JPH0576151B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an induction heating cooker used in general households.

BACKGROUND ART A conventional induction heating cooker of this type is shown in FIG. In Fig. 3, a heating coil 1, a power switching element 2 which is a transistor, a reverse conduction diode 3, a resonant capacitor 4, and a smoothing capacitor 5 are connected.
An inverter 7 is constituted by the yoke coil 6 and the yoke coil 6. Reference numeral 8 denotes a forward bias application circuit for turning on the power switching element 2, which is composed of a coupling coil 9 magnetically coupled to the heating coil 1 and a diode 10. Reference numeral 11 denotes a reverse bias applying circuit for turning off the power switching element 2, which is composed of a coupling coil 12 magnetically coupled to the heating coil 1, a smoothing capacitor 13, a rectifying element 14, and a driving switching element 15. 16 is a control circuit for turning on and off the drive switching element 15; 17 is a starting circuit; 18 is an AC power supply;
9 is a rectifier, 20 is a transformer, and a DC voltage rectified and smoothed by a rectifier 21 and a smoothing capacitor 22 is supplied to the control circuit 16. 23 is a load pot.

Next, the operation of the induction heating cooker shown in FIG. 3 at startup will be described with reference to the operation waveform diagram of FIG. 4. In FIG. 4, a indicates the output current I _O of the starting circuit 17, and b indicates the drive switching element 15.
c is the base current I _B of the power switching element 2, d is the terminal voltage V _C of the smoothing capacitor 13,
e is the base-emitter voltage V _BE of the power switching element, f is the collector-emitter voltage V _CE of the power switching element 2, and g is the current I flowing in the parallel circuit of the power switching element 2 and the reverse conducting diode 3. It is a waveform diagram of _C.

At t=t ₁ , I _O flows and drive switching element 15 turns off, I _B = I _O , power switching element 2 turns on, and the charging current of resonant capacitor 4 instantaneously flows through I _C. After that, since the DC voltage of the smoothing capacitor 5 is applied to the heating coil 1, I _C increases. _IB is supplied by the coupling coil 9 magnetically coupled to the heating coil 1, and the power switching element 2 can be maintained in a saturated state. Further, current is supplied to the smoothing capacitor 13 by the coupling coil 12, and V _C increases. I _O at t=t ₂
=o, when the drive switching element 15 is turned on, V _BE becomes negative due to V _C , resulting in a reverse bias state, and the power switching element 2 is turned off.

Then, a resonant circuit is formed between the heating coil 1 and the resonant capacitor 4, and a resonant voltage is applied to V _CE . Eventually, V _CE =o again, I _C <o, and current begins to flow through the reverse conduction diode 3.

Therefore, when the drive switching element 15 is turned off by the action of the control circuit 16 at t= _t3 , the output current of the coupling coil 9 is supplied to _IB , the power switching element 2 becomes saturated again, and the output from the coupling coil 12 is turned off. The smoothing capacitor 13 is also charged by the current, and V _C increases.

Thereafter, in the same manner, the power switching element 2 is turned on at t=t ₅ and t ₇ , and is turned on at t=t ₄ and t ₆ , so that a high frequency current flows through the heating coil 1, and the load pan 23 is heated by induction. do.

Problems to be Solved by the Invention In such conventional technology, since the voltage V _C of the smoothing capacitor 13 is extremely low immediately after startup, the reverse bias component of V _BE is insufficient, and the V ₁ , V ₂ , V ₃ such as V _CE peak voltage or
There was a problem in that the power switching element was easily destroyed by the dv/dt during the rising period of V _CE .

In view of the above problems, the present invention provides sufficient
High reliability is achieved by applying a sufficient reverse bias of V _BE by generating V _C and preventing damage to the power switching element due to the peak voltage of V _CE and dv/dt during the rise period of V _CE . The present invention provides an induction heating cooker.

Means for Solving the Problems To achieve this object, the induction heating cooker of the present invention includes an inverter including a heating coil and at least one power switching element, and a forward bias for turning on the power switching element. an application circuit, and a reverse bias application circuit that turns off the power switching element, and the reverse bias application circuit includes a coupling coil magnetically coupled to the heating coil, a smoothing capacitor, and a coupling coil magnetically coupled to the heating coil, and a smoothing capacitor between the coupling coil and the smoothing capacitor. a rectifying element connected to the smoothing capacitor, a drive switching element connected in series to the smoothing capacitor, and a drive switching element connected between both terminals of the smoothing capacitor, so that even when the inverter is stopped and there is no output from the coupling coil, the smoothing capacitor It consists of an auxiliary voltage source that maintains the voltage.

Function With this configuration, the induction heating cooker of the present invention applies sufficient reverse bias to the power switching element at startup, and is reliable by preventing damage caused by the peak voltage and dv/dt applied to the power switching element. It is possible to provide an induction heating cooker with high performance.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of an induction heating cooker according to an embodiment of the present invention.

In Figure 1, 1, 2, 3, 4, 5, 6, 7,
8, 9, 10, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23 are
It has exactly the same configuration as the conventional technique shown in FIG. In FIG. 1, the reverse bias application circuit 27 is
It is composed of a coupling coil 12 magnetically coupled to the heating coil 1, a smoothing capacitor 13, a rectifying element 14, a driving switching element 15, and an auxiliary voltage source 24.

The auxiliary voltage source 24 is composed of a transformer 25 and a diode 26.

The operation of the above configuration will be explained with reference to FIG. 2. In FIG. 2, a to g indicate waveforms at various parts of the circuit diagram shown in FIG. 1, as in the case of FIG. 4, but a, b, f, and g are almost the same as in FIG. 4.

Regarding V _C , a constant voltage V _CO is maintained by the action of the auxiliary voltage source 24 even before the inverter 7 operates. When the inverter 7 operates from this state, current is supplied from the coupling coil 12 to the smoothing capacitor 13, so that V _C is further charged from V _CO , resulting in a waveform as shown in FIG. 2.

Since V _BE is applied with V _C during reverse bias, a larger reverse bias can be obtained compared to conventional technology, so the power switching element may be destroyed by the peak and rising dv/dt of V _CE . There is no.

In this embodiment, the auxiliary voltage source 24 is provided with a dedicated transformer 25, but the secondary winding of the power transformer 20 for the control circuit may be wound with one additional wire, or a battery may be used, for example. An auxiliary voltage source may also be provided.

Effects of the Invention As is clear from the above embodiments, the induction heating cooker of the present invention is particularly advantageous in that it is provided with an auxiliary voltage source that maintains the voltage of the smoothing capacitor even when the inverter is stopped. Because sufficient reverse bias can be applied,
Destruction due to peak voltage and dv/dt applied to the power switching element can be prevented.

Therefore, a highly reliable induction heating cooker can be provided.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an induction heating cooker showing an embodiment of the present invention, Fig. 2 is an operation waveform diagram of the induction heating cooker shown in Fig. 1, and Fig. 3 is an induction heating cooking method in the conventional technology. FIG. 4 is an operating waveform diagram of the induction heating cooker shown in FIG. 3. 1... Heating coil, 2... Power switching element, 7... Inverter, 8... Forward bias application circuit, 12... Coupling coil, 13... Smoothing capacitor, 14... Rectifying element, 15... For drive Switching element, 24... Auxiliary voltage source, 27...
Reverse bias application circuit.

Claims (1)

[Claims] 1. An inverter including a heating coil and at least one power switching element, a forward bias application circuit that turns on the power switching element, and a reverse bias application circuit that turns off the power switching element. The reverse bias application circuit includes a coupling coil magnetically coupled to the heating coil, a smoothing capacitor, a rectifier connected between the coupling coil and the smoothing capacitor, and a drive switching element connected in series to the smoothing capacitor. and an auxiliary voltage source connected between both terminals of the smoothing capacitor to maintain the voltage of the smoothing capacitor even when there is no output from the coupling coil while the inverter is stopped. 2 The auxiliary voltage source is obtained by rectifying the output of a transformer connected to an AC power source.
Induction heating cooker described in section.