Description Of Operating Sequence; Variable Power Cooking Control; Inverter Power Supply Circuit; Turbo Defrost, Auto Cook - Panasonic NN-GT370M Service Manual

NN-GT370M

4 DESCRIPTION OF OPERATING SEQUENCE

4.1. Variable power cooking
control
High Voltage Inverter Power Supply (U) controls output power
by the signal from Digital Programmer Circuit (DPC). Power
relay always stay 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
HIGH
MEDIUM-HIGH
MEDIUM
MEDIUM-LOW
DEFROST
LOW
4.2.

Inverter power supply circuit

The Inverter Power Supply circuit powered from the line
voltage, 220V 50Hz AC input supplies 4,000V DC to the
magnetron tube, and functions in place ofthe H.V. transformer,
the H.V. capacitor and H.V. diode.
1. The AC input voltage 220V 50Hz 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.
OUTPUT MANUAL MICROWAVE
POWER(%) DUTY
APPROX.
ON(Sec.) OFF(Sec.)
100% 22
65% 22
50% 22
30% 22
30% 17
20% 13
4.3.

Turbo defrost, Auto cook

When the Auto Control feature is selected and the [Start] pad
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.
WEIGHT SELECTED
1.0KG
WEIGHT SELECTED
800g
0
4.4.

Grill cooking control

0
0
0
Grill cooking is accomplished by upper heaters only. One grill
5
cooking cycle is 33 seconds.
9
1. During grill cooking, the digital programmer circuit controls
power relay RY3´s ON-OFF time. In all three grill cooking
categories, power relay RY1 always stay ON, but RY3´s
ON-OFF time are shown in Figure.
GRILL
CATEGORY
ON (sec.)
1
2
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 RY3 & RY1´s duty ON-OFF time. In all
three combination cooking categories, power relay RY3 &
RY1's duty ON-OFF time are as shown in Figure.
COMBINATION
CATEGORY
1
2
3
8
Turbo Defrost
COOKING TIME
14min. 30sec.
Auto Reheat
COOKING TIME
8min. 00sec.
GRILL (RY3) MICROWAVE (DUTY)
OFF (sec.) ON (sec.)
33 0 0
24 9
GRILL(RY3) MICROWAVE(DUTY)
ON(sec.) OFF(sec.) ON(sec.)
27 6 6
21 12 12
14 19 19
OFF (sec.)
33
OFF(sec.)
27
21
14