JPS6333273B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an induction heating appliance having two or more induction heating devices.

[Prior art]

Conventionally, in an induction heating appliance that has two or more induction heating devices, the same type of pot is placed in each induction heating device, and the load power is controlled by changing the ratio of the period of time when the switching element is oscillated to operate induction heating and the period when oscillation is stopped. If the setting of the time ratio control circuit, which controls the average value of Since the soft start circuit operates so that the slow input current detection circuit can follow up, the frequency temporarily increases, creating a frequency difference between the induction heating device and the other induction heating device that is not operating the soft start, resulting in a humming noise. This caused a problem in practical use, as it was audible to humans.

〔the purpose〕

The present invention has been made in view of the above matters, and
It is an object of the present invention to provide an induction heating appliance that eliminates the humming noise that is the conventional drawback.

〔Example〕

FIG. 1a shows the main circuit of the invention.

In the figure, reference numeral 1 indicates that the input current is converted into voltage by a current transformer, rectified by a diode 23, and integrated by a capacitor 24. Differential amplifier has 2 resistors
5, 26, 27, 28, 29 and an OP amplifier 30, the output of which is supplied to the resistor 16 through the diode 18. 2 is a rectifier bridge, and the induction heating operating coil 5
(hereinafter referred to as the heating coil). The heating coil 5 is connected to a switching element 6 that turns it on and off. The switching element 6 uses a transistor, but GTO
etc. may also be used. Further, a resonant capacitor 8, which forms a resonant circuit together with a diode 7 and heating coil 5, is connected in parallel to the switching element 6. The zero cross circuit 9 connected to the positive side of the smoothing capacitor 4 becomes H when the power supply voltage is near zero.
The signal is input to the R input terminal of the flip-flop 10. The output Q of the flip-flop 10 is
It is connected to the AND gate 12 and also to the one shot circuit 22. When the output is H, the induction heating device oscillates and heats the pot, and when the output is L, the oscillation stops.

Timing circuit 1 that outputs a signal after t ^B when the voltage of the switching element becomes lower than vb in Figure 2 a.
The output of 1 is connected to the other input terminal of the AND gate 12, and the output terminal thereof is connected to the ON time control circuit 13.

The output of the ON time control circuit 13 is input to a drive circuit 21 and drives the switching element 6. The other input terminal of the ON time control circuit 13 is connected to a resistor 16 and diodes 17 and 18, which input a signal whose pulse width is inversely proportional to the voltage when a voltage is applied. Diode 17 is connected to soft start circuit 19.

The output Q of the flip-flop 10 is converted into a thin pulse by a one-shot circuit 22 and then inputted to one end of the OR gate 20 connected to the external output terminal A, and the other input terminal of the OR gate 20 is connected to the external input terminal B. be done. And at the OR gate 20
After being ORed, the signals are input to the soft start circuit 19, and a voltage or a gradually decreasing voltage is output.

On the other hand, the output terminal of the time ratio control circuit 14 that outputs an ON-OFF signal proportional to the power set by the power setting VR 15 is connected to the flip-flop 1.
Connected to 0.

FIG. 1b shows an induction heating device C in which external input and output terminals A and B of two induction heating devices A and B are connected.

FIGS. 2a and 2b are timing charts for explaining the operation of the main circuit shown in FIG.

Power setting VR when voltage is applied to induction heating device
The time H proportional to the power set by 15
Therefore, the output Q of the flip-flop 10 also becomes H. When the output Q of the flip-flop 10 becomes H, the one-shot circuit 22 generates a thin pulse,
It is input to the soft start circuit 19 through the OR20, and its output becomes VC in Figure 2a, and a gradually decreasing signal is output.
Input to ON time control circuit.

As shown in FIG. 2a, the voltage of V _CE is low because it is not oscillating and is less than vb, and the output of the timing circuit 11 becomes H, and the voltage from the AND gate 12 becomes H.
When is output, the ON time control circuit 13 outputs a signal _T1 defined by the voltage of the resistor 16. The signal passes through the drive circuit 21 and is applied to the switching element 6, which remains in the ON state during _T1 . When the switching element 6 is turned on, current flows through the heating coil 5. After T ₁ , switching element 6
When turned off, current flows through the resonant capacitor 8 of the resonant circuit determined by the resonant capacitor 8 and the heating coil 5, and the voltage of _VCE increases. The voltage of V _CE increases until the current flowing through the resonant capacitor 8 becomes zero, and when it reaches zero, the electric charge accumulated in the resonant capacitor 8 is released, and the direction of the current flowing through the heating coil 5 is reversed.

When the discharge current becomes zero, the energy accumulated in the heating coil 5 causes the current to continue to flow through the diode 7 and decrease until it reaches zero.

This point is set to be the same as after ^tB when V _CE becomes less than vb, and when the timing circuit 11 outputs an H signal, the ON time control circuit 13 outputs the voltage determined by the voltage of the resistor 16. A signal with a pulse width is output, but since the voltage across the resistor 16 is lower than the previous time, the pulse width becomes longer than _T4 , and the same operation is performed thereafter. In this way, the voltage of the soft start circuit 19 gradually decreases and the current of the heating coil 5 gradually increases, so the input current also increases, and when the current exceeds the current set by the differential amplifier, a voltage is generated at the output and the diode 18 is As a result, the pulse width of the output of the ON time control circuit 13 becomes shorter and the input current becomes lower, becoming the set input current and keeping it constant. At this time, that is, at time tc, when the other induction heating device starts oscillating, a signal is output from the external output terminal A' and from the external input terminal B of the induction heating device, which maintains the input current constant.
Soft start circuit 19 through OR gate 20
join. When this signal is applied, a soft start operation is performed and the period is shortened in the same way as explained above, but since both units are in soft start operation, there is no difference in frequency.

Even when the soft start operation ends and the time ratio control circuit 14 goes low, the output of the flip-flop 10 remains high, so oscillation continues, but the power supply voltage decreases and the zero cross circuit 9 outputs a high signal. Then, the flip-flop 10 is cleared and the output Q becomes L, and the AND gate 12
is closed, so no signal is output from the ON time control circuit and oscillation stops.

After that, when the time ratio control circuit outputs an H signal, the H signal from the flip-flop 10 passes through the one-shot circuit 23, and a thin pulse signal is generated.
It is output to the OR gate 20 and the external output terminal A, and operates in the same manner as described above, and the induction heating device connected to the external output terminal A also enters a soft start operation.

[Effect] As described above, according to the present invention, even if one induction heating device is in soft start operation, the induction heating devices connected to it are also forced to be in soft start operation, so there is no difference in frequency. Therefore, an induction heating appliance that does not generate humming noise can be provided.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of the induction heating device of the present invention, FIG. 1b is a schematic diagram of the induction heating device of the present invention, and FIG.
Figures a and b show the timing chart of Figure 1a. 5: Induction heating operating coil, 6: Switching element, 7: Rectifying element, 8: Resonant capacitor, 1
4: Time ratio control circuit, 19: Soft start circuit, 20: OR gate.

Claims (1)

[Claims] 1. An operating coil for induction heating of a load, a switching element connected in series to this coil, a resonant capacitor connected in parallel to this element and forming a resonant circuit together with the operating coil, and a rectifier connected in antiparallel to the switching element. an inverter control unit that causes the switching element to oscillate; a time ratio control circuit that stops the oscillation of the inverter and causes it to oscillate again to control power according to a time ratio; In an induction heating appliance having two or more induction heating devices equipped with a soft start circuit that increases the temperature, when the soft start circuit enters a soft start operation, the other induction heating devices are also forced to perform a soft start operation. An induction heating appliance characterized by being provided with such a means.