JPH0612705B2 - Induction heating cooker - Google Patents

Description

The present invention relates to an induction heating cooker in which a high-frequency current is supplied to an induction heating coil by an inverter that oscillates by self-excitation, and more specifically, it will be described as a transistor for interrupting a direct current of the induction heating coil. This paper proposes an induction heating cooker in which the drive circuit is composed of a simple circuit using a magnetic saturation transformer and the input power of the induction heating coil can be controlled.

FIG. 1 shows a main part of an induction heating cooker using a single-ended push-pull inverter. Transistors Q ₂ and Q ₁ are connected in series to the DC power source, and flywheel diodes D ₂ and D ₁ are connected in antiparallel to the transistors Q ₂ and Q ₁ , respectively. A series resonance circuit of an induction heating coil and a resonance capacitor C ₁ is connected to the parallel circuit of the transistor Q ₂ and the diode D ₂ . In this circuit, a predetermined control signal is applied to the bases of the transistors Q ₂ and Q ₁ , and the two are alternately turned on so that a high-frequency current flows through the induction heating coil L and a pan (not shown) placed on the coil L is placed. To heat. On / off control of both transistors Q ₁ and Q ₂ is performed by, for example, transistor Q ₂
Is driven at a constant frequency (20 kHz), the transistor Q ₁ is turned on within the off period, and the on-time length is changed to control the input power. However, in order to perform such control, a complementary circuit including two positive and negative power supplies and a transistor is required, the control circuit is extremely complicated, and a large number of parts are required.

The present invention has been made to solve such a conventional problem, and a drive circuit of a transistor for connecting and disconnecting a direct current of an induction heating coil is configured by a simple circuit using a magnetic saturation transformer to obtain an induction heating coil. The purpose of the present invention is to provide an induction heating cooker capable of controlling the input power of the.

Hereinafter, the present invention will be described in detail with reference to the drawings showing an embodiment thereof.
FIG. 2 is a circuit diagram of a main part of the electromagnetic cooker according to the present invention.
The part indicated by the dotted line is a known self-oscillation circuit using two transformers. The continuously formed primary winding N ₁ and secondary winding N ₂ of the first transformer T ₁ have one ends connected to the collectors of complementary connected transistors Q ₃ and Q ₄ having the same characteristics. , The common terminal of both windings is connected to the positive electrode A + of the DC power supply (not shown). The emitters of the transistors Q ₃ and Q ₄ are collectively the negative electrode A of the DC power supply.
It is connected to − and is also connected to one end of a parallel circuit of a diode D ₁ and a capacitor C ₂ , and the other end of the parallel circuit is a primary winding N of a magnetic saturation type second transformer T ₂ formed continuously.
₇ and the secondary winding N ₈ are connected to the common terminals, and the other terminals of the both windings N ₇ and N ₈ are connected to the bases of the transistors Q ₃ and Q ₄ , respectively. The cathode of the diode D ₃ connected to the windings N ₇ and N ₈ is connected to the positive electrode of the DC power supply via the starting resistor R ₁ . The tertiary winding N ₃ of the first transformer T ₁ and the tertiary winding N ₆ of the second transformer T ₂ are connected via the resistor R ₂ . In such a self-oscillation circuit, when the transistor Q ₃ is first turned on by applying a DC voltage, a current starts to flow between the collector and the emitter of the transistor Q ₃ and is electromagnetically coupled to the primary winding N ₁ of the first transformer. A voltage is induced in the rotating tertiary winding N ₃ , and this voltage induces a voltage in the primary winding N ₇ via the tertiary winding N ₆ of the second transformer T _{2 and} causes a positive voltage in the transistor Q ₃ . Feedback is applied, and the transistor Q ₃ is reliably turned on by a sufficient base current. Then, the magnetic saturation of the second transformer increases the current flowing through the resistor R _2, and the voltage across the winding N ₆ decreases, so that the feedback voltage decreases.

Then, the transistor Q ₃ is cut off, the transistor C ₄ is turned on next by the action of the capacitor C ₂ , and then the transistors Q ₃ and Q ₄ are turned on in the same manner.
Repeatedly turned off.

As a result, the rectangular wave voltage of the above-mentioned oscillation frequency (20 kHz) is obtained at the quaternary winding T ₄ of the first transformer T ₁ , but in the present invention, the primary winding N ₄ of the third transformer T ₃ is obtained. The output of the fourth winding N ₄ is given to ₉ . Third transformer T
₃ is of magnetic saturation transistor _Q 2, _{Q 1} on, the secondary winding to control the off N10,3 winding N
11, a fourth winding N for magnetic saturation control
12 and a fifth winding N13 are provided. The fifth winding N ₅ of the second transformer is connected to the rectifier circuit DB,
DC DB output Yes as to flow through the series circuit of 4 winding N12 and 5 winding N13, and controls the direct current by the variable resistor R ₃ that is interposed in the middle of the circuit.

One end of the third secondary winding N10 of the transformer T ₃ is connected to the base of the transistor Q _2, the other end diode D ₄
And one end of the parallel circuit of the capacitor C ₃ (diode D ₄
Is connected to the cathode side), and one end of the parallel circuit is connected to the emitter of the transistor Q _{2 and} the collector of the transistor Q ₁ . One end of the tertiary winding N11 is connected to the base of the transistor Q ₁ and the other end is a diode D ₅
And a transistor Q via a parallel circuit of a capacitor C _4
1 is connected to the emitter. And windings N10, N11
Whereas in the same polarity side terminal represented by black circles (N10) on the base side of the transistor Q _2, the other (N11) has the diode D ₅ side.

Between the positive electrode B + and the negative electrode B− of the DC power source, a series circuit of the transistors Q ₂ and Q _{1 and} a series circuit of the diodes D ₂ and D ₁ connected in anti-parallel to these are connected in the same manner as shown in FIG. Are connected, and the positive electrode B + and the diodes D ₂ and D
A series circuit of the induction heating coil L and the resonance capacitor C ₁ is connected between the connection point of _{No. 1 and} the connection point of _{No. 1} .

It is desirable that the second transformer T ₂ and the third transformer T ₃ are designed so that the times from when the transistors Q ₃ and Q ₄ are turned on to when they are saturated are substantially equal to each other, which allows the transistor Q _{1 to be} saturated. , Q _{2 the} dead time required can be easily obtained.

The configuration of the third transformer T ₃ is as shown in Figure 3, it is desirable to toroidal coil made using the two toroids, primary to 3 windings N ₉ ~N11 is wound over both core On the other hand, the quaternary winding N12 and the quintic winding N13 are wound around separate iron cores and wound so as to cancel the AC component.

The operation of the above circuit is as follows. That third transformer secondary by the induced square wave voltage to the first 4 winding N ₄ of the transformer T _1, 3 winding N10, the rectangular wave voltage is obtained even N11 is winding N10, N11 And transistors Q ₂ and Q
_Since the connection with ₁ has the opposite polarity, both transistors Q ₂ and Q ₁ reciprocally turn on and off repeatedly. Thus was windings N12 to increase the value of the variable resistor R ₃ and, N
When the direct current i flowing through 13 is kept small, the saturation of the third transformer is determined by the size and characteristics of its core, and the ON periods of the transistors Q ₁ and Q ₂ are long. On the contrary,
When the value of the variable resistor R ₃ is decreased and the direct current i is increased, the saturation of the transformer T ₃ is dominated by this current value. The larger the current i is, the earlier the saturation point is. The ON period of ₁ and Q ₂ becomes shorter.
In this way, the input power is adjusted in the induction heating cooker of the present invention. In this embodiment, the power supply for controlling the magnetic saturation is obtained by the fifth winding N ₅ of the first transformer, and the circuit configuration is simpler. Further, since the DC power supply i controls the ON periods of both the transistors Q ₂ and Q ₁ , there is an advantage that the control width of the input power can be widened.

FIG. 4 shows another embodiment of the present invention.

This circuit uses a self-excited oscillation type inverter as in the embodiment shown in FIG. 2, but is not a push-pull type. This embodiment will be described below.

The direct current obtained by rectifying the alternating current is given to the smoothing capacitor C ₀ , and the smoothed direct current is given to the series resonance circuit formed by connecting the induction heating coil L and the resonance capacitor C ₁ in series. The resonance capacitor C ₁ has a magnetic saturation transformer T ₄ of 1
Winding N21 and has a series circuit of the transistor Q ₀ is connected in parallel, it is connected in antiparallel flywheel diode D21 to the transistor Q _0. Resistor R22 of the magnetic reset bias current for supply to the base-emitter of the transistor Q ₀ is connected. Transistor Q
₀ based is continuous with the positive electrode of the DC power source through which is connected to the resistor R21 for starting and is continuous to the end of the secondary winding N22 of the transformer T _4.

The emitter of the transistor Q ₀ is connected to its cathode connected to the anode of a diode D22 to the connection point of the secondary winding N22, and a tertiary winding N23 of the transformer T _4, the electrolytic capacitor C21 through the diode D22 They are connected in parallel. The other end of the tertiary winding N23 is connected to the anode of the diode D23, is connected to the cathode to the emitter of the transistor Q _0.

4 winding N24 and the transformer T _4, through the DC current i 5 winding N25 is connected in series to Yes so as to cancel an alternating current component the series circuit in opposite polarity through a variable resistor R23 It is made to flow. Then configured using a toroidal coil made from the aforementioned transformer T ₃ and likewise two toroids as shown in also FIG. 5 the transformer T _4, the windings N24 and N25 for controlling the magnetic saturation of each other Wrap around the iron core and connect so as to cancel the AC component.

The operation of the circuit configured as described above is as follows. That is, when a DC power source (not shown) connected to the smoothing capacitor C ₀ is connected, the transistor Q is connected via the starting resistor R 21.
_{When a} voltage is applied to the base of ₀ , the transistor Q ₀ becomes slightly conductive, whereby the collector current I _C starts to flow. This collector current I _C is the winding of the primary and secondary windings N21 and N22 of the transformer T ₄ . It is fed back as the base current I _B of the transistor Q ₀ by the line ratio n21 / n22, and immediately I _B /
The transistor Q _{0 in} which the relation of I _C = n21 / n22 is maintained is in the conductive saturation state. This state is intermittent until the transformer T ₄ is magnetically saturated. While the voltage of such a polarity shown indicating positive by black dots during which the secondary winding N22 is generated, the voltage is the base-emitter forward voltage VBE of the transistor Q ₀
And the forward voltage VDF of the flywheel diode D21. Transformer T is EW of the following formula
The product causes magnetic saturation.

EW = ΔB × A × n21 × 10 ^−B (V · sec) E: Pulse voltage (V) applied to primary winding N21 W: Pulse width (sec) applied to primary winding N21 ΔB: Core saturation magnetic flux density of the (Gaussian) a: voltage V 1 ₌ n21 / n22 of the primary winding N21 since the voltage of the secondary winding N22 of the cross-sectional area of the core transformer T ₄ are clamped as previously described (VBE + VDF ) Is a constant value. Since the base current _{I B} is determined by the winding ratio n21 / n22 current amplification factor of the transistor _{Q 0} (hF
E) Choose the winding ratio a little higher than By setting the optimum base current to the transistor Q ₀
Will be given to.

And no longer induced voltage across the winding N22 the transformer T ₄ is magnetically saturated, the base of the transistor Q ₀ It until the voltage of the capacitor C ₂₁ which has been charged (=
VDF) is applied and a reverse bias current flows, which turns off the transistor Q ₀ . Therefore, thereafter, the resonance current with the resonance capacitor C ₁ flows through the induction heating coil L. When the polarity of the resonance current changes, a current flows through the diode D21, so that a voltage of the illustrated polarity is generated in the winding N21 at the end timing of the conduction period, which causes the winding N22.
Supplies the base current again to turn on the transistor Q ₀ . In this way, the circuit oscillates by itself and the coil L
A high-frequency current is passed through. The diode D
₂₃ and tertiary winding N23 is allowed to charge the capacitor C21, also serves to not tighten if excessive emitter-base voltage of the transistor Q _0.

Although the OFF timing of the transistor Q ₀ is governed by the saturation of the transformer T ₄ as described above, the magnetic saturation point is changed by changing the control DC current i by changing the variable resistor R23.

That is, when this DC current i is small, it is determined by the characteristics and dimensions of the iron core of the transformer T ₄ , and the ON period of the transistor Q ₀ is the longest. However, when this DC current i is increased,
As the magnetic saturation point is advanced, the transistor Q ₀
The ON period of becomes shorter. As a result, the input power can be adjusted. Also in the case of this embodiment, the input power can be adjusted with an extremely simple configuration.

As described above in detail, the induction heating cooker according to the present invention supplies the base current of the transistor in which the direct current of the induction heating coil is intermittent from the magnetic saturation transformer, and the current of the saturation control winding provided in the magnetic saturation transformer. The input power of the induction heating coil is controlled by changing the time when the magnetic saturation transformer is magnetically saturated, so that the induction heating cooker can be operated with a simple and inexpensive circuit using the magnetic saturation transformer. The heating power can be easily controlled, and an excellent effect that an inexpensive and highly reliable induction heating cooker can be provided is exhibited.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an essential part of an induction heating cooker using a single-ended push-pull inverter, FIG. 2 is a circuit diagram of the cooker of the present invention, FIG. _{3 is} a schematic structural diagram of a transformer T ₃ , and FIG. FIG. 5 is a circuit diagram showing another embodiment of the present invention, and FIG. 5 is a schematic structural diagram of the transformer T ₄ . L ... induction heating coil, C 1 _... resonant _{capacitor, T} 1, T
₂ , T ₃ , T ₄ ... Transformer, N12, N13, N24, N25 ...
Saturation control winding

Claims (1)

[Claims] 1. An induction heating cooker configured to supply a high-frequency current to an induction heating coil by a self-oscillating inverter, comprising: a magnetic saturation transformer for supplying a base current of a transistor for interrupting a direct current of the induction heating coil. A means for controlling the current in the saturation control winding wound around the magnetic saturation transformer, and controlling the current in the saturation control winding to change the magnetic saturation point of the magnetic saturation transformer to change the magnetic saturation point of the induction heating coil. An induction heating cooker characterized by being configured to control input power.