JPH04277488A - Induction heating cooking apparatus - Google Patents

Abstract

PURPOSE:To prevent destruction of a switching element caused by heat and embody a cooling structure in a small size and at low cost by lowering the limit value of the heating coil current when the operating cycle period or On duration of the element is short or when the temp. of element is high. CONSTITUTION:In the case using a deep pan as a load where the operating cycle period of a switch element 3 is short and the current in a heating coil 2 reaches its limit value, a control part 9 controls turning on/off of the switching element 3 within the range of a heating coil current limiting circuit 8 which generates limitation to the corresponding control values in N stages according to the results from sensing made by a heating coil current sensing circuit 6 and an operating cycle period sensing circuit 7, and thus the limit value is lowered. The control value is further lowered with the rise of the element 3 temperature when the operating cycle period or the On time is still shorter, and thereby the loss is reduced at the switching element 3, and its destruction due to excessive temp. rise is precluded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker used in general households.

0002

BACKGROUND OF THE INVENTION In recent years, induction heating cookers have become popular in general households as their superior features of safety, cleanliness, and high efficiency have been recognized. An induction heating cooker is configured to inductively heat a load pan that is magnetically coupled to the heating coil by applying a high frequency current of several tens of KHz to a heating coil wound in a spiral flat plate shape. is generated by turning on and off switching elements at high speed in a high-frequency inverter circuit that includes switching elements.

[0003] A conventional induction heating cooker will be explained below. FIG. 5 is a circuit diagram of a conventional induction heating cooker. In FIG. 5, 1 is an AC power supply, 2 is a heating coil,
3 is a switching element, 4 is an input current detection circuit that detects the input current from the AC power supply 1, and 5 is a switching element 3
6 is an inverter circuit that supplies high-frequency current to the heating coil 2 by turning on and off, 6 is a heating coil current detection circuit that detects the high-frequency heating coil current applied to the heating coil 2, and 8 is a heating coil current detection circuit that predetermines the heating coil current. A heating coil current limiting circuit 9 controls the switching element 3 to be turned on and off so that the input current from the AC power source 1 reaches a predetermined value within the range limited by the heating coil current limiting circuit 8. It is a control section that performs

In the conventional induction heating cooker constructed as described above, the limiting value of the heating coil current is a constant value regardless of its operating state, and there is a margin for the current rating of the switching element. It was set like this.

[0005]

[Problems to be Solved by the Invention] However, in the conventional configuration described above, since the limiting value of the heating coil current is constant, the heating coil current reaches the limiting value in a state where the on/off period of the switching element is short. If this is used, there is a disadvantage that the loss in the switching element becomes excessive, which may cause the switching element to be destroyed by heat, or to prevent this, the cooling structure for the switching element becomes larger and costs increase. There was a problem that the

The present invention solves the above conventional problems by reducing the heating coil current limit value when the on/off period of the switching element is short, when the on time is short, or when the switching element temperature is high. As a result, excessive loss in the switching element can be suppressed, and damage to the switching element due to heat can be prevented, and the cooling structure can be made smaller and smaller.
The purpose is to reduce costs.

[0007]

[Means for Solving the Problems] To achieve this object, the induction heating cooker of the present invention includes an AC power source, a heating coil, a switching element, and an input current detector that detects an input current from the AC power source. an inverter circuit that supplies a high-frequency current to the heating coil by turning on and off the switching element; a heating coil current detection circuit that detects the high-frequency heating coil current applied to the heating coil; an on/off cycle detection circuit that detects the on/off cycle of the switching element; a heating coil current limiting circuit that limits the heating coil current to a limit value in N stages corresponding to the on/off cycle of the switching element; The heating coil current limiting circuit is configured to include a control section that controls turning on and off of the switching element so that the input current from the AC power supply reaches a predetermined value within a range limited by the heating coil current limiting circuit.

[0008] In order to achieve this object, a second configuration includes an on-time detection circuit that detects the on-time of the switching element, and limits the heating coil current to a limit value of N stages corresponding to the on-time of the switching element. A heating coil current limiting circuit, and a control unit that controls turning on and off of the switching element so that the input current from the AC power supply reaches a predetermined value within the range limited by the heating coil current limiting circuit. do.

Furthermore, as a third configuration, a switching element temperature detection circuit for detecting the switching element temperature, a heating coil current limiting circuit for limiting the heating coil current to a limit value in N stages corresponding to the switching element temperature, and A control section is provided that controls turning on and off of the switching element so that the input current from the AC power supply reaches a predetermined value within a range limited by a coil current limiting circuit.

0010

[Operation] With this configuration, the switching element turns on and
If a load pan is used in which the heating coil current reaches the limit value with a short off period, the on/off period of the switching element is detected and the heating coil current limit value is lowered. It is possible to reduce the loss caused by This is because the loss generated in the switching element tends to increase as the on/off period becomes shorter or as the limit value of the heating coil current increases. Therefore, with the configuration of the present invention, the on/off period of the switching element increases. When the heating coil current is short, the loss can be reduced by lowering the heating coil current limit value.

Furthermore, the loss in the switching element can be similarly reduced by detecting the on-time instead of the on-off period and reducing the limiting value of the heating coil current when the on-time is short.

Furthermore, the temperature of the switching element is detected,
If the limiting value of the heating coil current is lowered as the switching element temperature rises, the loss in the switching element can be reduced as the switching element temperature rises, thereby preventing destruction of the switching element due to excessive temperature rise. It can be prevented.

[0013]

[Embodiment] (Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an AC power supply, 2 is a heating coil, 3 is a switching element, 4 is an input current detection circuit that detects the input current from the AC power supply 1, and 5 is a circuit that turns the switching element 3 on and off. 6 is an inverter circuit that supplies a high frequency current to the heating coil 2; 6 is a heating coil current detection circuit that detects the high frequency heating coil current applied to the heating coil 2; 7 is an ON circuit that detects the on/off period of the switching element 3; , an off-cycle detection circuit; 8 is a heating coil current limiting circuit that limits the heating coil current to an N-stage limit value corresponding to the on-off cycle of the switching element detected by the on-off cycle detection circuit 7; 9 is a heating circuit; This is a control unit that controls ON/OFF of the switching element 3 so that the input current from the AC power source 1 reaches a predetermined value within the range of the limit by the coil current limiting circuit 8.

The operation of the induction heating cooker constructed as described above will be explained using FIG. 2. Figure 2 (a
) is a graph showing the relationship between the on/off period and the switching element loss in the conventional example, in which the switching element loss increases as the on/off period becomes shorter in the operable on/off periods T1 to T4. Figure 2(b)
is a graph showing the relationship between the on/off period and the heating coil current limit value when the heating coil current limit value is set in three stages in the induction heating cooker of FIG. 1, and the on/off period is from T4 to T3, The limiting value of the heating coil current is decreased from I3 to I2 and I1 as the heating coil current becomes shorter as T2 and T1. Due to this effect, the loss in the switching element is reduced (
As shown in c), as a result, the maximum value P3 of switching element loss can be significantly reduced from the maximum value P1 of the conventional example.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3, 1 is an AC power supply, 2 is a heating coil, 3 is a switching element, 4 is an input current detection circuit that detects the input current from the AC power supply 1, and 5 is a circuit that turns the switching element 3 on and off. 6 is an inverter circuit that supplies high-frequency current to the heating coil 2; 6 is a heating coil current detection circuit that detects the high-frequency heating coil current applied to the heating coil 2; 10 is an on-time detection circuit that detects the on-time of the switching element 3; A heating coil current limiting circuit 8 limits the heating coil current to an N-stage limit value corresponding to the on time of the switching element detected by the on time detection circuit 10; 9 a heating coil current limiting circuit for limiting the heating coil current by the heating coil current limiting circuit 8; This is a control unit that controls ON/OFF of the switching element 3 so that the input current from the AC power source 1 reaches a predetermined value within a range.

With the above configuration, it is possible to detect the on-time of the switching element and reduce the limit value of the heating coil current when the on-time is short. Since the on-time of a switching element behaves in the same way in the on-off period and its increase/decrease, the loss in the switching element can be reduced by lowering the heating coil current limit value when the on-time is short.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings.

In FIG. 4, 1 is an AC power supply, 2 is a heating coil, 3 is a switching element, 4 is an input current detection circuit for detecting the input current from the AC power supply 1, and 5 is a circuit for turning on and off the switching element 3. 6 is an inverter circuit that supplies a high frequency current to the heating coil 2; 6 is a heating coil current detection circuit that detects the high frequency heating coil current applied to the heating coil 2; 11 is a switching element temperature detection circuit that detects the temperature of the switching element 3; A heating coil current limiting circuit 8 limits the heating coil current to a limit value in N stages corresponding to the temperature of the switching element detected by the switching element temperature detection circuit 11; 9 a heating coil current limiting circuit for limiting the heating coil current by the heating coil current limiting circuit 8; The switching element 3 is turned on and off so that the input current from the AC power supply 1 reaches a predetermined value within the range.
This is a control unit that controls turning off.

With the above configuration, if the temperature of the switching element 3 is detected and the limiting value of the heating coil current is lowered as the switching element temperature rises, the loss in the switching element will decrease as the switching element temperature rises. This makes it possible to prevent the switching element 3 from being destroyed due to excessive temperature rise.

Although the limiting value of the heating coil current was changed in three stages in the first embodiment, it is clear that the same effect can be obtained in N stages (N is an integer of 2 or more). Furthermore, although the circuits in the first, second, and third embodiments are represented by block diagrams, it is clear that a microcomputer may be used to perform some of these functions.

[0023]

[Effects of the Invention] As described above, the induction heating cooker of the present invention includes a heating coil current detection circuit that detects the high frequency heating coil current applied to the heating coil, and a heating coil current detection circuit that detects the on/off period of the switching element. an on/off period detection circuit, a heating coil current limiting circuit that limits the heating coil current to N-stage limit values corresponding to the on/off periods of the switching element, and within the limits of the heating coil current limiting circuit. By providing a control unit that controls on/off of the switching element so that the input current from the AC power source becomes a predetermined value, the heating coil current is limited when the on/off period of the switching element is short. As a result, it is possible to suppress the occurrence of excessive loss in the switching element, prevent destruction of the switching element due to heat, and downsize and reduce the cost of the cooling structure.

The second means includes an on-time detection circuit that detects the on-time of the switching element, and a heating coil current limiting circuit that limits the heating coil current to limit values in N stages corresponding to the on-time of the switching element. , and a control unit that controls turning on and off of the switching element so that the input current from the AC power supply reaches a predetermined value within the limit of the heating coil current limiting circuit. Similar effects can be obtained with a simple configuration.

Furthermore, as a third means, a switching element temperature detection circuit for detecting the switching element temperature, a heating coil current limiting circuit for limiting the heating coil current to a limit value in N stages corresponding to the switching element temperature, and By providing a control unit that controls on/off of the switching element so that the input current from the AC power supply reaches a predetermined value within the range of limitations by the coil current limiting circuit, the heating coil current is reduced when the switching element temperature is high. As a result, the generation of excessive loss in the switching element at high temperatures can be suppressed, and damage to the switching element due to heat can be directly prevented, making it possible to miniaturize the cooling structure. This makes it possible to reduce costs.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an induction heating cooker according to a first embodiment of the present invention.

[Figure 2] (a) is a graph showing the relationship between on/off periods and switching element loss in the conventional example; (b) is a graph showing the relationship between on/off periods and heating coil current limit value in the first embodiment; (c) is a graph showing the relationship between on and off periods and switching element loss in the first embodiment.

FIG. 3 is a circuit diagram of an induction heating cooker according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of an induction heating cooker according to a third embodiment of the present invention.

[Figure 5] Circuit diagram of a conventional induction heating cooker

[Explanation of symbols]

1 AC power supply 2 Heating coil 3 Switching element 4 Input current detection circuit 5 Inverter circuit 6 Heating coil current detection circuit 7 On/off cycle detection circuit 8 Heating coil current limiting circuit 9 Control section 10 On-time detection circuit

Claims (3)

[Claims] 1. An AC power supply, a heating coil, a switching element, an input current detection circuit for detecting an input current from the AC power supply, and a high-frequency current flowing to the heating coil by turning on and off the switching element. an inverter circuit that supplies a heating coil; a heating coil current detection circuit that detects a high frequency heating coil current applied to the heating coil;
an on/off cycle detection circuit that detects on/off cycles of the switching element; a heating coil current limiting circuit that limits the heating coil current to N-stage limit values corresponding to the on/off cycles of the switching element; An induction heating cooker, comprising: a control section that controls turning on and off of the switching element so that the input current from the AC power supply reaches a predetermined value within the range of limitation by the heating coil current limiting circuit. 2. An on-time detection circuit that detects the on-time of a switching element, a heating coil current limiting circuit that limits a heating coil current to a limit value in N stages corresponding to an on-time of the switching element, and the heating coil current. 2. The induction heating cooker according to claim 1, further comprising a control section that controls turning on and off of the switching element so that the input current from the AC power supply reaches a predetermined value within a range of limitations imposed by a limiting circuit. 3. A switching element temperature detection circuit that detects the switching element temperature, a heating coil current limiting circuit that limits the heating coil current to a limit value in N stages corresponding to the switching element temperature, and the heating coil current limiting circuit. 2. The induction heating cooker according to claim 1, further comprising a control section that controls turning on and off of the switching element so that the input current from the AC power supply reaches a predetermined value within a limited range.