JPS645434B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a control circuit and control method at the start and during heating of a heating device equipped with a controller such as a stored program type that can be programmed by a user. .

Conventional configurations and their problems In heating devices that use conventional stored program type controllers, such as microcomputers (hereinafter referred to as "microcomputers"),
There have been concerns about accidents in which power supply to the heating means is erroneously started due to malfunction of the control circuit due to noise or "runaway" caused by error or loss of function of the program counter in the microcomputer.

Hereinafter, the conventional heating device as described above will be explained with reference to the drawings.

FIG. 1 shows a control circuit diagram of a conventional heating device.

In FIG. 1, 1 is a microcomputer that controls heating, 2 and 3 are switching means for the power circuit section, and 3
-A is a contact opened and closed by switching means;
4 is a display tube for displaying cooking time and cooking contents, 5 is a magnetron, 6 is a transformer, 7 is a power source, 8 is a latch switch, and 9 is a start switch, and the latch switch 8 is turned on at the same time when the start switch 9 is pressed.

The operation of the control circuit configured as described above will be explained below.

First, by pressing the start switch 9, a command to start heating is input to the microcomputer 1.
The microcomputer 1 receives the control signal R of the switching means 2.
1 to High, then switching means 3
control signal R2 is set to High. By closing the contact 3-A of the switching means 3, a voltage is applied to the primary side of the transformer 6, and power supply to the magnetron 5 is started. As shown in FIG. 2, the output is performed by changing the ON time of the switching means 3, that is, the duty. When voltage is applied to the primary side of the transformer 6, current flows into the primary side of the transformer 6 (hereinafter referred to as "rush current").
It is abbreviated as ) flows and generates magnetic vibration sound.

Here, rush current will be explained using FIGS. 3 to 5.

FIG. 3 shows the relationship between the primary voltage V ₁ of the transformer 6 and the magnetic flux Φ ₁ of the iron core (not shown) of the transformer 6 when the transformer 6 is excited. As a result, the relationship between the on-phase of the switching means 3 and the magnetic flux Φ ₁ can be determined.

FIG. 4 shows the relationship between the primary voltage V ₂ and the amount of magnetic flux Φ ₂ when the transformer 6 is saturated.
Thereby, the relationship between the off phase of the switching means 3 and the magnetic flux Φ ₂ can be determined.

FIG. 5 shows the B-H curve of this transformer 6 and the magnitude of the rush current with respect to the ON phase of the switching means 3. Now, as shown in FIGS. 3 and 4, the ON point of the switching means 3 is set to a.
Let the off point be point b (that is, the point where the off phase is 1/4π).
The magnitude of the inrush current is the sum of the amount of change in magnetic flux ΔΦ ₁ from point a, which is the ON point, to point ap, where the direction of voltage V ₁ is reversed, and the magnetic flux Φ ₂ at point b, which is the OFF point, that is, (ΔΦ ₁ + Φ ₂ ). Now, ΔΦ ₁ = 2Φm, Φ ₂ = 0, and Φm =
From K·Bm (here, Bm is the magnetic flux density and K is a constant), an inrush current proportional to the magnetic flux density of +2Bm flows. As shown in FIG. 5, this magnitude is determined by the magnetic field strength _H1 and the rush current _I1 from point a plotted on the B-H curve.

This value is several tens of times the normal current I _n . The relationship between the on-phase of the switch means 3 and the inrush current is as shown in the lower part of FIG. 5, assuming that Φ ₂ =0. Therefore, in order to suppress this rush current to a small level, it is necessary to control the on-phase and off-phase of the switching means 3. Conventionally, the switching means 3 has been controlled by a microcomputer 1, as shown in FIG. FIG. 6 shows the timing chart. In Figure 6, V
is the power supply, and INT (CLK) is the clock signal used for the clock and timer. Switching means 3
For example, if it is a relay, the microcontroller will use INT
Relay control signal R ₂ is output after time T ₀ based on the rising point of the signal, that is, point A, and contact 3-
Close A. The contact point 3-A actually closes after the relay operating time _T1 has elapsed. Note that the time T ₀ is determined by the program of the microcomputer 1 and is always constant.

The problem here is that the relay operating time T ₁
As shown in FIG. 7, this operating time _T1 varies greatly due to variations in the relay coil drive voltage, ambient temperature, and between lots. Here, as shown in Figure 6, the standard operating time
The time _{T 0 is} determined by the program of the microcomputer 1 so that the inrush current becomes extremely small as _In with respect to T 1 .

However, as described above, since the operating time T ₁ varies, the on-phase of the contact 3-A varies from O to π, and the rush current also varies from I ₁ to -I ₁ . Therefore, the configuration of the conventional example has the following drawbacks.

(1) If large noise occurs on the power line, the microcontroller will malfunction.

(2) Magnetic vibration noise caused by rush current to the transformer is loud.

(3) The switching means must have a large contact rating and capacity, and it is necessary to minimize variations in operating time, etc.

(4) Contact welding occurs when, for example, a relay is used as the switching means.

Purpose of the Invention In view of the above drawbacks, the present invention provides a switching means 3.
The purpose of the present invention is to provide a heating device that can efficiently control the phase of the current and reduce the magnitude of rush current.

Composition of the Invention In order to achieve the above object, the heating device of the present invention is designed to reduce the operating time (and return time) of the switching means, whereas the conventional heating device outputs a switching means control signal after a certain period of time from a certain reference point. It is configured to detect this in advance and issue a signal for controlling the switching means so that the contact of the switching means is closed after a certain period of time from a certain reference point.

With this configuration, the opening and closing times of the contacts of the switching means can always be kept constant, and inrush current can be reduced.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 8 shows a control circuit diagram of a heating device in an embodiment of the present invention.

Compared to the conventional control circuit shown in Fig. 1,
In the control circuit shown in FIG. 8, another contact 3-B is connected to the switching means 3. Contact point 3 of this switching means (hereinafter referred to as relay) 3
-A and 3-B can make the operating time and return time the same by sharing the drive coil and making the contact materials and the distances between the contacts the same. The contact 3-B is used by the microcomputer 1 to detect the operating time and return time of the switching means 3. One end of contact 3-B is connected to a constant voltage power supply, for example +9V, and the other end is connected to microcomputer 1.
is connected to the input terminal I1 _of .

The operation of the control circuit for the heating device configured as described above will be described below. first,
It is necessary to detect the switching operation time and return time based on the current power supply situation, temperature, and switching means 3.

Therefore, as soon as the power is input to the microcomputer 1, the switching means control signal _R2 is set to High.
Contact 3-B detects when contact 3-A closes. That is, as shown in FIG. 9a, the microcomputer 1
The time required for the input signal _{I 1 to} become High (operating time T ₁ ) is detected. At this time, since the switching means 2 and the latch switch 8 are off, no voltage is applied to the primary side of the transformer 6, and the magnetron 5 is not oscillating.
Further, when the switching means control signal R ₂ is set to low, the time (operating time T ₂ ) until the input signal I ₂ becomes low is detected. And these operating times T ₁ ,
Only after detecting T ₂ does the heating device enter the heating start state. FIG. 9b shows the voltage applied to the coil of the relay 3 immediately after plug-in and under actual load (that is, while the microwave oven is in operation). Immediately after plug-in, the voltage applied to the coil of the relay 3 is V _a , whereas the voltage applied to the coil becomes V _b during the actual load because the relay 2 is on. Therefore, as shown in FIG. 9c, the operating time T ₁ of the relay 2 during plug-in becomes longer than the relay operating time T ₁ ' during the actual load. The operating time increases by Δt=T ₁ −T ₁ ′, but this Δt is almost constant because the coil power consumption of relay 2 is constant and the coil applied voltage ΔV=V _a −V _b is constant. becomes.

Now, the operating time of the switching means 3 is T _1a ,
Consider the case where T _1b and T _1c are different.
Therefore, the relay operating time under actual load is longer than the operating time when plugged in by Δt, so T _1a ′
= T _1a +Δt, T _1b ′=T _1b +Δt, T _1c ′=T _1c +Δt. As shown in FIG. 10, the microcomputer 1 has a certain reference point (i.e.
Be aware of the time T _M from the rising point of the INT signal until the contact 3-A of the switching means 3 closes, and calculate the operating times T _1a ′, T _1b ′, T _1c ′ of the switching means 3 from the time _TM. (T ₀ ′=T _M −T ₁ ′), the switching means control signal
Output R ₂ .

In other words, the contact 3-A is always turned on in the same phase as the power supply 7 to reduce the rush current. Further, the off phase of the power source 7 can be considered in the same way.

According to this embodiment, when the power supply 7 is input, the operating time and return time of the switching means 3 are detected in advance, and the time T _M from a certain reference point until the contact 3-A closes is kept constant. It can be done. Therefore, variations in the switching means 3, variations in the power supply voltage, etc. can be absorbed, and inrush current can be reduced.

Effects of the Invention As described above, the present invention detects the operation time and return time of the switching means in advance, uses the operation time and return time as reference points, and allows the switching operation to be performed at a predetermined timing. Items (1) The inrush current to the transformer is always small and the magnetic vibration noise can be reduced.

(2) The switching means is also good if it has a small contact rating and rated capacity, making it possible to reduce costs and downsize.

(3) The switching means can completely eliminate the serious problem of contact welding in the case of relays, etc., and furthermore, the durability can be dramatically improved.

It is possible to realize this, and its effects are significant.

[Brief explanation of the drawing]

Figure 1 is a control circuit diagram of a conventional heating device, Figure 2 is a diagram of the relationship between the menu and output of a heating device such as a microwave oven, Figures 3 and 4 are diagrams of the relationship between voltage V and magnetic flux Φ, and Figure 5 is a diagram of the relationship between voltage V and magnetic flux Φ. The figure shows the relationship between the B-H line of the transformer and the inrush current, Figure 6 shows the relationship between the phase control and timing of a conventional relay, Figure 7 shows the relationship between relay drive voltage and operating time, and Figure 8 shows the relationship between the relay's drive voltage and operating time. A control circuit diagram of a heating device in an embodiment of the invention, FIGS. 9a to 9c are diagrams showing a method of controlling a heating device in an embodiment of the invention, and FIG. 10 is a diagram of a switching means in an embodiment of the invention. FIG. 2 is a diagram regarding phase control and timing of FIG. 1...Microcomputer (controller),
3... Switching means, 5... Magnetron.

Claims (1)

[Claims] 1. A heating chamber for accommodating an object to be heated, a heating means provided in the heating chamber, a high-voltage transformer for supplying power to the heating means, a switching means for controlling the high-voltage transformer, and a switching means for controlling the operation of the switching means. The controller detects the operation time and return time of the switching means, performs the switching operation at a certain predetermined timing based on the operation time and the return time, respectively, and controls the high voltage transformer. A heating device configured to minimize inrush current.