Panasonic Inverter NN-H275, Service Manual

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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
OUTPUT ON-OFF TIME OF
POWERSETTING POWER(
%)
POWER RELAY B
(RY1)
APPROX. ON(SEC) OFF(SEC)
HIGH
P10 100% 22 0
P9 90% 22 0
P8 80% 22 0
MEDIUM-
HIGH P7 70% 22 0
MEDIUM P6 60% 22 0
P5 50% 22 0
P4 40% 22 0
MEDIUM-
LOW P3 30% 17 5
P2 20% 11 11
P1 10% 6 16
DEFROST P3 30% 17 5
7.2. 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
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 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.
7.3. Inverter turbo defrost
15