Panasonic NN-S543WF, Service Manual

Page: 36 / 62

DESCRIPTION OF OPERATING SEQUENCE
1. Variable power cooking control
The coil of power relay B (RY1) is energized intermittently by the digital
programmer circuit, when the oven is set at any power selection except
for High power position. The digital programmer circuit controls the
ON-OFF time of power relay B contacts in order to vary the output
power of the microwave oven from ”Low” to “High” power. One
complete ON and OFF cycle of power relay B is 22 seconds. The
relation between indications on the control panel and the output of the
microwave oven is as shown in table.
NOTE: The ON/OFF time ratio does not correspond with the
percentage of microwave power since approximately 2 sec-
onds are required for heating of magnetron filament.
2. Inverter Power Supply Circuit NEW H,V
This Inverter Power Supply Circuit supplies 4,000V DC to the magnetron
tube from the line voltage,120v 60Hz AC input. functions as 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 will be 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 up to 2,000V AC
and approximately 3V AC by means of transformer.
4. Then the half-wave doubler voltage rectifier circuit, consisting of the
HV 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 ciruit.
6. Then this signal will be fed back to the microcomputer in the DPC to
determine operating conditions and output necessary to control PWM
signal to the inverter Power Supply to control output power.
3. Inverter Turbo Defrost
When this Auto Control feature is selected and the Start Pad is tapped:
(A) 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.
(B) When cooking time the display window has elapsed, the oven tums
off automatically by a control signal from the digital programmer circuit.
- 9 -
POWER SETTING
OUTPUT
POWER(%)
APPROX.
ON-OFF TIME OF
POWER RELAY B (RY1)
ON (SEC) OFF (SEC)
HIGH
MEDIUM-HIGH
MEDIUM
MEDIUM-LOW
DEFROST
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
30%
22
22
22
22
22
22
22
22
15
8
22
0
0
0
0
0
0
0
0
7
14
0
Variable Power Cooking
P10
P9
P8
P7
P6
P5
P4
P3
P2
P1
P3
Inverter Turbo Defrost
SELECTED
WEIGHT
1.0LB
6.0LB
COOKING TIME
4 min.28 sec.
25 min.00 sec.