JPS6025178A - Induction heating cooking device - 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 2. Field of Industrial Application The present invention relates to an induction heating cooker to which induction heating is applied, which is used in general households.

Conventional Structure and Problems Conventionally, in this type of induction heating cooker, as shown in FIG. 1, a choke coil/L A series circuit of /4 and a first filter capacitor 6 is connected, and a parallel resonant circuit of a heating coil VF6 and a resonant capacitor 7, a transistor 8 and a flywheel diode 9 are connected to both ends of the capacitor 6.
A series circuit of an anti-parallel circuit is connected. When the transistor 8 performs a switching operation at an ultra-audio frequency, the heating coil/I/6 generates a high frequency magnetic field, generates an eddy current in the pot, and generates Joule heat. Therefore, the choke carp) v4, the heating coil 6, the capacitor 6.7, the transistor 8 and the diode 9 constitute the frequency conversion device 1o.

A second filter capacitor 11 is connected to the output terminal of the rectifier 3 in order to reduce high frequency noise from the frequency converter 10 flowing into the power supply.

A drive circuit 12, which generates a periodic drive signal for the transistor 8, is supplied with power from the input terminal of the rectifier 3 and causes the transistor 8 to switch at an ultra-audible frequency. In addition to the above-mentioned basic heating operation, it is necessary to arbitrarily vary and set the output during actual cooking, and for this purpose, the frequency of the output signal of the drive circuit 12 has been varied. In that case, in order to make the output variable over a large range suitable for stewed dishes, the frequency change must also be extremely large, and the number of devices that receive interference noise increases due to the wide range of interference noise frequencies, and switching Transistor 8 now requires a fast switching time. Further, as another means for varying the output, there is a duty control means that periodically turns on and off the oscillation of the frequency converter 1o to control the energization ratio. A drawback of this method is that the pot noise generated at the start of each cycle of duty control is periodically generated and becomes unpleasant to the ears.

Here, the cause of the pot noise at startup is due to the mechanical vibration of the pot when the accumulated charge in the capacitor 5.11 flows through the heating coil/L/6 when the transistor 8 is turned on. Therefore, the higher the voltage of the capacitor 6 at startup, the louder the pot noise will be.

In the circuit configuration shown in FIG. 1, when the transistor 8 is off (non-oscillating), the capacitors 11 and 7 are charged to the maximum value of the power supply 1, so there is a problem that the above-mentioned pot noise becomes extremely high. Ta.

OBJECTS OF THE INVENTION The present invention solves the conventional problems and provides the user with an induction heating cooker in which the variable output setting (l) is increased by a duty control means that does not generate pot noise.

Structure of the Invention The induction heating cooker of the present invention has a choke coil and a first filter capacitor connected to the rectified output terminal of a rectifier connected to a commercial power supply, and a heating coil Jf [capacitor] connected to both ends of the first filter capacitor. a frequency converter configured by connecting a resonant circuit and a first switching means for exciting it, and connecting a rectifier in antiparallel to the filter capacitor 5, and a second filter capacitor connected to the rectifier output terminal of the rectifier. and a second switching means connected in series, a zero-point synchronous circuit that inverts in synchronization with the zero-voltage point of the commercial power supply, and an on-signal supplied to the second switching means by the output of the zero-point synchronous circuit. The switching device also includes a drive circuit that supplies a periodic ON signal to the first switching means, and a delay circuit that delays the start of operation of the drive circuit.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 2 shows the basic circuit of the present invention, in which a choke coil/l/4 and a first filter capacitor 5 are connected to the rectifier output terminal of a rectifier 3 connected to a commercial power supply 1 via a power supply switch 2. A resonant circuit consisting of a heating coil v6 and a resonant capacitor 7, and a first switching means 13 for exciting it are connected to both ends of the first filter capacitor 60, and a rectifying element 14 is connected to the filter capacitor 5. A frequency converter 1o configured by connecting parallel 6''-digits in series, and a second filter capacitor 1'1 and a second filter capacitor 1' connected to the rectified output terminal of the rectifier 3
a fill circuit in which switching means 16 are connected in series, a zero-point synchronous circuit 16 that inverts in synchronization with the zero-voltage point of the commercial power supply 1, and an output of the zero-point synchronous circuit 16 to the second switching means 16 and the on-signal means 13. It has a drive circuit 17 that supplies a periodic ON signal, and a delay circuit 18 that delays the start of operation of this drive circuit 17.

Next, the specific circuit will be explained with reference to FIG. The first switching means 13 is composed of an anti-parallel connection of an NPN transistor 8 and a flywheel diode 9, and the second switching means 16 is composed of a thyristor 19 and a diode 2.
It consists of 0 connected in anti-parallel.

Here, the transistor 8 and the thyristor 19 are not particularly limited as long as they are switching elements operated by a control signal, for example, a field effect transistor (FET).
There is no problem in operation even if a gate turn-off thyristor (GTO) or the like is used.

The zero point synchronous circuit 16 has a power transformer 21 connected to the AC input terminal of the rectifier 3. The secondary winding has a monter tap, and the rectified output, which is single-phase full-wave rectified by a diode 22.23, is divided by a voltage dividing resistor 24.25 and then connected to the base of a transistor 26. . Further, a diode 27 and a smoothing capacitor 28 are further connected to the cathode terminals of the diodes 22 and 23, and the smoothed DC voltage is stabilized by a resistor 29 and a Zena diode 3o, and is used in other electronic circuits. It is a constant voltage power supply.

The zero-volt synchronous pulse generated between the collector and emitter of the transistor 26 is connected to a D-flip-flop 31 (for example, NPD4013 manufactured by NEC Corporation, hereinafter referred to as D-F/
It is abbreviated as 1r. ), and its data input terminal is supplied with a high level input by an oscillation control switch 32 during oscillation. D-F/ys1
The thyristor 19 is connected to the output terminal of the thyristor 19 via the limiting resistor 33.
A trigger signal is supplied to the gate terminal of the delay circuit 18, and an output is supplied to the input resistor 34 of the delay circuit 18.

The output signal from the D-F/F 31 is supplied to an integrating circuit consisting of a resistor 34 and a capacitor 35 that constitute the delay circuit 18, and a voltage detection circuit consisting of a Zener diode 36 and a transistor 37 connected between the terminals of the capacitor 35. Ru.

The drive circuit 17 is not particularly limited as long as it is a pulse generation circuit that periodically generates a Parnu output, but in this embodiment, an unstable multi-by-break composed of transistors 38 and 39 is used. Here, the emitter terminal of the transistor 38 is connected to the collector terminal of the transistor 37, and the 1-range gate 38 is off and the transistor 39 is on until the transistor 37 becomes conductive.
- The base current is supplied to the transistor 8, and the chair frequency converter 1o is not excited at all. transistor 3
At the same time as transistor 7 is turned on, transistor 39 is turned off for a predetermined period of time. A base current is passed through transistor 8 via Li resistors 40 and 41, and thereafter, the frequency conversion device 1o The heated carp) v6 inductively heats a pan (not shown).

Its operation will be explained according to FIG. FIG. 4a shows the cathode terminal voltage of the diodes 22 and 23 which substantially full-wave rectify the commercial power supply 1. FIG. This voltage is supplied to the base terminal of the transistor 26 via the resistor 24, so when the power supply is zero volts, there is no base current and the transistor 26
is offset, the positive pulse of Figure 4 is D −F / y
It is supplied to the clock input terminal of 31 every cycle. On the other hand, the oscillation control switch 32 is turned on at an arbitrary phase and the fourth
When an arbitrary repetitive waveform is input to the D-F/F31 as shown in Figure C, it is synchronized with the rising point of the clock input and the waveform shown in Figure 4D is displayed.
The output will be as follows. Therefore D −F / F 3
The rise and fall of the output of 1 are always synchronized with the zero point of the power supply. Here, the control of the oscillation signal is illustrated by the Nutwitch 32, but the output of a low frequency oscillator that can be easily obtained with an unstable multi-by-break configuration is connected instead, and its output 10 /; -, : - By varying the pulse width, it is possible to arbitrarily set the repetition period and time ratio of the output waveform shown in FIG. 4d.

At the same time as the output of the D-F/F 31 (FIG. 4 d) rises, a gate current flows through the resistor 33 and the thyristor 19 becomes conductive. At that time, the terminal voltage of the capacitor 5 is approximately equal to the maximum value of the commercial power supply, as shown in FIG. 4, since the transistor 8 is not conducting yet. /
4 constitutes a series resonant circuit and vibrates. It is easy to make the lowest point of the vibration near zero if the loss in the series resonant circuit is small, so if the transistor 8 starts switching in synchronization with the vicinity of the lowest point, the heating coil) v
The current flowing through the pot can be started from an extremely low value, and the eddy current in the pot is a soft start that rises from zero, so the pot does not make any noise.

However, if the resistance of the circuit of choke coil V4, capacitor 11, and thyristor 19 is reduced so that the lowest point of capacitor 6 becomes zero, the voltage of capacitor 6 may be affected by resonance depending on the page. It is expected that this will happen. In that case, capacitor 6° diode 9. Since a closed loop of the heating coil I/6 occurs, current flows through the heating coil A/6 even if the transistor 8 is not conductive, and there is a possibility that a pot noise may be generated before starting. On the other hand, in this embodiment, a diode 1 is connected antiparallel to the capacitor 6.
4 is connected to prevent the generation of reverse voltage. diode 1
The current of 4 is shown in FIG. 4j. This diode 14 makes it possible to completely reduce the voltage across the capacitor 6 to zero (strictly speaking, approximately θ1V is generated, but since it matches the forward voltage of the diode 9, no current flows through the heating coil 6). It is possible to prevent the occurrence of pot noise. capacitor 6
The voltage of the fourth voltage drops to zero once due to the capacitor 11, but the voltage of the commercial power supply 1 rises with the progress of the phase.
It will rise again as shown in the figure. Output of D-F/F31 (4th
d) is applied to an integrating circuit consisting of a resistor 34 and a capacitor 36, and the capacitor 35 has a waveform as shown in FIG. 4e. Here, when the breakdown voltage of the zenadanode 36 is shown by a broken line, the output transistor 37 is turned on and off as shown in FIG. 4f.

When the point at which the transistor 37 is turned on is set at the point at which the voltage of the capacitor 5 rises from zero, the collector voltage of the transistor 8 gradually rises from zero as shown in FIG. The waveform (FIG. 4h) can also be soft-started. Once started, the terminal voltage of capacitor 6 becomes a high ripple voltage waveform as shown in FIG.
This results in a high ripple voltage as shown in Figure i. Therefore, D−F/
Since the fall of the output waveform of F31 is synchronized with the zero point, the current of the heating coil v6 and the voltage of the capacitor 11 are also zero even when the motor is stopped. Therefore, the pot noise does not occur even when the machine is stopped, and the voltage of the capacitor 11 is also zero, so the charge in the capacitor 6 can be transferred again when the machine is started next time.
It is possible to prevent the pot noise from occurring when restarting. This means that in time ratio control when you want to lower the output by a very small amount than the output of continuous oscillation, the oscillation stop cycle may be one cycle, but even in that case, it is possible to prevent the generation of pan noise. That's true.

As described in detail, the induction heating cooker of the present invention has the following features: (1) Prevents pot noise when starting up so as not to cause discomfort to the user.

■ During duty control (time ratio control), the above pot noise does not occur even with a wide range of output settings.

■ At startup, the capacitor's short-circuit current does not flow to the switching element, making the element highly reliable and economical.

It has the following effects.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a conventional induction heating cooker;
FIG. 2 is a circuit diagram of the induction heating cooker of the present invention, FIG. 3 is a circuit diagram showing an embodiment of the induction heating cooker, and FIG.
FIG. 3 is a waveform diagram showing operational waveforms of the illustrated embodiment. 5...Filter capacitor, 6...Heating coil, 14 Baler 1o...Frequency converter, 13...First nutching! , 15...second switching means, 16...zero point synchronization circuit, 17...
...Drive circuit, 18...Delay circuit.

Claims (1)

[Claims] A choke coil and a first filter capacitor are connected to the rectifier output terminal of a rectifier connected to a commercial power supply, and a resonant circuit consisting of a heating coil and a resonant capacitor and a first resonant circuit that excites the resonant circuit are connected to both ends of the first filter capacitor. a frequency converter configured by connecting a switching means and a rectifier connected in antiparallel to the filter capacitor, and a filter circuit comprising a second filter capacitor and a second switching means connected in series to the rectifier output terminal of the rectifier. and a zero-point synchronization circuit that inverts in synchronization with the zero-voltage point of the commercial power supply, and an output of the zero-point synchronization circuit that supplies an on signal to the second switching means and a periodic on signal to the first switching means. An induction heating cooker comprising a drive circuit that supplies the power and a delay circuit that delays the start of operation of the drive circuit.