JPH02257589A - Rush current preventer circuit for microwave oven - Google Patents

Abstract

PURPOSE:To maintain the operational safety of a device even if to actuation of a relay occurs and also to miniaturize the device by turning on the single- throw contact of a switching means for exciting the relay and inserting a heater in the primary winding of a high-tension transformer via the double-throw contact of the switching means until this relay contact is turned on. CONSTITUTION:When a heating mode is set for microwave heating, then a single-throw contact 11 is turned on, while a double-throw contact 12 is connected on one side indicated at the second letter of the Japanese alphabet or KATAKANA. Although in this condition turning on a starting switch 2 causes a relay 5 to be excited, a time of a few milliseconds is required until a contact 5a in the relay is turned on. Curing this time, a heater 4 is allowed to be inserted in the primary winding 71 of a high-tension transformer 7 in series to the winding, whereby a rush current may be reduced to its low level. After that, when the normally off contact 5a in the relay 5 is turned on, the heater 4 is set in its short-circuited condition, and therefore supply voltage in its entirety is fed to the primary winding 71 of the high-tension transformer 7, whereby a magnetron can be oscillated.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention provides a microwave generator driven by a voltage obtained by boosting an AC power supply voltage using a high-voltage transformer, and a heater driven by the AC power supply voltage. Both of these relate to an inrush current prevention circuit for a microwave oven that selects one or both at any time.

(Prior Art) FIG. 3 shows this type of conventional inrush current prevention circuit. In the figure, the common terminal ■ of the changeover switch 3 is connected to one AC power supply terminal to which the AC power supply 1 is connected via the start switch 2, and the normally open side terminal ◎ of this changeover switch 3 and the other AC A heater 4 is connected between the power supply terminal and the power supply terminal. Further, a relay 5 is connected between the normally closed terminal of the changeover switch 3 and the other AC power supply terminal. Furthermore, one end of a parallel connection circuit consisting of a normally open contact (hereinafter simply referred to as a contact) 5a of a relay 5 and a resistor 6 is connected to the normally closed terminal Φ of the changeover switch 3, and the other end of this parallel connection circuit is connected to the normally closed terminal Φ of the changeover switch 3. The end thereof is connected to the live side of the primary winding 71 of the high voltage transformer 7 . The neutral side of this secondary winding 71 is connected to the other AC power supply terminal. On the other hand, a magnetron drive circuit 8 is connected to the secondary winding 72 and the auxiliary winding 73 of the high voltage transformer 7, and this magnetron drive circuit 8 causes a magnetron (not shown) to oscillate. Note that the iron core 74 of the high voltage transformer 7 is the secondary winding 7
It is grounded together with the live side of 2.

Here, if the microwave oven is set to microwave heating, the changeover switch 3 is held in the state shown in the figure, and when the start switch 2 is turned on in this state, the relay 5 is energized. This energization of the relay 5 turns the contact 5a into an on state (hereinafter referred to as "on"), and the AC power supply voltage is supplied to the primary winding 71 of the high voltage transformer 7. As a result, the magnetron drive circuit 8 causes a magnetron (not shown) to oscillate.

By the way, when the AC power supply voltage is applied to the relay 5 by turning on the start switch 2, the contact 5a turns on with a delay of an operating time (several milliseconds), but during this time, the primary winding of the high voltage transformer 7 A resistor 6 is inserted into the wire 71. Therefore, by using the relay 5 whose operating time of the contact 5a is approximately equal to the width of the inrush current waveform, inrush current can be prevented.

(Problems to be Solved by the Invention) The conventional inrush current prevention circuit described above uses a resistor 6 that is designed to allow current to flow only for a short period of time. Therefore, when the contact 5a does not turn off even if the start switch 2 is turned on and voltage is supplied to the relay 5, that is, when the relay 5 becomes inactive, current continues to flow through the resistor 6, causing it to burn out. , there was a problem that it could cause a fire.

Furthermore, even if it is assumed that the resistor 6 will only allow current to flow for a short period of time, it must be at least about 20 W, and there is a problem in that the device becomes larger accordingly.

This invention was made in order to solve the above-mentioned problems, and its purpose is to provide an inrush current prevention circuit for a microwave oven that is safe even if the relay does not operate, and that allows the device to be miniaturized. shall be.

[Purpose of the invention]

(Means for Solving the Problem) The present invention has a bipolar switching means having a single-throw contact and a double-throw contact that can change the on/off relationship depending on the heating mode, and a normally open contact. a relay, the single throw contact of the switching means and the relay are connected in series between the AC power supply terminals, the normally open contact of the relay and the primary winding of the high voltage transformer are connected in series to the AC power supply terminal, and the One end of the heater is connected to the AC power supply side of the normally open contact of the relay, and the other end of the heater is switched and connected to the live side and neutral side of the primary winding of the high voltage transformer by the double throw contact of the switching means. It is characterized by

(Function) In this invention, the single-throw contact of the switching means is turned on to excite the relay, and the relay is energized until the contact of this relay is turned on.
Since the heater is inserted into the primary winding of the high-voltage transformer through the double-throw contact of the switching means, in addition to the heater provided as a function of the microwave oven, the resistor used only to prevent rush current is no longer required. Since the heater originally has a large capacity, there is no risk of burnout even if current continues to flow through the heater for a long time due to non-operation of the relay, etc.

As a result, it is safe even if the relay does not operate, and
An inrush current prevention circuit for a microwave oven that enables miniaturization of the device is obtained.

(Embodiment) FIG. 1 is a circuit diagram showing an embodiment of the present invention, and in the figure, the same elements as in FIG. 3 are given the same reference numerals, and the explanation thereof will be omitted. Here, instead of the changeover switch 3, a single-throw contact 11 is used, which can change the on/off relationship depending on the heating mode and have different operating times.
A double-pole changeover switch 10 having a double-throw contact 12 and a double-throw contact 12
is used. In this case, the relay 5 and the single-throw contact 11 are connected in series between the AC power supply terminals via the start switch 2. Further, the contact 5a of the relay 5 and the primary winding 71 of the high voltage transformer 7 are similarly connected in series between the AC power supply terminals via the start switch 2. Further, one end of the heater 4 is connected to the AC power supply side of the contact 5a, and the common side terminal (■) of the double-throw contact 12 is connected to the other end of this heater, and one switching terminal of the double-throw contact 12 is connected to the other end of the heater 4. The switch terminal ◎ is connected to the neutral side of the primary winding 71 of the high voltage transformer 7, and the other switching terminal ◎ is connected to the neutral side of the primary winding 71 of the high voltage transformer 7.
Each is connected to the live side of 1.

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

First, when the heating mode is set to microwave heating, the single-throw contact 11 is turned on, and the double-throw contact 12 is connected to the O side. When the start switch 2 is turned on in this state, the relay 5 is excited, but it takes several m5ec for the contact 5a to turn on. During this time, the heater 4 is inserted in series with the primary winding 71 of the high voltage transformer 7, thereby suppressing the rush current to a low level. After that, if the normally open contact 5a of the relay 5 is turned on, the heater 4
becomes a short-circuited state, and the power supply voltage is directly supplied to the primary winding 71 of the high-voltage transformer 7, thereby making it possible to cause the magnetron to oscillate.

Next, if the heating mode is set to heater heating,
The single-throw contact 11 remains in the off state, and the double-throw contact 12 is switched to the Φ side. If the start switch 2 is turned on in this state, power supply voltage is supplied to the heater 4, but since the single-throw contact 11 is turned off, the relay 5 remains de-energized.

Therefore, heating is performed only by the heater 4.

Next, if the heating mode is set to simultaneous heating with the heater and microwave, that is, combination heating, the selector switch 10 will turn on the double-throw contact 12 after the single-throw contact 11 is turned on. It is designed to switch from the side to the Φ side. As a result, the heater 4 is energized after the inrush current caused by the high voltage transformer 7 is suppressed, thereby enabling combination heating.

Thus, according to this embodiment, the single-throw contact 11 of the changeover switch 10 is turned on to energize the relay 5, and the primary voltage of the high-voltage transformer 7 is activated via the double-throw contact 12 until the relay 5a is turned on. Since the heater is inserted into the winding 71,
In addition to eliminating the need for resistors other than the heater 4, which is a function of the microwave oven, the heater 4 already has a large capacity, so even if current continues to flow through the heater for a long time due to a relay not working, etc. No more worries about burnout.

FIG. 2 is a circuit diagram showing the configuration of another embodiment of the present invention, in which the same reference numerals as in FIG. 1 indicate the same elements. In place of the changeover switch 10 in FIG. 1, a switch 13 having single-throw contacts 14 and 15 and a relay 16 having a change-over contact 16a are used. The series circuit of the single-throw contact 15 and the relay 16 is connected to the AC power terminal via the start switch 2, and the other end of the heater 4 is connected to the primary winding of the high voltage transformer 7 by the switching contact 16a. It is configured to be switched between the live side and the neutral side of the line 71.

In this embodiment, the single-throw contact 14 is turned on and the single-throw contact 15 is turned off during microwave heating, and the single-throw contact 14 is turned off and the single-throw contact 15 is turned on during heater heating. On the other hand, during combination heating, single-throw contacts 14 and 15 are turned on at the same time, but relay 16 has a longer operating time than relay 5, and contact 5a
The switching contact 16a changes from the ◎ side to the ■
It is configured to switch to the side. As a result, after the inrush current caused by the high voltage transformer 7 is suppressed by the heater 4, the AC power supply voltage is supplied to the primary winding of the high voltage transformer 7 and the heater 4, thereby causing the same combination heating as described above. In each of the above embodiments, the circuit configuration is based on combination heating, but if combination heating is not performed, the operating time of the single-throw contact 11 and the double-throw contact 12 may be different, or There is no need for relays 5 and 16 to have different operating times; they are simply bipolar switching devices with single-throw and double-throw contacts that can turn on and off to each other depending on the heating mode. All you need is the means.

【Effect of the invention〕

As is clear from the above explanation, according to this invention,
A heater is inserted into the primary winding of the high voltage transformer from the time the relay is energized until the contact of this relay turns on.
゛In addition to eliminating the need for resistors other than the heater, which is a function of the microwave oven, the heater has a large capacity to begin with, so even if current continues to flow through the heater for a long time due to relay inoperation, it will not burn out. You don't have to worry about it anymore. As a result, it is possible to obtain an inrush current prevention circuit for a microwave oven that is safe even if the relay does not operate, and also allows for miniaturization of the device.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a circuit diagram showing the configuration of another embodiment, and FIG. 3 is a conventional inrush current prevention circuit for a microwave oven. 2...Start switch, 4...Heater, 5.16
... Relay, 5a... Normally open contact, 7... High voltage transformer, 8... Magnetron drive circuit, 10... Changeover switch, 11.14.15... Single throw contact, 12...
・Double throw contact, 13...switch, 16a...switching contact.

Claims (1)

[Claims] In a microwave oven in which one or both of a microwave generator driven by a voltage boosted from an AC power supply voltage by a high-voltage transformer and a heater driven by an AC power supply voltage are selected at any time, each can be turned on or off depending on the heating mode. comprising a bipolar switching means having a single-throw contact and a double-throw contact that can change the relationship between At the same time, the normally open contact of the relay and the primary winding of the high voltage transformer are connected in series to the AC power supply terminal, one end of the heater is connected to the AC power supply side of the normally open contact of the relay, and the heater An inrush current prevention circuit for a microwave oven, wherein the other end is selectively connected to a live side and a neutral side of a primary winding of the high voltage transformer by a double throw contact of the switching means.