Heating device having function of detecting location of foodstuff container

Abstract

 A heating device having a function of detecting a location of a foodstuff container is provided. The heating device includes an induction coil, an inverter circuit, a first current-detecting circuit, a signal processing circuit and a controlling unit. The first current-detecting circuit is used for detecting a first current flowing through the induction coil and generating a first current-detecting signal. The signal processing circuit is used for generating a current phase signal according to the first current-detecting signal. The controlling unit is used for generating at least a first control signal according to a cooking option. According to a duration difference or a phase difference between the first control signal and the current phase signal, the controlling unit determines an area of the foodstuff container overlying the induction coil with respect to an area of the induction coil or a location of the foodstuff container relative to the induction coil.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a heating device, and more particularly to a heating device having a function of detecting a location of a foodstuff container.

BACKGROUND OF THE INVENTION

[0002] Nowadays, a variety of heating devices such as gas stoves, infrared oven, microwave oven and electric stove are widely used to cook food. Different heating devices have their advantages or disadvantages. Depending on the food to be cooked, a desired heating device is selected.

[0003] Take an induction cooking stove for example. When a current flows through the induction coil of the induction cooking stove, electromagnetic induction is performed to produce eddy current, thereby heating a foodstuff container. Depending on the location of the foodstuff container relative to the induction coil, the heat quantity for heating the foodstuff container by the induction coil and the current magnitude of the induction coil are varied. For example, in a case that the area of the foodstuff container overlying the induction coil with respect to the area of the induction coil is very high (e.g. 95%), the heat quantity for heating the foodstuff container by the induction coil is high. In this situation, the reactive power of operating the induction coil and the current magnitude are both reduced. On the other hand, in a case that the area of the foodstuff container overlying the induction coil with respect to the area of the induction coil is too low or the foodstuff container is largely deviated from the induction coil, the heat quantity for heating the foodstuff container by the induction coil become very low (or zero). In this situation, the reactive power of operating the induction coil and the current magnitude are both increased. As such, the induction cooking stove is possibly burnt out. For solving this problem, the induction cooking stove needs to have a function for accurately detecting the location of the foodstuff container.

[0004] The conventional induction cooking stove uses a micro-control unit (MCU) to calculate a ratio of a root-mean-square (rms) value of an input current to a root-mean-square (rms) value of an induction coil current, thereby determining the proper location of the foodstuff container. Since the frequency of the induction coil current is high (e.g. 20k∼50kHz), the sampling rate should be high and the calculating amount and speed of the micro-control unit should be increased to calculate the root-mean-square value of the induction coil current. Since the calculating process is complicated, the fabricating cost of the induction cooking stove is increased.

[0005] In a case that the magnitudes of the induction coil current and the input current are both very high, a current transformer (CT) or a sense resistor is necessary for reducing the circuit magnitudes. After the circuit magnitudes are reduced, a current signal ratio is adjusted by an amplifying circuit, and then the reduced induction coil current and the reduced input current are sampled by a sampling circuit. Since the impedance matching of the amplifying circuit, the current transformer and the sampling circuit have respective tolerances and the current signals are readily interfered by noise, the current magnitude obtained by the micro-control unit has a large error, which is equal to the overall error resulted from the current transformer, the amplifying circuit and the sampling circuit. In this situation, the accuracy of determining the location of the foodstuff container is adversely affected by the noise. Moreover, when the location of the foodstuff container is changed, the ratio of the root-mean-square value of an input current to the root-mean-square value of the induction coil current is acquired with undue experiments. The accuracy of the ratio is usually unsatisfied.

SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a heating device having a function of detecting a location of a foodstuff container without complicated calculation and undue experiments. The function of detecting the location of the foodstuff container may be implemented by a micro controller with slower calculating amount and speed.

[0007] Another object of the present invention provides a heating device having a function of detecting a location of a foodstuff container with high accuracy and reduced error.

[0008] A further object of the present invention provides a heating device capable of judging whether the components of the heating device is abnormal in order to overcome the problem of burning out the heating device.

[0009] In accordance with an aspect of the present invention, there is provided a heating device having a function of detecting a location of a foodstuff container. The heating device includes an induction coil, an inverter circuit, a first current-detecting circuit, a signal processing circuit and a controlling unit. The induction coil is used for heating the foodstuff container. The inverter circuit is used for receiving a rectified voltage and generating a driving voltage to drive the induction coil. The first current-detecting circuit is serially connected with the induction coil for detecting a first current flowing through the induction coil, thereby generating a first current-detecting signal. The signal processing circuit is connected to the first current-detecting circuit for generating a current phase signal according to the first current-detecting signal. The controlling unit is used for generating at least a first control signal according to a cooking option, thereby controlling the inverter circuit. According to a duration difference or a phase difference between the first control signal and the current phase signal, the controlling unit determines an area of the foodstuff container overlying the induction coil with respect to an area of the induction coil or a location of the foodstuff container relative to the induction coil, thereby adjusting an operation of the inverter circuit.

[0010] In accordance with another aspect of the present invention, there is provided a heating device having a function of detecting a location of a foodstuff container. The heating device includes an induction coil, an inverter circuit, a first current-detecting circuit, a signal processing circuit and a controlling unit. The induction coil is used for heating the foodstuff container. The inverter circuit is used for receiving a rectified voltage, thereby generating a driving voltage to drive the induction coil. The first current-detecting circuit is serially connected with the induction coil for detecting a first current flowing through the induction coil, thereby generating a first current-detecting signal. The signal processing circuit is connected to the first current-detecting circuit for generating a current phase signal according to the first current-detecting signal. The controlling unit is used for generating at least a first control signal according to a cooking option, thereby controlling the inverter circuit. According to a duration difference or a phase difference between the first control signal and the current phase signal, the controlling unit determines an area of the foodstuff container overlying the induction coil with respect to an area of the induction coil or a location of the foodstuff container relative to the induction coil, thereby adjusting an operation of the inverter circuit. If the duration difference or the phase difference between the first control signal and the current phase signal exceeds a predetermined range, the controlling unit judges that the location of the foodstuff container is improper or abnormal and controls the inverter circuit to be operated in a pan detection mode. In the pan detection mode, the inverter circuit is operated at an increased switching frequency or a reduced duty cycle, or the inverter circuit is disabled.

[0011] The above contents of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG 1 is a schematic circuit block diagram illustrating a heating device having a function of detecting a location of a foodstuff container according to an embodiment of the present invention;

[0013] FIG 2A is a schematic view illustrating the location of the foodstuff container relative to the induction coil in the heating device of the present invention;

[0014] FIG 2B is a schematic view illustrating another location of the foodstuff container relative to the induction coil in the heating device of the present invention; and

[0015] FIG 3 is a timing waveform diagram schematically illustrating the corresponding current signals and control signal processed in the heating device of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

[0017] FIG 1 is a schematic circuit block diagram illustrating a heating device having a function of detecting a location of a foodstuff container according to an embodiment of the present invention. As shown in FIG 1, the heating device 1 includes a rectifier circuit 11, a filtering circuit 12, an inverter circuit 13, an induction coil 14, a first current-detecting circuit 15, a signal processing circuit 16, a controlling unit 17 and a user interface unit 18.

[0018] In this embodiment, the rectifier circuit 11 is a bridge rectifier circuit. An input voltage V_in is rectified into a rectified voltage V_r by the rectifier circuit 11. The filtering circuit 12 is connected to an output terminal of the rectifier circuit 11. The filtering circuit 12 is used for filtering off the high-frequency noise contained in the rectified voltage V_r. In this embodiment, the filtering circuit 12 includes a filter capacitor C_a. In some embodiments, the filtering circuit 12 may include plural inductors and plural capacitors (not shown). The induction coil 14 is disposed inside a heating panel 10 for heating a foodstuff container 2.

[0019] The power input terminal of the inverter circuit 13 is connected to the filtering circuit 12. The power output terminal of the inverter circuit 13, the induction coil 14 and the first current-detecting circuit 15 are connected with each other in series. In this embodiment, the inverter circuit 13 includes a first switch element Q₁, a second switch element Q₂, a first capacitor C₁ and a second capacitor C₂. The first switch element Q₁ and the second switch element Q₂ are connected with each other in series. A first connecting node between the first switch element Q₁ and the second switch element Q₂ is connected to the first current-detecting circuit 15. The first capacitor C₁ and the second capacitor C₂ are connected with each other in series. A second connecting node between the first capacitor C₁ and the second capacitor C₂ is connected to a first terminal of the induction coil 14. The first connecting node between the first switch element Q₁ and the second switch element Q₂ is served as a first power output terminal of the inverter circuit 13. The second connecting node between the first capacitor C₁ and the second capacitor C₂ is served as a second power output terminal of the inverter circuit 13. The control terminal of the first switch element Q₁ and the control terminal of the second switch element Q₂ are connected to the controlling unit 17. Under control of the controlling unit 17, the first switch element Q₁ and the second switch element Q₂ are conducted in an interleaved manner according to a first control signal S₁ and a second control signal S₂. As such, an AC driving voltage V_o is generated by the inverter circuit 13 to drive the induction coil 14.

[0020] In response to an enabling status of the first control signal S₁ and a disabling status of the second control signal S₂, the first switch element Q₁ is conducted but the second switch element Q₂ is shut off. As such, the electric energy of the rectified voltage V_r is transmitted to the induction coil 14 through the first switch element Q₁ and the second capacitor C₂. In this situation, the driving voltage V_o is equal to the positive component of the rectified voltage V_r, so that the positive component of the rectified voltage V_r is received by the induction coil 14. Whereas, in response to a disabling status of the first control signal S₁ and an enabling status of the second control signal S₂, the first switch element Q₁ is shut off but the second switch element Q₂ is conducted. As such, the electric energy of the rectified voltage V_r is transmitted to the induction coil 14 through the first capacitor C₁ and the second switch element Q₂. In this situation, the driving voltage V_o is equal to the negative component of the rectified voltage V_r, so that the negative component of the rectified voltage V_r is received by the induction coil 14.

[0021] In this embodiment, the first current-detecting circuit 15 is a current transformer. The primary side of the current transformer 15, the induction coil 14 and the power output terminal of the inverter circuit 13 are connected with each other in series. The secondary side of the current transformer 15 is connected to the signal processing circuit 16. The current transformer 15 is used for detecting the first current I₁ flowing through the induction coil 14. In addition, by the current transformer 15, the first current I₁ is reduced and a corresponding first current-detecting signal V_s1 is generated. In other words, the waveform, time sequence and phase of the first current-detecting signal V_s1 are identical to those of the first current I₁.

[0022] The signal processing circuit 16 is interconnected between the first current-detecting circuit 15 and the controlling unit 17. According to the first current-detecting signal V_s1, the signal processing circuit 16 issues a current phase signal Sp to the controlling unit 17. In this embodiment, the signal processing circuit 16 includes a comparing circuit. According to the first current-detecting signal V_s1, the comparing circuit outputs the current phase signal Sp. In a case that the first current I₁ is switched from a negative status to a positive status, the current phase signal Sp in an enabling status is issued from the comparing circuit to the controlling unit 17. Whereas, in a case that the first current I₁ is switched from the positive status to the negative status, the current phase signal Sp in a disabling status is issued from the comparing circuit to the controlling unit 17.

[0023] In some embodiment, the comparing circuit compares the first current-detecting signal V_s1 with a reference voltage (not shown). If the first current-detecting signal V_s1 is greater than the reference voltage, the current phase signal Sp in the enabling status is issued from the comparing circuit to the controlling unit 17. Whereas, if the first current-detecting signal V_s1 is smaller than the reference voltage, the current phase signal Sp in the disabling status is issued from the comparing circuit to the controlling unit 17.

[0024] According to a user's cooking option, the operating frequencies and the durations of the first control signal S₁ and an enabling status of the second control signal S₂ are adjusted. The user's cooking option includes for example a powering off selective item, a powering on selective item, a heat quantity selective item, a heating time selective item, a fast heating selective item or a slow heating selective item. As the operating frequencies and the durations of the first control signal S₁ and an enabling status of the second control signal S₂ are adjusted, the power magnitude transmitted to the induction coil 14 from the inverter circuit 13, the magnitude of the first current I₁ and the heat quantity for heating the foodstuff container 2 by the induction coil 14 are changed. In addition, according to a duration difference or a phase difference between the first control signal S₁ and the current phase signal S_p, the controlling unit 17 determines an area of the foodstuff container 2 overlying the induction coil 14 with respect to an area of the induction coil 14 or a location of the foodstuff container 2 relative to the induction coil 14, thereby adjusting an operation of the inverter circuit. In this embodiment, the duration difference or the phase difference between the second control signal S₂ and the current phase signal Sp is equal to the duration difference or the phase difference between the first control signal S₁ and the current phase signal Sp. In some embodiments, according to the duration difference or the phase difference between the second control signal S₂ and the current phase signal Sp, the controlling unit 17 determines an area of the foodstuff container 2 overlying the induction coil 14 with respect to an area of the induction coil 14 or a location of the foodstuff container 2 relative to the induction coil 14.

[0025] Hereinafter, the principle of determining an area of the foodstuff container 2 overlying the induction coil 14 with respect to an area of the induction coil 14 or a location of the foodstuff container 2 relative to the induction coil 14 according to the duration difference or the phase difference between the first control signal S₁ and the current phase signal Sp will be illustrated in more details.

[0026] The user interface unit 18 is connected to the controlling unit 17 for receiving the user's cooking option and indicating the operating message. The user's cooking option includes for example a powering off selective item, a powering on selective item, a heat quantity selective item, a heating time selective item, a fast heating selective item or a slow heating selective item. In this embodiment, the user interface unit 18 is a touch screen for implementing the user's cooking option. In addition, the operating message is also shown on the touch screen.

[0027] In this embodiment, the heating device 1 further includes a second current-detecting circuit 19. The second current-detecting circuit 19 includes a detecting resistor R_s. The detecting resistor R_s is interconnected between the filtering circuit 12 and the inverter circuit 13 for detecting a second current I₂ flowing through the inverter circuit 13, thereby generating a second current-detecting signal V_s2 to the controlling unit 17. According to the second current-detecting signal V_s2, the controlling unit 17 calculates the second current I₂, which is relatively higher.

[0028] An example of the controlling unit 17 includes but is not limited to a pulse frequency modulation (PFM) controller, micro controller, a micro processor or a digital signal processor (DSP). Each of the first switch element and the second switch element is a metal oxide semiconductor field effect transistor (MOSFET), a bipolar junction transistor (BJT) or an insulated gate bipolar transistor (IGBT).

[0029] FIG 2A is a schematic view illustrating a location of the foodstuff container relative to the induction coil in the heating device of the present invention. As shown in FIG 2A, the foodstuff container 2 is placed over the middle portion of the induction coil 14. The area of the foodstuff container 2 overlying the induction coil 14 with respect to the area of the induction coil 14 is very high. For example, the area of the foodstuff container 2 overlying the induction coil 14 (A1) is 95% of the area of the induction coil 14. Since the heat quantity for heating the foodstuff container 2 by the induction coil 14 is high, both of the reactive power of operating the induction coil 14 and the first current I₁ are relatively lower. In this situation, the duration difference or the phase difference between the first control signal S₁ and the current phase signal S_p is within a predetermined range (e.g. 1µs∼7µs). According to the duration difference or the phase difference, the controlling unit 17 will judge whether the area of the foodstuff container 2 overlying the induction coil 14 with respect to the area of the induction coil 14 or a location of the foodstuff container 2 relative to the induction coil 14 is suitable. In addition, according to the duration difference or the phase difference, the controlling unit 17 controls the inverter circuit 13 to output the heat power or heat quantity set by the cooking option. Meanwhile, the maximum heat power or heat quantity outputted from the inverter circuit 13 is equal to the rated value.

[0030] FIG 2B is a schematic view illustrating another location of the foodstuff container relative to the induction coil in the heating device of the present invention. As shown in FIG 2B, the foodstuff container 2 is not completely placed over the middle portion of the induction coil 14. The area of the foodstuff container 2 overlying the induction coil 14 with respect to the area of the induction coil 14 is very low. For example, the area of the foodstuff container 2 overlying the induction coil 14 (A2) is 15% of the area of the induction coil 14. Since the heat quantity for heating the foodstuff container 2 by the induction coil 14 is low, both of the reactive power of operating the induction coil 14 and the first current I₁ are increased in comparison with FIG 2A. In this situation, the duration difference or the phase difference between the first control signal S₁ (or the second control signal S₂) and the current phase signal S_p exceeds the predetermined range (e.g. > 7µs). According to the duration difference or the phase difference, the controlling unit 17 will judge that the location of the foodstuff container 2 is improper or abnormal. Meanwhile, the controlling unit 17 controls the inverter circuit 13 to be operated in a pan detection mode. In the pan detection mode, the first switch element Q₁ and the second switch element Q₂ of the inverter circuit 13 are operated at a higher switching frequency or a lower duty cycle. Alternatively, the induction coil 14 is disabled in order to prevent from burning out the heating device 1 because the foodstuff container 2 is improperly or abnormally positioned or no foodstuff container 2 is placed on the induction coil 14.

[0031] In another case that the foodstuff container 2 is placed over the middle portion of the induction coil 14 but the area of the foodstuff container 2 is very small (for example area of the foodstuff container 2 overlying the induction coil 14 (A1) is 30% of the area of the induction coil 14), the duration difference or the phase difference between the first control signal S₁ (or the second control signal S₂) and the current phase signal Sp is within the predetermined range. In comparison with the case of FIG 2A, both of the reactive power of operating the induction coil 14 and the first current I₁ are increased. In addition, the root-mean-square (rms) value of the second current I₂ or the second current-detecting signal V_s2 will be smaller than a first current threshold value (e.g. 1A). For preventing from burning out the heating device 1, the heat power or heat quantity outputted by the inverter circuit 13 is reduced under control of the controlling unit 17. Meanwhile, the maximum heat power or heat quantity outputted from the inverter circuit 13 is lower than the rated value. That is, for complying with different sizes of foodstuff containers, the duration difference or the phase difference between the first control signal S 1 (or the second control signal S2) and the relation between the second current I₂ and the first current threshold value should be taken into consideration.

[0032] If the controlling unit 17 judges that the duration difference or the phase difference between the first control signal S₁ (or the second control signal S2) and the current phase signal Sp is within the predetermined range and the second current I₂ is smaller than the first current threshold value, it is meant that a relatively smaller foodstuff container 2 is placed over the middle portion of the induction coil 14. In this situation, the heat power or heat quantity outputted by the inverter circuit 13 is reduced under control of the controlling unit 17, so that the maximum heat power or heat quantity outputted from the inverter circuit 13 is lower than the rated value. Whereas, if the controlling unit 17 judges that the duration difference or the phase difference between the first control signal S₁ (or the second control signal S₂) and the current phase signal Sp is within the predetermined range and the second current I₂ is greater than the first current threshold value, it is meant that a normal-sized foodstuff container 2 is placed over the middle portion of the induction coil 14. In this situation, the controlling unit 17 controls the inverter circuit 13 to output the heat power or heat quantity set by the cooking option, so that the maximum heat power or heat quantity outputted from the inverter circuit 13 is equal to the rated value.

[0033] FIG 3 is a timing waveform diagram schematically illustrating the corresponding current signals and control signal processed in the heating device of FIG 1. As shown in FIG 3, the waveform and time sequence of the first current-detecting signal V_s1 are identical to those of the first current I₁. Since the current phase signal Sp is obtained by the signal processing circuit 16 according to the first current-detecting signal V_s1, the time sequence of the current phase signal S_p is substantially identical to that of the first current I₁. In other words, the duration difference (d) or the phase difference (d) between the control signal (S₁ or S₂) and the current phase signal Sp is equal to the duration difference (d) or the phase difference (d) between the control signal (S₁ or S₂) and the first current I₁. As such, the controlling unit 17 may calculate the duration difference (d) or the phase difference (d) between the control signal (S₁ or S₂) and the first current I₁ according to the current phase signal Sp. The process of calculating the duration difference (d) or the phase difference (d) between the control signal (S₁ or S₂) and the current phase signal Sp is simplified because huge amount of sampling data is no loner needed. In this circumstance, even if the frequency of the first current I₁ flowing the induction coil 14 is high (e.g. > 20 kHz), the controlling unit 17 may be implemented by a micro controller with slower calculating amount and speed. For example, at a first time spot t₁, a timer (not shown) of the controlling unit 17 is activated to count time in response to the first control signal S₁ in the enabling status; and at a second time spot t₂, the timer of the controlling unit 17 stops counting time in response to the current phase signal S_p in the enabling status. As a consequence, the duration difference (d) or the phase difference (d) between the first control signal S₁ and the current phase signal S_p will be calculated without difficulty.

[0034] In this embodiment, the first switch element Q₁ and the second switch element Q₂ are operated in a zero voltage switching (ZVS) manner. In a case that the first switch element Q₁, the second switch element Q₂, the first capacitor C₁, the second capacitor C₂, the induction coil 14 or any other software or hardware component has a failure or is abnormal, the first switch element Q₁ and the second switch element Q₂ fail to be operated in the zero voltage switching (ZVS) manner. In this situation, the switching current is too large or the first current I₁ is largely increased. Meanwhile, the duration difference or the phase difference between the first control signal S₁ (or the second control signal S₂) and the current phase signal Sp is below the predetermined range (e.g. < 1µs). If the duration difference or the phase difference between the first control signal S₁ (or the second control signal S₂) and the current phase signal Sp is below the predetermined range, it is meant that one or more components of the heating device 1 has a failure or is abnormal. For preventing from burning out the heating device 1, the heat power or heat quantity outputted by the inverter circuit 13 is reduced under control of the controlling unit 17. Meanwhile, the maximum heat power or heat quantity outputted from the inverter circuit 13 is lower than the rated value. Alternatively, the heating device 1 is disabled.

[0035] In the above embodiments, the heating device 1 determines the location of the foodstuff container 2 according to the duration difference (d) or the phase difference (d) between the control signal (S₁ or S₂) and the current phase signal S_p. The process of calculating the duration difference (d) or the phase difference (d) is simplified because huge amount of sampling data is no loner needed. In this circumstance, the controlling unit 17 may be implemented by a micro controller with slower calculating amount and speed. As such, the heating device 1 is cost-effective. In a case that the foodstuff container 2 is not completely placed over the middle portion of the induction coil 14 and the area of the foodstuff container 2 overlying the induction coil 14 with respect to the area of the induction coil 14 is reduced, the duration difference (d) or the phase difference (d) between the control signal (S₁ or S₂) and the current phase signal Sp is increased. Whereas, in a case that the area of the foodstuff container 2 overlying the induction coil 14 with respect to the area of the induction coil 14 is increased, the duration difference (d) or the phase difference (d) between the control signal (S₁ or S₂) and the current phase signal S_p is reduced. Since the duration difference (d) or the phase difference (d) between the control signal (S₁ or S₂) and the current phase signal Sp is detectable by an instrument (e.g. an oscilloscope) without undue experiments.

[0036] Moreover, after the signal processing circuit 16 generates the current phase signal Sp according to the first current-detecting signal V_s1, the controlling unit 17 will calculate the duration difference (d) or the phase difference (d) between the control signal (S₁ or S₂) and the current phase signal S_p according to the current phase signal S_p. As such, the error of detecting the foodstuff container 2 is reduced, the possibility of being interfered by noise is reduced and the accuracy of detecting the foodstuff container 2 is enhanced. Moreover, since the duration difference (d) or the phase difference (d) can be used to judge whether the components of the heating device is abnormal, the problem of burning out the heating device 1 is overcome.

[0037] While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.

Claims

1. A heating device having a function of detecting a location of a foodstuff container, said heating device comprising:

an induction coil for heating said foodstuff container;

an inverter circuit for receiving a rectified voltage and generating a driving voltage to drive said induction coil;

a first current-detecting circuit serially connected with said induction coil for detecting a first current flowing through said induction coil, thereby generating a first current-detecting signal;

a signal processing circuit connected to said first current-detecting circuit for generating a current phase signal according to said first current-detecting signal; and

a controlling unit for generating at least a first control signal according to a cooking option, thereby controlling said inverter circuit,

wherein according to a duration difference or a phase difference between said first control signal and said current phase signal, said controlling unit determines an area of said foodstuff container overlying said induction coil with respect to an area of said induction coil or a location of said foodstuff container relative to said induction coil, thereby adjusting an operation of said inverter circuit.

2. The heating device according to claim 1, wherein said signal processing circuit comprises a comparing circuit for generating said current phase signal in an enabling status or a disabling status according to said first current-detecting signal.

3. The heating device according to claim 2, wherein if said first current-detecting signal is greater than a reference voltage, said current phase signal in said enabling status is issued from said comparing circuit to said controlling unit, wherein if said first current-detecting signal is smaller than said reference voltage, said current phase signal in said disabling status is issued from said comparing circuit to said controlling unit.

4. The heating device according to claim 1, wherein if said duration difference or said phase difference between said first control signal and the current phase signal exceeds a predetermined range, said controlling unit judges that said location of said foodstuff container is improper or abnormal and controls said inverter circuit to be operated in a pan detection mode, wherein in said pan detection mode, said inverter circuit is operated at an increased switching frequency or a reduced duty cycle, or said inverter circuit is disabled.

5. The heating device according to claim 1, further comprising:

a rectifier circuit for rectifying an input voltage into said rectified voltage;
and

a filtering circuit connected to said inverter circuit and said rectifier circuit.

6. The heating device according to claim 5, further comprising a second current-detecting circuit, which is interconnected between said filtering circuit and said inverter circuit for detecting a second current flowing through said inverter circuit, thereby generating a second current-detecting signal.

7. The heating device according to claim 6, wherein if said duration difference or said phase difference between said first control signal is within a predetermined range and said current phase signal and said second current is smaller than a first current threshold value, said controlling unit controls said inverter circuit to output reduced heat power or heat quantity such that the maximum heat power or heat quantity outputted from said inverter circuit is lower than a rated value.

8. The heating device according to claim 7, wherein if said duration difference or said phase difference between said first control signal and said current phase signal is within said predetermined range and said second current is greater than said first current threshold value, said controlling unit controls said inverter circuit to output the heat power or heat quantity set by said cooking option, so that the maximum heat power or heat quantity outputted from said inverter circuit is equal to said rated value.

9. The heating device according to claim 1, wherein if said duration difference or said phase difference between said first control signal and said current phase signal is below a predetermined range, said controlling unit judges that one or more components of said heating device has a failure or is abnormal, and said controlling unit controls said inverter circuit to output reduced heat power or heat quantity such that the maximum heat power or heat quantity outputted from said inverter circuit is lower than a rated value, or said heating device is disabled.

10. The heating device according to claim 1, wherein according to said first control signal and said current phase signal, a timer of said controlling unit is activated to count time or stops counting time, thereby calculating said duration difference or said phase difference between said first control signal and said current phase signal.

11. The heating device according to claim 1, wherein said inverter circuit comprises:

a first switch element having a control terminal connected to said controlling unit;

a second switch element connected to said first switch element, wherein a first connecting node between said first switch element and said second switch element is served as a first power output terminal of said inverter circuit;

a first capacitor; and

a second capacitor connected with said first capacitor in series, wherein a second connecting node between said first capacitor and said second capacitor is served as a second power output terminal of said inverter circuit,

wherein under control of said controlling unit, said first switch element and said second switch element are conducted in an interleaved manner according to said first control signal and a second control signal, so that said driving voltage is generated by said inverter circuit to drive said induction coil.

12. The heating device according to claim 1, further comprising a user interface unit, which is connected to said controlling unit for receiving said cooking option and indicating an operating message.

13. A heating device having a function of detecting a location of a foodstuff container, said heating device comprising:

an induction coil for heating said foodstuff container;

an inverter circuit for receiving a rectified voltage and generating a driving voltage to drive said induction coil;

a first current-detecting circuit serially connected with said induction coil for detecting a first current flowing through said induction coil, thereby generating a first current-detecting signal;

a signal processing circuit connected to said first current-detecting circuit for generating a current phase signal according to said first current-detecting signal; and

a controlling unit for generating at least a first control signal according to a cooking option, thereby controlling said inverter circuit,

wherein according to a duration difference or a phase difference between said first control signal and said current phase signal, said controlling unit determines an area of said foodstuff container overlying said induction coil with respect to an area of said induction coil or a location of said foodstuff container relative to said induction coil, thereby adjusting an operation of said inverter circuit,

wherein if said duration difference or said phase difference between said first control signal and the current phase signal exceeds a predetermined range, said controlling unit judges that said location of said foodstuff container is improper or abnormal and controls said inverter circuit to be operated in a pan detection mode, wherein in said pan detection mode, said inverter circuit is operated at an increased switching frequency or a reduced duty cycle, or said inverter circuit is disabled.

Drawing