4.1. Variable power cooking
control
High Voltage Inverter Power Supply (U) controls output power
by the signal from Digital Programmer Circuit (D.P.C.). Power
relay always stays ON, but PWM (Pulse Width Modulation)
signal controls microwave output power.
NOTE:
The ON/OFF time ratio does not correspond with the
percentage of microwave power since approximately 2
seconds are required for heating of magnetron
filament.
Variable Power Cooking
POWER SETTING
OUTPUT
POWER(%)
APPROX.
MANUAL MICROWAVE
DUTY
ON(SEC)
OFF(SEC)
HIGH
100%
22
0
MEDIUM-HIGH
70%
22
0
MEDIUM
60%
22
0
MEDIUM-LOW
45%
22
0
DEFROST
35%
18
4
LOW
25%
14
8
4.2. Inverter power supply circuit
The Inverter Power Supply circuit powered from the line
voltage, 120V 60Hz AC input supplies 4,000V DC to the
magnetron tube, and functions in place of the H.V. transformer,
the H.V. capacitor and H.V. diode.
1. The AC input voltage 120V 60Hz is rectified to DC voltage
immediately.
2. DC voltage will be supplied to the switching devices called
IGBT. These devices are switched ON-OFF by the 20 to 40
KHz PWM (pulse width modulation) signal from the
microcomputer in the DPC.
3. This drives the High voltage transformer to increase voltage
up to 2,000V AC.
4. Then the half-wave doubler voltage rectifier circuit,
consisting of the H.V. diodes and capacitors, generates the
necessary 4,000V DC needed for the magnetron.
5. Output power of the magnetron tube is always monitored by
the signal output from the current transformer built into the
inverter circuit.
6. This signal is fed back to the microcomputer in the DPC to
determine operating conditions and output necessary to
control PWM signal to the Inverter Power Supply for control
of the output power.
4.3. Auto Menu cooking
When the Auto Menu feature is selected and the [Start] button
is tapped:
1. The digital programer circuit determines the power level and
cooking time to complete cooking and indicates the
operating state in the display window.
2. When cooking time in the display window has elapsed, the
oven turns off automatically by a control signal from the
digital programmer circuit.
4.4. Grill cooking control
Grill cooking is accomplished by upper heaters only. One grill
cooking cycle is 33 seconds.
1. During grill cooking, the digital programmer circuit controls
power relay RY4´s ON-OFF time. In all three grill cooking
categories, power relay RY1 always stay ON, but RY4´s
ON-OFF time are shown in Figure.
GRILL
CATEGORY
GRILL (RY4)
MICROWAVE (DUTY)
ON (sec.)
OFF (sec.)
ON (sec.)
OFF (sec.)
1
33
0
0
33
4.5. Combination Cooking
Combination cooking is accomplished by microwave and grill
cooking (upper heaters) being done synchronously during one
combination cooking cycle. One combination cooking cycle is
33 seconds.
1. During combination cooking, the digital programmer circuit
controls power relay RY4 & RY1´s duty ON-OFF time. In all
three combination cooking categories, power relay RY4 &
RY1’s duty ON-OFF time are as shown in Figure.
COMBINATION
CATEGORY
GRILL(RY4)
MICROWAVE(DUTY)
ON(sec.)
OFF(sec.)
ON(sec.)
OFF(sec.)
1
27
6
6
27
2
21
12
12
21
3
14
19
19
14
4 DESCRIPTION OF OPERATING SEQUENCE
8
NN-CF770M
Summary of Contents for NN-CF770M CPH
Page 2: ...2 NN CF770M ...
Page 3: ...3 NN CF770M ...
Page 5: ...1 FEATURE CHART 2 CONTROL PANEL 5 NN CF770M ...
Page 6: ...3 SCHEMATIC DIAGRAM 3 1 CPH 6 NN CF770M ...
Page 7: ...3 2 RPH 7 NN CF770M ...
Page 31: ...10 7 How to check the semiconductors using an OHM meter 31 NN CF770M ...
Page 32: ...11 EXPLODED VIEW AND PARTS LIST 11 1 EXPLODED VIEW 32 NN CF770M ...
Page 39: ...12 DIGITAL PROGRAMMER CIRCUIT 12 1 SCHEMATIC DIAGRAM 39 NN CF770M ...
Page 40: ...40 NN CF770M ...
