Note: Descriptions are shown in the official language in which they were submitted.
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TURNTABLE MOTOR DRIVING CIRCUIT FOR A DIRECT CURRENT
MICROWAVE OVEN
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a turntable motor
driving circuit for a direct current microwave oven, and
more particularly to an improved turntable motor driving
circuit for a direct current(DC) microwave oven which can
1o use a general alternating current(AC) motor as a turntable
driving motor.
2. Description of the Related Art
As publicly known, a microwave oven generates
microwave of about 2,450MHz per second by utilizing a
magnetron in order to heat/cook food. Frictional heat is
generated by changing a molecule alignment direction of the
food to be cooked hundreds of thousands times per second
due to the microwave, so that the food is heated/cooked by
2o the frictional heat.
In the microwave oven, a high voltage of about 2KV is
boosted from a rated commercial AC power supply by a high
voltage, and then doubled into a high voltage of 4KV by a
voltage doubling circuit and supplied to the magnetron.
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Therefore, the magnetron generates a high frequency
microwave.
FIG. 1 is a circuit diagram illustrating a general
power supply driving device for an AC microwave. The power
supply driving device includes a primary switch 10, a door
lamp 12, a fan motor 16, a turntable motor 20, a first to
a third relay switches 14, 18, and 22, a high voltage
transformer 24, a high voltage capacitor HVC, a high
voltage diode HVD, and a magnetron MGT.
1o The primary switch 10 is switched on by a close
operation of a cooking chamber door, so that an AC voltage
is supplied from the commercial alternating current power
supply AC to a primary coil 24a of the high voltage
transformer 24.
The door lamp 12 is turned on to illuminate a cooking
chamber by receiving the commercial AC utility power supply
AC, when a door sensing switch (not shown) is switched off
by opening of the cooking chamber door, and the first relay
switch 14 is inversely switched on.
2o The fan motor 16 serves to ventilate a cooking chamber
and prevents the magnetron MGT from heat generation during
the cooking operation. At a state that the primary switch
10 is switched on, if the second relay switch 18 is
switched on when a certain cooking function is performed,
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the fan motor 16 is driven by receiving the commercial AC
power supply.
The turntable motor 20 is an AC driving motor,
disposed at a lower portion of the cooking chamber, for
rotating a turntable which supports a vessel containing the
food. At a state that the primary switch 10 is switched on,
if the third relay switch 22 is switched on together with
the second relay switch 18 when a certain cooking function
is performed, the turntable motor 20 is driven by the
1o commercial AC power supply AC.
On the other hand, the high voltage transformer 24
receives the AC utility power supply through the primary
coil 24a thereof, and generates a high voltage
corresponding to respective winding ratios through a
secondary coil 24b thereof, according to the switch-on
operation of the primary switch 10. The voltage doubling
circuit consisting of the high voltage capacitor HVC and
the high voltage diode HVD doubles the high voltage
generated from the high voltage transformer 24, and
2o supplies the doubled high voltage to the magnetron MGT.
The operation of the conventional power supply driving
device for the AC microwave oven will be now described.
When the door sensing switch is switched off according as
the cooking chamber door is open by a user, the first relay
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switch 14 is inversely switched on, then the door lamp 12
is turned to light on by receiving the commercial AC power
supply AC. Here, since the primary switch 10 maintains a
switched-off state, the high voltage transformer 24 does
not receive the commercial AC power supply AC. Accordingly,
the high voltage transformer 24 cannot perform the
operation for generating the high voltage.
Conversely, when the cooking chamber door is closed
and the primary switch 10 is switched on, the high voltage
1o transformer 24 receives the AC power supply AC, and thus
the microwave oven is prepared for the operation of the
cooking function.
At this time, when the user operates a certain cooking
function, the magnetron MGT is driven to generate a
microwave, simultaneous with driving the fan motor 16 and
the turntable motor 20 by the switched-on of the second
relay switch 18 and the third relay switch 22. Therefore,
the food rotated on the turntable in the cooking chamber
is heated/cooked by the microwave generated from the
magnetron MGT.
Meanwhile, since the conventional power supply driving
device for the conventional AC microwave oven is designed
to be driven merely by the AC power supply, and thus cannot
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be used in the fields, vehicles, ships and airplanes where
the AC power supply is difficult to be supplied.
In order to overcome such a disadvantage, there has
been suggested a DC microwave oven having an inverter for
inverting the DC such as a portable battery power supply,
which can be utilized in various transportations including
vehicles and in the fields, into the AC.
In the DC microwave oven, a door lamp and a fan motor
are driven directly by the DC power supply, while a DC
1o motor is utilized as a turntable motor for driving a
turntable in a cooking chamber to be driven by the DC power
supply.
However, since the DC microwave oven employs the
high-priced DC motor as the turntable motor for driving the
turntable, the whole manufacturing cost of the DC microwave
oven is increased. As a result, consumers must pay
additional increased cost for purchasing the DC microwave
oven.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to
provide a turntable motor driving circuit for a DC
microwave oven which the manufacturing cost can be
remarkably reduced by using a low-priced AC motor as a
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turntable motor for the DC microwave oven and driving the
turntable motor by inverting a DC power supply into an AC
power supply.
Another object of the present invention is to provide
a turntable motor driving circuit for a DC microwave oven
which can easily generate a DC power supply required for
other driving circuit terminals through the driving circuit
for driving an AC motor as the turntable motor.
In order to achieve the above-described obj ects of the
1o present invention, there is provided a turntable motor
driving circuit for a DC microwave oven including: a
control unit for generating a driving control pulse for
inverting a DC into an AC according to an input to start
a cooking function; an inverter unit for inverting a DC
voltage of the DC power supply into an AC voltage by
receiving the driving control pulse from the control unit;
a transformation unit for transforming the AC voltage
inverted by the inverter unit into a predetermined voltage;
and a turntable motor having an AC motor, and being driven
2o by the AC voltage transformed by the transformation unit.
Preferably, the driving control pulse from the control
unit includes a plurality of pulse signals whose periods
are alternately inverted, and the inverter unit includes
a plurality of power transistors to be alternately turned
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on/off by respectively receiving the plurality of driving
control pulses.
More preferably, in accordance with one aspect of the
present invention, the turntable motor driving circuit for
the DC microwave oven further includes: a rectification
section for rectifying the AC voltage induced by the
transformation unit; and a voltage regulator for regulating
and outputting the DC voltage rectified by the
rectification section. Here, the voltage by the voltage
1o regulator is supplied to other operation circuit terminals
as an operation power supply.
In accordance with the present invention, the whole
manufacturing cost of a microwave oven is remarkably
reduced by using the low-priced AC motor as the turntable
motor which rotates the turntable where food is mounted,
which results in reduction of the purchase price of the
microwave oven.
BRIEF DESCRIPTION OF THE DRAWINGS
2o The present invention will become better understood
with reference to the accompanying drawings which are given
only by way of illustration and thus are not limitative of
the present invention, wherein:
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FIG. 1 is a circuit diagram illustrating a general
power supply driving device for an AC microwave oven;
FIG. 2 is a circuit diagram illustrating a turntable
motor driving circuit for a DC microwave oven in accordance
with a preferred embodiment of the present invention; and
FIG. 3 is a waveform diagram for explaining an
operation of inverting a direct current into an alternating
current in order to drive a turntable motor in accordance
with the preferred embodiment of the present invention.
to
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A turntable motor driving circuit for a DC microwave
oven in accordance with the present invention will be
described in detail with reference to the accompanying
drawings.
FIG. 2 is a circuit diagram illustrating the turntable
motor driving circuit for the DC microwave oven in
accordance with a preferred embodiment of the present
invention. The turntable motor driving circuit includes a
2o DC power supply 30 for generating a DC voltage of about
12V, a door lamp 32, and a fan motor 36. The door lamp 32
and the fan motor 36 are respectively turned on to
illuminate and driven to be rotated by receiving the DC
voltage from the DC power supply 30 according to switching
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operations of a first relay switch 34 and a second relay
switch 38.
The turntable motor driving circuit also includes a
door sensing switch DSW for sensing an open/close operation
of door of a microwave oven, and performing a switching
operation, a driving circuit 46 for generating alternate
driving pulses at predetermined intervals according to the
switching operation of the door sensing switch DSW and
first and second field effect transistors 48 and 50 for
1o respectively receiving the alternate driving pulses from
the driving circuit 46, and performing an alternate ON/OFF
operation.
In addition, the turntable motor driving circuit
includes a high voltage transformer 52 for receiving the
DC power supply from the battery power supply 30 through
primary coil 52a thereof and transforming the DC power
supply into a high voltage AC power supply through
secondary coil 52b, in accordance with the alternate ON/OFF
operation of the first and second field effect transistors
48 and 50, and first and second interlock switches SWl and
SW2, switched according to the open/close state of the
cooking chamber door, for allowing or preventing the DC
voltage from supplying from the high voltage transformer
52.
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There are also provided a high voltage capacitor HVC
and a high voltage diode HVD for doubling a high voltage
AC, a surge interrupt capacitor SC for interrupting a surge
voltage induced by the high voltage transformer 52, and a
magnetron MGT for generating a microwave by receiving the
AC voltage doubled by the high voltage capacitor HVC and
the high voltage diode HVD.
According to an aspect of the preferred embodiment of
the present invention, a microcomputer 54, first and second
to power transistors 56 and 58 and a transformer 60 as a
push-pull circuit, and an AC motor as a turntable motor are
used. In addition, a bridge diode 64 and a voltage
regulator 66 are utilized so as for respectively rectifying
and regulating the AC voltage from the transformation unit
60 .
On the other hand, the microcomputer 54 controls a
cooking state of food according to an input of a function
button by the user. In addition, the microcomputer 54
alternately generates first and second driving control
pulses whose periods are inverted for predetermined
intervals through a first and second control output
terminals E1 and E2, thereby alternately turns on/off the
first and second power transistors 56 and 58.
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The first and second power transistors 56 and 58 are
alternately turned on/off by receiving the first and second
driving control pulses from the first and second control
output terminals E1 and E2 of the microcomputer 54 through
respective base terminals of the first and second power
transistors 56 and 58.
The transformer 60 receives, for example, a DC voltage
of 12V from the DC power supply 30 through the primary coil
60a, and transforms the DC voltage into an AC voltage of
l0 21V required for driving the turntable motor 62 through
secondary coil 60b, in accordance with the alternate ON/OFF
operation of the first and second power transistors 56 and
58.
The turntable motor 62 of an AC motor receives the AC
voltage of 21V which is transformed by the transformer 60,
and rotates a turntable (not shown) in a cooking chamber.
Meanwhile, the bridge diode 64 rectifies and outputs the
AC voltage from the transformer 60, and the voltage
regulator 66 converts the rectified DC voltage into a
2o constant voltage of 15V which is supplied to one terminal
of the door sensing switch DSW.
Accordingly, the driving circuit 46 is driven by
receiving the DC voltage of 15V from the voltage regulator
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66 through a power supply terminal Vcc according to the
switch-on state of the door sensing switch DSW.
The operation of the turntable motor driving circuit
for the DC microwave oven of the present invention will be
described in detail with reference to FIGS. 2 and 3.
When the cooking chamber door (not shown) of the DC
microwave oven is open, the door sensing switch DSW senses
the open of the cooking chamber door and is switched off.
Accordingly, the first relay switch 34 is switched on, and
to thus the door lamp 32 is lighted by receiving the DC
voltage from the DC power supply 30.
In addition, when the cooking chamber door is open,
the first and second interlock switches SWl and Sw2 are
switched on, and thus interrupts the application of the DC
voltage to the primary coil 52a of the high voltage
transformer 52.
In this state, when the cooking chamber door is closed
after positioning the food on the turntable in the cooking
chamber, the door sensing switch DSW is switched on by
2o sensing the close of the cooking chamber door. Accordingly,
the first relay switch 34 is switched off, and thus the
door lamp 32 is turned off.
On the other hand, at a state that the door sensing
switch DSW is switched on, a certain function button (not
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shown) for commanding to start cooking is inputted, the
microcomputer 54 generates the first and second driving
control pulses whose periods are alternately inverted
through the first and second control output terminals El
and E2 (See FIG. 3).
In addition, the first and second power transistors
56 and 58 respectively receive the first and second driving
control pulses through their respective base terminals, and
are alternately turned on/off at predetermined intervals.
to Accordingly, in the transformer 60, the DC voltage of
12V from the DC power supply 30 is supplied to the primary
coil 60a, and then the transformed AC voltage of 21V is
induced through the secondary coil 60b (See FIG. 3).
As a result, the turntable motor 62 of an AC motor
receives the AC voltage of 21V from the transformer 60, and
rotates the turntable where the food is positioned.
Here, the bridge diode 64 rectifies the AC voltage of
21V induced through the secondary coil 60b of the
transformer 60, and the voltage regulator 66 regulates the
rectified DC voltage to a constant direct current voltage
of 15V.
The driving circuit 46 is driven by receiving the DC
voltage of 15V from the voltage regulator 66 through the
power supply terminal Vcc via the door sensing switch DSW,
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and generates the first and second driving control pulses
whose high pulses are alternately inverted through the
first and second output terminals 01 and 02.
Therefore, the first and second field effect
transistors 48 and 50 respectively receive the first and
second driving control pulses through their base terminals,
and are alternately turned on/off in order for allowing the
AC voltage to be induced to the primary coil 52a of the
high voltage transformer 52.
1o On the other hand, the high voltage transformer 52
generates a high AC voltage through the secondary coil 52b
according to a winding ratio with the primary coil 52a, and
thus the surge voltage is vanished by the surge voltage
interrupt capacitor SC. Therefore, the magnetron MGT
receives the high voltage AC doubled by the high voltage
capacitor HVC and the high voltage diode HVD, and generates
the microwave.
As a result, the microwave generated from the
magnetron MGT heats/cooks the food on the turntable while
2o being rotated by the turntable motor 62 of an AC motor.
According to the present invention constructed as
above, since a low-priced AC motor can be employed to a DC
microwave oven as a turntable motor which rotates a
turntable, whole manufacturing cost of the DC microwave
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oven can be remarkably reduced results in reduction of the
purchase price of the DC microwave oven.
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
effected therein without departing from the sprit and scope
of the present invention as defined by the appended claims.
