JPS6116632Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a multi-mouth induction heating cooker.

As a method to control the output of an induction heating cooker,
Three control methods can be considered: first, a constant duty and variable frequency control method; second, a variable duty and frequency control method; and third, a constant frequency and variable duty control method. In the case of single-mouth heating, there is no problem in adopting any of the three methods above, but when using multiple-mouth heating,
If the first two methods are adopted, each heating unit has a different frequency, and there is a problem in that a low frequency beat sound is generated due to interference between the heating units. Therefore, the third method is suitable for multi-mouth heating cookers.

1 and 2 show a conventional four-burner induction heating cooker, and FIG. 1 shows an independent oscillation drive circuit OSC for each of the first to fourth heating units _U1 to _U4 .
An example is shown below. Each heating unit U ₁ to _{U 4}
have the same configuration, each with two NPNs connected in series between the oscillation drive circuit OSC and DC power supply terminals 1 and 2.
type transistors Q ₁ and Q ₂ , an output transformer T that alternately supplies drive signals from the oscillation drive circuit OSC to the bases of transistors Q ₁ and Q ₂ , and a transistor
The load circuit 3 includes a series circuit of an induction heating coil and a resonant capacitor connected in parallel to _Q1 . In a multi-mouth cooker with such a configuration, each unit
Even if the oscillation drive circuits OSC of U ₁ to _{U 4} are adjusted so that their oscillation frequencies are the same, each oscillation drive circuit
The frequency drift of the OSC is not constant, and a difference in frequency occurs over time, making it impossible to prevent the above-mentioned beat sound generation.

Figure 2 shows another conventional example, in which the oscillation drive circuit
This is an example in which the heating units _U1 to _U4 share one OSC. With such a configuration, the frequency of each unit U ₁ to _{U 4} can be kept constant, but the number of types of windings of the output transformer T becomes very large as shown in the figure. In this case, nine types including the primary winding are required.
In reality, it is almost impossible to wind such a large number of windings around one transformer.

The present invention has been devised in consideration of the above circumstances, and solves the above-mentioned problems by adopting a configuration as shown in FIG. The figure shows the principle of an embodiment of the circuit of the present invention, and shows the heating unit.
U ₁ to _{U 4} include a series circuit consisting of a PNP transistor Q ₁ ′ and an NPN transistor Q ₂ whose collectors are commonly connected to each other, and a higher potential voltage than the DC power supply terminal 1 is applied to the emitter of the PNP transistor Q ₁ ′. A low potential voltage is also supplied from the DC power supply terminal ₂ to the emitter of the NPN transistor Q2. A load circuit 3 consisting of an induction heating coil and a resonant capacitor is connected in parallel to the PNP transistor Q ₁ ', and one set of the transistor series circuit and the load circuit 3 constitutes one heating unit. The four heating units U ₁ to _{U 4} are given drive signals from one oscillation drive circuit OSC,
This takes place via the output transformer T. That is, the output of the secondary winding a of the output transformer T is
Base-emitter a of PNP transistor Q1 _'
The output of the secondary winding b is applied to the base-emitter b of the NPN transistor _Q2 via a control circuit to be described later. Oscillation drive circuit OSC
, currents in opposite directions alternately flow through the primary winding of the output transformer T at a constant frequency, for example, 20 KHz, and the secondary windings a and b have the same phase, so the transistors q ₁ and Q The base of ₂ is a rectangular signal (Fig. 6A,
B) is output.

Figure 4 shows a specific circuit example of one heating unit _U1 , where L is a load made of ferrous metal, specifically an induction heating coil that heats a cooking pot, and C is a resonant coil connected in series to this. Capacitors D ₁ and D ₂ are freewheeling diodes connected anti-parallel to transistors Q ₁ ' and Q ₂ , respectively. In this example, PNP
An equivalent circuit of a PNP transistor Q ₁ ' is obtained by a quasi-complementary connection circuit formed by connecting a Darlington type transistor q ₁ and an NPN type transistor q ₂ . Such a quasi-complementary connection circuit has a smaller capacity than a single large-capacity PNP transistor.
It has the advantage of being low cost. A resistor R ₁ and a diode D ₃ are connected in parallel between the secondary winding _a and the base of the transistor q 1 , and the diode D ₃ has a direction opposite to the base-emitter current path of the transistor q ₁ . _Q3 is an NPN type transistor inserted together with a resistor _R2 between the secondary winding b and the base of the transistor _Q2 , and its emitter is connected to the base of the transistor _Q2 . A diode _D4 is connected in the opposite direction between the resistor _R2 and the transistor _Q3 . Reference numeral 4 denotes an output control circuit which controls the output of the transistor Q ₂ during the period in which the output of the secondary winding b is at "H" level, that is, a signal that turns on the transistor Q ₂ .
The power supplied to the load is adjusted by changing the on-period of the power supply.

5 and 6 show the on/off operation of transistors Q ₁ ′ and Q ₂ and the corresponding load circuit 3.
This shows the change in the current flowing through the Signals A and B are signals applied to the bases of transistors Q ₁ ′ and Q ₂ , respectively;
Signal C shows the waveform of the current flowing through the load circuit 3. Figure A shows the maximum output state, and Figure B shows the state where the output is reduced.

When the transistor _Q2 is first turned on by the "H" level pulse of the signal B, the drive current _I1 flows through the induction heating coil L, the resonant capacitor C, and the transistor.
flows through Q ₂ , turns off transistor Q ₂ and turns on transistor Q ₁ ′, then the induction heating coil L,
A circulating current _I2 flows through the resonant capacitor C and the diode _D1 . When this circulating current I ₂ becomes zero, the current flowing through the load circuit 3 is reversed and a driving current I ₃ flows through the transistor Q ₁ ', the resonant capacitor C and the induction heating coil L. Then, the transistor Q ₁ ' is turned off and the transistor Q ₂ is turned on again, but the circulating current I ₄ flows through the diode D ₂ , the resonant capacitor C and the induction heating coil L for a while. In this way, one cycle of the current flowing to the load circuit 3 is completed. As shown in Figure 6 A and B, the on-off period of the transistor Q ₁ ' is 1:1, and the ratio of the on-off period of the transistor Q ₂ , that is, the off period of the transistor Q ₁ ', is the maximum period. By controlling the on-period within a shorter period, desired power can be supplied to the load.

As described above, according to the multi-hole induction heating cooker of the present invention, the driving frequency of each heating unit can be made constant, so the problem of generation of beat noise due to mutual interference between the units is solved. In addition, since the emitter of the PNP transistor is connected to the high potential side of the DC power supply, the output winding of the oscillation drive circuit can be made one common to each heating unit, which greatly simplifies the circuit of the heating unit. I can't help it. Furthermore, since the load circuit is connected in parallel to the transistor on the high potential side of the power supply voltage and variably controls the on/off period of the transistor on the low potential side,
Power can be adjusted under conditions where the drive frequency is constant.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of one conventional example, Fig. 2 is a circuit diagram of another conventional example, Fig. 3 is a circuit diagram of an embodiment of the present invention, and Fig. 4 is a circuit diagram of an embodiment of the present invention.
The figure is a specific circuit diagram of the same example, FIG. 5 is a circuit diagram for explaining the operation, and FIG. 6 is a signal waveform diagram. _U1 to _U4 ...first to fourth heating units,
OSC...Oscillation drive circuit, T...Transformer, 3...
...Load circuit, 4...Control circuit.

Claims (1)

[Scope of utility model registration request] Series circuit of PNP type transistor and NPN type transistor with collectors commonly connected, above
A DC power supply that applies a high potential voltage to the emitter of the PNP transistor and a low potential voltage to the emitter of the NPN transistor, connected between the collector connection point of the transistor series circuit and the high potential terminal of the DC power supply. The heating unit includes a load circuit consisting of an induction heating coil and a resonant capacitor, and a control circuit connected to the base of the NPN transistor to vary the conduction period of the NPN transistor. and a multi-mouth induction heating cooker in which on/off signals alternately applied to the control circuit are commonly generated by one oscillation drive circuit.