JPS6074378A - 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 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, this type of induction heating cooker has a rectifier 3 connected to a commercial power source 1 via a power switch 2, as shown in FIG.
A series circuit of a choke coil 4 and a filter capacitor 6 is connected to the output terminal of the filter capacitor 6, and a parallel resonant circuit of a heating coil 6 and a resonant capacitor 7 and an antiparallel circuit of a transistor 8 and a flywheel diode 9 are connected to both ends of the filter capacitor 6. The series circuit with the circuit is connected. When the transistor 8 performs a switching operation at an ultra-audio frequency, the heating coil 6 generates a high frequency magnetic field, which generates an eddy current in the pot and generates Joule heat. and choke coil 4
, a heating coil 6, a filter capacitor 6, a resonant capacitor 7, a transistor 8, and a flywheel diode 9 constitute a frequency conversion device 1o. Power is supplied from the input terminal of the transistor 8 to switch the transistor 8 at an ultra-audible frequency.

In addition to the above-mentioned basic heating operation, it is necessary to arbitrarily change and set the output to I/FF for actual cooking, and for this purpose, the frequency of the output signal of the drive circuit 11 has been changed. In that case, in order to make the output variable range wide enough to be suitable for stewed dishes, the frequency must also be extremely loud during changes, and the number of devices that receive interference noise increases due to the widening of the interference noise frequency, and the transistor 8 necessitated fast switching times. Another means for varying the output is a duty control means that periodically turns on and off the oscillation of the frequency converter 1o to control the energization ratio. The drawback of this method is that a pot sound is generated when the power is turned on in synchronization with the duty cycle, which is unpleasant to the ears.

Here, the cause of the pan noise at startup is due to the mechanical vibration of the pan when the accumulated charge in the filter capacitor 6 flows through the heating coil 6 when the transistor 8 is turned on. Therefore, the higher the voltage of the filter 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 filter capacitor 6 is charged to the maximum capacity 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 above-mentioned problems of the prior art and provides an induction heating cooker that does not generate pot noise and has a wide variable range of output settings using a duty control means.

Structure of the Invention The induction heating cooker of the present invention includes 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 and a resonance capacitor connected to both ends of the first filter capacitor. A frequency conversion device comprising a series circuit of a resonant circuit consisting of a resonant circuit and a first switching means that excites the resonant circuit, and a second filter capacitor and a second switching means connected in series to the rectified output terminal of the rectifier. a filter circuit, a zero-point synchronization circuit that inverts the output in synchronization with the zero voltage point of the commercial power source and supplies an on signal to the second switching means, and detects a rate of change in the terminal voltage of the first filter capacitor. a trigger circuit that generates a signal when the rate of voltage change reaches zero for the first time; and a trigger circuit that is connected to the output of the trigger circuit and outputs an ON signal with a predetermined repetition period to a first switching means. The drive circuit transfers the charge charged in the first filter capacitor to the second filter capacitor before startup, and sets the lowest point of the terminal voltage of the second filter capacitor with no accumulated charge. Since the device is detected and activated, it is possible to realize a duty control means that does not generate pan noise when activated.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 2, a choke coil 16 and a first filter capacitor 16 are connected to the rectified output terminal of a rectifier 14 connected to a commercial power supply 12 via a switch 13, and both ends of the first filter capacitor 16 are heated. coil 18
A frequency conversion device 21 is constructed by connecting a series circuit consisting of a parallel resonant circuit consisting of a resonant capacitor 19 and a first switching means 2o that excites the parallel resonant circuit. Also, rectifier 1
A filter circuit 24 in which a second filter capacitor 22 and a second switching means 23 are connected in series is connected to the rectified output terminal 4. A zero-point synchronization circuit 25 is connected to the input terminal of the rectifier 14 and inverts the output in synchronization with the zero voltage point of the commercial power supply 12, and supplies an ON signal to the second switching means 23.The first filter capacitor 16 The terminal '11b pressure ■ is input to the rate of change detection circuit 26, which generates an output to the trigger circuit 27 every time the rate of change dV/d t of ■ becomes zero.
The drive circuit 28 synchronizes with the time when t becomes -V zero once.
Generates output to. Thereafter, the drive circuit 28 receives a predetermined pulse 11 (7 pulses) until a stop signal is received from the trigger circuit 27.
) continue to supply the drive signal to the first switching means 20;

FIG. 3 provides a more detailed explanation of the block diagram of the embodiment shown in FIG. 2. Hereinafter, the operation of each part will be explained together with FIG. 4, which shows waveforms of each part. A transformer 29 connected to the commercial power supply 12 has two taps on its secondary winding, full-wave rectification with diodes 30 and 31, and full-wave rectification with diodes 32 and 32.
It performs half-wave rectification. The full-wave rectified output (FIG. 4a) is voltage-divided by voltage-dividing resistors 32' and 33, and then connected to the base of a transistor 34.

Further, a diode 35 and a smoothing capacitor 36 are further connected to the cathode terminals of the diodes 30 and 31, and the smoothed DC voltage is passed through a resistor 37 and a Zener diode 3.
It is highly stabilized and serves as a constant voltage power supply for other electronic circuits.

The zero-volt synchronous pulse (Fig. 4b) generated between the collector and emitter of the transistor 34 is the clock of a D-flip-flop 39 (for example, μPD-4013 manufactured by NEC ■, hereinafter abbreviated as D-F/F). It is connected to the input terminal, and the data input terminal is supplied with a high level input during oscillation by the oscillation control switch 40 (the fourth
Figure C). A trigger signal is supplied from the output terminal of the DF/F 39 to the gate terminal of the thyristor 42 via a resistor 41 (FIG. 4d). Thyristor 4 is activated by the trigger signal.
2 becomes conductive, the accumulated charge in the first filter capacitor 16 is transferred to the second filter capacitor 22, and the terminal voltage of the first filter capacitor 16 becomes a high ripple waveform as shown in FIG. 4e. Further, the terminal voltage of the second filter capacitor 22 also has a high ripple waveform as shown in FIG. 4i. Capacitor 43 forming rate of change detection circuit 26
A differentiating circuit with a resistor 44.45 connected in series with the resistor 44.45 is connected between the terminals of the first filter capacitor 16, and a differential circuit with a resistor 44.45 connected in series with the first Input the differential waveform of the terminal voltage (2) of the filter capacitor 16 (solid line in FIG. 4f). In addition, a constant negative voltage ( (dotted chain line in FIG. 4f) is supplied as a reference voltage. The output of the comparator 46 is passively coupled by a resistor 51 and is used as the output of the rate of change detection circuit 26 to configure the trigger circuit 27. is supplied to the clock terminal of the comparator 46 shown in FIG. 4f.
As can be seen from the input signal, the output of the comparator 46 (Fig. 4q) is inverted at the point where the rate of change (dV/dt) of , dV/d t becomes zero, and the output of the comparator 46 changes from low to high. D-F/F52 reads the D terminal signal at the rising edge of the clock input and generates the output at the 0 terminal, so the D terminal of D-F/F62 and D-F/F62 are connected to each other.
If the D terminal of F39 is connected, the output waveform of D-F/F52 changes as shown in the fourth diagram. This D-F/F
The output signal of 62 is divided by voltage dividing resistors 63 and 54 and connected to the base of transistor 65.

The drive circuit 28 is not particularly limited as long as it is a pulse generation circuit that periodically generates pulse output, but in this embodiment, an unstable multivibrator composed of transistors 66 and E57 is used. Here, the emitter terminal of the transistor 56 is connected to the collector terminal of the transistor 65, and since the transistor 66 is turned off and the transistor 57 is turned on until the transistor 55 becomes conductive, a base current is supplied to the NPN transistor 58. Therefore, the frequency conversion device 21 is not excited at all.

At the same time as transistor 65 turns on, transistor 57
is turned off for a predetermined time (high output period in the fourth diagram), and the base current is passed through the NPN transistor 58 through the resistor 69.60, after which the output frequency converter 21 of the unstable multivibrator is excited. Heating coil 18 inductively heats a pot (not shown).

In this embodiment, the oscillation control switch 40 is used to control the oscillation signal, but the output of a low-frequency oscillator, which can be easily obtained with a configuration such as an unstable multivibrator, is connected here instead. By making the pulse width variable, it is possible to arbitrarily set the repetition period and energization ratio of the output waveform as shown in FIG. 4C.

To explain the problem of pot noise here, when the frequency converter 2'1 is not excited, the terminal voltage of the second filter capacitor 22 is [8, 0 and When the output of the D-F/F 39 (FIG. 4 d) rises at the zero point of the power supply and the thyristor 42 becomes conductive, the charge accumulated in the first filter capacitor 16 is transferred to the second filter capacitor 22. , as shown in FIG. 4e, the terminal voltage V of the first filter capacitor 16 drops rapidly. It is the change detection circuit 26 that detects the point in time when this terminal voltage ■ reaches the lowest point, that is, dV
When /dt becomes zero for the first time, an output is sent to the trigger circuit 27, and the frequency converter 21 is excited by the drive circuit 2. Then NPN transistor 68
When conductive, there is almost no accumulated charge in the first filter capacitor 16, so there is no discharge of the accumulated charge through the heating coil 18, and no pot noise is generated due to mechanical vibration of the pot. be.

The first switching means 20 has been described using an anti-parallel circuit of an NPN transistor 68 and a damper diode 61, but instead of a transistor, a C1TO (gate turn-off thyristor) or a FET (field effect transistor) can be used to turn on or off using a control signal. There are no restrictions as long as the element can be turned off.

Further, as the second switching means 23, a thyristor 4 is used.
2 and a diode 62 connected in antiparallel, but it goes without saying that the IJ3 can be replaced with a triac. As described in detail, the induction heating cooker based on the present invention has the following characteristics: 1. To prevent a pot sound from causing discomfort to a user.

2. During duty control a (energization ratio control), the above pot noise does not occur even if a wide range of output settings are made.

Use 3 # When the capacitor is excited, the short-circuit current of the capacitor does not flow to the switching element, making the element highly reliable and economical.

It has the following effects.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of a conventional induction heating cooker, and FIG. 4 is a waveform diagram showing operating waveforms of an embodiment. 21... Frequency conversion device, 24... Filter circuit, 26... Zero point synchronization circuit, 26...
... Rate of change detection circuit, 27... Trigger circuit,
28... Drive circuit.

Claims (1)

[Claims] A rectifier output terminal of a rectifier connected to a commercial power supply [A choke coil and a first filter capacitor are connected, and the first
a frequency converter comprising a series circuit of a resonant circuit consisting of a heating coil and a resonant capacitor and a first switching means for exciting the resonant circuit connected to both ends of the filter capacitor; and a second filter connected to the rectified output terminal of the rectifier. a filter circuit in which a capacitor and a second switching means are connected in series; a zero point synchronization circuit that inverts an output in synchronization with the zero voltage point of the commercial power supply and supplies an on signal to the second switching means; a change rate detection circuit that detects the rate of change in the terminal voltage of the filter capacitor; a trigger circuit that generates a signal when the rate of voltage change reaches zero for the first time; and a first circuit connected to the output of the trigger circuit. An induction heating cooker 0 configured with a drive circuit that supplies an ON signal of a predetermined repetition period to a switching means of