Patent Publication Number: US-6664523-B1

Title: Microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source

Description:
TECHNICAL FIELD 
     The present invention relates to a microwave oven, and more particularly to a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source, which is capable of being prevented from holding the previous status of contacts in a microswitch caused by the large amounts of current which are remaining when usig direct current. 
     BACKGROUND ART 
     FIG. 1 shows a microwave oven for heating/cooking food using microwaves. The microwave oven contains a case  20  for forming a cooking chamber  22 , a door  21  for opening/closing the cooking chamber  22 , a tray  24  being installed in the cooking chamber  22 , and a panel  25  for controlling operations of the microwave oven. 
     FIG. 2 is a partial cutaway view of FIG. 1. A pair of latch hooks  28   a ,  28   b  are installed in the door  21 , and catch openings  27   a ,  27   b  are formed corresponding to each latch hook  28   a ,  28   b  at a front plate  26  of the case  20 . If the door  21  is pushed shut, the latch hooks  28   a ,  28   b  will engage the catch openings  27   a ,  27   b  to hold the door  21  shut. 
     At the back side of the panel  25  is provided a device chamber (not shown). In the device chamber are installed a magnetron for generating microwaves and a high voltage transformer HVT for generating a high voltage supplied to the magnetron, and so on. In supplying an AC power to the high voltage transformer HVT, this high voltage transformer HVT generates a predetermined high voltage to drive the magnetron. Then, the magnetron radiates microwaves of about 2,450 MHz frequency to heat/cook food. 
     As shown in FIG. 2, microswitches MS 1 , MS 2 , MS 3  are installed at the back side of the front plate  26  of the case  20 . FIGS. 3 a , and  3   b  are schematic diagrams and symbols of each microswitch MS 1 , MS 2 , MS 3 , respectively. The microswitches MS 1 , MS 2 , MS 3  have a slight interval at the contacts, and a mechanism of a snap action. The microswitches MS 1 , MS 2 , MS 3  have a contact mechanism to open/close by the determined operation and force in a sealing case, and is a small switch for arranging a pushing mechanism of the actuator switch located on the outside of the case. That is, the microswitch is one of the contact type detectors, which detects something contacted according to releasing the inside contacts when something  6  closes to a push button  1 , and begins to push the push button  1 , and applies more than a predetermined force F to the push button  1 . In FIG. 3, the reference numeral  2  is a movable spring, and the reference numeral  3  is a movable contact. The reference numeral  4  is a fixed contact b, and the reference numeral  5  is a fixed contact a. COM, NO, and NC are a common terminal, a normally open terminal, and a normally closed terminal, respectively. In FIG. 3 b , the contact a  7  is a point of contact which conducts first when the microswitch is operated, and which connects the common terminal COM into the normally open terminal NO. The contact b  7  is a point of contact which conducts when the microswitch is not operated, and which connects the common terminal COM into the normally close terminal NC. 
     The microswitches MS 1 , MS 2 , MS 3  have each operating button  31 ,  32 ,  33 , respectively. At the back side of the front plate  26  are installed a pair of movable members  29   a ,  29   b  to adjoin the catch openings  27   a ,  27   b . Then, the movable members  29   a ,  29   b  are fixed for pivoting by each pin  23   a ,  23   b , and are fixed elastically by each spring  41   a ,  41   b.    
     In FIG. 2, if the door  21  is pushed close, the microswitches MS 1 , MS 2 , MS 3  are operated by the latch hooks  28   a ,  28   b  which are inserted in the catch openings  27   a ,  27   b . That is, when the movable members  29   a ,  29   b  are pushed by each latch hook  28   a ,  28   b , the movable members  29   a ,  29   b  are rotated against the elasticity of the springs  41   a ,  41   b . Therefore, the operating button  31  is pushed by the upper movable members  29   a , and the operating buttons  32 ,  33  are pushed by the lower movable members  29   b , respectively. 
     Meanwhile, since the conventional microwave oven has been made to be operated using the AC common power source of 110V/220V for supplying high alternating current, we cannot use the microwave oven in a place where alternating current is not available. 
     To overcome the above described problem, an AC/DC type microwave oven has been developed, and has been comprised as shown in FIG.  4 . In FIG. 4, An AC/DC type microwave oven comprises an AC driving load  30 , a DC driving load and DC/AC converting part  40 , and a microwave oscillator  50 . The AC driving load  30  is driven by an AC input power. The DC driving load and DC/AC converting part  40  includes the DC driving load being driven by a DC input power, and the DC/AC converter converting the DC input power into an AC power. The microwave oscillator  50  is supplied by only one of the AC input power or the DC/AC power converted by a DC/AC converter, and generates microwaves. 
     The AC driving load  30  is driven by alternating current, which includes a lamp and a fan motor, etc., which are connected to the AC power source. A power switch (not shown) to determine the supplying status of AC is connected to the AC power source. The DC driving load being driven by direct current, which includes a lamp and a fan motor, etc., which are connected to the DC power source. A power switch (not shown) to determine the supplying status of DC is connected to the DC power source. The direct current forms a differentiated DC circuit net discriminated as an AC circuit net. Then, direct current is connected to the input side of the DC/AC converting part  40  which supplies alternating current. The microwave oscillating part  50  includes a high voltage transformer HVT which receives the AC power, a high voltage condenser HVC, a high voltage diode HVD, and a magnetron MGT. The operation of the microwave oscillating part  50  is described the same way as shown in FIG.  1 . 
     Therefore, according as the AC power source supplies alternating current to the AC driving load  30 , and the DC power source supplies direct current to the DC driving load and DC/AC converting part  40 , respectively, the conventional AC/DC type microwave oven is operated. 
     In the above-described AC/DC type microwave oven, the DC driving load and DC/AC converting part  40  is designed for the user to use the AC/DC type microwave oven out-of-doors, using the power source of an automobile battery. Generally, however, the common AC power source supplies small amounts of current within  15 A, but the battery of the automobile using DC supplies large amounts of current from 50A to 70A. 
     If the microwave oven is operated by using the automobile battery, the microswitches MS 1 , MS 2  have the possibility of a faulty operation. 
     That is, in case the large amounts of current is supplied through the microswitches MS 1 , MS 2 , the contact of the microswitches MS 1 , MS 2  can remain in there contacting status. When the user pulls the door  21  so that the cooking chamber is open, the operating buttons  31 ,  32  of the microswitches MS 1 , MS 2  can remain in their depressed status. According as the primary switch PD and secondary switch SD of the DC driving load and DC/AC converting part  40  are held in their closed status, and then current is supplied to the DC driving load and DC/AC converting part  40 , so the AC/DC type microwave oven has the problem of encountering a malfunction. 
     DISCLOSURE OF INVENTION 
     The present invention has been made to overcome the problems with microwave ovens described in the foregoing paragraphs, and accordingly it is the first objective of the present invention to provide a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source. 
     It is the second objective of the present invention to provide a microwave oven for heating/cooking food safely by preventing overcurrent of a microswitch for controlling a DC power source. 
     To achieve the above objectives, the present invention provides a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source. In a microwave oven having a case forming a cooking chamber, a door for opening/closing the chamber, a high voltage transformer for generating a high voltage, and a magnetron for generating microwaves driven by the high voltage being outputted from the high voltage transformer, a microwave oven comprising: means for detecting opening/closing of the door; means for controlling for outputting a driving signal corresponding to the detected result; and means for opening/closing for controlling a power source supplied to the high voltage transformer according to receiving the driving signal. 
     The means for detecting is a microswitch which is a detector for detecting the openinig/closing of the door. 
     The means for opening/closing is an electromagnetic relay for controlling an opening/closing of an input power source to open/close a contact according to the driving signal, wherein the relay is an electromagnetic relay for controlling a supply of large amounts of current from 50A to 70A. 
     To achieve the above objectives, the present invention provides an interlock device of a microwave oven. In a microwave oven having a case forming a cooking chamber, a door for opening/closing the chamber, a high voltage transformer for generating a high voltage, and a magnetron for generating microwaves driven by the high voltage being outputted from the high voltage transformer, an interlocking device of a microwave oven comprising: microswitches for detecting opening/closing of the door; microcomputer for outputting a driving signal corresponding to the detected result; and a relay for opening/closing for controlling a power source supplied to the high voltage transformer according to receiving the driving signal. 
     The relay is an electromagnetic relay for controlling a supply of large amounts of current from 50A to 70A. 
     To achieve the above objectives, the present invention provides a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source. In a microwave oven using microwaves, the microwave oven comprising: a DC circuit part for converting direct current supplied by a DC input power source into alternating current, and for supplying the converted alternating current; an opening/closing means for connecting between the DC input power source and the DC circuit part; a current dividing means being connected to the means for opening/closing, and for dividing a part of current supplied by the means for opening/closing when the means for opening/closing is switched on; and a microwave oscillating means for being driven by an output voltage of the high voltage transformer, and for generating microwaves. 
     The current dividing means is a relay connected to the opening/closing means in parallel. The present invention further comprises resistors for being connected to the opening/closing means and/or the relay current dividing means in series, respectively, and for regulating each rate of current through the opening/closing means and the relay, respectively. 
     To achieve the above objectives, the present invention provides a device for preventing overcurrent of a microswitch comprising: a microswitch for opening/closing the connection between DC input power source and a DC circuit part being supplied direct current; and a current dividing means being connected to the microswitch in parallel, and for dividing a part of current through the microswitch when the microswitch is switched on. 
     According to the present invention, a microwave oven is capable of preventing overcurrent of a microswitch by using a relay, and so on. A microwave oven can be heating/cooking food safely according to being prevented from a holding of the previous status of contacts in a microswitch by preventing overcurrent of a microswitch for controlling a DC power source. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objective and other advantages of the present invention will become more apparent by being described in detail in a preferred embodiment thereof with reference to the attached drawings, in which: 
     FIG. 1 is a cutaway view of a conventional microwave oven; 
     FIG. 2 is a partial cutaway view of FIG. 1 for explaining a microswitch and the operation of the opening/closing of the conventional microwave oven; 
     FIGS. 3 a  and  3   b  are a schematic diagram and symbols of the microswitch, respectively; 
     FIG. 4 is a block diagram of an AC/DC type microwave oven developed herein; 
     FIG. 5 is a block diagram of a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source according to the first embodiment of the present invention; 
     FIG. 6 is a block diagram of a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source according to the second embodiment of the present invention; 
     FIGS. 7 a  and  7   b  are a block diagram and symbols of relays of FIGS. 5 and 6, respectively; 
     FIG. 8 is a schematic diagram of a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source according to the first embodiment of the present invention; and 
     FIG. 9 is a schematic diagram of a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source according to the second embodiment of the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The present invention will become more apparent by describing in detail in a preferred embodiment thereof with reference to the attached drawings. If the parts of the present invention are the same as a conventional microwave oven as shown on FIGS. 1 and 3, the illustration can be abbreviated, and can be cited using the same reference numerals. 
     FIG. 5 is a block diagram of a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source according to the first embodiment of the present invention. In a microwave oven having a case forming a cooking chamber, a door for opening/closing the chamber, a high voltage transformer for generating a high voltage, and a magnetron for generating microwaves driven by the high voltage being outputted from the high voltage transformer, this microwave oven according to the first embodiment comprising: microswitches  100 ,  110  for detecting the opening/closing of the door; microcomputer  150  for controlling being outputted a driving signal corresponding to the detected result; and a relay  220  for opening/closing for controlling a power source supplied to the high voltage transformer according to receiving the driving signal; a DC/AC converter  300  for converting direct current supplied by a DC input power source into alternating current, and for supplying to the high voltage transformer; and a microwave oscillator  400  being driven by an output voltage of the high voltage transformer, and for generating microwaves. The relay  220  is an electrical relay which is opening/closing a supply of input power by opening/closing contacts according to the driving signal, and opens/closes a supply of large amounts of current from 50A to 70A. 
     FIG. 8 is a schematic diagram of a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source according to the first embodiment of the present invention. This microwave oven according to the first embodiment comprises an AC circuit part  500 , a DC circuit part  600 , and a microwave oscillating part  400 . The AC circuit part  500  supplies a high voltage transformer  410  with alternating current by an AC input power source, and the DC circuit part  600  supplies to the high voltage transformer  410  which converts alternating current after converting direct current supplied by a DC input power source into alternating current, and the microwave oscillating part  400  generates microwaves by means of the output voltage of the high voltage transformer  410 . The DC circuit part  600  uses relays  221 ,  222  for opening/closing a DC input power source. The opening/closing of the door is detected by microswitches  100 ,  110 , microcomputer produces the driving signal to the relays  221 ,  222  corresponding to the detected result, so the relays  221 ,  222  can open/close the DC input power source. 
     The microwave oven contains microswitches MS 1 , MS 2 , MS 3  for controlling operations of each first switches PA, PD, each second switches SA, SD, and each monitor switches MA, MD. Substantially, the first microswitch MS 1  operates along with the first switches PA, PD, the second microswitch MS 2  operates along with the second switches SA, SD, and the third microswitch MS 3  operates along with the monitor switches MA, MD, respectively. 
     The high voltage transformer  410  contains many coils  411 ,  412 ,  413 ,  414 , and is driven by the AC circuit part  500  or the DC circuit part  600  to generate a high voltage of about 2,000V. 
     The AC circuit part  500  contains the first lamp L 1 , the first fan motor FM 1 , and the first and second switches PA, SA and the monitor switch MA for controlling an AC power. 
     If the first and second switches PA, SA are switched on and the monitor switch MA is switched off, the first lamp L 1  and the first fan motor FM 1  are driven, and the AC input power source supplies alternating current to the high voltage transformer  410  simultaneously. Then, the high voltage transformer  410  generates a high voltage, and a magnetron MGT generates microwaves by means of the high voltage. 
     The DC circuit part  600  contains the second lamp L 2 , the second fan motor FM 2 , a DC/AC converter  300  for converting direct current supplied by DC input power source into alternating current, and the relays  221 ,  222  along with a monitor switch MD for controlling a DC power. 
     The DC/AC converter  300  contains a commutator  330 , a commutator motor M for rotating the commutator  330 , and two pairs of brushes  321 ,  322 ,  323 ,  324  being contacted to the outer circle of the commutator  330 . Two pairs of brushes  321 ,  322 ,  323 ,  324  consist of one of input brushes  321 ,  323  being connected to direct current, and one of output brushes  322 ,  324  being connected to the high voltage transformer  410 . The pair of input brushes  321 ,  323  is contacted to the outer circle of the commutator  330 , and supplies direct current to the commutator  330 . The pair of output brushes  322 ,  324  is contacted to the outer circle of the commutator  330  and converts direct current supplied by the input brushes  321 ,  323  into alternating current, when the commutator  330  is rotated. 
     As shown in FIG. 2, microswitches MS 1 , MS 2 , MS 3  are installed at the back side of the front plate  26  of the case  20 . The microswitches MS 1 , MS 2 , MS 3  have each operating button  31 ,  32 ,  33 , respectively. At the back side of the front plate  26  is installed a pair of movable members  29   a ,  29   b  to adjoin the catch openings  27   a ,  27   b . Then, the movable members  29   a ,  29   b  are fixed for pivoting by each pin  23   a ,  23   b , and are fixed elastically by each spring  41   a ,  41   b.    
     If the door  21  is pushed close, the microswitches MS 1 , MS 2 , MS 3  are operated by the latch hooks  28   a ,  28   b  which are inserted in the catch openings  27   a ,  27   b . That is, when the movable members  29   a ,  29   b  are pushed by each latch hook  28   a ,  28   b , the movable members  29   a ,  29   b  are rotated against the elasticity of the springs  41   a ,  41   b . Therefore, the operating button  31  is pushed by the upper movable member  29   a , and the operating buttons  32 ,  33  are pushed by the lower movable member  29   b , respectively. 
     Therefore, when the AC power source supplies alternating current to the AC circuit part  500 , and the DC power source supplies direct current to the DC circuit part  600 , respectively, the AC/DC type microwave oven is operated. 
     In the microwave oven according to the first embodiment of the present invention, the microswitches  100 ,  110  detect the opening/closing of the door, microcomputer  150  produces the driving signals to the relays  221 ,  222  corresponding to the detected results, and the relays  221 ,  222  are to open/close the supply of the DC input power source. When the microwave oven is supplied with large amounts of current from 50A to 70A, the microwave oven does not use the microswitches  100 ,  110  directly to control the supply of the DC input power source, but use the relays  221 ,  222  capable of not generating the holding of the previous status of contacts, instead of the microswitches  100 ,  110 . Therefore, the microwave can be used more safely. 
     FIG. 6 is a block diagram of a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source according to the second embodiment of the present invention. This microwave oven comprising: a DC/AC converter  300  for converting direct current supplied by a DC input power source into alternating current, and for supplying the converted alternating current to the high voltage transformer; microswitches  100 ,  110  for openinig/closing a connection between the DC input power source and the DC/AC converter  300 ; current dividers  200 ,  210  being connected to the microswitches  100 ,  110  in parallel, and for dividing a part of current supplied by the microswitches  100 ,  110  when the microswitches  100 ,  110  are switched on; and a microwave oscillator  400  for being driven by an output voltage of the high voltage transformer, and for generating microwaves. The microswitches  100 ,  110  are operated by the door for opening/closing the cooking chamber. The current dividers  200 ,  210  include relays being connected to the microswitches  100 ,  110  in parallel, and include resistors being connected to the microswitches  100 ,  110  and/or the relays  200 ,  210  in series. The resistors can regulate rates of current through the microswitches  100 ,  110  and the relays  200 ,  210 . When overcurrent is supplied to the microswitches  100 ,  110 , the microwave oven is capable of being prevented from the holding of the previous status of contacts accordingly as a part of overcurrent is consumed by operations of the relays  200 ,  210 . 
     FIGS. 7 a  and  7   b  are a block diagram and symbols of relays of FIGS. 5 and 6, respectively. The relay called an electromagnetic relay has a hinge-type relay and a plunger-type relay, etc. Because the characteristic of isolation of the plunger-type relay is excellent, and the capability of contact is large, the plunger-type relay is used as an electromagnetic contactor, an electromagnetic switch, and an auxiliary relay of power type, etc. In the plunger type relay, a moving-iron is moving linearly in an electromagnetic coil according to being excited or being degaussed by the electromagnetic coil, and a mechanism of contact being connected to the moving-iron is opened/closed by using the movement of the moving-iron. The exciting represents flowing current, while the degaussing represents not flowing current. The reference numeral  9  is a coil, the reference numeral  10  is an independent contact, the reference numeral  11  is a normally open terminal, and the reference numeral  12  is a normally closed terminal. When current flows through the coil  9 , the coil part becomes an electromagnet to pull the independent contact  10 , and the independent contact  10  is connected to the normally open terminal  11  instead of the normally closed terminal  12 . Then, current is used for magnetizing the coil  9 . As shown in FIG. 7 b , contact a  13  means the status of connecting the independent contact  10  to the normally open terminal  11  when current flows through the coil  9 . Contact b  13  means the status of connecting the independent contact  10  to the normally closed terminal  12  when current is not flowing through the coil  9 . 
     FIG. 9 is a schematic diagram of a microwave oven capable of preventing overcurrent of a microswitch for controlling a DC power source according to die second embodiment of the present invention. This microwave oven according to the second embodiment comprises an AC circuit part  500 , a DC circuit part  600 , and a microwave oscillating part  400 . The AC circuit part  500  supplies a high voltage transformer  410  with alternating current by an AC input power source, and the DC circuit part  600  supplies to the high voltage transformer  410  which converts alternating current after converting direct current supplied by a DC input power source into alternating current, and the microwave oscillating part  400  generates microwaves by means of the outputting voltage of the high voltage transformer  410 . The operation of the AC circuit part  500  and the microwave oscillating part  400  are the same as above-described in the first embodiment. The opening/closing of the DC input power source in the DC circuit part  600  is accomplished by means of the microswitches  100 ,  110 . Therefore, this microwave oven can prevent the holding of the previous status of large amounts of current in the microswitches  100 ,  110  by using differentiated current dividers  201 ,  211 . The microwave oven according to the second embodiment contains the first relay  201 , and the second relay  211  being connected to the microswitches  100 ,  110  in parallel. The relays  201 ,  211  are turned on when the microswitches  100 ,  110  are turned on, respectively. Accordingly, at least a part of current through the microswitches  100 ,  110  is flowing through the relays  201 ,  211 . 
     Since direct current being supplied by the DC input power source is divided by the microswitches  100 ,  110  and the relays  201 ,  211 , the amounts of current through the microswitches  100 ,  110  can be reduced. Accordingly, the holding of the previous status of contacts in the microswitches  100 ,  110  is capable of being prevented, and the operations of the microswitches  100 ,  110  are accomplished safely. 
     The second embodiment according to the present invention, however, uses the relays  201 ,  211  which are the means for dividing a part of current through the microswitches  100 ,  110 , and uses a device of a non-contact switch, etc. 
     This microwave oven can heat/cook food by using both the DC input power source and the AC input power source. Then, this microwave oven contains a differentiated selecting switch (not shown) to operate selectively the DC circuit part  600  or the AC circuit  500 . 
     Meanwhile, each resistor  102 ,  112 ,  202 ,  212  is connected to the relays  201 ,  211  and the switches PD, SD in series. This resistors  102 ,  112 ,  202 ,  212  are used for current-limiting. As each resistor  102 ,  112 ,  202 ,  212  is controlled adequately, the rates of current through the microswitches  100 ,  110  and the relays  201 ,  211  are capable of being regulated. When the rates of current are regulated by using the resistors  102 ,  112 ,  202 ,  212 , the microswitches  100 ,  110  are capable of being prevented easily from the holding of the previous status of contacts. 
     In the second embodiment, however, according to present invention, this microwave oven adapts the relays  201 ,  211  for preserving the first and second microswitches MS 1 , MS 2 , and adapts an additional relay for preserving the third microswitch MS 3  as shown in FIG.  2 . 
     As above-described, this microwave oven according to the present invention is capable of preventing from the holding of the previous status of contacts in the microswitches by being prevented the overcurrent of the microswitches. Accordingly, this microwave oven is capable of being prevented from faulty operations of the microswitches, and the heating/cooking of the microwave oven is accomplished safely. 
     While the present invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be affected therein without departing from the spirit and scope of the invention as defined by the appended claims.