JPS5933783A - 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 The present invention relates to an induction heating cooking device, and more particularly to an induction heating cooking device configured to use a pulsating current obtained by full-wave rectification of alternating current as a power source and continuously oscillate a high-frequency inverter including an induction heating coil. Concerning vessels.

In induction heating cookers driven by pulsating current power,
Normally, a start signal for starting the inverter to oscillate and a timing signal for determining the load are output at the power supply valley.

However, when the cooking pot as a load is removed, no-load detection is performed using a timing signal at the trough of the pulsating voltage.
If a start signal is output at the detection backward valley, the problem arises that the inverter does not oscillate normally because the power supply voltage has not reached a stable state of 1.

The present invention has been made in consideration of such circumstances.

That is, the present invention converts the above-mentioned activation signal and timing signal into
It outputs alternately in synchronization with the troughs of the pulsating voltage.
Once no load is detected using a timing signal, a start signal is output one cycle after the power supply voltage reaches a normal value.

Examples will be described in detail below. In FIG. 1, (1) is a commercial AC power supply, (2) is a power switch, (8) is a rectifier circuit, (4) is a choke coil, and (5) is a filter capacitor that bypasses high frequency components. (6) is an induction heating coil, (7) is a resonant capacitor, (8) is a switching element such as a transistor, and (9) is a damper diode, and these constitute a high frequency inverter α1. αη is a cooking pot, and α2 is a current transformer that detects the load current flowing through the induction heating coil. (6)
is a step-down transformer, and q→ is a constant voltage circuit, which outputs a constant voltage VDD. α is a diode that rectifies the alternating current obtained on the secondary side of transformer α4 by half, and αQ is this diode Q! 9
'i through the half-wave rectified voltage V2. α71 is a timing signal generation circuit that receives the output of this valley detection circuit Q→ and outputs a load detection operation timing signal, and (G) similarly detects the valley. Part detection surface Iil! This is a starting signal generating circuit that receives the output of α@ and outputs all starting signals, and both the timing signal and the starting signal are generated in synchronization with the trough of the pulsating voltage. DI is the detection signal by the current transformer (a) and the filter capacitor (5)
This is a load detection circuit that inputs the terminal voltage (1), and outputs an "L" level signal when a small object such as a knife is loaded or there is no load. This load detection circuit α is activated when it receives a timing signal. Also, the start signal is from this load detection circuit (1
It is also used as a time reset signal.

(E) is the detection signal and voltage Vl of the current transformer @
Inverter αovil - about 20 KHz
Inverter self-excited oscillation circuit that oscillates at a frequency of r:A
υ is a Nant gate that uses the inverter automatic oscillation circuit) and the output signal of the load detection circuit 00 by two people, @ is a Nant gate? This is a drive circuit in which the output of υ is applied to the inverting circuit (via the inverting circuit), which provides an on/off current to the base of the transistor (8). To this drive circuit), the activation signal generated from the activation signal generation circuit (g) is applied to the inverted circuit ai! )
It can be added via .

Figure 2 shows a specific example of the voltage valley detection circuit, the α-inversion timing signal generation circuit (17), and the start signal generation circuit (to). (E) (Foundation) divided by n and the comparator input to its ■ input terminal,
A constant voltage VDD is divided by a resistor (c) and input to the e input terminal. The output (3) of the comparator (c) is input to the inverting circuit (to) through a resistor and a capacitor for preventing external noise. The output of the inverting circuit (to) is converted into a pulse signal synchronized with the rising edge of the comparator output v3 through a differentiating circuit consisting of a capacitor and a resistor (connected to the constant voltage VDD). This pulse signal is further outputted as a timing signal v4 via an inverting circuit. The output of the inverter circuit) passes through a differentiator circuit consisting of a capacitor (b) and a resistor connected to the ground, and then becomes the comparator output.
It is converted into a pulse signal synchronized with the falling edge of 3. This pulse signal further passes through an inversion circuit OI and is output as a starting signal (6). Resistor (6) (6) and diode (6
) vI are for protecting the inverting circuit (to) OI, respectively. Also, the capacitor prevents the comparator from oscillating.

Next, the entire operation of the above configuration will be explained using FIG.

When the load is suitable and heating is being performed normally, the timing signal V4 and the start signal 5 are output alternately every cycle in synchronization with the troughs of the pulsating voltage. Transistor (
8) The pressure VCE between the emitter and lifter is set at a predetermined frequency (
It becomes a high frequency voltage of 20 KHz), and the line in the envelope # is,
Draw a waveform similar to the pulsating flow 11IL source voltage. however,
The terminal voltage Vl of the filter capacitor (5) is:
The phase is slightly delayed compared to the commercial AC waveform. This delay time is indicated by τ in the figure. This delay time r is θ of comparator ■
Modified by changing the voltage level of the input terminal. That is,
If the e input terminal voltage level is set to the voltage value at the time when time τ has elapsed since the input voltage ■2 to the ■ input terminal of the comparator ■ is 0, the inverter α0w1.
At the deepest point of the valley of the source voltage, the comparator (c) output is set to “H”ν
This can be reversed. Therefore, the timing signal is
Inverter aQ electric Hw1. Pressure-1) Output immediately after reaching zero. Further, the activation signal 5 is outputted before the power supply voltage of the inverter α1 decreases and reaches the deepest point of the inverter α1.

Under normal heating conditions, the first activation signal (6) activates the drive circuit (6) and turns on the transistor (8).
The oscillation of inverter αq starts. Thereafter, the inverter αQ continues to oscillate by the operation of the inverter automatic oscillation circuit (inverter automatic oscillation circuit) upon detecting the impur 100 oscillation state. Well, since the load detection signal output from the load detection circuit α in synchronization with the timing signal ■4 is “■(”, the output of the inverter self-excited oscillation circuit (1) is inverted and output from the Nant gate. e]), is further inverted by the inverting circuit (), and is applied to the drive circuit ().

On the other hand, if the cooking pot Ql)'Th is removed from the heating stand during heating, the output of the load detection circuit α becomes "L" due to the timing pulse V 4 (4), and the output of the load detection circuit α becomes "L"
) becomes "H" regardless of the output of the self-excited oscillation circuit (1), the output of the inverting circuit (2) is fixed at "L", and the drive circuit (FJ@) does not operate. After one subsequent cycle,
Due to the starting pulse V s (b), the driving times Ii! ! (A) is energized and inverter αQ starts oscillating. However, since the output of the automatic oscillation circuit (1) is not transmitted to the drive circuit (to the drive circuit), the inverter OQ only increases the attenuation.

When such activation signal ■6 is given, the cooking pot αυ
If 1 is placed, the state of damped vibration caused by the starting signal 5 is different from the damped oscillation in an unsuitable load or no-load state, so this is determined and the subsequent arrival of the starting signal 5 causes self-excited oscillation. is started. Since the voltage VCE has already reached a stable value when the activation signal V5(b) is output, there is no risk that the damped vibration described above will become an abnormal waveform. That is, if this voltage VCE is low, the problem of damped oscillation pulses also does not occur.

As described above, the induction heating cooker of the present invention alternately outputs the start signal and the timing signal for load detection at the troughs of the pulsating power supply voltage, so an inappropriate load is detected by the timing signal. After the - period has elapsed, that is, after the inverter power supply voltage reaches a stable state, the activation signal is output. Therefore, the oscillation caused by the start signal has an amplitude depending on the state of the load, and malfunctions in load discrimination due to fluctuations in the vIL source voltage are suppressed.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of an embodiment of the present invention, FIG. 2 is a main circuit diagram, and FIG. 6 is an operating waveform diagram. (6)...Induction heating coil, αQ...
High frequency inverter, H... pulsating voltage valley detection circuit, aη... timing signal generation circuit, (c)
...Start signal generation circuit, α...Load detection circuit, In)...In 7V-T self-excited oscillation circuit, (A)...Drive circuit.

Claims (1)

[Claims] 1) An inverter that includes an induction heating coil, a pulsating current power source that drives the inverter and is obtained by full-wave rectification of commercial alternating current, and a start signal to the inverter at the trough of the pulsating power source voltage. and a timing signal generation circuit that generates a timing signal for detecting a load at the trough of the pulsating power supply voltage, each of the start signal generation circuit and the timing signal generation circuit An induction heating cooker characterized in that an output signal is alternately output every cycle of a pulsating power supply voltage.