JP2512531B2 - Induction heating cooker - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an induction heating cooker.

2. Description of the Related Art The structure of a conventional induction heating cooker will be described with reference to the circuit diagram of FIG.

In FIG. 5, reference numeral 1 is a DC power source with a power source voltage E,
This DC power supply 1, the heating coil 3 for heating the pan 2, and the switching element 4 are connected in series, the resonance capacitor 5 is connected in parallel to the heating coil 3, and the reverse conducting diode 6 is connected in parallel to the switching element 4. Connect the inverter circuit 7
Is composed. The switching element 4 is on / off controlled by the control circuit 8.

Operation of the induction heating cooker configured as described above
This will be described with reference to the operation waveform charts of FIGS.

First, the switching element 4 is turned on by the control circuit 8 and the current _{IL is} passed through the heating coil 3. Next, the switching element 4 is turned off and the heating coil 3 and the resonance capacitor 5 resonate. This resonance vibration is the voltage across the switching element 4.
V _CE has a waveform that oscillates around the power supply voltage E. Next, the timing at which the switching element 4 is turned on is point B, which is delayed by a certain time from point A in FIG. 6 in which the voltage V _CE across the switching element 4 becomes equal to the power supply voltage E.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-described conventional configuration, as shown in FIG. 6 (a), when the output is small, the voltage across the switching element 4 after resonance does not become zero and the voltage V _G remains. Since the switching element 4 is turned on in this state, an inrush current I _G flows to the switching element 4 and there is a problem that the switching element 4 is destroyed or the loss becomes large. When the capacitance of the resonance capacitor 5 is reduced, the voltage V _G does not remain, but the oscillation frequency (= 1 / T) increases and the loss of the switching element 4 increases, so the capacitance of the resonance capacitor cannot be reduced.

Also, in the conventional configuration, the oscillation frequency (= 1 / T) changes from 1 / Ta to 1 / Tb depending on the size of the output and the pan 2, and in the induction heating cooker with multiple burners, the pan 2 interferes due to the deviation of the oscillation frequency. It had a problem that sound was generated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an induction heating cooker capable of safely operating a switching element and heating at a constant oscillation frequency.

Means for Solving the Problems In order to solve the above problems, the present invention provides a DC power supply, a heating coil for heating a pot, a first diode, and a first switching element connected in series, A second diode and a second switching element, which are connected in series to both ends of, and a resonance capacitor is connected in parallel to the series circuit of the first diode and the first switching element or both ends of the heating coil. And an inverter circuit configured to control ON / OFF of the first and second switching elements, and the controller controls the voltage across the first switching element or the current of the heating coil. A first on-timing detector for detecting the on-timing of the first switching element and the voltage across the second switching element. Has a second on-timing detector for detecting the on-timing of the second switching element by the current of the heating coil, and the first and second output signals of the first and second on-timing detectors. The configuration is such that the ON timing of the switching element is controlled.

Further, the present invention includes the inverter circuit and a control unit, and the control unit limits the on / off timings of the first and second on-timing detection units and the first and second switching elements. And a first oscillator according to the same oscillation frequency signal of the oscillator output and the output signals of the first and second on-timing detectors.
And a configuration for controlling the on / off timing of the second switching element.

Operation With the above configuration, the second switching element is provided, and the first and second on-timing detectors output the on-timing output signal when the voltage across the first and second switching elements is 0 V or less, for example. By doing so, the voltage across the first and second switching elements is 0V.
It is driven at the following times to prevent inrush current from flowing through the switching element as in the conventional case.

Further, by providing an oscillator, the first and second switching elements are turned on at a constant oscillation frequency.
It is controlled off and the pot is heated at a constant oscillation frequency. Therefore, even if it is used for heating multiple burners, the interference noise of the pan due to the difference in oscillation frequency does not occur.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of an induction cooking device showing one embodiment of the present invention. In FIG. 1, reference numeral 11 is a DC power supply of a power supply voltage E, and this DC power supply 11, a heating coil 13 for heating a pot 12, a first diode 14, and a first switching element 15 are connected in series. A second diode 17 and a second switching element 18 connected in series with the resonance capacitor 16 are connected in parallel to both ends of the heating coil 13 to form an inverter circuit 19. Reference numeral 20 is a control circuit for controlling the on / off of the first and second switching elements 15 and 18.

FIG. 2 shows a block diagram of the control circuit 20. In FIG. 2, 21 is an output setting unit for setting the output, 22 is an output detecting unit for detecting the output, and outputs the set value set by the output setting unit 21 and the output detected by the output detecting unit 22. The comparison unit 23 compares and sets the ON time T ₁ of the first switching element 15 by the ON time setting unit 24 so that the set value and the output match.
The first drive unit 26 performs the first switching according to the timing detected by the first ON timing detection unit 25 that detects the ON timing of the first switching device 15 by the voltage V _CE1 across the first switching device 15. Drive element 15. Reference numeral 27 is an oscillator for limiting the on / off timings of the first and second switching elements 15 and 18, and the oscillator 27 determines the first on-timing of the first switching element 15 at startup. Further, 28 is the second switching element 18 due to the voltage V _CE2 across the second switching element 18.
The second drive unit 29 is a second on-timing detector that detects the on-timing of the
The second switching element 18 at the timing detected by 28
Is turned on, and the second switching element 18 is turned off at the timing determined by the oscillator 27.

The operation and control method of the induction heating cooker configured as described above will be described in detail with reference to the operation waveform diagram of FIG.

First, at start-up, the first drive unit 26 turns on the first switching element 15 at the timing when the output of the oscillator 27 changes from the low level to the high level, and after the on-time T ₁ set by the on-time setting unit 27 The switching element 15 of No. 1 is turned off.
Then, the heating coil 13 and the resonance capacitor 16 resonate with the resonance period T ₂ . Here, the capacitance of the resonance capacitor 16 is set so that T ₂ << T with respect to the oscillation period T, and the amplitude of the voltage across the resonance capacitor 16 is increased. Second
The second on-timing detector 28 detects a period in which the voltage V _CE2 across the switching element 18 is 0 V or less, and the second driver 29 turns on the second switching element 18 during this period. From the point where the voltage V _{CE2 at} both ends becomes 0V, the current I _C2 flows into the second switching element 18, and the second switching element 18 is turned off at the timing when the output of the oscillator 29 changes from the low level to the high level. Then, the heating coil 4 and the resonance capacitor 5 resonate with the resonance period T ₂ , and the capacitance of the resonance capacitor 16 is small and the amplitude of the voltage across the resonance capacitor is large. _{Therefore, the} voltage V _CE1 across the first switching element 15 becomes 0 V or less. It also appears when the period is small output. Second switching element
Since there is an ON time T _{3 of} 18, the oscillation frequency does not increase and the loss of the first switching element 15 is small. And the first
The first on-timing detector 25 detects a period in which the voltage V _CE1 across the switching element 15 is 0 V or less, and the first driver 26 turns on the first switching element 15 during this period. After that, the same feedback loop is repeated, and the output setting unit 21
The set value set in step 1 and the output detected by the output detection unit 22 are stable in the ON time T ₁ of the first switching element 15 at which the output is detected. Since the control is performed as described above, the first and second switching elements 15 and 18 have their respective voltages V _CE1 and V _CE2.
Turns on at 0V and can operate safely. Also, because the oscillation cycle T is constant, the oscillation frequency (= 1 / T) does not change depending on the size of the output and the load, and even when used for heating multiple burners
No two interferers.

The on-timing of the first switching element 15 in the first on-timing detecting section 25 and the on-timing of the second switching element 18 in the second on-timing detecting section 28 are the first or second switching element. The current I of the heating coil 13 is detected by the voltages V _CE1 and V _CE2 across the terminals 15 and 18.
_It may be detected by _L.

In addition, in this embodiment, the resonance capacitor 16 is connected to the heating coil 13
4 is connected in parallel, but as shown in FIG. 4 (a), it may be connected in parallel to both ends of the series circuit of the first diode 14 and the first switching element 15, and further, in FIG. b)
Alternatively, as shown in FIG. 4 (c), the same effect can be obtained by reversing the connection order of the series circuit and the heating coil 13.

EFFECTS OF THE INVENTION As described above, according to the present invention, the second switching element is provided in the inverter, and the first and second on-timing detection sections have, for example, a voltage of 0 V between both ends of the first and second switching elements. By detecting the on-timing of the first and second switching elements and controlling the on-state by the following, the voltage between both ends of the first and second switching elements can be turned on at 0 V, and the first and second switching elements can be turned on. The device can be operated safely. Further, by providing an oscillator, it is possible to realize an excellent induction heating cooker in which heating can be performed at a constant oscillating frequency and the interference noise of the pan due to the difference in oscillating frequency does not occur even when using multiple burners.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an induction heating cooker showing an embodiment of the present invention, FIG. 2 is a block diagram of a control circuit of the induction heating cooker, and FIGS. 3 (a) and 3 (b) are the same induction, respectively. Operation waveform diagram of the heating cooker, FIGS. 4 (a) to 4 (c) are circuit diagrams of an induction heating cooker showing another embodiment of the present invention, and FIG. 5 is a circuit diagram of a conventional induction heating cooker. , Fig. 6 (a), (b)
FIG. 3 is an operation waveform diagram of a conventional induction heating cooker. 11 …… DC power supply, 12 …… pot, 13 …… heating coil, 14 ……
First diode, 15 ... First switching element, 16
...... Resonant capacitor, 17 …… Second diode, 18 ……
Second switching element, 19 ... Inverter circuit, 20 ...
... Control circuit (control section), 25 ... first on-timing detection section, 27 ... oscillator, 28 ... second on-timing detection section.

Claims (2)

(57) [Claims] 1. A DC power source and a heating coil for heating a pan,
A second diode connected in series with the first diode and the first switching element and connected in series with both ends of the heating coil.
A diode and a second switching element are connected in parallel, and a series circuit of the first diode and the first switching element or an inverter circuit configured by connecting a resonance capacitor in parallel to both ends of the heating coil, and A control unit for controlling ON / OFF of the first and second switching elements, wherein the control unit controls an ON timing of the first switching element by a voltage across the first switching element or a current of the heating coil. A first on-timing detector for detecting, and a second on-timing detector for detecting the on-timing of the second switching element by the voltage across the second switching element or the current of the heating coil, According to the output signals of the first and second on-timing detectors, the first and second switch Induction heating cooker which is configured to control the on-timing of the device. 2. A direct current power source, a coil for heating a pan, and a first
And a first switching element are connected in series, a second diode and a second switching element connected in series at both ends of the heating coil are connected in parallel, and the first diode and the first switching element are connected in parallel. A series circuit of switching elements or an inverter circuit configured by connecting a resonant capacitor in parallel to both ends of the heating coil, and a control unit for controlling ON / OFF of the first and second switching elements. The unit includes a first on-timing detector that detects the on-timing of the first switching element based on the voltage across the first switching element or the current in the heating coil, and the voltage across the second switching element or the voltage across the second switching element. Second detecting the ON timing of the second switching element by the current of the heating coil
Of the first and second switching elements, and an oscillator for limiting the on / off timings of the first and second switching elements, and outputs the output signals of the first and second on-timing detection sections and the oscillator output. The same oscillating frequency signal turns on the first and second switching elements.
An induction heating cooker configured to control the off timing.