JPS58679B2 - Dengen Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit suitable for application to high frequency heating devices such as induction heating devices and dielectric heating devices.

2. Description of the Related Art A so-called induction heating device is already known, which uses high-frequency signals to heat containers (pots, pots, etc.) used for cooking.

As shown in Fig. 1, this device has a relatively mechanically strong insulating plate 1, and an induction coil, generally called a work coil, is placed at a desired position on one surface, that is, the lower surface 1a. 2 is provided.

The induction coil 2 is wound spirally around the center of the insulating plate 1, for example, and is attached to the lower surface 1a.

This induction coil 2 is driven by a signal obtained by a drive system shown in FIG.

In FIG. 2, 4 represents a commercial AC source, 5 represents a power switch, and 6 represents a rectifier circuit.

The rectified output obtained by the rectifier circuit 6 is supplied as a drive signal to the above-mentioned induction coil 2 via a choke coil 7 and a resonance capacitor 8, respectively. A switching element, in this example 5CR11, is connected to which the desired switching signal (its frequency is about 20 to 100 KHz) is connected.
is supplied.

12 indicates an oscillator for obtaining this switching signal.

Note that the capacitor 13 is for smoothing, and the diode 14 is for damper.

Therefore, with the container 3 to be heated, such as a pot or kettle, placed on the other surface of the insulating plate 1, that is, the upper surface 1b, a drive signal that is intermittent with a high frequency signal (20 to 100 KHz) is applied to the induction coil 2. When supplied, the container 3 generates heat due to the eddy current product due to the high frequency magnetic field generated by the coil 2, so the container 3 is heated and can be used for cooking.

For the container 3, a material that is easily induction heated by high frequency heat is selected, and as is well known, this can include a magnetic material such as iron (in other words, a material with high electrical resistance).

By the way, such an induction heating device has the following drawbacks since it is necessary to drive the device with a relatively large amount of electric power.

That is, since this device 10 supplies a large current of several tens of amperes to the induction coil 2 side as described above, the rectifier circuit 6
This has the drawback that the rectification loss increases and the device 10 cannot be driven efficiently.

Furthermore, since the rectifier circuit 6 handles a large current, the diodes generate a large amount of heat, and therefore, accessory parts such as a heat sink and an air cooling means must be provided, which has the disadvantage of increasing the size of the rectifier circuit 6.

The present invention reliably eliminates these drawbacks with a relatively simple configuration.

That is, in the present invention, a pair of switching elements with opposite polarities are connected in parallel with an AC source, and when one switching element is used as an original switching element, the other switching element is used as a damper element. This power supply circuit is configured to be used as a power supply circuit.

A power supply circuit according to the present invention will be described below with reference to the drawings, and this example shows a case in which the power supply circuit is applied to a power supply circuit for an induction heating device as described above.

Therefore, although parts corresponding to those in FIG. 2 are given the same reference numerals and their explanations are omitted, the induction coil 2 is connected to both ends of the AC source 4 without going through the rectifier circuit 6.

In the present invention, as shown in the figure, a pair of switching elements 20A and 20 are connected in parallel with the AC source 4, that is, between the pair of power supply paths 4a and 4b, the forward directions of which are opposite to each other.
B is mediated.

These pair of switching elements 20A and 20B provide substantially the same function as the rectifier circuit 6.

Note that this circuit 20 is referred to as a switching circuit.

The switching elements 20A and 20B are S as shown in the figure.
Semiconductor controlled rectifier elements such as CR can be used.

By the way, in the following description, the element 20A whose direction from one power supply path 4a to the other power supply path 4b is selected as the forward direction will be referred to as a first switching element, and the other element will be referred to as a second switching element.

The switching circuits 20 are each driven by a signal obtained by the control circuit 30 shown below, but when one of the switching elements is performing its original operation, the other one is driving the damper. It is controlled so that it operates as an element.

Next, this control circuit 30 will be explained. 21 is a transformer, 22 is a rectifier circuit, and the rectified output is supplied as the operating voltage to the oscillator 12 for obtaining the above-mentioned switching signal.

It is assumed that a switching signal Sb as shown in FIG. 4C is obtained from the oscillator 12.

In the present invention, during the positive half cycle period of the AC signal So (FIG. 4A), the first switching element 20A
is operated as a switching element, and operated as a second switching element during the negative half cycle period.

Therefore, during the positive half cycle period, the second switching element 20B acts as a damper element, and during the negative half cycle, the first switching element 20A acts as a damper element.

In this case, since each switching element is constituted by an SCR, during the period TD immediately after switching, which is the damper period (see Figure 4), a switching signal is sent to the switching element, which is the damper element, to turn it on. (hereinafter referred to as a damper signal) will be required.

From this point of view, in this example, the switching signal Sb is used and is supplied to the phase shifter 23, so that the fourth
The damper signal Sc shown in the figure is obtained.

The switching signal Sb and damper signal Sc obtained as described above are applied to the corresponding switching elements 20A and 2, respectively.
0B gate terminal 25a.

25b via drive circuits 24A and 24B.

By the way, each switching element 20A.

Since the operation of 20B changes every half cycle, first and second changeover switches 26A and 26B are provided before and after the drive circuits 24A and 24B, respectively, and are switched by mutual movement. so that the damper signal Sc is alternately supplied to each switch every half cycle.
The wires are connected as shown in the figure.

Here, contact P indicates a switching contact during a positive half cycle, and contact N indicates a switching contact during a negative half cycle.

The illustrated example shows the former switching state. In addition, in order to switch these changeover switches 26A and 26B every half cycle, for example, the AC signal So obtained from the secondary coil 21b of the transformer 21 is guided to the flip-flop circuit 27, and the AC signal So is synchronized with the power supply frequency, that is, the AC signal So. It is sufficient to obtain the switching signal Sa (FIG. 4B) and supply it to the switches 26A and 26B as a switching signal.

Next, the operation of the circuit will be explained using the positive half cycle as an example.

During the positive half cycle, the switching signal Sa causes the switch 26A to
26B are all switched as shown in the figure, so the first switching element 20A has a switching element Sb,
A damper signal Sc is supplied to each of the second switching elements 20B.

Therefore, the AC signal So switched by the switching signal Sb is supplied to the induction coil 2 as a drive signal.

In other words, a drive signal modulated by the AC signal So is supplied to the induction coil 2.

During the switching period Ts (see FIG. 4), a positive pulse current shown in FIG. 4E flows through the first switching element 20A, and during the damper period TD, the positive pulse current shown in FIG.
B is the negative pulse current (damper current) shown in Fig. 4E.
Eventually, the sum of these currents will flow through the induction coil 2.

Therefore, a pulsed drive signal (voltage) Se shown in FIG. 4F is generated on the anode side of the first switching element 20A.

During the negative half cycle, the operation is opposite to that described above, and the induction coil 2 can be driven in any cycle.

The operating waveforms during the negative half cycle are shown in Figures G to J.
At this time, the current Sd' flowing through the induction coil 2 is obtained in a reversed state compared to that during the positive half cycle, and therefore the polarity of the drive signal Se' is also reversed.

As explained above, in the present invention, instead of providing a rectifier circuit, a switching circuit 20 consisting of a pair of switching elements 20A and 20B and its control circuit 30 are provided, and the same operation as with a rectifier circuit is performed using induction as a load. It is designed so that it can be given to the coil 2.

Therefore, in the present invention, since the power supply circuit 10 can be configured without a rectifier circuit, the rectification loss caused by the presence of the diode forming the rectifier N path can be reduced to zero.

Therefore, it has a feature that the induction coil 2 can be driven efficiently.

Of course, the same operation as before can be achieved even with low power, so
This has the effect of realizing this type of power supply circuit which is highly economical.

Therefore, a power supply circuit for high power can be provided.

In addition, since the rectifier circuit can be omitted and no heat dissipation means or the like is required, it also has the practical effect of being able to be made smaller.

Therefore, the present invention is extremely suitable for application to a power supply circuit in a high-frequency heating device such as an induction heating device, which requires a large amount of electric power and whose efficiency is important.

Needless to say, the present invention can also be applied to power supply circuits such as high voltage generation circuits.

In addition, in the embodiment described above, SC is used as a switching element.
Although R is used, other semiconductor controlled rectifying elements or transistors may be used.

In addition to the above-mentioned example, the high-frequency heating device may of course be a dielectric heating device using a high-frequency electric field generating element such as a magnetron.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an example of an induction heating device, Fig. 2 is an electrical configuration diagram thereof, Fig. 3 is a connection diagram showing an example of a high frequency heating device according to the present invention, and Fig. 4 is an explanation of its operation. FIG. 2 is an induction coil, 4 is an AC source, 5 is a power switch, 20
2 is a switching circuit consisting of a pair of switching elements 20A and 20B; 30 is its control circuit; 12 is an oscillator; 23 is a phase shifter; 27 is a flip-flop circuit;
6A and 26B are changeover switches.

Claims (1)

[Claims] 1 In a power supply circuit in which a load using this source as a power source is connected to an alternating current source, a pair of switching elements with opposite polarities are connected to the alternating current source in parallel, and one of these switching elements A power supply circuit characterized in that when one switching element is used as a switching element, the other switching element is used as a damper element.