JPH031480A - Microwave oven - Google Patents

Abstract

PURPOSE:To prevent spread of fire by forming a narrow conductive pattern for checking disconnected by firing of the circuit board in such an arrangement as to surround a pattern for flowing of the main circuit current, and shutting OFF the power when this checking pattern is disconnected. CONSTITUTION:Because a high voltage is impressed on tab terminals 5a, 5c, 5d, 5e of a noise filter 4 to generate flowing of a large current, crack initiation will cause discharging and firing, and a printed circuit board 11 will burn. A pattern 14 for checking is formed so as to surround the charging part patterns 13a, 13d to which tab terminals are soldered, and thereby burn of the circuit board 11 will disconnect the patterns. Now the potential of a lead 12 relative to an electronic control circuit 29 is varied from 0V to VDD. This circuit 29 senses it and actuates a relay 3, and also opens the power supply circuit for the filter 4. When current feed to this filter 4 is stopped, discharge in the crack part is stopped and also spread of fire is prevented.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a microwave oven in which electric circuit elements such as coils and relays provided in the front stage of a high-frequency heating circuit are mounted on a printed circuit board. It is.

(Prior Art) A microwave oven that drives a magnetron by obtaining power from a commercial power supply is equipped with a noise filter to prevent noise from being superimposed on the power supply system. This noise filter includes a capacitor, an actuator, etc., and these electric circuit elements are mounted on a printed circuit board, and Faston terminals are press-fitted into each tab terminal on the input/output side.

(Problem to be solved by the invention) It is common for the wiring pattern of a printed circuit board to change its width depending on the current value.The wiring pattern for carrying a large current is wide, and on the other hand, the wiring pattern for passing only a weak current is wide. is formed narrowly. The noise filter is provided with a wide wiring pattern for passing the current of the high frequency heating circuit, that is, the main circuit current. Tab terminals, relay contacts, etc. are soldered to the wiring pattern that carries the main circuit current, the so-called live part pattern. Cracks may occur. For this reason, a layer short circuit occurs during actual heating, and there is a risk that the printed circuit board will catch fire and spread.

This problem is not limited to noise filters, but is a common problem in microwave ovens in which electric circuit elements such as coils and relays are mounted on a printed circuit board before a high-frequency heating circuit.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a microwave oven that can prevent the enlargement of the burnt area of a printed circuit board and the spread of fire to other parts.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a microwave oven in which electric circuit elements such as coils and relays provided upstream of a high-frequency heating circuit are mounted on a printed circuit board, in which the main wiring pattern of the printed circuit board is It is characterized by comprising a check conductive pattern that is formed to surround a pattern through which a circuit current flows and is disconnected when the circuit board ignites, and a disconnection means that detects disconnection of the check conductive pattern and cuts off the power supply. It is something.

(Function) In this invention, a narrow check conductive pattern that is cut off when the board ignites is formed so as to surround the pattern through which the main circuit current flows, and when the check conductive pattern is cut off, the power supply is cut off. Even if a live part ignites, it is possible to prevent the burned area from expanding and the fire from spreading to other areas.

(Embodiment) FIG. 1 is a circuit diagram showing the overall configuration of an embodiment of the present invention. In the figure, a power plug 1 connected to a commercial power source includes a fuse 2 and a relay 3 as a disconnecting means.
via one tab terminal 5a, 5 of the noise filter 4.
c is connected.

A tab terminal 5b provided side by side with these tab terminals 5a and 5c is grounded. Further, the other tab terminals 5d and 5e of the noise filter 4 are connected to the thermal relay 16. It is connected to a high frequency heating circuit 24 via a door switch 17 and a relay 23.

Further, a short switch 18 is connected between the line connecting the door switch 17 and the relay 23, and a parallel connection circuit of the interior light 19, RT motor 20, and fan motor 21 and the relay 22 are connected in series. There is. here,
The high-frequency heating circuit 24 includes a high-voltage transformer 25, a high-voltage capacitor 26, a high-voltage rectifier 27, and a magnetron 28. A narrow check pattern 14 is formed around the charged part of the noise filter 4, and is cut off when the board ignites. One end of this check pattern 14 is grounded, and the other end is connected to the electronic control circuit 29.
It is connected to the. This electronic control circuit 29 obtains electric power from the front stage of the door switch 17 and controls the excitation of the relays 22 and 23 using an operation switch (not shown). De-energize.

FIG. 2 is a circuit diagram showing details of the noise filter 4.

Here, the tab terminals 5a and 5c are each connected to one end of the mutual induction winding of the reactor 10 via the jumper wire 6, and the other end of the mutual induction winding of the reactor 10 is connected to the jumper wire 6. via the tab terminal 5d,
5e. Further, a resistor 7, a series connection circuit of a capacitor 8, and a capacitor 9 are connected in parallel to one end of the mutual induction winding of the reactor 10, and a tab terminal 5b is connected to the mutual junction point of the capacitor 8. There is.

FIG. 3(a) is a side view of the noise filter 4 in which these components are mounted on a printed circuit board 11, and FIG. 3(b) is a pattern layout diagram of this printed circuit board 11. In FIG. 3, a pair of charging portion patterns 13a and 13d are formed at one end and the other end of a printed circuit board 11, respectively.
b and 13c are each formed in pairs.

Further, the ground pattern 15 is formed between the charging portion patterns 138. Among these, the tab terminals 5a, 5c, and jumper wire 6 are connected to the charging part pattern 13a, and the resistor 7, capacitor 8.9, and reactor 10 are connected to the charging part pattern 13b.
are soldered to each other. In addition, charging part pattern 13
A reactor 10 and a jumper wire 6 are soldered to c, a jumper wire 6 and tab terminals 5d and 5e are soldered to a live part turn 13d, and a capacitor 8 is soldered to a ground pattern 15.

On the other hand, among the live part patterns 138 to 13d, the live part pattern 13 is particularly prone to cracks in soldering parts.
A check pattern 14 that looks like a cursor is formed so as to surround a and 13d, and a lead wire 12 is soldered to the end of the check pattern 14.

The operation of this embodiment configured as described above will be explained below.

The relay 3 has a normally closed contact, and a commercial power supply voltage is supplied to the electronic control circuit 29 via the noise filter 4.

If the door is closed, the door switch 17 is turned on and the short switch 18 is turned off.

Here, when a switch on the front panel (not shown) is operated, the electronic control circuit 29 activates the relay 22. 23 is excited.

Therefore, operating power is supplied to the high-frequency heating circuit 24, the interior illusion 19 lights up, the RT motor 20 rotates the table, and the fan motor 21 is driven to perform cooking.

When the specified cooking is completed, the electronic control circuit 29
de-energizes relays 22, 23 and opens the door, door switch 17. is turned off, and the short switch 18 is turned on. In this case, the noise filter 4 effectively removes high frequency noise generated from the high frequency heating circuit 24 during cooking.

Incidentally, when manufacturing and assembling this microwave oven, there are a total of 27 half-mounted portions of each component mounted on the printed circuit board 11, as shown in FIG. After fixing the noise filter 4, the next step is to connect the tab terminal 5a.
, 5c, 5d, and 5e to connect circuits by press-fitting Faston terminals, etc., if too much force is applied, cracks may occur in the soldered parts. In addition, soldering parts are heated and cooled during daily use, and at this time, the thermal expansion coefficient of the metal tab terminals 5a to 5d and the printed circuit board 11, which is made of a paper finol resin laminate. Differences in soldering may cause cracks and scratches in the soldered parts.

As is well known, the tab terminals 5a, 5 of this noise filter 4
Since a high voltage is applied to terminals c, 5d, and 5e, and a large current flows through them, if a crack occurs in the soldered portion, the continuation of the discharge causes ignition, and the printed circuit board 11 burns out.

In this case, since the check pattern 4 is formed to surround the live part patterns 13a and 13d to which the tab terminals 5a, 5c, 5d, and 5e are soldered, the printed circuit board 1
When the check pattern 14 is burnt out, the check pattern 14 is cut off. As a result, the lead wire 12 to the electronic control circuit 29
The potential changes from OV (ground potential) before disconnection to DC power supply voltage VDD. The electronic control circuit 29 detects this and excites the relay 3, and also causes the relay 3 to hold itself and opens the power supply circuit of the noise filter 4.

In this way, when the power supply to the noise filter 4 is stopped, the discharge at the cracked portion is also stopped, and the spread of fire is also prevented.

In the above embodiment, the check pattern 14 surrounds the charging part patterns 13a and 13d, but if other charging part patterns are also surrounded at the same time, the effect can be further improved.

Furthermore, although the above embodiment describes the substrate of the noise filter, the present invention is not limited to this.
It goes without saying that the present invention can also be applied to a microwave oven in which electric circuit elements such as coils and relays are mounted on a printed circuit board before a high-frequency heating circuit.

〔Effect of the invention〕

As is clear from the above explanation, according to this invention,
A narrow check conductive pattern that is disconnected when the board ignites is formed so as to surround the pattern through which the main circuit current flows, and the disconnecting means cuts off the power when the check conductive pattern is disconnected. Even if a fire ignites due to electrical discharge, soldering can prevent the burned area from expanding and the fire from spreading to other areas.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the overall configuration of an embodiment of the present invention, Fig. 2 is a circuit diagram showing details of a noise filter constituting the embodiment, and Fig. 3(a) shows its components. A side view of the device mounted on the printed circuit board, FIG. 3(b), is a pattern layout diagram of this printed circuit board. 3...Relay, 4...Noise filter, 5a to 5e
...Tab terminal, 9...Capacitor, 10...Reactor, 11...Printed circuit board, 13a-13d...
・Charge part pattern, 14... Check pattern, 2
4... High frequency heating circuit, 29... Electronic control circuit.

Claims (1)

[Claims] In a microwave oven in which electric circuit elements such as coils and relays provided upstream of a high-frequency heating circuit are mounted on a printed circuit board, among the wiring patterns of the printed circuit board, the circuit elements are formed so as to surround the pattern through which the main circuit current flows. 1. A microwave oven comprising: a check conductive pattern that is disconnected when the check conductive pattern is ignited; and a disconnection means that detects disconnection of the check conductive pattern and shuts off the power supply.