Panasonic Microwave Ovens with Inverters Technical Manual page 17

Inverter Power Supply Circuit Explanation
The inverter power supply circuit uses the AC line 120V, 60Hz to supply 4,000V
DC to the magnetron tube.
The AC input voltage is rectified by the bridge rectifier DB701
DC voltage is applied to the Switching IGBT (Insulated Gate Bipolar Transistor)
circuit.
Note: The IGBT is a cross between the bipolar and MOSFET transistors.
The high voltage transformer is driven by a PWM (Pulse Width Modulated) signal
generated by the microprocessor in the DPC (Digital Programmer Circuit). The
transformer is a component in the resonance circuit of the oscillator. Therefore,
a change in load or the power level affects the frequency of the drive signal.
Typically, the frequency ranges between 20KHz to 40KHz.
The high voltage transformer generates approximately 2,000V DC or more in the
secondary winding and approximately 3V AC in the filament winding.
The half wave rectifier circuit, (D701, D702) generates the necessary 4,000V DC
needed to drive the magnetron.
A signal from the current-sensing transformer CT701 in the inverter circuit is
used to monitor the power output from the magnetron. This signal is applied to
the microprocessor in the DPC to determine the working condition and the output
necessary to control the PWM signal supplied to the inverter to control the power
output.
Warning:
It's neither necessary nor advisable to attempt measurement of the high voltage.
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