JPS5937690A - 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 cooker, particularly a no-load one.

The small object load is determined using the inverter activation signal output period.

Conventionally, known load detection methods for this type of cooker include a method that uses a magnet attracted to a cooking pot, and a method that detects the magnitude of current flowing through a diode that constitutes an inverter. However, the former method cannot heat pots made of materials that do not attract magnets, such as 18-8 stainless steel pots and 18-10 stainless steel pots, and the diode current detection method also depends on the thickness and size of the 18-8 stainless steel. , there is a risk that it will be judged as an inappropriate load.

The present invention provides a cooking appliance that employs a novel load detection method that eliminates the drawbacks of the load detection method ζ as described above.

Examples will be described below based on the figures. Funeral 1 Figure 1 = Leave (
1) is an AC power supply, (21 is a power switch, (31 is a rectifier circuit, (4) is a choke coil, (5) is a filter capacitor, (6) is an induction 0-hole heating coil, (7I is this induction heating A resonant capacitor connected in series to the coil (6) (81 is a resonant capacitor (71 is a switching element connected in parallel to
These are diodes connected in antiparallel to O181, and these constitute an inverter GCj. Gl) is a cooking pot serving as a load, (04-1) is a current transformer that detects the load current, and (Q, ff2) is a current transformer that detects the input current. +IZ is a current transformer (C
A load detection circuit inputs the detection signal of ITr2) to determine the load, and ++31 is a startup circuit that outputs a startup signal with a predetermined synchronization (approximately 1.7 sec), and can be constituted by an oscillator. a4 is the filter capacitor (5)
+t5 is Ch.
This is a drive circuit that provides on/off signals to the gate of T O (31).
1e, it is applied to one input end of the Nando game (17). In addition, the output of the load detection circuit a7J and the start signal are applied to the other input terminal of the NAND game (lη) via the inverting circuit UHinoki.The output of the NAND game H7 is applied to the drive circuit (old) and make it work.

FIG. 2 shows a specific example of a load detection circuit (14) and a starting circuit u3, which are objects of the present invention, and shows a current transformer (0'I
'2') The sensing current is connected to a resistor (1 keg and a variable resistor (tl
The magnetic pressure is converted at
-2) is input to the e side input terminal. This comparator (IC
-2), the constant voltage VQQ is connected to the input terminal on the ■ side of the resistor I22.
1 (23) and the variable resistor (24). The output of the comparator (I(3-2)) is input to the NAND game H71 via a diode and an inverting circuit.

A voltage signal obtained by charging a constant voltage v'OQ to a capacitor 1281 via a resistor (2η) is applied to the e-side input terminal of the comparator (IC-1) constituting the starting circuit (13), and the other
A voltage signal obtained by dividing the constant voltage ycc by a resistor -C31 is applied to the side input terminal. t3nc3a is a resistor and diode connected between the e-side input terminal and output terminal of the comparator (IC-1), C33) and the comparator (IC-1).
) is a resistor connected between the ■ side input terminal and output terminal. The output of the comparator Cl0-1) is connected to the diode (29
and the line between the inverting circuit (c): two are added, while the capacitor C31) and the resistor C4! The force y is applied to t61 through the differential circuit consisting of j.
[The output of 0 is Nando game H as mentioned above? ) is entered.

The starting circuit (131) has an oscillation function. In other words, the constant voltage YCC generated by turning on the source switch (21) is charged to the capacitor (281, and this charged voltage is applied to the comparator (I).
C-1) ■When the side group rate level is reached, the output becomes “H”
At the same time, the capacitor [28
The charged load of 1 begins to radiate through the resistor L31) diode (2).At this time, due to the resistance (toughness), the level of the comparator (lo-1) decreases. Due to the discharge of the capacitor 128) for a certain period of time (about 1.2eθC
), the output of the comparator (IC-1) is inverted and becomes “H”.
Return to level. This operation is repeated, and the comparator (1
0-1) outputs a 1L level pulse with a constant period (approximately 1°2θθC), which is used as a starting signal. In this example, the output time ("L" level period) of the activation signal is set to about 110 meθC. This is shown by period tO in Figure 6 (Bl).

Next, the operation in the proper load heating state will be explained with reference to FIG. 3 IAI. First, the first activation signal is the comparator (IC-1
), the falling part of this activation signal is converted into a pulse by the next-stage differentiating circuit and applied to the Nand gaiter.

At this time, the other input of the Nant gate (1e) is at the "H° level, so its output is "H," and the other input of the next stage Nant gate is the "L level signal of the comparator (ro-i). is applied via the inverting circuit (current), so H“
level, hence this gate (input at 1 is “H”, “H”
・The “L” level activation signal is applied to the drive circuit (I5). Due to the operation of the drive circuit +tS, the G T O
C81 is turned on and the inverter (10) starts oscillating.

Then, power is supplied to the cooking pot till and the input current accordingly shows a relatively large value, so the detection signal from the current transformer (OT2) is large and therefore the charging curve of the capacitor 21) also becomes steep.

The voltage applied to the e-side input terminal of the number comparator (IC-2) increases from the (1) side to the level V+ within the activation signal output period to, and changes the output to the "L" level. Due to this "L" inversion, the output of the comparator (10-1) is also fixed at this 1L level via the diode 125). As a result, the capacitor is not charged and the oscillation operation is stopped. +1.61 startup circuit (131 signal input side terminal is “
Since it is fixed at H., this gate (tlG) is in an open state, and the self-excitation signal generated from the self-excitation signal generating circuit (2) is inverted and sent to the Nant gate +1.7) at the next stage. Since the other input of this NAND gate η is "H", this gate is also in an open state (= present), and the self-excitation signal is inverted here and added to the driver 3Q circuit (one). Then, the inverter tune continues self-oscillation.

On the other hand, if the load is a small object load or no load, Fig. 6 IB+
As shown in Figure 2, the start signal causes inverter 0 to oscillate, but since the input to the load is small, the charging voltage of the capacitor (2υ) is generated by the comparator (IO) within the start signal generation period to.
-2) ■The side base rate level V+ is not reached. The output of the number comparator Ha-2) maintains the H level. During the period when the activation signal is being output, its output is converted into an H level signal via the inverting circuit ρ0 and is added to the However, during the start signal non-output period, the power of the Nandt gate (lη) is fixed at "L", so the inverter (Il) does not oscillate during this period. , the inverter (10) oscillates only during the start signal output period to.
Approximately 11 Qmsec, the period is approximately i,)ee.

Therefore, there is no risk that the small load will be heated due to this intermittent oscillation.

In this way, the induction heating cooker of the present invention detects the input T4N that accurately reflects the power supplied to the load, and converts the detected current signal into a voltage via a time constant circuit within the start signal output period (2). Since it converts into a level signal and determines whether the load is suitable or not based on the magnitude of the level, it is possible to accurately identify pots made of 18-8 stainless steel or 18-10 stainless steel, which do not attract magnets.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a main circuit diagram, and Fig. 6 (A) (Bl is an operating signal waveform diagram. 111...Inverter, a'lJ... Load detection circuit, (131...starting circuit, (14+...self-excitation signal generation circuit, 01...drive port circuit).

Claims (1)

[Claims] 1. An inverter including an induction lIO heating coil, a load detection circuit that detects the current of the power source that drives the inverter and determines whether the load is suitable or not for electromagnetic coupling to the induction heating coil, and a load detection circuit that detects the current of the power source that drives the inverter and determines whether the load is suitable or not for electromagnetic coupling to the induction heating coil, and a A startup circuit that oscillates and outputs a startup signal, an automatic oscillation circuit that detects the oscillation state of the inverter and generates a self-excited oscillation signal after oscillating and startup the inverter with the startup signal, and a self-excited oscillation circuit that generates a self-excited oscillation signal from the self-excited oscillation circuit and the startup circuit. (receives the output and drives the inverter)
The load detection circuit includes a time constant circuit that operates when the start signal is output by the start circuit, and the suitability or unsuitability of the load is determined from the output of the constant number circuit (2). An induction heating cooker.