JPS62149Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an output control device for a high frequency induction heating device used in a so-called electromagnetic cooker or the like.

Induction cookers are generally equipped with a current transformer or the like on the input side of the commercial alternating current to detect input current (or input power), etc.
Also, depending on the type of electromagnetic cooker, its maximum output (for example, 1.2KW) is also set in advance. This output is also configured to be arbitrarily selected using a volume for output control.

Therefore, when using a pot made of cast iron or enamel, even when adjusting the volume to supply this maximum output, the GCS etc. used in the cooker body Since the switching element is designed so that a current within its permissible value flows or a voltage (anode voltage) is applied to the switching element, there is little risk of it being destroyed.

By the way, for example, 18-
8 If you use a stainless steel pot, etc. and adjust the volume to give the maximum output in the same way as described above,
Even if the input power is suppressed below the rated value by the above-mentioned current transformer, there is an extremely high risk that the switching element will be destroyed because a current or voltage exceeding the allowable value is applied to the switching element.

Therefore, in order to prevent the use of pans made of such non-magnetic materials, safety is generally increased by detecting the material using a magnetic switch, but with this type of configuration, the range of pans that can be used is limited. There are limitations and drawbacks.

The present invention is capable of heating a non-magnetic pot by giving a certain amount of output, and when a current exceeding the permissible value flows in the switching element or voltage is applied. There,
The aim is to ensure this protection.

For this purpose, if a so-called current transformer is inserted into the current circuit leading to the anode of the switching element, the anode current can be detected by this, and this can provide sufficient protection. This current transformer has drawbacks such as a wide variation depending on the product, a large deterioration over time, a general high cost, and a cumbersome manufacturing process. Furthermore, as will be clear from the drawings to be described later, the purpose of detection cannot be achieved unless this current transformer is inserted between the switching element and the damper diode, but generally speaking, the current transformer cannot be inserted between the switching element and the damper diode. Since diodes generate a large amount of heat, they are mounted on a common heat sink, and the circuit and mechanical structure is such that this heat sink is mechanically cut off and a current transformer is inserted between them. There are also drawbacks that make it very difficult.

Considering the above points, it is not a good idea to insert a current transformer into the anode current circuit of this switching element.

From this point of view, the present invention is designed to appropriately control the output by using a simpler circuit and obtaining an electrical value equivalent to the anode current of the switching element.

An example of the apparatus according to the present invention will be described below with reference to the drawings.

1 is the main circuit, that is, the induction heating device body, 2a and 2b are input terminals for commercial AC current, 3 is a rectifier circuit,
4 is a smoothing circuit, 5 is a work coil, 6 is a variable frequency oscillator, 7 is a drive circuit to which the oscillation output is supplied, and 8 is a switching element to which the output from the drive circuit 7 is supplied, for example.
Consists of GCS. 9 is a damper diode connected in parallel to GCS8, 10 is a resonance capacitor inserted into work coil 5 so as to form a parallel resonance circuit, and 11 is for detecting input power (or input current). A sensor, ie, a current transformer, 12 is an input power (or input current) detection circuit. The drive circuit 7 includes a transistor 13 whose base is supplied with a signal from the oscillator 6.
, and a pair of bushable output transistors 14a and 14b whose collectors are connected to their respective bases. 15
a and 15b are power terminals of positive polarity +B and negative polarity -B, respectively.

As the voltage V applied to the control terminal 6a of the variable frequency oscillator 6 increases, the oscillation frequency f increases as shown in FIG. It is assumed that the height is as low as possible.

17 is an output control circuit, and to explain this, 18 is a DC power supply terminal, and a series circuit of resistor 19 - variable resistor 20 - resistor 21 is connected between this and the ground. , the output of the variable resistor 20 is connected to the minus input terminal of the operational amplifier 22, and the output from the above-mentioned input power detection circuit 12 is connected to the plus input terminal of the operational amplifier 22. The output of the amplifier 22 is voltage-divided by resistors 23a and 23b and applied to the control terminal 6a of the oscillator 6. This variable resistor 20 is a so-called output control volume, and by bringing this variable resistor 20 close to the power supply terminal 18 side, the output voltage of the amplifier 22, that is, the divided voltage V
As shown in FIG. 2, the frequency of the oscillator decreases and the output P increases. Such circuits are well known in the art.

In the present invention, a detection circuit 24 for detecting the driving power of the drive circuit 7 is provided, and this detection circuit 2
The detection output from 4, that is, the drive power of the drive circuit 7, is at a certain level (a preset level).
In this state, the output from the drive circuit 7 is prevented from increasing any further.

As shown in FIG. 1, the detection circuit 24 includes an operational amplifier 25 and voltage dividing resistors 26a and 2 connected in series between the DC power supply terminal 18 and the ground.
6b is connected to the positive input terminal of the amplifier 25, and voltage dividing resistors 27 and 28 are connected between the DC power supply terminal 18 and the negative polarity side power supply terminal of the drive circuit 7.
Connect the series circuit of , and connect the connection point Q to the amplifier 2
5 to the negative input terminal of the amplifier 2.
5 is connected to the connection point Z between the resistor 19 and the variable resistor 20 through the diode 29.

According to such a configuration, the output from the switching element 8 can be arbitrarily changed by adjusting the variable resistor 20 when using a normal enamel pot or the like. In this case, the set voltage by the variable resistor 20 and the input power detection circuit 12
The input voltage V of the oscillator 6 is controlled by comparing it with the output voltage of the oscillator 6 to stabilize the output. In this case, even if the variable resistor 20 is set to the maximum value, the switching element 8 is set in advance so that a current is supplied or an anode voltage is generated within its permissible value.

FIG. 3 is a waveform diagram showing the gate current of the switching element 8, and the current shown by the solid line is the maximum output state when the above-mentioned enamel pot is used. T is the on period of the switching element 8;
T' is the off period.

Next, when using the 18-8 stainless steel pot, the output can be adjusted in the same way as described above by adjusting the variable resistor 20, but now by setting it to the maximum output state, the output can be adjusted as described at the beginning. As shown in FIG.
The output of the iron is also increased compared to when using an enamel pot. The waveform indicated by the dotted line in Figure 3 is 18-8
It shows the gate current of the switching element 8 when a stainless steel pot is used, and the portion indicated by diagonal lines is longer and requires an extra output from the drive circuit 7.

Therefore, electric power is required in the drive circuit 7, and as a result, the voltage at the power supply terminal of the drive circuit 7, especially the voltage on the minus-B side, drops, that is, approaches the ground potential. This is power terminal 1
This is because the lead wire for supplying direct current that connects the drive circuit 7 and the drive circuit 7 has a resistance component 30 as shown by the dotted line in FIG. Of course, without using this resistance component, we actively
A resistor with a low resistance value may be inserted. In addition, the capacity V of the power supply itself supplied to the drive circuit 7
Since A (power) is constant, as described above, the voltage drops by the amount that the current increases.

When the power supply voltage of the drive circuit 7 drops in this way, the potential at point Q shown in FIG. 1 approaches the ground potential (increases in terms of potential), and this causes
When the voltage rises above the reference potential of the positive input terminal of the amplifier 25, the diode 29 turns on, and as a result,
Since the potential at point Z is lowered, this is equivalent to lowering the potential set by the variable resistor 20, and an increase in the output of the switching element 8 can be suppressed.

As explained above, according to the present invention, not only can pots such as enamel be used as before, but also stainless steel pots, etc., whose use was previously restricted, can be used freely. On the occasion of
It has features such as not causing any damage to the switching element 8.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an example of an output control device according to the present invention, and FIGS. 2 and 3 are waveform diagrams for explaining its operation. 8 is a switching element, 7 is a drive circuit, 6
2 is a variable frequency oscillator, and 24 is a drive power detection circuit of the drive circuit.

Claims (1)

[Scope of utility model registration request] A drive including a main circuit that rectifies a commercial alternating current using a rectifier, controls the rectified current using a switching element, and supplies the rectified current to a work coil, and an output transistor that controls the switching element, which is connected between a pair of power supply terminals. circuit and
It has a detection circuit that detects a voltage drop in one of the power supply terminals of the pair of power supply terminals due to an increase in the current of the output transistor, and an output control circuit that controls the output of the output transistor, and the detection output of the detection circuit is constant. 1. An output control device for a high-frequency induction heating device, characterized in that the output control circuit is controlled by the output of the detection circuit to suppress the output of the output transistor when the output is above a level.