door hook
door release button
pilot switch
screw
latch switch
screw
Fig.2-5 b
2
2
.
.
4
4
.
.
1
1
D
D
O
O
O
O
R
R
I
I
N
N
T
T
E
E
R
R
L
L
O
O
C
C
K
K
S
S
W
W
I
I
T
T
C
C
H
H
Drawing 2-5(a) is the circuit and construction diagram
of the door interlock switch of brand, EM-D975
microwave oven. It mainly consists of latch switch (S1,
S2), pilot switch (S3), door hook and starting
mechanism of the door interlock switch.
door closed
assistant latch switch
pilot switch
main latch switch
fuse
S
S
S
L
E
N
2
3
1
(a)
Fig.2-5
There fixed hooks on the oven door, and opened two
rectangle hole at the corresponding place at the right of
the oven and the hook. Inside each rectangle hole,
there fixed a micro switch. When the oven door closed,
the two hook on it would insert into the rectangle hole,
and just push down several micro switches. At that
time, S1, S2 are closed, S3 is cut off, and the
microwave oven is under preparation of working. To
that mechanical control microwave oven, no sooner
you turn the time switch to set the heating time than the
power would be supplied to the back to start the oven. To
those touch control microwave oven, hardly do you set the
heating time and power, and touch the start button when the
power would supplied to the back to start the oven. When
press down the door release button, S1, S2 are cut off, S3 is
closed, and the microwave oven would stop operating
immediately. Provided due to some man - made or the
appliance itself reasons, when the door is open, S1, S2 are
closed, due to the pilot switch (S3) still at conducted
condition would make the 230V voltage short-circuited and
fused the fuse, and will never let the microwave oven
working when the door is open. From this we can
understand the function of the interlock switch is when the
door is unclosed, the oven wouldn’t work, when the door is
opened when the oven is working, it would stop the working
immediately (FIG.2-5b).
2
2
.
.
4
4
.
.
2
2
T
T
I
I
M
M
E
E
A
A
N
N
D
D
P
P
O
O
W
W
E
E
R
R
D
D
I
I
S
S
T
T
R
R
I
I
B
B
U
U
T
T
O
O
R
R
transformer
4
S
5
S
timer & power motor
Fig.2-6
230V
Time and power distributor is mainly composed of timer
motor and two sets of gear switch S4 and S5. When the
timer is at zero position, the gear switches are cut off,
when the heating time is settled, the gear switch is
closed. When started the oven, the time motor starts
working. When it reaches the settled time, it would cut
off the gear switch (s4) to step the oven working. The
gear switch (S5) is designed for controlling the output
of the microwave oven, actually for controlling the
output of the magnetron. It mainly by the method which
make the magnetron working internally at the same
working point to change the output of the magnetron.
This method was called “CONDUCTION RATIO
CONTROL”. But there is another method which is
called “ELECTRIC LEVEL CONTROL” which is
through changing the working point (such as anode
voltage or magnetic field) to change the output of the
magnetron. Because of conduction ratio control
method is low cost, high function and high reliability, it is widely used for those microwave oven which have the
power control function.
FIG.3-1 is the power control circuit diagram of brand microwave oven, WP700. This is a typical instance of
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