JPH08124667A - Safety circuit for microwave oven - Google Patents

Abstract

PURPOSE: To provide a highly safe circuit having no heating or damage of the circuit or an element. CONSTITUTION: This safety circuit is a safety circuit constituted on a printed board in a microwave oven, which has a power source pattern 18 on the printed board and a safety protecting pattern 19 of the same potential as 0V of the printed board around it. When an insulation deterioration occurs in the power source pattern 18 and the safety protecting pattern 19, a resistive element 20 is inserted to a part of the power source pattern 18 to limit the current at a short circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety circuit constructed on a printed circuit board in a microwave oven.

[0002]

2. Description of the Related Art Conventionally, a microwave oven for heating food by a high frequency oscillator oscillates an ultra-short wave of 2 to 3 MHz, and therefore various measures have been taken in terms of safety against radio wave radiation. For example, the door switch provided on the door handle is interlocked with the latch switch inserted in the power supply line of the high frequency oscillator, and even if the door is accidentally opened while heating food, The latch switch is opened to stop the power supply to the high-frequency oscillator and to stop the oscillation instantaneously.

Further, the relay for driving the high-frequency oscillator has a circuit structure in which the drive voltage of the relay itself is not supplied when the door is opened, and plays the role of a dual safety device for the microwave oven together with the latch switch. . By the way, the drive power supply circuit to the relay is usually formed on a printed circuit board provided inside the microwave oven. However, the pattern on the printed circuit board, especially the power source pattern, may be deteriorated in insulation due to environmental conditions in which the microwave oven is placed, for example, high temperature and high humidity, water drops, carcasses of insects such as cockroaches and the like. When this insulation deterioration occurs, even if the door is accidentally opened while the food is being heated, the relay does not turn off and remains in the excited state, and does not serve as a safety device.

Regarding this problem, Japanese Patent Laid-Open No. 6-45
There is a microwave safety circuit disclosed in Japanese Patent Publication No. 063. The safety circuit of this microwave oven will be described with reference to FIGS. FIG. 3 is an example of a circuit diagram of a microwave oven including a pattern diagram on a printed circuit board. First, when the door is closed, in the power supply pattern 18, the voltage supplied from the commercial power supply 3 is stepped down by the step-down transformer 9,
It is applied as a power supply voltage for driving to the relay coil 8b via the power supply pattern 17 and the door switch 5 in the main body circuit 1. The door detection circuit 15 determines that the door is closed by this voltage, and the signal is sent to the microcomputer 14. The microcomputer 14 receives this signal and transmits a drive signal to the switching transistor 16 in response to a user's operation command for heating food or the like. The relay coil 8b is excited by this signal, the relay contact 8a on the main circuit 1 side is closed, a high frequency is oscillated by the high frequency oscillator 7, and the food or the like is heated.

When the door is opened while the food is being heated, the door switch 5 is opened and the power supply voltage for driving is not supplied to the relay coil 8b. Therefore, the relay contact 8a on the main circuit 1 side is opened and the high voltage generating circuit is opened. The power supply to 6 is stopped, and high frequency is not oscillated by the high frequency oscillator 7. When the door switch 5 is opened at the same time, the latch switch 4 interlocked with the door switch 5 is opened, so that the high voltage generating circuit 6 is not supplied with power, and this action also stops the high frequency oscillation. The above two functions are configured as a double safety function of this microwave oven.

However, at this time, the power supply patterns 17 and 18
If the insulation deterioration occurs in and the short-circuited state, the power supply voltage is always supplied to the relay coil 8b regardless of whether the door is opened or closed. The power supply voltage is also applied to the door detection circuit 15. Therefore, the door detection circuit 15 determines that the door is open. The microcomputer 14 receives this signal and outputs a signal for oscillating a high frequency when the user gives a driving instruction. In such a case, if the latch switch 4 fails and remains closed, the radio wave remains oscillated from the high frequency oscillator 7 even when the door is opened.

Therefore, in the invention disclosed in Japanese Patent Laid-Open No. 6-45063, a relay coil 8b for driving the high-frequency oscillator 7 from a terminal on one side of the connector 13 on the printed circuit board in the pattern of this circuit is shown in FIG. And around the power supply pattern 18 leading to the door detection circuit 15,
A pattern 19 (hereinafter referred to as a safety protection pattern) having the same potential (0 V) as when the door is opened is provided. By doing so, even when insulation deterioration occurs in the power supply pattern 18 and the safety protection pattern 19 of the printed circuit board, the signal from the door detection circuit 15 causes the microcomputer 14 to operate.
Recognizes that the door is opened and stops the radio wave oscillation of the high frequency oscillator 7.

[0008]

The above-mentioned safety circuit of the microwave oven has the above-mentioned safety when the door is opened, in other words, when the door switch 5 is opened. However, when the door is closed, in other words, when the door switch 5 is closed, the voltage of the power supply pattern 17 causes a short-circuit current to flow through the door switch 5 to the power supply pattern 18 and the safety protection pattern 19. As a result, the step-down transformer 9, the rectifying diode 10 and the like generate heat, and the elements may be damaged in some cases.

Therefore, an object of the present invention is to solve the above-mentioned technical problem and to insert a resistance element in series at one place of a power supply pattern to limit the current at the time of short-circuiting, thereby providing a more safe electronic device. Is to provide a range.

[0010]

In order to achieve the above object, in a safety circuit for a microwave oven according to a first aspect of the present invention, at least a part of an energization control circuit of a high frequency oscillator for heating and cooking is provided on a printed circuit board. In a safety circuit of a microwave oven including a patterned structure, a first pattern formed on a printed circuit board and given a potential from a power supply side is electrically insulated from the first pattern on the printed circuit board. A second pattern which is formed in a state and which guides a driving voltage to an energization control circuit of the high frequency oscillator; a resistance element which is provided on the printed circuit board and connected to the second pattern; and the second pattern. A protective pattern formed on the printed circuit board so as to surround the printed circuit board, and the potential of the first pattern provided outside the printed circuit board via a predetermined switch. In which it characterized in that it comprises a connection circuit for applying to the second pattern connected to said resistor element.

The safety circuit for a microwave oven according to a second aspect is the safety circuit for a microwave oven according to the first aspect, wherein the protection pattern is connected to a ground potential on a printed circuit board. It is what Further, a safety circuit for a microwave oven according to a third aspect is the safety circuit for a microwave oven according to the first or second aspect, wherein a predetermined circuit is provided for applying to the resistance element connected to the second pattern. The switch is characterized by interlocking with the door.

The safety circuit for a microwave oven according to a fourth aspect of the present invention is the safety circuit for a microwave oven according to any one of the first to third aspects, wherein the second pattern is door detection for detecting an open / closed state of the door. It also introduces a potential to the circuit, and is characterized in that a diode is interposed at each of the connection portions with the energization control circuit and the door detection circuit.

[0013]

According to the first aspect of the present invention, the energization control circuit of the high-frequency oscillator for heating and cooking has a first pattern to which a potential is applied from the power supply side, and the high-frequency oscillator is electrically insulated from the first pattern. The second pattern for guiding the drive voltage to the energization control circuit and the protection pattern formed so as to surround the second pattern are pattern-formed on the printed circuit board.

The resistance element is connected to the second pattern, and a connection circuit for applying the potential of the first pattern to the resistance element via a predetermined switch is provided outside the printed circuit board. It is configured. With this configuration, the current value flowing into the second pattern is limited by the resistance element. Therefore, even if insulation between the second pattern and the protection pattern is deteriorated and a short circuit occurs, the current flowing from the first pattern to the second pattern is limited by the resistance element, and the first pattern is opened regardless of whether the door is opened or closed. It is possible to prevent heat generation and damage of the rectifying diode and the like provided in the preceding stage. As the resistance element, a diode may be used as well as a normal resistance element, and the switching resistance thereof may be used.

According to the second aspect of the invention, when the second pattern and the protection pattern are short-circuited due to insulation deterioration, the protection pattern is connected to the ground potential on the printed circuit board, so that the door is opened. Even if it is closed, power is not supplied to the energization control circuit and the high frequency does not oscillate from the high frequency oscillator. Further, according to the invention of claim 3, the door switch, which is interposed to apply the voltage to the resistance element connected to the second pattern, is interlocked with the door, so that when the door is opened, power is supplied to the energization control circuit. The high frequency does not oscillate from the high frequency oscillator.

According to the fourth aspect of the present invention, the second pattern also introduces a potential to the door detection circuit that detects the open / closed state of the door, and is connected to the energization control circuit and the door detection circuit. A diode is interposed in each part. There is no adjacent pattern after the location where this diode is inserted, and insulation deterioration does not occur. Therefore, it is possible to reduce the area where attention must be paid to insulation deterioration.

[0017]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a circuit diagram of a microwave oven including a pattern diagram according to an embodiment of the present invention. The circuit of the microwave oven in FIG. 1 is roughly divided into a main body circuit 1 and a control circuit 2. A commercial power supply 3 (usually obtained from a household outlet) is connected to the main body circuit 1, and power is supplied to a high voltage generation circuit 6 via a latch switch 4. Further, the high voltage generation circuit 6 is determined to be energized by the relay contact 8a.
The high frequency oscillator 7 connected to the high voltage generation circuit 6 oscillates a high frequency by being supplied with a voltage. Further, the latch switch 4 is interlocked with a door switch 5 provided on a door (not shown), and when the door is opened, the latch switch 4
Is also open.

The control circuit 2 is wholly formed on one printed circuit board. The control circuit 2 includes a main circuit 1
The AC power supply voltage is supplied from this. This AC power supply voltage is stepped down by a step-down transformer 9, rectified by a rectifying diode 10 and a smoothing capacitor 11, and then supplied to a microcomputer 14 as a driving DC voltage via a regulator 12.

A circuit including a door detection circuit 15, a relay coil 8b, and a transistor 16 for controlling the excitation of the relay coil 8b is provided, and these circuits are connected to the microcomputer 14. By the way, in order to apply the power supply voltage to the circuit of the door detection circuit 15 and the relay coil 8b, the following pattern is formed on the printed board. That is, the first to take out the power supply voltage rectified by the rectifying diode 10 and the smoothing capacitor 11.
Power supply pattern 17 as a pattern and door detection circuit 1
5 and the power supply pattern 18 as the second pattern for guiding the drive voltage to the relay coil 8b, and the safety protection pattern 19 formed so as to surround the power supply pattern 18 and connected to the 0V potential of the printed circuit board are formed on the printed circuit board. Has been done. The 0V potential of the printed circuit board is the same potential as when the door is opened, that is, the chassis ground.

The power supply pattern 17 is formed from the cathode side of the rectifying diode 10 to one terminal of the connector 13 that controls the exchange of external signals, and is provided outside the printed circuit board and provided on the main circuit 1 side. It is connected to one terminal of the door switch 5. The other terminal of the door switch 5 is connected to the other terminal of the connector 13 described above. A small pattern 21 for connection is formed on the printed circuit board including this terminal and in the vicinity of this terminal. The resistance element 20 is connected between the small pattern 21 and the power supply pattern 18 described above. The safety protection pattern 19 is provided so as to pass below the main body of the mounted resistance element 20 on the printed circuit board and surround the power supply pattern 18.

In the circuit including the pattern diagram of FIG. 4 shown in the section of the prior art, since the patterns are close to each other, not only between the power supply pattern 18 and the safety protection pattern 19, but also the power supply pattern 17 and the safety pattern. The possibility of insulation deterioration with the protection pattern 19 is also considered sufficiently. On the other hand, in this embodiment, the power supply pattern 17 and the safety protection pattern 1
The respective patterns are arranged at positions sufficiently separated from each other so as not to cause insulation deterioration.

Next, the operation of this circuit diagram will be described.
First, when the door is closed, the DC voltage rectified by the rectifying diode 10 and the smoothing capacitor 11 of the control circuit 2 is taken out by the power supply pattern 17, and the main circuit 1 of the main circuit 1 is output through one terminal of the connector 13. Via the door switch 5, the other terminal of the connector 13, the small pattern 2
1, the resistor element 20, and the power supply pattern 18, and is applied to the door detection circuit 15 and the relay coil 8b of the control circuit 2.

The door detection circuit 15 determines whether the door is opened or closed depending on the presence or absence of the voltage supplied from the power supply pattern 18 when the door switch 5 is opened or closed. For example,
When the door switch 5 is closed, the power supply pattern 17 is passed through the door switch 5 and the resistance element 20.
8 is applied, and as a result, power is supplied to the door detection circuit 15. Therefore, the door detection circuit 15 determines that the door is closed. On the other hand, when the door switch 5 is open, the voltage applied from the power supply pattern 17 to the power supply pattern 18 is cut off by the door switch 5, so that power is not supplied to the door detection circuit 15. Therefore, the door detection circuit 15 determines that the door is open.

The microcomputer 14 confirms the open / closed state of the door on the basis of the detection signal from the door detection circuit 15, and outputs a signal for driving the relay coil 8b to the switching transistor 16 in response to a user's operation command when the door is in the closed state. Send. The switching transistor 16 is turned on by this signal, and the relay coil 8b is excited when the drive voltage from the power supply pattern 18 is applied. When the relay coil 8b is excited, the relay contact 8a
Is turned on and the commercial power supply 3 is applied to the high voltage generation circuit 6, so that the high frequency oscillator 7 oscillates a high frequency.

When the door is open, the door switch 5 is opened and the power supply voltage is not supplied to the power supply pattern 18, so that the relay coil 8b is not excited. Therefore, the relay contact 8a is turned off, and the high frequency oscillation from the high frequency oscillator 7 is stopped. At the same time, since the latch switch 4 is interlocked with the door switch 5, the latch switch 4 is also opened, and power is not supplied to the high frequency generation circuit 6, so that the latch switch 4 also prevents the high frequency from the high frequency oscillator 7. Oscillation is stopped and they have a double safety function.

The above is the basic operation in this normal circuit configuration. However, it is assumed that insulation deterioration between the power supply pattern 18 and the safety protection pattern 19 has occurred. At this time, the safety protection pattern 19 is connected to the 0V potential of the printed circuit board, that is, the 0V potential of the door detection circuit 15. Therefore, when insulation deterioration occurs, the power supply pattern 18
Has a potential of zero. Therefore, power is not supplied to the relay coil 8b and the relay contact 8a is turned off.
The high frequency oscillation from the high frequency oscillator 7 is stopped.

Further, even if insulation between the power supply pattern 18 and the safety protection pattern 19 is deteriorated for some reason and a short circuit occurs between the patterns, the resistance element 20 connected between the power supply pattern 18 and the small pattern 21 causes The power supply pattern 17 is not connected to the ground potential. Therefore, even if the door is closed and the door switch 5 is closed, the step-down transformer 9 and the rectifying diode 10 connected to the power supply pattern 17 are not directly grounded. Therefore, short circuit current flows due to grounding,
The step-down transformer 9 and the rectifying diode 10 will not generate heat or be damaged.

Further, the resistance element 20 has an electric power permissible value such that the resistance element 20 is not destroyed, the detection potential can be normally detected when the door is opened and closed, and the resistance value can freely drive the relay coil 8b. You may choose to. Also, FIG.
FIG. 9 shows a circuit diagram including a pattern diagram of another embodiment of the present invention. The circuit diagram of FIG. 2 is obtained by further improving the circuit diagram of FIG. 1 described above, and the circuit configuration and the circuit operation are the same as the circuit diagram of FIG.

FIG. 2 is a view showing the door safety circuit 1 in the circuit diagram of FIG. 1 between the power supply pattern 18 and the relay coil 8b and between the power supply pattern 18 and the relay coil 8b.
During the pattern to 5, each first diode 22
And the second diode 23 is inserted. The safety protection pattern 19 is provided so as to surround the power supply pattern 18 extending from one terminal of the resistance element 20 to the anode side of each of the first diode 22 and the second diode 23.

The inserted diode may be freely selected as long as it has a rated value with respect to the voltage and current supplied to the power supply pattern 18 to the extent that it is not damaged. The power supply pattern after the portion inserted by these diodes, that is, the pattern from the cathode side of the first diode 22 to one terminal of the relay coil 8b, and the resistance in the door detection circuit 15 from the cathode side of the second diode 23. The pattern up to one terminal of
Since there is no adjacent pattern, the pattern range of the power supply pattern 18 that may cause insulation deterioration can be narrowed down. This makes it possible to reduce the area where attention must be paid to insulation deterioration.

Besides, various design changes can be made without departing from the scope of the present invention.

[0032]

As described above, according to the safety circuit of the microwave oven of the first aspect, the safety protection pattern is provided around the power source pattern which is the drive voltage potential of the relay on the printed circuit board, and the safety pattern is provided in a part of the power source pattern. By inserting a resistance element and limiting the current at the time of short circuit, even if the power supply pattern and the safety protection pattern are short-circuited due to insulation deterioration, the short-circuit current does not flow to the control circuit or circuit element regardless of whether the door is open or closed. It is possible to provide a highly safe microwave oven in which circuits and elements do not generate heat and are not damaged.

Further, according to the safety circuit of the microwave oven of claim 2, the safety protection pattern is the 0V potential of the door detection circuit,
That is, it is connected to the chassis ground of the microwave oven. As a result, the safety protection pattern causes insulation deterioration with the power supply pattern and does not supply the drive voltage to the relay coil even if a short circuit occurs, so high-frequency oscillation can be stopped without fail, providing a microwave oven with even greater safety. can do.

According to the microwave oven safety circuit of the present invention, the door switch is turned on and off in conjunction with opening and closing of the door. When the door is opened, no voltage is supplied to the control circuit, so high-frequency oscillation is not performed, which is an effective function for the user. According to the safety circuit of the microwave oven of claim 4, the first and second diodes inserted in the power supply pattern, which is the drive voltage potential of the relay,
Since there is no adjacent pattern after the inserted portion, insulation deterioration does not occur, so that the possibility of occurrence can be reduced.

[Brief description of drawings]

FIG. 1 is a safety circuit of a microwave oven including a pattern diagram according to an embodiment of the present invention.

FIG. 2 is a safety circuit of a microwave oven including a pattern diagram according to another embodiment of the present invention.

FIG. 3 is a safety circuit including a pattern diagram of a conventional microwave oven.

FIG. 4 is a safety circuit including a pattern diagram of a conventional improved microwave oven.

[Explanation of symbols]

 1 Main Circuit 2 Control Circuit 4 Latch Switch 5 Door Switch 7 High Frequency Oscillator 8a Relay Contact 8b Relay Coil 15 Door Detection Circuit 18 Power Supply Pattern 19 Safety Protection Pattern 20 Resistive Element 21 Small Pattern 22 First Diode 23 Second Diode

Claims (4)

[Claims] 1. A safety circuit of a microwave oven, wherein at least a part of an energization control circuit of a high-frequency oscillator for heating and cooking is formed on a printed circuit board in a safety circuit of the microwave oven. A first pattern to which a potential is applied and a second pattern which is formed on a printed circuit board in an electrically insulated state from the first pattern and which guides a drive voltage to a conduction control circuit of a high frequency oscillator. A resistance element provided on the printed circuit board and connected to the second pattern, a protection pattern formed on the printed circuit board so as to surround the second pattern, and provided outside the printed circuit board, A connection circuit for applying the potential of the first pattern to the resistance element connected to the second pattern via a predetermined switch. Safety circuit of the microwave oven according to claim. 2. The safety circuit for a microwave oven according to claim 1, wherein the protection pattern is connected to a ground potential on a printed circuit board. 3. The safety circuit of the microwave oven according to claim 1, wherein a predetermined switch for applying to the resistance element connected to the second pattern is interlocked with a door. Safety circuit for microwave oven. 4. The safety circuit for a microwave oven according to claim 1, wherein the second pattern also introduces a potential to a door detection circuit that detects an open / closed state of the door, and energization control is performed. A safety circuit for a microwave oven, characterized in that a diode is interposed between the circuit and the connection with the door detection circuit.