2.1. Variable power cooking
control
High Voltage Inverter Power Supply (U) controls output power
by the signal from Digital Programmer Circuit (DPC). Power
relayalways stay on, butPWM (PulseWidth 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
BPQ EPG ON(SEC) OFF(SEC)
TURBO 1000W 100% 22 0
HIGH — 90% 22 0
DEFROST 270W 25% 15 7
MEDIUM 600W 60% 22 0
LOW 440W 45% 22 0
SIMMER 300W 30% 22 0
WARM 100W 10% 8 14
2.2. Inverter power supply circuit
The Inverter Power Supply circuit powered from the line
voltage, 230V 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 ACinput voltage230V 50Hz isrectified to DCvoltage
immediately.
2. DC voltagewill besupplied to theswitching 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 drivesthe Highvoltage transformerto increasevoltage
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 powerof themagnetron tubeis alwaysmonitored by
the signal output from the current transformer built into the
inverter circuit.
6. This signalis fedback to the microcomputerin theDPC to
determine operating conditions and output necessary to
control PWM signal to the Inverter Power Supply for control
of the output power.
2.3. Turbo defrost, Auto cook
When the Auto Control feature is selected and the Start pad is
tapped:
1. Thedigital programercircuit determinesthe powerlevel and
cooking time to complete cooking and indicates the
operating state in the display window.
2. When cookingtime inthe display windowhas elapsed,the
oven turns off automatically by a control signal from the
digital programmer circuit.
2.4. Sensor cooking
Auto sensor cooking without setting a power level or selecting
a time. All that is necessary is to select an Auto Sensor
Program before starting to cook.
Understanding Auto Sensor Cooking
As the food cooks, a certain amount of steam is produced.
If the food is covered, this steam builds up and eventually
escapes from the container. In Auto Sensor Cooking, a
carefully designed instrument, called the steam sensor
element, senses this escape of steam. Then, based upon
the Auto Sensor Program selected, the unit will
automatically determine the correct power level and the
proper length of time it will take to cook the food.
NOTE:
Auto Sensor Cooking is successful with the foods and
recipes found in the Auto Sensor Cooking Guide.
Because of the vast differences in food composition,
items not mentioned in the Cooking Guide should be
prepared in the microwave oven using power select
and time features. Please consult Variable Power
Microwave Cookbook for procedures.
2 DESCRIPTION OF OPERATING SEQUENCE6
NN-SD452W/ NN-ST462M / NN-ST452W