Panasonic KX-G8300 Service Manual And Technical Manual page 45

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2-2. Antenna unit
Circuit Operation:
Modulator board (PQUP820ZA)
The modulator board consists of the modulator circuit, trigger circuit, DC-DC converter.
1) Modulator Circuit
Circuit Operation:
This circuit generates high-voltage pulse signals for the magnetron. The DC output (approx. 300 V) from the
DC-DC converter charges the pulse forming network (L801~L804, C805~C808) via the charging choke
(L810).
The pulse forming network (PFN) capacitance and charging choke (L810) inductance form a resonant
circuit, and the PFN voltage is charged to approximately double the DC voltage of the DC-DC converter.
Diode D803 prevents the stored energy of the PFN from flowing back to the power supply side (DC-DC
converter side). When the SCR (D802) receives a trigger signal from the trigger circuit, the SCR is turned
ON, and the stored energy from the PFN is discharged through the SCR and primary winding of the pulse
transformer (T801), and voltage pulses of the required width determined by the characteristic impedances
of the PFN and of the pulse transformer are generated in the primary windings of the pulse transformer.
The pulse transformer serves to step up the pulse voltage of the primary to the high voltage (Approx 3kV)
required to drive the magnetron.
Relay (RLY801) serves to change the PFN configuration in accordance with the pulse width (long/short)
selection signal which is supplied from the display unit via driver Q803.
When the long pulse mode is selected, the PFN consists of L802 ~ L804 and C806 ~ C808, and pulses
with a width of approximately 0.5usec are generated.
When the short pulse mode is selected, the PFN consists of L801 and C805, and pulses with a width of
approximately 0.08usec are generated.
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Fig. 44
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