JPS6154180A - Induction heating implement - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an induction heating appliance having two or more units of 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 during which induction heating is performed by oscillating the switching element and the period during which oscillation is stopped. If the setting of the time ratio control circuit, which controls the average value of Because the soft start circuit operates so that the slow input current detection circuit can follow the current, 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 sound. This caused audible noise to humans, which caused problems in practical use.

〔the purpose〕

The present invention has been made in view of the above-mentioned 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. 1(a) shows the main circuit of the present 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 resistance 25゜26・27-28-
29 and an operational amplifier 3o, the output of which is supplied to the resistor 16 through a diode 18. Reference numeral 2 denotes a rectifier bridge, which is connected to an induction heating operating coil 5 (hereinafter referred to as a heating coil) through a smoothing circuit consisting of a rectified Chikok coil 3 and a smoothing capacitor 4. The heating coil 5 has a switching element 6 that turns it on and off.
It is connected to the. Although a transistor is used as the switching element 6, a GTO or the like may also be used. Further, the switching element 6 includes a diode 7 and a heating coil 5.
A resonant capacitor 8, which together forms a resonant circuit, is connected in parallel.

A zero cross circuit 9 connected to the positive electrode side of the smoothing capacitor 4 inputs an H signal to the R input terminal of the flip-flop 10 when the power supply voltage approaches zero. The output Q of the flip-flop 10 is connected to an AND gate 112, and
It is also connected 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.

The output of the timing circuit 11, which outputs a signal after tB when the voltage of the switching element becomes lower than vb in FIG. 2(a), is connected to the other input terminal of the AND gate 12, and its output terminal is Connected to the ON time control circuit.

The output of the ON time control circuit 13 is connected to the drive circuit 21.
and drives the switching element 6. O
Connected to the other input terminal of the N-time control circuit 13 are a resistor 16, a diode 17, and a diode 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 clip-flop lO is one shot.

After converting it into a narrow pulse in a circuit 22, the signal is inputted to one end of an OR gate 20 connected to an external output terminal A, and the other input terminal of the OR gate 20 is connected to an external input terminal B. After being ORed by the OR gate 20, the signals are input to the soft start circuit 19, and a voltage whose voltage gradually decreases is output.

On the other hand, the output terminal of the time ratio control circuit 4 which outputs an ON-OFF signal proportional to the power set by the power setting VR15 is connected to the flip-flop 10.

FIG. 1(b) shows an induction heating appliance (c) in which external input/output terminals A to E of two induction heating devices (a) and (b) are connected.

FIGS. 2(a) and 2(b) are timing charts for explaining the operation of the main circuit shown in FIG. 1(a), and the following description will be made along these charts.

When a voltage is applied to the induction heating device, the time becomes H which is proportional to the power set by the power setting VR15, and the output Q of the flip-flop 0 also becomes H. When the output Q of the flip-flop 10 becomes H, it is made into a thin pulse by the one-shot circuit 22, and is input to the soft start circuit 19 through 0R20, and its output becomes VC in Fig. 2(a), and a gradually decreasing signal is output. The signal is input to the ON time control circuit through the diode 17.

As shown in FIG. 2(a), the voltage of VCE is low because it is not oscillating and is below Vb, and the output of the timing circuit 11 becomes H. When H is output from the AND gate 12, the ON time control circuit 13 A signal -8-T1 defined by the voltage of the resistor 16 is output. 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. When the switching element 6 is turned off after T+, a 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 yca increases. The voltage of VCE increases until the current flowing through the resonant capacitor 8 becomes zero, and when it becomes zero, the current flowing through the resonant capacitor 8
In order to discharge the charges accumulated in the heating coil 5, the direction of current flow in the heating coil 5 is reversed.

When the discharge current becomes zero, the current continues to flow through the diode 7 due to the energy stored in the heating coil 5 and decreases to zero.

This point is set to be the same as after jB when VCE becomes less than vb, and when the timing circuit 11 outputs an H signal, the pulse specified by the voltage from the ON time control circuit 3 to the resistor 16 is set. The width signal is output, but
The voltage across resistor 16 is lower than the previous time, so the pulse width is T.
, and the same behavior occurs after that. 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. ON because it is applied to the resistor 16 through
The pulse width of the output of the 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 tc, the other induction heating device's power; oscillation When starting, a signal is output from the external output terminal A' and is applied to the soft start circuit 19 through the OR gate 20 from the external input terminal B of the induction heating device where the input current is kept constant. 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.

After the soft start operation is completed, the time ratio control circuit 14
Even if becomes L, the output of flip-flop 10 is held at H, so oscillation continues, but when the power supply voltage drops and the zero-cross circuit 9 outputs an H signal, flip-flop 10 is cleared and output. Q becomes L, AND
Since the gate 12 is closed, a signal is output from the ON time control circuit.

oscillation stops.

After that, when H is output from the time ratio control circuit, the signal from flip-flop]O to H passes through the one-shot circuit 23, and a thin pulse signal is output to the OR gate 20 and external output terminal A, and the same as above. The induction heating device connected to the external output terminal AK also enters 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, and therefore, It is possible to provide an induction heating device that does not generate humming noise.

[Brief explanation of drawings]

Figure 1 is an electric circuit diagram of the induction heating device of the present invention, Figure 1 (b
) is a schematic configuration diagram of the induction heating device of the present invention, FIG. 2(a)
and U(b) shows the timing chart of FIG. 1(a). 5: Induction heating operating coil, 6: Switching element, 7: Rectifying element, 8: Resonant capacitor,
14 Two-time ratio control circuit, 19: Soft start circuit, 20: OR gate. Agent: Patent attorney Aihiko Fuku (and 2 others)? 4 2
Figure 2 of tσ (b)

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 resonant capacitor connected in antiparallel to the switching element. a rectifying 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; and a load current that gradually increases when the inverter oscillates. In an induction heating appliance having two or more induction heating devices equipped with a soft-start circuit that increases the temperature to 1000 Ω, when the soft-start circuit enters soft-start operation, the other induction heating devices are also forced to enter soft-start operation. An induction heating appliance characterized by being provided with a means for doing so.