Panasonic NN-GD371S, Service Manual, Page: 7 / 32

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 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)
950W 100% 22 0
270W 30% 14 8
600W 70% 22 0
440W 50% 22 0
300W 30% 22 0
100W 10% 13 9
4.2. Inverter power supply circuit
The Inverter Power Supply circuit powered from the line
voltage, 230-240V 50Hz 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 230-240V 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.
4.3. Inverter defrost, Auto menu &
Auto reheat
When the Auto Control 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. Table shows the
corresponding cooking times for respective serving by
categories.
Weight Deforst (Meat Items) for BPQ models:
SELECTED WEIGHT COOKING TIME
1000 g 20 min.00 sec.
Weight Deforst (Small Piece) for EPG &WPG models:
SELECTED WEIGHT COOKING TIME
1000 g 19 min.00 sec.
Weight Cook (Fresh Vegetables)
For BPQ models:
SELECTED WEIGHT COOKING TIME
200 g 5 min.40 sec.
For EPG & WPG models:
SELECTED WEIGHT COOKING TIME
200 g 4 min.56 sec.
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 DESCRIPTION OF OPERATING SEQUENCE
7
NN-GD371S / NN-GD361M / NN-GD351W