Power Supply Circuit - Icom IC-25A Instruction Manual

RF power output is fed to D4 in the PA unit and rectified, then fed to the indicator driver IC
through the level adjust resistor R110.
POWER SUPPLY CIRCUIT
This circuit employs a multipurpose voltage regulator, ІСб. It puts out a constantly activated 8V,
R8V which is operative during receive, and T8V which is operative during transmit. R8V isput out
from Pin 6, and T8V is put out from Pin 8 of IC6. By grounding Pin 5, R8V goes OV and T8V is
actuated, thus the set will be turned to transmit mode.
PLL (PHASE LOCKED LOOP) UNIT
LOCAL OSCILLATOR CIRCUIT
This circuit produces 40.677MHz signal with O1, and the signal at 3 times this frequency, i.e.,
122.03MHz, are taken from the collector of Q1.
When the operating frequency, has 5KHz digit, D1 is turned OFF and C2 is inserted in series into
the serial capacitor of the crystal. Thus the output frequency of the local oscillator is shifted
+5KHz.
MIXER, LOW PASS FILTER, AND AMPLIFIER CIRCUIT
The output signals from the local oscillator circuit and the VCO signals are mixed by the MOS
FET mixer O5. The output signals are fed to the low-pass filters to filter out only the signals
below 15MHz. The output signals from the filter are amplified to the proper drive level (more _
than 3Vp-p) of the programmable divider IC1 by O2. Then the signals are fed to Pin 12 of IC1
through C9.
ТТ ТТ ABCD L D/A
ADRS DATA
40.677 X3MHZ
DRIVER UNIT CPU
PROGRAMMABLE DIVIDER CIRCUIT
The input signals at Pin 12 of the PLL IC, IC1, consists of programmable divider, reference fre-
quency generator and phase detector, are divided by the BCD input signals at Pins 6 ~ 9 and its
digit signals at Pins 2 ~ 5.
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