Panasonic NN-CS599S, Service Manual

Page: 7 / 42

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)
HIGH 100% 22 0
MEDIUM-HIGH 70% 22 0
MEDIUM 55% 22 0
MEDIUM-LOW 40% 22 0
LOW 20% 13 9
DEFROST 30% 17 5
4.2. Inverter power supply circuit
The Inverter Power Supply circuit powered from the line
voltage, 220-240V 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 220-240V 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. Steam defrost, Auto cook &
Steam reheat
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. Table shows the
corresponding cooking times for respective serving by
categories.
Steam Defrost
SELECTED WEIGHT COOKING TIME
1.0 kg 15 min.50 sec.
Auto Cook (Vegetable)
SELECTED WEIGHT COOKING TIME
100 g 1 min.30 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.
4.4. Convection & Grill Convection
cooking control
The digital programmer circuit controls the ON-OFF time of the
heater in order to control oven cavity temperature.
1. After selecting desired oven cavity temperature of
Convection/Grill Convection (the range of selected oven
temp is 100°C-300°C) and pressing [Start] pad, a high level
signal comes out of the micro computer and applies to
power relays, RY5 and RY9.
2. When RY5 & RY9 are switched to ON, power source
voltage is applied to the convection heater & upper heater
(center one), and the heaters turn on.
3. The digital programmer circuit senses the oven cavity
temperature through oven temp sensor (thermistor). When
the oven temperature reaches the set temperature, DPC
stops supplying high level signal to the power relays, and
the heaters turn off.
4. After the convection heater and upper heater (center one)
turn off, the oven temperature will continue increasing for a
while and then decrease as shown in Figure.
When the oven temperature drops below the set
temperature, the digital programmer circuit senses the
signal and starts supplying a high level signal to RY5 again.
NOTE:
•
For "CONVECTION" function, after preheating, RY9
would no longer be switched to ON.
• For "GRILL CONVECTION" function after
preheating, RY9 would be switched ON-OFF by the
signal from the digital programmer circuit.
4 DESCRIPTION OF OPERATING SEQUENCE
7
NN-CS599S