the effect of reducing heat generation due to loss can be obtained.

Regarding the circuit of the present invention, the peak value 1cpeak of the current of the switching element 26 and the output (rug) of the AC power supply 22 are
The following relationship substantially holds true between Tin and input power Pin. Therefore, Pin = 1200W, Vifi = 1
In the case of 00V, Icpeak=26.7m, which is half of the conventional technology. In addition, even if the coupling between the heating coil and the load is poor, this can be handled by increasing the withstand voltage of the resonant capacitor, as in the conventional technique.

Further, since the emitters of the transistor 27 and the transistor 3o are at the same potential, no insulation such as a pulse transformer or a photocoupler is required inside the control unit 36, and the configuration is simplified.

In addition, in this circuit, the ripple in the circuit is small, so the smoothing capacitor can be made small.

In this embodiment, a current of approximately the same magnitude always flows between the windings IL-+-0 and c-b of the single-winding transformer 26, so the windings are used efficiently and can be made small. There is an advantage.

FIG. 6 is a circuit diagram of an induction heating iron showing a second embodiment of the present invention. In FIG. 6, the transformer 37 has a secondary winding, and the secondary winding is connected to a load circuit 38 consisting of a series circuit of a heating coil 39 and a resonant capacitor 4o, as shown in FIG. is different, but other things are the same.

The operation of this embodiment is the same as that of the previous embodiment except for the applied voltage vL and current It of the load circuit 38, and vL.

1 changes depending on the number of turns between ei and e. That is, a
If the number of turns between -b and d -e is the same, the value will be the same as in the case of Figure 1, but if, for example, the number of turns between a and e is made twice the number of turns between a and b, V, 2x, IC will be 2x.

Therefore, in this case, the size of the comparative transformer may be slightly larger than in the case of claim 1, or there is a degree of freedom in designing the constants of the heating coil and the resonant capacitor.

In the above two embodiments, two switching elements are turned on and off in synchronization with the resonant period of the load circuit, but conventional methods also apply when driving at a frequency higher than the resonant frequency or at a lower frequency. Current flows through the diode 28 and diode 31 in the same way that current flows through the diode of the technology described above, heating the load.

Effects of the Invention As is clear from the above embodiments, the induction heating device of the present invention reduces the current flowing through the switching element by about half by providing a single-turn transformer or a transformer.
The switching element can be made smaller and have lower loss, and the control section can be simplified.

In addition, by connecting a load circuit to the secondary side of the transformer,
A degree of freedom is created in the constant design of the heating coil and the resonant capacitor, and the voltage or current of the heating coil and the resonant capacitor can be set to arbitrary values.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an induction heating iron according to a first embodiment of the present invention, FIGS. 2, 3, and 4 are operating waveform diagrams thereof, and FIG. 6 is a circuit diagram of an induction heating iron according to a first embodiment of the present invention. FIG. 6 is a circuit diagram of an induction heating iron according to the prior art, and FIGS. 7, 8, and 9 are operational waveform diagrams thereof. 21...DC power supply, 26...Auto transformer, 32...Load circuit, 26...Switching element, 29...Switching element ,
33...Heating coil, 34...Resonance capacitor, 37...Transformer. Name of agent: Patent attorney Shigetaka Awano and 1 other person21
- Road current 1 Freeze 22 - AC power supply 23 - Arrangement 1 Ugly = 1,000 1 24 - Flat bone content, 29 - Switching element 32 - Load circuit 33 - Power [Retsu Coil 34-Shinshitsu Container 35--Control Figure Figure 2/...-L5 Temperature 2 Meter-Compassionate Indulgence Source 23-M-Hard Ranut, Motor 5. 24- Smooth content Z6. Z9-・-Switching element 35--Kazuchi ■Go p 37-Transformer 38-Load rotation/--IC"t* 'It 5X 2゛°-AC 1+〝3-Set, 5jt play 4゛-° Smooth content n...-yIL load surface road road...Large heat coil I3- Coexistence content 14--control 4I pH node

Claims (2)

[Claims] (1) A DC power supply, an autotransformer whose midpoint is connected to one end of the DC power supply, a load circuit connected to both ends of the autotransformer, and both ends of the autotransformer and the other terminal of the DC power supply. an induction heating device comprising switching elements connected between the two, and a control section that alternately controls on and off the switching elements, the load circuit comprising a series circuit of a heating coil and a resonant capacitor. (2) a DC power supply, a transformer having the middle point of the primary winding connected to one end of the DC power supply, a load circuit connected to the secondary winding of the transformer, and both ends of the primary winding of the transformer and the DC power supply; An induction heating device comprising switching elements each connected between the other terminals of a power source and a control unit that turns each switching element on and off alternately, the load circuit comprising a series circuit of a heating coil and a resonant capacitor.