JPS61188879A - Electromagnetic induction heater - 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] [Field of Industrial Application] The present invention is directed to an electromagnetic induction cooker such as an electromagnetic cooker in which a heating coil is energized and the magnetic flux generated in the coil inductively heats an object to be heated. This invention relates to a heating device.

[Prior art]

In this type of conventional electromagnetic induction heating device, which is applied to electromagnetic cookers and the like, the electricity supply to the heating coil is controlled on and off by a switching element to generate magnetic flux for induction heating in the heating coil, and the A coil current limiting circuit for adjusting the level of the control signal input to the switching element is subjected to feedbank control in accordance with the amount of current of the heating coil detected by a detection means such as a current transformer, thereby controlling the energization of the heating coil. A configuration that keeps the amount constant is generally used.

However, in the conventional configuration described above, if the power supply voltage input to the heating coil changes, the input signal level in the coil current limiting circuit also changes significantly, so the amount of current flowing through the heating coil is detected accordingly. Countermeasures must be taken, such as changing the current transformer to one that matches the level, and one type of control circuit board cannot be used in common for various power supply voltages, making it extremely versatile. It had the disadvantage of being lacking in sexuality.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned problems in the conventional example, and provides an electromagnetic induction heating device having a versatile control circuit configuration that can be commonly used with various power supply voltages. The purpose is to

[Structure of the invention]

The electromagnetic induction heating device of the present invention includes a switching element that controls on/off energization of the heating coil to generate magnetic flux for induction heating in the heating coil, and a switching element that controls the signal level input to this switching element. A coil current limiting circuit that controls the amount of current flowing through the coil; and a coil current limiting circuit that detects the input voltage to the heating coil and controls the coil current limiting circuit so that when the detected level becomes high, the input signal level to the input switching element becomes low. Even if the input voltage that supplies power to the heating coil is different,
This feature is characterized in that it can be handled using the same circuit configuration without requiring any changes.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to FIGS. 1 and 2.

Figure 1 shows the circuit configuration of the electromagnetic induction heating device of this embodiment, which is used in an electromagnetic cooker. , a smoothing capacitor 3, a heating coil 4 that generates magnetic flux for induction heating, and a resonant capacitor 5 that forms a resonant circuit with the heating coil 4. A switching circuit consisting of a diode 6 and a transistor 7 is connected between both terminals of the resonant capacitor 5, and the resonance of the resonant circuit caused by the switching action of the transistor 7 causes a high frequency current to flow through the heating coil 4. A circuit 8 is configured.

A control signal is input to the base of the transistor 7 from the first control circuit 9 via the drive circuit 10, and the transistor 7 is configured to be turned on and off in accordance with the control signal.

A current transformer 11 is coupled to the energization path of the heating coil 4, and the secondary side of the current transformer 11 is connected to the first control circuit 9, which detects the amount of energization of the heating coil 4. In response to the detected value of the current transformer 11, the coil current limiting circuit 9a of the first control circuit 9 receives the detected value and inputs a negative feedback control signal to the base of the transistor 7 via the drive circuit 10 using a circuit configuration described later. is configured to do so.

Further, a second control circuit 12 for detecting the power supply voltage is connected to the power supply line that supplies power to the inverter circuit 8. This control circuit 12 detects a power supply voltage from the power supply path via voltage dividing resistors 13 and 14, compares the detected value with a reference voltage Vrf, 1 in a comparator 15, and outputs the output of this comparator 15 as follows. Two AND gates 16 in the stage
17, respectively.

On the other hand, on the secondary side of the current transformer 11, the high voltage winding side branch 1
1a and a low-voltage winding side branch 11b, it is connected to the next stage first control circuit 9, and the high-voltage winding side branch 11a and low-voltage winding side branch 11b are connected to each other. Switching elements 18 and 19 such as transistors are connected. The output of the AND gate 16 of the first control circuit 9 is input to the base of the transistor 18, and the output of the AND gate 17 is input to the base of the transistor 19. Two shunts 11a and llb on the secondary side of the current transformer 11 are configured to be selectively conductive.

The coil current limiting circuit 9a of the first control circuit 9 is composed of an OP amplifier 20 as shown in FIG.
The input signal sent from the secondary side of 1 is the reference voltage Vrf,
2, negative feedback is applied to the base of the transistor 7 of the inverter circuit 8 by an amount proportional to the difference value, thereby keeping the amount of current flowing through the heating coil 4 constant.

The operation of this electromagnetic induction heating device will be explained separately in the case where, for example, a power supply voltage of 100V is input and the case where a power supply voltage of 220V is input, as follows.

εl] When a power supply voltage of 100V is input, the power supply voltage at this time is the voltage dividing resistor 13 of the second control circuit 12.
・Reference voltage Vrf that is input to the ■ input terminal of the comparator 15 via 14 and input to the e input terminal of the comparator 15
, compared with 1. This reference voltage Vrf, 1 is set to the same level as the output from the voltage dividing resistors 13 and 14 when the power supply voltage is 150V, so the comparator 15 outputs an L (low voltage level) signal at this time. . next stage A
Each of the ND gates 16 and 17 has an H (high voltage level) signal constantly input to one of its input terminals, and a signal from the comparator 15 to the other input terminal of these gates 16 and 17. A signal is input.

The AND gate 17 inverts this L signal to an H signal and inputs it, so its output becomes an H signal and the current transformer 11
The transistor 19 of the next low voltage winding branch 11b is turned on and this branch 11b becomes conductive. On the other hand, since the output of the AND gate 16 is an L signal at this time, the transistor 18 of the high voltage winding branch 11a is not turned on. As a result, the OP amplifier 20 of the coil current limiting circuit 9a [
The signal input to the input terminal has a relatively low level, and the difference from the reference voltage Vrf,2 becomes a correspondingly smaller value. Therefore, the amount of current flowing through the heating coil 4 is changed to the current transformer 1.
1. The control signal level for negative feedback control via the first control circuit 9, drive circuit 10, and transistor 7 is also 100
v is limited to a low value commensurate with the power supply voltage.

[2] When a power supply voltage of 220V is input In this case, the signal level input to the ■ input terminal of the comparator 15 of the second control circuit 12 is the reference voltage input to the e input terminal of the comparator 15. Since Vrf becomes higher than 1, the output of the comparator 15 becomes an H signal. Therefore, among the AND gates 16 and 17 in the next stage, the output of the AND gate 16 is an H signal,
The output of the AND gate 17 becomes an L signal. On the secondary side of the current transformer 11, the H signal of the AND gate 16 is input to the base of the transistor 18, which turns on, and the high voltage winding side shunt 11a becomes conductive. As a result, the signal input to the (1) input terminal of the OP amplifier 20 of the coil current limiting circuit 9a has a sufficiently higher level than in the case of the 1oov power supply voltage, and the difference from the reference voltage Vrf,2 becomes that much larger. Therefore, the negative feedback control amount applied to the base of the transistor 7 is also changed to a high value commensurate with the power supply voltage of 220V in accordance with the change in the amount of current flowing through the heating coil 4.

In this embodiment, the reference voltage of the comparator 15 of the second control circuit 12 is set to 1 so that it can correspond to two levels of power supply voltage.
In addition to preparing only one stage, two shunts, a high voltage winding side shunt 11a and a low voltage winding side shunt 11b, are prepared as electric paths connecting the secondary side of the current transformer 11 and the coil current limiting circuit 9a. Although the case where the configuration is shown is shown, it goes without saying that by appropriately preparing multiple stages according to the type of power supply voltage, it can be used in common across various power supply voltages.

〔Effect of the invention〕

As described above, the electromagnetic induction heating device of the present invention uses a predetermined control circuit to detect the input voltage to the heating coil, and when the detection level is high (when the detection level is high), the switching element that controls energization of the heating coil is switched on and off. Since the coil current limiting circuit is controlled so that the input signal level of Effects such as being able to reduce the cost of the heating device can be achieved.

[Brief explanation of the drawing]

FIG. 1 is an overall circuit diagram showing one embodiment of the present invention, and FIG. 2 is a circuit diagram showing a specific configuration of a part thereof. 4 is a heating coil, 7 is a transistor (switching element), 8 is an inverter circuit, 9a is a coil current limiting circuit,
11 is a current transformer, lla is a high-voltage winding side shunt, llb is a low-voltage winding side shunt, 12 is a second control circuit, 13 and 14 are voltage dividing resistors, 15 is a comparator, and 16 and 17 are AND gates. , 18・
19 is a transistor, and 20 is an OP amplifier. Figure 2

Claims (1)

[Claims] 1. A switching element that controls on/off the energization of the heating coil to generate magnetic flux for induction heating in the heating coil, and controls the amount of energization of the heating coil by controlling the signal level input to this switching element. A coil current limiting circuit, and a control circuit that detects the input voltage to the heating coil and controls the coil current limiting circuit so that when the detected level increases, the input signal level to the switching element decreases. An electromagnetic induction heating device featuring: