JPH0690951B2 - Induction heating cooker - Google Patents

Description

TECHNICAL FIELD The present invention relates to an induction heating cooker used in general households,
It is characterized by the drive circuit of the transistor that constitutes the high frequency inverter.

2. Description of the Related Art Conventionally, this type of induction heating cooker uses a general DC base drive circuit composed of a DC power supply, a control switching element, and a current limiting resistor, or is not known, but is shown in FIG. Such a current transformer drive circuit was used.
In FIG. 3, reference numeral 15 is a DC power supply, 16 is a heating connel, 17 is a transistor, 18 is a resonant capacitor, and 22 is a diode, and these members constitute a resonant inverter.
Reference numeral 19 denotes a coupling coil electromagnetically coupled to the heating coil 16, which operates as a current transformer and generates a current having the same waveform as the heating coil 16. When the transistor 17 is conducting, the current of the heating coil 16 becomes equal to the collector current of the transistor 17, so that a base current proportional to the collector current flows. The coupling coil 19 constitutes a forward base current supply circuit 20.
Reference numeral 23 is a control circuit of the inverter, which conducts / blocks the transistor 17 together with the blocking element 24 in an appropriate state.

Problems to be Solved by the Invention In the DC base drive circuit as described above, there are problems that the control switching element and the current limiting resistor are expensive and the loss is large, and in the forward base current supply circuit of FIG. In the presence of a disturbance such as a momentary fluctuation of the power supply, the conduction start of the transistor 17 becomes unstable, and when it is remarkable, it stops.

Means for Solving the Problems In order to solve this problem, the present invention provides a DC power source, a heating coil and a transistor connected in series, a resonance capacitor connected in parallel to the heating coil or the transistor, and A forward base current supply circuit having a coupling coil electromagnetically coupled to the heating coil, and a starting circuit supplying a starting current to the base of the transistor, the coupling coil having the heating connel as a primary winding, It is used as a current transformer that outputs a current according to the value of the current flowing in the heating coil, the starting circuit generates a starting current for each conduction period of the transistor, and the forward base current supply circuit and the starting circuit It is an induction cooker connected to the base.

Operation With the above-described configuration, a current is supplied from the coupling coil to the base of the transistor, and the starting current by the starting circuit is only a minute current such that the forward base current supply circuit starts to supply the current for conducting the transistor. Further, since the coupling coil functions as a current transformer, the supplied forward base current has a value according to the heating coil current and the collector current of the transistor. Further, the starting circuit supplies a starting current for each conducting period of the transistor to cause stable oscillation.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In FIG. 1, 1 is a DC power supply, 2 is a heating coil, 3 is a transistor, and a DC power supply 1 and a heating coil 2 are provided.
Are connected in series. Reference numeral 4 denotes a resonance capacitor connected in parallel to the heating coil 2 or the transistor 3 and constitutes a resonance circuit together with the heating coil 2. Reference numeral 7 is a pan serving as a load, which is induction-heated by the heating coil 2. Reference numeral 8 denotes a diode connected in parallel with the transistor 3, through which the regenerative current of the resonance circuit flows. Then, the DC power supply 1, the heating coil 2, the transistor 3, the resonance capacitor 4, the diode 8
The inverter is configured by. Reference numeral 5 is a coupling coil that is electromagnetically coupled to the heating coil 2. The heating coil 2 serves as a primary winding and acts as a current transformer that outputs a current according to the current value flowing through the heating coil 2. Generates waveform current. The coupling coil 5 constitutes a forward base current supply circuit 6. The forward base current supply circuit 6 is connected to the base of the transistor 3. 11 is a DC power supply, 9 is a transistor, 10 is a resistor,
Together with the transistor 9, the starting circuit 14 is configured.
The starting circuit 14 is connected to the base of the transistor 3 to supply a starting current, and its control is performed by the control circuit 12. Reference numeral 13 is a transistor, which conducts and shuts off by the signal of the control circuit 12 to shut off the transistor 3.

The embodiment of FIG. 1 will be described with reference to the waveform chart of FIG. In FIG. 2, I _C is the collector current of the transistor 3, I _B is the base current of the transistor 3, I _T is the current of the coupling coil 5, I _S is the output current of the starting circuit 14, that is, the starting current, and S9 and S13 are the transistors, respectively. 9, transistor 13
Represents the conduction timing of.

As can be seen from I _C , I _B , and I _T , the base current I _{B that} is approximately proportional to the collector current I _C is obtained by the forward base current supply circuit 6. The base current I _B has a value corresponding to the heating coil current because the coupling coil 5 acts as a current transformer. If the state shown in FIG. 2 continues, oscillation continues without the starter circuit 14, but if I _T is disturbed by disturbance due to momentary fluctuations in the power supply, the base current I will rise when S ₁₃ is cut off.
_B may not be obtained from the forward base current supply circuit 6, and oscillation may stop. In the induction heating cooker of the present invention, since the conduction of the transistor 3 is started by the starting current I _S even in such a case, a current flows through the heating coil and the base current.
I _B is supplied from the forward base current supply circuit 6, and oscillation continues stably.

The necessary starting current may be an extremely small value because the forward base current supply circuit 6 may start supplying the current for making the transistor 3 conductive. That is, if the starting current I _S that causes the transistor 3 to shift from the complete cutoff region to the region where the collector current I _C slightly flows is supplied, the current is supplied from the coupling coil 5 to the base of the transistor 3 and the collector current I _C is amplified. Then, the current supplied from the coupling coil 5 increases, and the transistor 3 rapidly transitions to the conductive state.

Although the present invention has been described above based on the embodiment of FIG. 1, a diode may be connected in series to the coupling coil 5 or a diode connection may be made in antiparallel to the cutoff element 13. The resonance capacitor 4 may be connected to the heating coil 2 in parallel. In the second figure, the initial only starting current I _S of the conduction period of the transistor 3 is flowing, it may be flowed starting current I _S to all conduction period. Further, a direct current power supply may be connected to the collector or the emitter of the transistor 13 and a reverse bias may be applied when the transistor 3 is cut off.

EFFECTS OF THE INVENTION As described above, according to the present invention, a sufficient current operation stability of a transistor can be ensured only with a minute current from a starter circuit, and thus a switching element with a large current rating is not required and cost reduction can be achieved. It is a thing. Further, since the coupling coil acts as a current transformer, the supplied forward base current has a value according to the heating coil current, so that a resistor for stabilizing the value of the forward base current is not particularly required, and the cost is low. Moreover, there is no loss in resistance,
As a result, the efficiency of the device can be improved. Furthermore, since the collector current that flows during the ON period of the transistor is almost equal to the heating coil current, by supplying the forward base current from the coupling coil that is electromagnetically coupled to the heating coil as a current transformer, the optimum value according to the collector current can be obtained. The forward base current of (3) flows and the loss of the transistor can be reduced. Furthermore, since the starting circuit supplies the starting current for each conduction period of the transistor,
Even if there is a disturbance such as a momentary fluctuation of the power source, the oscillation can be stably maintained, and the induction heating cooker can operate stably.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an induction heating cooker according to an embodiment of the present invention, FIG. 2 is a waveform diagram explaining the operation of the embodiment of FIG. 1, and FIG. 3 is a circuit diagram showing a conventional example. is there. 1 ... DC power supply, 2 ... Heating coil, 3 ... Transistor, 4 ... Resonant capacitor, 5 ... Coupling coil, 6 ...
Forward base current supply circuit, 14 …… Starting circuit.

Claims (1)

[Claims] 1. A forward base current supply having a direct current power source, a heating coil and a transistor connected in series, a resonant capacitor connected in parallel with the heating coil or the transistor, and a coupling coil electromagnetically coupled to the heating coil. A current and a starting circuit for supplying a starting current to the base of the transistor, wherein the coupling coil uses the heating coil as a primary winding and outputs a current according to a current value flowing in the heating coil. An induction heating cooker which is used as a transformer, wherein the starting circuit generates a starting current for each conduction period of the transistor, and the forward base current supply circuit and the starting circuit are connected to the base of the transistor.