JPS60198083A - 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 A> Industrial Application Field The present invention relates to an induction heating cooker having a load detection circuit for detecting a load or no load on small items.

Mouth) The conventional induction heating cooker uses a full-wave rectifier circuit to convert the AC'rL source into a full-wave II! By supplying this full-wave rectified power to the inverter circuit and generating a high-frequency current in the induction heating coil in the inverter circuit, the heating coil generates a high-frequency alternating magnetic field and the heating coil is placed close to the heating coil. This method uses induction heating for metal cooking utensils.

These induction heating cookers are designed to prevent users from getting burnt due to undesired heating of small objects such as knives and forks, and from wasting power consumption due to oscillation in no-load conditions. The inverter oscillation is stopped by detecting the small object load or no-load state.

By the way, in conventional induction heating cookers, for example,
As shown in No.-213170, it is possible to change the ON/OFF ratio of the switching element according to the setting value in the input setting circuit to the load, and if the setting value is the same, it will turn ON or OFF regardless of the difference in load. The input to the inverter was adjusted while keeping the OFF ratio constant. Then, load detection is performed by comparing an ON ratio signal proportional to the ON period ratio of this switching element with an input terminal signal corresponding to the AC input current to the inverter circuit, that is, the human power, and the ON ratio signal is determined as the input current signal. When the voltage was lower than that, it was determined that there was no load or a small object was loaded, and the inverter oscillation was stopped.

By the way, in an induction heating cooker with such a configuration, the switching element can be turned on by setting in the input setting circuit.
When the inverter oscillates with a constant OFF ratio and the iron pot is placed close to the heating coil, the equivalent inductance of the heating coil becomes large and the resonance period, that is, the OFF period of the switching element becomes longer. The corresponding ON period of the switching element also becomes longer. Therefore, a sufficient input current to the inverter circuit is obtained, and the load is determined to be suitable, and inverter oscillation is continued.

On the other hand, if a pot made of non-magnetic or weakly magnetic material, such as an 18-8 stainless steel pot, is placed close to the heating coil, and the inverter oscillates with the same switch element ON/OFF ratio as described above, The equivalent inductance of the heating fill becomes smaller, the OFF period (resonance period) of the switching element becomes shorter, and the ON period of the switching element also becomes shorter accordingly. For this reason, even if the inverter oscillates at the same ON/OFF ratio as the above-mentioned iron pot, sufficient input current to the inverter circuit cannot be obtained, and even if the 18-8 stainless steel pot is of sufficient size, small objects There is a problem in that the inverter oscillation is stopped based on the determination.

C) Purpose of the Invention The present invention has been developed in view of the points mentioned above, and provides a load detection circuit that can be used with a pot made of weakly magnetic metal such as an 18-8 stainless steel pot. The purpose of the present invention is to provide an induction heating cooker that uses zero.

2) Structure of the Invention The induction heating cooker of the present invention sets human power to an inverter. Due to this setting 1. A manual setting means that outputs a set value corresponding to the signal level, and a detection signal υ that detects the input power of 1.
human power detection means that outputs ', and compares the setting signal and the detection signal to set a signal, and when the signal level is higher than the detection signal level, increases the ON period of the switching element, and increases the set signal level to the detection signal level 13. an ON period adjustment circuit that reduces the ON period of the switching element when the level is lower than the ON period; a signal having a level corresponding to the ON period length of the switching element is used as a reference signal; and this reference signal and the detection signal from the input detection means are combined. The load detection circuit compares the reference signal and stops the oscillation operation of the inverter when the level of the reference signal is higher than the detection signal level.

E) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the induction heating cooker of the present invention, and (1) is ACf;! :, current power source, (2> is a full-wave rectifier circuit that full-wave rectifies the AC tlL voltage from this AC power source (1), and (3) smoothes the full-wave rectified voltage from this full-wave rectifier circuit (2). It is a smooth conde.〈4)
shows an inverter circuit connected to the above full-wave rectifier circuit (2) via this smoothing capacitor <3>, an induction heating coil (5), and a resonant capacitor (4) constituting a resonant circuit with this heating coil (5). )(6), a switching transistor (7) for generating a resonant N current in this resonant circuit, and a tamper diode (8) connected in antiparallel to this switching transistor (7). (9) is an input power detection circuit that detects the input power input to the inverter circuit (4) by the full-wave rectifier circuit (2) and τ that detects the input current supplied from the AC power supply (1). Specifically, it is configured to output a detection signal of a level corresponding to an input terminal detected by a current transformer (not shown). (10) is -" The divided voltage level of the constant voltage Vs generated from the AC voltage 1 (1) changes according to the operator's operation, and this divided voltage sets the human power of the in-hark circuit (4) l\ The input setting means (11) receives the setting signal from the input setting means (lO) and outputs a SonotoStar 1 signal that gradually rises from zero or low voltage to the setting signal level. The soft scoot circuit is shown in which a first charging capacitor (12) is charged according to the L configuration signal level and generates a soft star 1 signal between its terminals, and the charge of this capacitor (12) is discharged. [The first discharge transistor (1
3). (14) -1- The signal from the start circuit (11) is manually input to the input terminal r, and the detection signal from the human power detection circuit (9) is input to the e input terminal. comparator, (15) is the comparator (
14) A holding capacitor that holds a voltage corresponding to the output, and the charged charge is transferred to the second discharge transistor (16).
). (17) shows a voltage dividing circuit consisting of a resistor, and the holding capacitor (1
5) The voltage between the terminals is divided at a predetermined ratio and output as a reference signal. (18) is a second charging capacitor (20) that is charged with a constant voltage Vs via a resistor (19), and a third discharge that discharges the charged charge of the second charging capacitor (20). A charging IE consisting of a transistor (21)
In the circuit, this discharge 1 to transistor <21) is turned on.
, OFF generates a triangular wave voltage between the terminals of the second charging capacitor (20). (22) is a second comparator which receives the terminal voltage of the charging capacitor (20) at its e input terminal and the signal from the charging/discharging circuit (18) at its input terminal;
outputs an OFF timing signal that determines the OFF timing. (23) indicates a drive circuit that turns on and off the switching transistor (7) in the in-harc circuit (4), and the drive circuit turns on and off the switching transistor (7) in the above-mentioned second comparator circuit (22).
The switching transistor (7) is turned off by the OFF timing signal from. (24) detects that the voltage of the swinging transistor (7) has deviated from a predetermined voltage, and the drive circuit <23
) is an ON timing detection circuit that generates an ON timing signal that changes the timing to turn on the switching transistor (7), and this ON timing signal is determined by J.
The third discharge transistor (21) of the distribution/discharge circuit (18)
) is also given to the base. (25) detects the peak current flowing in the switch/channel transistor (7) by detecting the negative voltage appearing in the voltage of the switch transistor (7). The figure shows a peak current detection circuit in which the negative peak of the collector voltage of the J2 register (7) is based on a predetermined value.
When the voltage becomes high, the output terminal of the first fan (14) is lowered to a low potential level.

(26) compares the detection signal υ from the human force/force detection circuit (9) with the reference signal from the distribution pressure IA and l path (17), and calculates the basic value 1. (27) is a reset circuit that receives the small object detection signal from the small object detection circuit (26) and resets the drive circuit (23). Showing 5,
At the same time as this reset, the first, second, and third discharge transistors (13), (16), and (21) are turned on.

In such an induction heating cooker, a metal cooking utensil is placed close to the heating 7 film (5), and input power is set by a manual setting means (10) ξ [7, a power switch (not shown) is turned on. When turned on, the AC voltage from the AC power source (1) is full-wave rectified by the full-wave rectifier circuit (2), smoothed by the capacitor (3), and then supplied to the in-hark circuit (4). At the same time, the drive circuit (23') is activated for a long time, and the switching transistor (1') is turned off for a long time.
7) turns on. On the other hand, depending on which swing input, J
The second constant voltage Vs also rises, and this constant voltage Vs causes the first software L start circuit (
11〉's first charge - 17 Tenri (12) is gradually charged, the voltage gradually rises from the charging capacitor (12) terminal, and the input setting means (10) reaches the (7') KQ constant signal level. A soft signal is generated,
It is manually input to the input terminal of the first comparator (14). In addition, the input power detection circuit (9 is an inverter circuit (4)
) A detection signal corresponding to the input power of l~ is inputted to the e input terminal of the first frequency converter (14). The first comparator (14) compares the soft start signal and the detection signal, and when the soft start signal is higher than the detection signal, "
On the other hand, when the soft start signal is lower than the detection signal, it outputs a ++L II times signal. It is held by the "H11" and "L" signals from this first comparator (14); After charging and discharging,
A voltage Vcs corresponding to the period length of the H" and "L" signals is held by this holding -1 tensioner (15) and is applied to the input terminal of the second "1 inverter (22)."
-2 When the constant voltage Vs rises, the third charging capacitor of the charging/discharging circuit (18) is charged via the resistor (19).
Charging starts at 20>, and this charging voltage vc2 is input to the input terminal 2 of the second comparator 22). The second comparator (22) compares the above Vct and Vct, and when 1fVc2 becomes higher than ■C1, it gives an OFF timing signal to the drive circuit (23), and this drive circuit (23> is a switching transistor) sister (7).
) is turned off. Thereafter, the inverter circuit (4) charges and discharges the capacitor (6) due to the heating 7I coil (5) and the resonant capacitor (6). →ノ”(
6) detects that the collector voltage of the switching transistor (7) has sufficiently decreased due to the discharge of - [sends an ON timing signal to the drive circuit (23) and switches].
At the same time as turning on the switching transistor (7).

The third discharge transistor (21) of the distribution/discharge circuit (18)
) is turned on to discharge the accumulated charge in the charging capacitor (20) and start recharging the charging capacitor 120)-\. Thereafter, I/Hertha oscillation continues in the same manner. : Holding condenser (15) terminal type J, IVct,
The second charging capacitor (15) terminal voltage VC2 is shown in Figure 2A, the second comparator (22> output is shown in Figure 2B,
The ON timing signal is shown in FIG. 2C, and the collector voltage of the switching transistor (7) is shown in the second diagram.

In this way, when the oscillation of the inverter circuit (4) is started, the detection signal VA of the level corresponding to the input power to the inverter circuit (4) detected by the input power detection circuit (9) is the first one. :l is applied to the e input terminal of the 14). When this detection signal VAL level is lower than the soft start signal level of the soft start circuit (ll), the output of the first TJ comparator 14) becomes H and charges the holding circuit (15). 2-
The input terminal VCI of the capacitor (15), which is supplied to the θ input terminal (r) of the booster (22), is set to 4. Second charging of the charging/discharging circuit (18): Indenna (20) is -
(When the voltage Vct exceeds the above Vex when the second comparator (22) reaches the second comparator (22) when the voltage Vct exceeds the above Vex, the second comparator (22) or OjF timer)
The time it takes to issue a signal, i.e.

The ON time of the switching transistor (7) becomes long (as a result, the human power to the impark circuit (4) increases. Conversely, the 3VA level outputs a power start signal when the input power detection circuit (9) detects the input power). When higher than the level, the first]
-1 amparator (14) output becomes “L”, the accumulated charge in the holding capacitor (15) is discharged, and its terminal voltage J
The king VCL decreases and the second co-parator (22
) is input to the θ input terminal. Therefore, contrary to the above, the ON time of the transformer (7) is shortened, and the input power to the inverter circuit (4) is also reduced. ,
2, the ON time of the switching transistor (7) is automatically adjusted so that the detection signal VA from the human power detection circuit (9) is equal to the sonostart signal level. Even if a compatible cooking utensil such as "C5" is placed close to the induction heating coil (5), the set output will not reach 1 in a constant soft start state as shown in Figure 3.
゜Stand up.

On the other hand, the small object detection circuit (26) has a holding ratio proportional to the ON time of the switching transistor (7) = +7 de/'
The reference signal υVK is obtained by dividing the knee voltage VCL at the terminal (15) by the voltage dividing circuit (17), and the human power detection circuit (
9) is constantly compared with the detection signal VA from 9). Therefore, when the inverter oscillation of the induction heating cooker starts or during inverter oscillation, small loads such as knives and forks are placed close to the heating coil (5) instead of cooking utensils, or no load is placed where nothing is placed. state, the equivalent inductance of the heating coil (5) is large,
Since it is difficult to input human power to the inverter circuit (4), the terminal voltage Vc of the holding capacitor (15) is adjusted to be high so as to lengthen the ON time of the switching transistor (7). Correspondingly, the reference signal level emitted from the voltage dividing circuit (17) becomes higher than the detection signal VA that can be output from the human power detection circuit (9), and the load detection circuit (26) detects small objects and no load. and sends a small object detection signal to the reset circuit (27). As a result, the reset circuit (27) sends an oscillation stop signal to the drive circuit (23) to stop the oscillation of the inverter circuit (4), and also causes the first, second, and third discharge transistors (13) (16 )(21)
The first charging capacitor (12), the holding capacitor (15), and the second charging capacitor (2o) are turned on, respectively.
The charge is discharged. Also, 18-8 can be used as a cooking utensil.
When inverter oscillation is performed by placing a pot made of a weakly magnetic material such as stainless steel near the heating filter (5), the heating coil (5)
) has a small equivalent inductance, and even if the ON time of the switching transistor (7) is relatively short, the specified input power can be obtained. m is adjusted.

As a result, the reference signal VK from the voltage dividing circuit (17)
The current level decreases and does not exceed the level of the detection signal issued from the input current detection circuit (9), and oscillation continues without the load detection circuit (26) detecting small objects.

Effects of the Invention As described above, the induction heating cooker of the present invention adjusts the ON time of the switching element so that the input power to the inverter becomes the set input, and adjusts the signal level according to the ON time of the switching element. When the level of the signal becomes higher than the signal level corresponding to the input power, small objects and no load are detected. It will not be detected as a load and the inverter oscillation will stop.
Accurate load detection is possible for all metal cooking utensils.
The variety of cooking utensils that can be used for cooking increases, increasing the versatility of this type of cooking device.

[Brief Description of the Drawings] Figure 1 is a circuit diagram of the induction heating cooker of the present invention, Figure 2 A and B
, C, D are signal waveform diagrams at each point of the induction heating cooker of the present invention,
FIG. 3 is a signal waveform diagram showing the rise of input power to the inverter due to soft start. (1>... AC power supply, (2)... Full wave rectifier circuit, (
4)...Inverter circuit, (9)...Input power detection circuit, (1o)...Input setting means, <11)...Soft start circuit, (14)(22)...Comparator,
(15)... Holding = 1 ndenna, (17)... Voltage dividing circuit, (18>... Charge/discharge circuit, (23)... Drive circuit, (26)... Small object detection circuit. Applicant Sanyo Electric Co., Ltd. Agent Patent Attorney Shizuo Sano Figure 1 4 Procedures Amendment (Method) - July 4, 1980 To the Commissioner of the Japan Patent Office Suitable 1 Indication of Case Patent Application No. 52719 of 1988 No. 2, Name of the invention Induction heating cooker 6, Relationship to the case of the person making the amendment Patent applicant name (188) Sanyo Electric Co., Ltd. 4, Agent address 2-18 Keihan Hondori, Moriguchi City Contact information: Telephone number (Tokyo) 835-1111 @ #T Center resident Nakagawa 5, Date of amendment order (shipment date) 6. Subject of amendment O: Brief explanation of drawings in the specification. 7. Contents of amendment 0: In the specification, Page 17, line 4, amend as follows.

Claims (1)

[Claims] 1) A full-wave rectifier circuit formed by full-wave rectifying an AC power source, an induction heating filter coupled to this full-wave rectifier circuit, and a resonant capacitor that forms a resonant circuit together with this induction heating coil.
The main component is an inverter circuit, which is connected to this resonant circuit and is configured with a switching element for generating a resonant current in this resonant circuit, and the switching element is turned ON.
, in the induction heating cooker that causes a resonant current to flow through the resonant circuit to generate an alternating magnetic field in the induction heating coil by turning off the induction heating coil, and inductively heats a cooking utensil that is placed close to the heating coil and serves as a load. manual setting means for outputting a setting signal according to the setting level by setting the input power to the inverter; and input detection means for detecting the input power to the inverter and outputting a detection signal corresponding to the detection level. , compare the setting signal and the detection signal, and if the setting signal level is higher than the detection signal level, increase the ON period of the switching element and output the setting signal.
ON period adjusting means for reducing the period of 0NJtl1 of the switching element 1 when the level of the switching element is lower than the detection signal level;
A signal with a level corresponding to the ON period length of the switching element is used as a reference signal, and this base wall signal is compared with the detection signal from the input detection means. An induction heating cooker consisting of a load detection circuit that stops oscillation operation.