Control circuit for a refrigerator combined with a microwave oven

A control circuit for a refrigerator combined with a microwave oven includes signal delay selecting and comparing circuitry start sensing circuitry timer circuitry and load driving circuitry in order to properly control operations of the refrigerator and the microwave oven. The control circuit eliminates unnecessary delay time of the operation of the microwave oven during operation of the refrigerator, and makes the refrigerator operate after start-up of the microwave oven is completed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a control circuit for electrical machinery and 
applicances, and more particularly to a control circuit for a refrigerator 
combined with a microwave oven. 
2. Description of the Prior Art 
It is possible that electrical machinery and applicances are provided with 
at least two inductive loads such as a motor and a compressor, or a 
refrigerator and a microwave oven, etc. 
In a conventional refrigerator combined with a microwave oven, a delay 
circuit is provided to each load which makes the load operate after a 
predetermined delay time. Such a delay circuit protects the refrigerator 
and the microwave oven from being initially overloaded when they are 
operated simultaneously. 
However, there is not protective or control circuitry to protect against 
the start-up of the refrigerator during the operation of the microwave 
oven. Moreover, it is not necessary or desirable to delay the operation of 
the microwave oven, when the compressor of the refrigerator is in an OFF 
state or when a stable current is supplied through the operating 
refrigerator. In other words, such a delayed start-up of the microwave 
oven encumbers the user, causing inconvenience. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a control circuit, 
which protects against overloads and the like by delayed operation with 
respect to the load selected from at least two inductive ones requiring 
high driving current. 
To accomplish the above object, a control circuit is provided according to 
the present invention to comprise: 
a temperature adjusting means having an operational amplifier, one terminal 
of which is connected to a variable resistor to determine the input bias 
level; 
a temperature sensing and controlling means having a differential amplifier 
which receives the hysteresis output of the temperature adjusting means 
and compares this hysteresis output with the bias current of a temperature 
sensing thermister; 
a delay selecting and comparing means having a signal comparator connected 
to the differential amplifier of the temperature sensing and controlling 
means and a logic circuit connected to the differential amplifier via a 
diode; 
a start sensing means having a flip-flop toggled by a switch in order to 
sense the start of the microwave oven; 
a display means connected to the inverting output terminal of the flip-flop 
to display the operation of the microwave oven; 
a timer means controlling the delay of the operation of the loads; and, 
a load driving means having transistors and relays receiving signals from 
the signal comparator and the timer in order to control the drive of the 
loads. 
According to the present invention, the microwave oven may be used 
regardless of the prior operation of the refrigerator and thus these loads 
can be operated simultaneously. However, when the user wants to operate 
the refrigerator during the use of the microwave oven, the operation of 
the refrigerator is delayed to avoid instantaneous overloads due to 
simultaneous operation of the microwave oven and the refrigerator. 
Consequently, the lifetime of the circuit elements of the products is 
prolonged and safety is ensured against overcurrent.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
In FIG. 1, there is shown a control circuit to control the operation of two 
loads, i.e. one for the refrigerator and the other for the microwave oven. 
In conventional technology, to drive the compressor of the refrigerator, it 
is well known to control the operation of the compressor by sensing the 
temperature of the refrigerating compartment and comparing the temperature 
with a preset one. To set the temperature of the refrigerating 
compartment, the temperature adjusting section 100 is provided with a 
operational amplifier OP.sub.1 so as to have the current hysteresis width 
according to the temperature. 
The inverting terminal of the operational amplifier OP.sub.1 is connected 
to its output terminal in order to perform a negative feedback and the 
non-inverting terminal is connected to resistors R.sub.1, R.sub.2, and 
R.sub.3 and the variable resistor VR which are connected with each other 
in order to divide the power source voltage Vcc applied to the 
non-inverting terminal of the operational amplifier OP.sub.1. Preferably, 
the resistor R.sub.2 is in parallel connection with the variable resistor 
VR to make linear the characteristics of the voltage of the variable 
resistor. 
Temperature sensing and control section 200 causes the refrigerator to 
operate and to stop operating when the temperature of the refrigerating 
compartment reaches the present temperature. 
To this end, a differential amplifier OP.sub.2 receives the preset 
temperature output of the temperature setting section and compares it with 
the sensed temperature. The non-inverting terminal (+) of the differential 
amplifier OP.sub.2 is connected to the operational amplifier OP.sub.1 
through a resistor R.sub.4 and also connected to its own output terminal 
through a resistor R.sub.5 to perform feedback operation. 
The inverting terminal (-) of the differential amplifier OP.sub.2 is 
connected to a thermister TH and a resistor R.sub.7 connected in parallel. 
Power source Vcc is applied through the resistor R.sub.7. Therefore, the 
voltage according to the temperature of the refrigerating compartment is 
applied to the differential amplifier OP.sub.2 by the thermister TH, and 
in turn the differential amplifier OP.sub.2 compares this voltage level 
with the hysteresis output of the operational amplifier OP.sub.1, 
resulting in that it outputs a high level or a low level in order to 
determine the operation of the refrigerator. 
The operation of the loads is determined by the output of the differential 
amplifier OP.sub.2. When the control circuit is constructed so as to 
operate the refrigerator and the microwave oven simultaneously, the 
refrigerator requires a large current (ten plus several Amperes) when it 
starts its operation and a relatively small current (several Amperes) 
during its normal operation. However, the microwave oven always requires a 
large current (tens of Amperes) in normal operation as well as at starting 
time. 
Therefore, it is noted that the control process may be varied according to 
the operating states of the refrigerator and the microwave oven. 
The delay selecting and comparing section 300 is provided with a signal 
comparator 20 whose terminal A.sub.1 is connected to the output terminal 
of the differential amplifier OP.sub.2. The signal comparator 20 is 
connected to the clock generator 10 and such waveforms as shown in FIG. 3 
are applied or output therefrom. When the output A of the differential 
amplifier OP.sub.2 is high level as shown in portion II of FIG. 2, the 
output from the terminal Q' operates the driving section 700 of the 
refrigerator which will be described in detail later. 
The terminal A.sub.2 of the signal comparator 20 is grounded via a 
capacitor C.sub.1 and connected through a resistor R.sub.8 and the diode 
D.sub.2 to the timer section 600 which will be described later in detail. 
The output temrinal of the differential amplifier OP.sub.2 is connected 
through a diode D.sub.1 to a logic circuit which gives signals to delay 
the operation of the second load. The logic circuit comprises AND gates 
G.sub.1 and G.sub.2, an OR gate G.sub.3 and a NOT gate G.sub.4. One input 
terminal of the AND gate G.sub.1 is connected to the NOT gate G.sub.4 and 
one input terminal of the AND gate G.sub.2 is connected to the delay 
circuit having a resistor R.sub.9 and a capacitor C.sub.2 with a 
predetermined delay time. The other input terminals of the AND gates 
G.sub.1 and G.sub.2 are connected to the start sensing section 400 of the 
microwave oven, the second load, which will be described later in detail. 
The output of the AND gates G.sub.1 and G.sub.2 are applied to the OR gate 
G.sub.3. The output of the OR gate G.sub.3 of the logic circuit is applied 
to the timer section 600 having a timer 30 for the user to set the 
operating time of the microwave oven. The timer 30 is provided with a 
clock section 40 for receiving clock pulses. 
The start sensing section 400 of the microwave oven, the second load, is 
provided with a one-touch type start switch SW of the microwave oven and a 
flip-flop FF responsive to ON/OFF operation of the start switch SW which 
is connected to the clock terminal C of the flip-flop FF. The output 
terminal Q of the flip-flop FF is connected to the input terminals of the 
AND gates G.sub.1 and G.sub.2, the output terminal Q thereof is connected 
to the display section 500 of the microwave oven which will be described 
later in detail and the reset terminal R thereof is connected to the timer 
section 600 through a diode D.sub.10. 
In the display section 500 for displaying the oepration of the microwave 
oven, the base of a transistor Q.sub.1 is connected to the terminal Q of 
the flip-flop FF through a resistor R.sub.12. The emitter of the 
transistor Q.sub.1 is grounded and the collector thereof is connected to 
the power source Vcc through a resistor R.sub.13 as well as to the base of 
a transistor Q.sub.2 through a resistor R.sub.14. 
The emitter of the transistor Q.sub.1 is grounded and its collector is 
connected to the power source Vcc through a light emitting diode L and a 
resistor R.sub.15 which are conected in series. 
On the other and, the load driving section 700 comprises driving circuits 
for the refrigerator and the microwave oven. 
In the refrigerator driving circuit, the base of a transistor Q.sub.3 is 
connected to the output terminal of the signal comparator 20 through a 
resistor R.sub.16. The emitter of the transister Q.sub.3 is grounded and 
its collector is connected to a relay RY.sub.1 of the refrigerator which 
is in turn connected to the power source Vcc. 
In the microwave oven driving circuit, the base of a transistor Q.sub.4 is 
connected to the timer section 600 through a resistor R.sub.17. The 
emitter of the transistor Q.sub.4 with a grounded collector is connected 
to a relay RY.sub.2 of the microwave oven which is then connected to the 
power source Vcc. 
The operation of the control circuit of the present invention will now be 
described in detail. 
When the first load is in operation, but the second load is in an OFF 
state, the waveforms A.sub.1 and A.sub.2 in the portion F of FIG. 3 and 
applied to, and the waveform Q' is output from, the comparator 20, 
respectively, corresponding to the portion I of the waveform A shown in 
FIG. 2. Therefore, the portion I of the waveform C of FIG. 2 drives the 
first load driving circuit. 
When the second load starts to operate during the operation of the first 
load, the high level signals, such as in the portion II of the waveforms A 
and B shown in FIG. 2, are applied to the comparator 20, through the diode 
D.sub.1 to the NOT gate G.sub.4 and the AND gate G.sub.1, and also to the 
AND gate G.sub.2 through the delay circuit, comprising the resistor 
R.sub.9 and the capacitor C.sub.2 respectively. Simultaneously, the high 
level output from the terminal Q of the flip-flop FF in the start sensing 
section 400 is applied to the AND gates G.sub.1 and G.sub.2. 
At this moment, the compatator 20 receives or generates the waveforms G of 
FIG. 3. Therefore, only somewhat delayed output of the AND gate G.sub.2 is 
applied to the OR gate G.sub.3 which generates high level output. 
Consequently, the timer 30 of timer section 600 becomes enabled and the 
timer 30, which operates as long as preset by the user, makes the second 
load driving circuit operate. 
At this moment, since the output from the output terminal Q of the 
flip-flop FF becomes low, the transistor Q.sub.1 of the display section 
500 becomes off and the transistor Q.sub.2 is turned on. Consequently, the 
light emitting diode L becomes ON and indicates that the second load is 
operating. 
After that, the timer 30 stops operating and a low level signal is applied 
to the reset terminal R of the flip-flop FF. At this moment, since the 
outputs from terminals Q and Q of the flip-flop FF are unterchanged, the 
terminal Q outputs a high level and turns on the transistor Q.sub.1 and 
turns off the transistor Q.sub.2, thereby indicating that the second load 
is not operating. 
When the first and second loads are started at the same time, the waveforms 
A and B as shown in the portion III of FIG. 2, are applied respectively to 
the signal comparator 20, which operates the first load driving circuit by 
its output as shown in the portion J of FIG. 3, and to the AND gates 
G.sub.1 and G.sub.2 after being delayed as long as the charge time 
.DELTA.t.sub.1 of the capacitor C.sub.2 of the delay circuit in case of 
the AND gate G.sub.2, thereby the starting and stopping of the timer 30 is 
delayed as long as the delay time .DELTA.t.sub.1 and .DELTA.t.sub.2 
respectively. Therefore, the second load driving circuit is operated by 
the waveform D according the operation of the timer 30. Hence, it is found 
that there is no problem regarding the delayed operation of the second 
load. 
If the second load in an is started to operate with the first load OFF 
state, the signals of the wave forms A and B of the portion IV of FIG. 2 
are generated. When the start switch SW is touched, a high level signal 
comes out of the AND gate G.sub.2, due to the high level output of the 
flip-flop FF and the low level output of the operational amplifier 
OP.sub.2. Then, the high level signal is applied to the timer 30 through 
the OP gate G.sub.3. 
Thus, the second load driving circuit is operated by the timer 30, and the 
waveforms in the portion H of FIG. 3 are applied to the signal comparator 
20 through the diode D.sub.2 and the resistor R.sub.8. In this state, the 
comparator 20 outputs a low level signal and thus cannot drive the first 
load. On the other hand, both the transistor Q.sub.2 and the LED L become 
ON, because the transister Q.sub.1 becomes OFF due to the low level signal 
coming out from the terminal Q of the flip-flop FF. 
When the first load is started during the operation of the second load, the 
waveforms in the portion V of FIG. 2 are generated and applied to the 
comparator 20 and also the AND gates G.sub.1 and G.sub.2. Therefore, the 
comparator 20 delays generating its output until the timer ends its 
operation and so, the waveform in the portion of I shown in FIG. 3 comes 
out from the teminal Q' of the comparator 20. 
In other words, the first load is protected against overload because the 
operation of the first load is delayed until the operation of the second 
load is stopped. 
As described above, the operation of the control circuit of the present 
invention depends on the circumstances as shown in the truth table of FIG. 
4. In FIG. 4, the numerals 1 and 0 referenced to the loads indicate ON and 
OFF state of the first and second loads respectively. The numeral 1 
referenced to the delay time, indicates the operation after the lapse of 
thre delay time, and O indicates the operation within the delay time. FIG. 
4 may be regarded as the functional truth table applied to the present 
invention. 
Whereas the present invention has been described in particular relation to 
the drawings attached hereto, it should be understood that other and 
further modifications, apart from those shown or suggested herein, may be 
made within the spirit and scope of this invention.