JPS633113Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a high frequency induction heating device suitable for use in a so-called electromagnetic cooker.

BACKGROUND TECHNOLOGY AND PROBLEMS Immediately after the power switch is turned on, in an electromagnetic cooker, in order to detect whether the pot placed on the work coil is suitable as a load for the cooker, A so-called search pulse is issued and the switching element is instantaneously driven (on/off) through the drive circuit for the duration of that pulse.
The device is designed to detect whether the pot is suitable or not within a short period of time. For this purpose, the electromagnetic cooker is provided with a load detection circuit and a search pulse generation circuit, and conventionally, the search pulse generation circuit is unilaterally controlled by the output of the load detection circuit.

When each of these circuits is configured with an operational amplifier, for example, it takes time for the load detection circuit to invert (invert the output signal based on a change in the magnitude of the two inputs), and during that time the search pulse is generated. There is a risk that the circuit will operate in an unstable state, supplying erroneous signals to the drive circuit, causing the switching element to malfunction, and damaging it.

Purpose of the Invention In view of the above-mentioned points, the present invention is designed to avoid damage to the switching element without causing an unstable operation period and thus causing the switching element to malfunction.

Summary of the invention This invention applies a detection voltage corresponding to the main current flowing through the work coil and a reference voltage from a reference voltage source to a load detection circuit, and outputs a voltage to the output side based on the magnitude of the detection voltage with respect to the reference voltage. Obtain a binary signal, supply the binary signal to a search pulse generation circuit, generate a search pulse in one of the states of the binary signal, supply the search pulse to an oscillation circuit, and generate a search pulse. In the high-frequency induction heating device, the oscillation operation is performed during the off (or on) period of the search pulse, thereby driving the switching element, in which the output from the search pulse generation circuit is
The feature is that positive feedback is provided to one of the input sides of the load detection circuit, and as a result,
This ensures that the period during which oscillation (oscillation for GCS switching) is stopped in the search state can be obtained reliably.

Embodiment Hereinafter, an example of the apparatus according to the present invention will be described with reference to the drawings. 1a and 1b are power terminals connected to commercial AC power terminals, 2 is a power switch, 3 is a rectifier circuit, 4 is a smoothing circuit, 5 is a work coil, 6 is a damper diode, 7 is a switching element such as GCS,
8 is a resonance capacitor, 9 is a drive circuit, 10
1 is an oscillation circuit, 11 is a control circuit for controlling the oscillation frequency of the oscillation circuit 10, and 12 is a DC power supply terminal to which, for example, 12V is applied. Reference numeral 13 denotes a resistor, ie, a sensor, for detecting the magnitude of the current flowing through the work coil 5, and the voltage obtained across the resistor is amplified by an amplifier circuit 14 and supplied to a load detection circuit 15.

The load detection circuit 15 includes a reference voltage source 16 that generates a reference voltage for load detection, and a comparison circuit 17. The output from the amplifying circuit 14 (referred to as voltage V ₁ ) is supplied to its negative input terminal, and the reference voltage (referred to as voltage V ₂ ) is supplied to its + input terminal.

The output from such a load detection circuit 15 (referred to as V ₃ ) is supplied to a search pulse generation circuit 18 at the next stage.

As this circuit 18, a so-called hysteresis width oscillation circuit using an operational amplifier 19 can be used, as is clear from FIG. A series circuit consisting of a resistor 20 and a capacitor 21 is connected between the DC power supply terminal 12 and the ground, and its connection Q is supplied to the negative input terminal of the amplifier circuit 19, so that the output of the load detection circuit 15 described above is + input terminal.

Furthermore, in the present invention, the output of such a search pulse generation circuit 18 is supplied to the + input terminal of the above-mentioned comparison circuit 17 through the diode 22,
In other words, it is configured to provide positive feedback.

Next, the operation of such a configuration will be explained. Regarding the search pulse generation circuit 18, when the input of its + input terminal is at a high level, that is, in the state of input 1, the search pulse P shown in FIG. 2 is obtained on the output side, and the next The oscillation circuit 10 connected to the stage is
It is assumed that when its input is at a low level (input 0), that is, when the output of the search pulse generation circuit 18 is 0, it performs an oscillating operation.

A load (pan) is placed on the work coil 5, and the power switch 2 is turned on. In this state, the terminal 12 is connected to the load detection circuit 15 and the pulse generation circuit 18, respectively.
A drive current is supplied through the reference voltage source 16, and a predetermined voltage _V2 is obtained from the reference voltage source 16. Immediately after turning on this power switch 2,
Since current is not yet supplied to the work coil 5,
In the case of the load detection circuit 15, the + input terminal side becomes a higher level than the - input terminal side, and its output _V3 becomes 1, thereby causing the search pulse generation circuit 18 connected to the next stage to output the signal shown in Fig. 2. The search pulse P shown is obtained. Then, when the level of this search pulse P is 0, that is, during a time T ₁ (for example, 0.15 seconds), the oscillation circuit 10 oscillates and the GCS 7 performs a switching operation. As a result, a high frequency current is supplied to the work coil 5, and the magnitude of the current is detected by the resistor 13. At this time, if the pot on the work coil 5 is inappropriate, for example in the case of a non-magnetic pot such as a stainless steel pot, a large current flows through the coil 5, resulting in a large voltage drop due to the resistor 13, and V ₁ < V ₂ , and the output V ₃ of the load detection circuit 15 maintains the state of 1,
Therefore, the search pulse P as shown in _FIG .
GCS7 is switched and driven. Incidentally, one period _T2 of this search pulse P is selected to be, for example, 1.2 seconds. Although not shown, normally an alarm signal is generated during a period _T1 in synchronization with this pulse P.
I try to warn people that the pot is inappropriate.

On the other hand, if the pot on the work coil 5 is appropriate, the current flowing through it is small, and therefore the voltage drop due to the resistor 13 is also small, so the voltage
V ₁ becomes larger than V ₂ . This is how the reference voltage V ₂ is set in advance. like this
When V ₁ > V ₂ , the output from the load detection circuit 15 becomes 0, and therefore the search pulse generation circuit 18
The oscillation operation stops and its output becomes 0. That is, the oscillator 10 continuously performs an oscillating operation, and thus a continuous high frequency current is supplied to the work coil 5, thereby continuing the heating operation. Thereafter, the control circuit 11 controls the oscillation frequency of the oscillation circuit 10, thereby adjusting the output. This configuration is well known. still,
Generally, the control circuit 11 is automatically brought to a predetermined low output control position when the power is turned on.

Further, in the present invention, the output of the search pulse generation circuit 18 is positively fed back to the + input terminal of the load detection circuit 15 through the diode 22. Therefore, if the pot currently placed on the work coil 5 is inappropriate and the search pulse P shown in FIG. 2 is repeatedly obtained from the search pulse generation circuit 18, this search pulse Each period T ₂ of P
In this case, the − input terminal of the load detection circuit 15 is always at a high level, that is, V ₁ <V ₂ , and this circuit 15
As a result, output 1 is obtained and the search pulse generation circuit 18
The + input terminal of the input terminal also becomes input 1. Therefore, the oscillation output of the oscillation circuit 10 can be reliably stopped during this period _T2 .

That is, according to this circuit, during the period _T2 in which the search pulse P is 1, the output can be generated stably and reliably, and therefore, the output from the search pulse generation circuit 18 will not be interrupted by mistake. , that is, the output becomes 0, and even though an inappropriate load is placed on the work coil 5, the oscillation circuit 10
This has the feature that it is possible to reliably avoid defects such as continuous oscillation.

Effects of the Invention As explained above, according to the present invention, the output of the search pulse generation circuit whose oscillation operation is controlled by the output from the load detection circuit is redirected to the load detection circuit 1.
5, the time _T2 during which oscillation of the oscillation circuit 10 is stopped can be compensated for by this circuit, thereby preventing unstable operation. So, with this
This feature allows the GCS to be prevented from being inadvertently damaged.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing an example of a high frequency induction heating device according to the present invention, and FIG. 2 is a signal waveform diagram for explaining the same. 5... Work coil, 6... Damper diode, 7... Switching element, 9... Drive circuit, 10... Oscillation circuit, 15... Load detection circuit,
18...Search pulse generation circuit.

Claims (1)

[Scope of utility model registration request] A high frequency current is supplied to the work coil by turning on and off the switching element, and a detection voltage corresponding to the main current passing through the work coil and a reference voltage from a reference voltage source are respectively applied to the load detection circuit. A binary signal is obtained on the output side based on the magnitude of the detection voltage with respect to the reference voltage, and the binary signal is supplied to a search pulse generation circuit, which generates a search pulse in the state of either of the binary signals. generates a search pulse, supplies the search pulse to an oscillation circuit, and causes the oscillation circuit to perform an oscillation operation during the off (or on) period of the search pulse, thereby driving the switching element. In the induction heating device, the output from the search pulse generation circuit is
A high-frequency induction heating device characterized in that positive feedback is provided to one input side of the load detection circuit.