Electric heating – Microwave heating – With control system
Reexamination Certificate
1999-08-11
2001-12-18
Hoang, Tu Ba (Department: 3742)
Electric heating
Microwave heating
With control system
C219S720000, C219S722000, C219S724000
Reexamination Certificate
active
06331699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microwave heating apparatus that consumes less electric power in a standby state.
2. Description of the Prior Art
FIG. 1
shows an example of the electric circuit diagram of a conventional microwave heating apparatus. This microwave heating apparatus has a plug
1
that is connected to a commercial alternating-current electric power, a step-down transformer
2
for stepping down the voltage of the commercial electric power taken in via the plug
1
, a full-wave rectification circuit
3
, a smoothing capacitor
4
, load circuits RL, a three-terminal voltage regulator
5
, and a CPU
6
.
The CPU
6
, by monitoring the state of a switch
11
, detects a door being opened or closed, so that, if the door is opened in the middle of heating operation, the heating operation will be stopped. Moreover, the CPU
6
controls the load circuits RL. The load circuits RL include, for example, various sensors such as an AH (absolute humidity) sensor and a weight sensor, and a relay circuit. The relay circuit controls supply of electric power to a magnetron.
The step-down transformer
2
has a primary coil
2
a
connected to the plug
1
, and has a secondary coil
2
b
connected to input terminals of the full-wave rectification circuit
3
. The smoothing capacitor
4
has one end connected to a high-voltage-side output terminal of the full-wave rectification circuit
3
, and has the other end connected to a low-voltage-side output terminal thereof. For example, in Japan, a source voltage of 100 V fed in via the plug
1
is applied, as a voltage AC
1
, to the primary coil
2
a
of the step-down transformer
2
so as to induce a stepped-down voltage across the secondary coil
2
b.
This voltage appearing across the secondary coil
2
b
is subjected to full-wave rectification by the full-wave rectification circuit
3
and then to smoothing by the capacitor
4
so as to be made into a direct-current voltage DC
1
of about 18 V. This voltage DC
1
is used to drive the load circuits RL. The CPU
6
receives a direct-current voltage DC
2
that is regulated by the three-terminal voltage regulator
5
so as to have about 5 V. This voltage DC
2
is applied, on its high-voltage and low-voltage sides, to the terminals VCC and VSS, respectively, of the CPU
6
.
Having a circuit configuration as described above, this microwave heating apparatus has the following disadvantage. Even when the microwave heating apparatus is in a standby state, i.e. even when it is not in operation for cooking, the same voltage as when it is in operation is applied through the step-down transformer
2
to the load circuits
5
. As a result, electric power of about 2 W is unnecessarily consumed as iron loss, copper loss, and the like as well as by the load circuits including the various sensors and the relay circuit.
As an improvement to such a microwave heating apparatus that unnecessarily consumes electric power in a standby state, Japanese Laid-Open Patent Application No. H7-217906 proposes a microwave heating apparatus that is so configured as to consume less electric power in a standby state.
FIG. 2
shows the circuit configuration of this microwave heating apparatus. The microwave heating apparatus operates from a power source
51
, and has loads
52
such as a heating member and a motor, main door switches
53
and
54
that are turned off or on as a door is opened or closed, a monitor switch
55
, a door switch
56
that is turned on or off as the door is opened or closed, and relay switches
57
and
58
.
The microwave heating apparatus also has a CPU
61
that serves as a data processing device, and a power supply circuit
62
for producing direct-current electric power on which the CPU
61
and other circuits operate. The microwave heating apparatus further has an output circuit
63
for driving the above-mentioned relay switches
57
and
58
, a key input circuit
64
for allowing setting of a cooking program for heating operation and entry of an instruction for starting heating operation, and a door switch detection circuit
65
for detecting the open/closed state of the door; these three circuits are driven and controlled under the control of the CPU
61
.
FIG. 2
shows a state in which the door is closed. In this state, the main door switches
53
and
54
are on, the door switch
56
is off, and the monitor switch
55
is in the terminal “b” position. Moreover, the relay switches
57
and
58
are off, and thus no electric power is supplied to the loads
52
, the CPU
61
, or other circuits.
When the door is opened from this state, the main switches
53
and
54
are turned off, and the monitor switch
55
is brought into the terminal “a” position. Moreover, the door switch
56
is turned on, and thus electric power starts being supplied only to the CPU
61
. The CPU
61
, when it starts receiving electric power through the power supply circuit
62
, first turns on the relay switch
57
through the output circuit
63
. Accordingly, the CPU
61
continues receiving electric power even when the door is closed next time and the door switch
56
is turned off.
The CPU
61
, at the same time as it turns on the relay switch
57
, sets a period of time to be counted by a timer, so that, when the once opened door is closed again, the timer starts counting the period of time. Unless, in the meantime, a key input signal is obtained from the key input circuit
64
or a door open/close signal is obtained from the door switch detection circuit
65
, the CPU
61
turns off the relay switch
57
when the timer finishes counting the period of time. Accordingly, when no heating operation is taking place, supply of electric power to the CPU
61
is shut off securely, and thus no electric power is consumed in a standby state.
However, this microwave heating apparatus has its own disadvantage. For example, some of its functions require energizing of the CPU
61
but do not necessarily require heating operation, such as the function of displaying on a display unit, for confirmation, cooking conditions such as heating power and heating time under which heating operation is to be performed or cooking recipe data indicating a cooking method and appropriate heating conditions, or the function of executing a cooking menu selection program. Even to perform such a function, it is necessary to energize the CPU
61
first by performing an extra step of opening the door once.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a microwave heating apparatus that consumes less electric power in a standby state.
To achieve the above object, according to one aspect of the present invention, a microwave heating apparatus is provided with: a load; a control circuit for controlling and driving the load; a power source for supplying electric power to the load and the control circuit; and a transformer for stepping down the voltage of the electric power supplied from the power source to the load and the control circuit. Here, the microwave heating apparatus operates in one of two modes, namely a first mode and a second mode, that allow different amounts of electric power to be supplied to the load and the control circuit, and the voltage applied to the primary coil of the transformer is lower in the second mode than in the first mode.
According to another aspect of the present invention, a microwave heating apparatus is provided with: a heating member; a control circuit for driving and controlling the heating member; a power source for supplying electric power to the heating member and the control circuit; a door provided so as to shut a heating chamber in which to place food; and an operation member for opening the door when the door is in a closed state. Here, when the user operates the operation member, electric power starts being supplied from the power source to the control circuit.
REFERENCES:
patent: 3876956 (1975-04-01), Levinson
patent: 3961152 (1976-06-01), Staats
patent: 4296296 (1981-10-01), Eichelberger et al.
patent: 4341409 (198
Ito Kohei
Kondou Sakae
Ota Tomoko
Otani Hideaki
Hoang Tu Ba
Sharp Kabushiki Kaisha
LandOfFree
Microwave heating apparatus requiring reduced power in a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Microwave heating apparatus requiring reduced power in a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Microwave heating apparatus requiring reduced power in a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2592944