5
door closed
assistant latch switch
pilot switch
main latch switch
fuse
S
S
S
L
E
N
2
3
1
(a)
Fig.2-5
anode current
I
b
(mA)
an
od
e
vo
lt
ag
e
e
b
(k
V)
m
Fig.2-4
between the cathode and anode of the magnetron, a filament voltage to the cathode filament of the magnetron.
The working process of the magnetron: When the anode volt-age gradually rises from zero, the anode current is
approx.zero, the power is very small as well. When the anode voltage rises to “THRESHOLD” voltage value, the
magnetron starts oscillating, and the anode current would increase obviously, provided the anode voltage rises a
little more, the anode current would increase a lot (FIG.2-4), and would reach the rate value quickly.
If the anode voltage is undulating, it would cause the anode
current swing fiercely, even made the magnetron stop
oscillating. For keeping a steady output, the power supply circuit
of the oven must supply a stead direct current voltage. The
filament voltage of the magnetron must be supplied by an
alternating current voltage. For simplifying the circuit, it would be
supplied by the same leakage magnetic transformer with the
anode power (high voltage power). The filament of the
magnetron which the present used microwave ovens are all
treated through some special technology, and all have the cold
start character. But when in cold start, there still is a very strong
surge electric field attached to the surface of the anode, and
would be harmful to the anode. In order to reduce the surge
voltage, the filament of the magnetron must be connected as the
FIG.2-3 shown. In this figure, when the anode current of the
magnetron circulates, the filament current should flow to the FA
end from the lower end.
2
2
.
.
3
3
C
C
O
O
O
O
L
L
I
I
N
N
G
G
S
S
Y
Y
S
S
T
T
E
E
M
M
In the working process of the microwave oven, the magnetron often makes the anode temperature rise due to
anode loss
caused by the electronics strike the oven surface and the heat radiate of the cathode. To prevent the anode
temperature rise too high, thus affect the working steady and its life span, it is necessary to cool the magnetron.
According to the different models and rate output of the magnetron, compelling wind cooling and flowing water-
cooling can be adopted. Usually, the home used microwave oven adopts the compelling wind cooling method,
and all are fixed with cooling fin.
Cooling system includes fan motor, air duct, air entrance, air vent etc. The flowing direction of the cooling wind
should. Be parallel to the cooling fin of the magnetron. Generally, we adopt the method of air blast rather than air
absorb. And all the cabinet of the oven is with air entrance and air vent, the hot wind blowing through the
magnetron is guided with air tube to improve the cooling effect. In the technical parameter chart of the
magnetron, it usually will give out the requirement of cooling wind. A shortage of cooling wind would damage the
character of the magnetron, even burn out the magnetron. The amount that the fan blasted should not be less
than the requirement. When fix the fan, attention must be paid to prevent the cool wind from blowing directly to
the glass part of the magnetron to avoid blasting.
2
2
.
.
4
4
E
E
L
L
E
E
C
C
T
T
R
R
I
I
C
C
C
C
O
O
N
N
T
T
R
R
O
O
L
L
S
S
Y
Y
S
S
T
T
E
E
M
M
.
.
To those mechanical control microwave oven, electric control system mainly composes of interlock switch, timer,
power distributor and thermal cutout, etc. The electric
control system of those tough control microwave oven
is mainly composed of interlock switch, computer
controller and thermal cutout, etc.
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, EMN-109
microwave oven. It mainly consists of latch switch (S1,
S2), pilot switch (S3), door hook and starting
mechanism of the door interlock switch.
