JPS5958775A - 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 Field of the Invention The present invention relates to an induction heating cooker for induction heating of metallic steel by generating an alternating field of superaudible frequencies.

Conventional row configuration and its problems Conventionally, such high-frequency induction heating cookers use semiconductor switching elements to convert the frequency of large power, and their on/off operation excites a resonant circuit to perform induction heating. was. However, in order to obtain the necessary heating power for the heating coil, the current value of the heating coil is large, and the semiconductor that switches it is also required to have a large current switching ability. For this reason, semiconductor drive circuits require a large power supply capacity, and require a large ##, transformer, and large-capacity smoothing condenser, which is a major impediment to reducing the size, weight, and price of products.

OBJECTS OF THE INVENTION The present invention solves this problem by electromagnetically coupling a detection coil to a heating coil, detecting a part of the high frequency power, and using the pulse output as a drive signal for the impark half-JJ font. The aim is to reduce the size, weight, and cost of induction heating cookers by reducing the power supply capacity of the circuit to a large 1.

Structure of the Invention In order to achieve the above object, a heating coil and a semiconductor switching element are connected in series to a DC power source, and an inverter device having a resonant capacitor forming a resonant circuit with the heating coil is provided. The output of a detection coil attached in an electromagnetically coupled manner to detect the terminal voltage of the coil is supplied to the semiconductor switching element via a switching circuit that turns on and off. A drive circuit is provided.

DESCRIPTION OF THE EMBODIMENTS An actual iM array of the present invention will be described in detail below with reference to FIGS. 1 and 2.

An inverter device 4 is connected to a DC output terminal of a full-wave rectifier 3 connected to a commercial power source 1 via a power switch 2. In the inverter device 4, a π-type filter circuit including two capacitors 5 and 6 and a choke coil 7 is connected to the DC output terminal of the rectifier 3, and a heating coil 7 and a resonance capacitor 8 are connected to the output terminal of the capacitor 6. A parallel resonant circuit and a series circuit of the transformer/star 9 are connected, and a flywheel diode 10 is connected in anti-parallel between the collector and emitter of the transistor 9.

Here, if a direct current i1 source such as an automobile power source is used instead of the commercial power source, the rectifier and the like described above are also unnecessary.

Furthermore, the π-type filter of the inverter can also be eliminated if there is no problem in terms of its effect on the power supply. Next, the drive circuit for the inverter 4 will be explained. A power supply circuit 11 is connected to a secondary output terminal of a power transistor connected between AC input terminals of the rectifier 3. In Figure 1, a half-wave rectifier circuit consisting of a diode 12 and a smoothing capacitor 13, and a resistor 1
4 and a Zener diode 15, a full-wave rectification system is used, or a power transformer 10 is used.
Depending on the application, it is possible to select between eliminating the voltage and dividing the voltage from the DC output terminal of the rectifier 3.

The output terminal 16 of the power supply circuit 11 is connected to a trigger circuit 1, a timer circuit 18 operated by the output thereof, and a starting circuit 19. Both signals are composed of NOR gates that generate an output of 1'' when under heating conditions.Here, the protection circuit 21 includes a circuit for detecting abnormal temperatures of pots and internal parts, a circuit for detecting small objects, and other equipment. It is sufficient that the circuit includes all protection circuits for protecting the user, and that the output changes to 1' when any one of the protection circuits detects an abnormality.The output waveform is shown in Figure 2q. 3, the trigger circuit 17 is a voltage comparator 2 that compares the terminal voltage ratio of the transistor 9 with the solid line 2A and the reference voltage 2A broken line.
The output transistor 24 is composed of a capacitor 23 that differentiates the output of the transistor 2, and an output transistor 24 that is made conductive by its charging current.When the voltage of the transistor 9 becomes lower than the reference voltage, the output transistor 24 becomes conductive temporarily. (Figure 2C) On the other hand, the timer circuit 18 is a programmable UJT (hereinafter referred to as PUT)
This is a timer circuit using the timer circuit 18 (abbreviated as ) 25, whose gate voltage (broken m in FIG. 2 d) is obtained by dividing the output heart pressure (FIG. 2 q) of the starting circuit 19. Output transistor 26 is an NPN transistor that is conductive when its gate is experiencing heart pressure. Therefore, when the protection circuit 21 detects an abnormality or the starting switch 20 is not working, the output of the starting circuit 19 is zero and the output transistor 26 is non-conductive. The output waveform of transistor 26 is shown in FIG. 2e. Also, even after PUT25 is ignited after a certain period of time, the voltage between its gate and cathode remains P'UT
Since the output transistor 25 is short-circuited, the gate voltage becomes substantially zero and the output transistor 26 becomes non-conductive. Here P.U.
A resistor 2 and a timer capacitor 28 are connected to the anode of T25 as a time constant circuit (2V), and a resistor 270
The low resistance value must be selected to provide sufficient anode current to P'UT 25 to maintain conduction after P'UT 25 has fired. On the other hand, this PUT25
The collector of the output transistor 24 of the trigger circuit 17 is connected to the anode terminal of the transistor 9, and when the terminal voltage of the transistor 9 falls below the reference voltage (the broken line in FIG. 2a), the transistor 24 temporarily becomes conductive. P(JT2
The anode current of PUT 25 is bypassed to transistor 24 and becomes zero, and PUT 25 becomes non-conductive. (Figure 2C
2 shows the collector current of the trans/star 24. ) so I~
Then, the non-conducting state continues until the capacitor 28 is charged and reaches the voltage (dashed line in FIG. 2d) on the game day.
The 4-wire state is maintained until 4 becomes conductive again.

If the output of the timer circuit 18 (output of the transistor 26 (Fig. 2 e)) which has been turned on in this way is inverted and given as the base current of the transistor 9, the timer circuit 1
The transistor 9 is turned on only during this time, and pressure is applied to both heating coils ψ111; of the DC power supply. Thereafter, the transistor 9 becomes non-conductive and a free oscillating current flows through the heating coil 7 and the resonant capacitor 8. The terminal voltage of the heating coil at this time has the waveform shown by f in Figure Pj2, and the current flowing through the transistor 9 and diode 10 has the waveform shown in Figure 2. However, in order to produce a large output with an inverter, the transistor 9 also needs a large capacity, so even though it is a base current, it is necessary to increase the output signal of the timer circuit, but the power supply circuit 11 also has a large current. In order to switch, it is necessary to increase the capacity of the power supply circuit 11 and use a switching element with a large current rating. Regarding the power supply part for the load: 1 ton, recently C
With the generalization of ICs such as MOS, logic circuits are moving to lower power consumption, and it is necessary to increase the capacity to 11 just to drive transistor 9, making the power transformer larger.

Heat generation in the power supply section, high prices, etc. are major problems for the delay in purchasing.

Therefore, paying attention to the fact that the terminal 1a of the heating coil 7 has a waveform shown in FIG. By using the base drive power source as the base drive power source, the above-mentioned problems can be solved all at once.

That is, the output of the detection coil 30 and the output of the gate element 31 (FIG. 2 e) obtained by inverting the transistor 26 are respectively connected to the inputs of the OR circuit of diodes 32 and 33, and the resistor 34 is valved from the OR output. base y of transistor 9
Connect to 161 child. In this case, the voltage at the output 1 of the gate element is usually selected to be smaller than the output voltage of the detection coil 30, during the first cycle at start-up and when the output of the 1 yellow output coil drops to 1: only diode 33. resistance 3
4 to the base of transistor 9.

On the other hand, the output of the transistor 26 is applied to the transistor 37 with the in-phase output level of the two-stage inverting gate elements 35 and 36 to obtain an on-off output as shown in the second diagram. The collector of the transistor 3 is connected to the base terminal of the transistor 9, and when removed while the timer circuit 18 is performing a timer operation, the base signal of the transistor 90 is inhibited.

That is, in order to speed up the turn-off time of the transistor 9, excess carriers accumulated in the base are released by the transistor 37, and unnecessary signals from the detection coil 30 (positive signals other than the shaded area in FIG. 2) are prohibited. By doing so, we aim to improve efficiency.

The base current of transistor 9 is shown in FIG.

or,! - By connecting the emitter terminal of the dimetator 3 to a negative power supply and applying a reverse bias voltage to the base of the transistor 9 when it is conductive, it is possible to further increase the speed of the transistor 9.

A negative polarity power source can be easily obtained by providing another secondary winding in the power transformer 10 shown in FIG. 1, but it can also be obtained by rectifying the output voltage of the detection coil 30.

FIG. 3 shows a second embodiment in which a negative polarity power source is also obtained from the detection coil 30.

The detection coil 3o is a winding 30a that drives the transistor 9.
and a winding 30b for negative polarity power supply.
0a has the same effect as the winding 30 in FIG. The winding 3ob charges the smoothing capacitor 40 by half-wave rectification with the rectifier diode 41 using the output voltage when the transistor 9 is conductive, and connects the positive terminal of the capacitor 40 to the emitter of the transistor 9. Negative polarity wire 42 obtained in this way
The emitter of the transistor 37 is grounded (the negative terminal of the capacitor 40), and a negative bias is applied to the base terminal of the transistor 9 to shorten the switching speed. A resistor 43 inserted between the positive power source and the base of the transistor 37 allows the base current of the transistor 37 to flow, but the current is turned on and off by the transistor 44 whose collector and emitter are connected between the base and emitter of the transistor 37. Ru. Base of transistor 44 and gate element 3
A series circuit of a Zena diode 45 and a resistor 46 is connected between the output terminals of the transistor 1. Here, the positive power supply voltage is ■A,
When the negative electrode negative power supply voltage ■B and the Zener voltage of the Zener diode 45 are expressed as Vz, it is selected so that it always becomes ■B〈■Z〉■■A4-VB, so the output terminal of the gate element 31 is set to ゛1P. When transistor 9 is driven, transistor 44 becomes conductive and bypasses the base current of transistor 370, so transistor 37 becomes non-conductive and transistor 9 is driven. and gate element 31
When the voltage becomes Q'' and the supply of the drive signal from the gate element to the transistor 9 is stopped, the transistor 44 becomes non-conductive and the transistor 37 becomes conductive to apply a base reverse bias to the transistor 9.

Effects of the Invention As described above, the present invention supplies the necessary force from the detection coil coupled to the heating coil for large current driving of the transistors of the inverter, so the following effects can be expected.

1. Since the Iu# capacity for the control circuit can be reduced, equipment can be made smaller and lower in price.

2. Only one high-current switching element is required for high-speed operation, and the time span during which the current (VV) flows is short, so there is little loss in the switching element.

3 Even if the input voltage of the inverter suddenly decreases due to an open power failure, etc., and the output voltage of the detection coil decreases, it is automatically backed up by the power supply of the 1m circuit, so even transient
It is stable in the evening.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a waveform diagram illustrating the operation of FIG. 1, and FIG. 3 is a circuit diagram showing another embodiment of the present invention. 4- Inverter circuit, 7- Heating coil, 8- Resonant capacitor, 9. Transistor, 30... Detection coil.

Claims (1)

[Claims] A heating coil and a semiconductor switching element are connected in series to a DC power source, and an inverter device is equipped with a resonant capacitor that forms a resonant circuit with the heating coil, and is attached by electromagnetic coupling to detect the terminal voltage of the heating coil. The output of the detection coil is supplied to the semiconductor switching element via a switching circuit that turns on and off. An induction heating cooker with a drive circuit.