Power Supply Circuits - Icom IC-7800 Service Manual Addendum

(3) DDS LO CIRCUIT
The 40 MHz reference system clock is amplified at the
amplifiers (Q701, IC602, IC603), and is then applied to the
DSP IC (IC601). The applied signal is quintupled in the IC,
then uses 200 MHz DSP system clock signal.
The 200 MHz clock signal is divided 1/400, and then uses as
the 500 kHz sampling frequency of the A/D converter
(IC501).

3-6 POWER SUPPLY CIRCUITS

3-6-1 VOLTAGE LINES (DC-DC UNIT)
LINE
Common 15 V line from the REG unit. The volt-
C15V age is applied to the LOGIC unit via the J3,
pin 6.
Common 8 V from the REG unit. The signal is
H8V applied to the regulator circuits on the DC-DC
unit.
The same voltage as the +15 line passed
through the switching relay (RL142). The voltage
+15V is applied to the PA200W board (via J420, pins 1
and 2), LOGIC (via the J820, pins 4–6) and
MAIN (via the J450, pin 3) units.
Common –12 V converted from the +15 V line
and regulated by the –12V regulator circuit
–12V (IC121). The voltage is applied to the LOGIC (via
the J820, pin 3) and MAIN (via the J450, pin 2)
units.
Common 5 V converted from the H8V line and
regulated by the VDD1R5 regulator circuit
VDD1R5
(IC101). The voltage is applied to the LOGIC unit
via the J821, pin 2.
Common 5 V converted from the H8V line and
regulated by the VDD5 regulator circuit (IC81).
5V The voltage is applied to the LOGIC (via the
J821, pin 4) and MAIN (via the J450, pin 10)
units.
The same voltage as the H8V line passed
through the switching relay (RL142). The voltage
+8V
is applied to LOGIC (via the J820, pin 7) and
MAIN (via the J450, pin 4) units.
Common 5 V converted from the +8V line and
regulated by the +5V regulator circuit (IC61). The
+5V
voltage is applied to the LOGIC (via the J820,
pin 8) and MAIN (via the J450, pin 4) units.
Common 3 V converted from the +8V line and
regulated by the +3R3V regulator circuit (IC41).
+3R3V The voltage is applied to the LOGIC (via the
J820, pin 9) and MAIN (via the J450, pins 6–8)
units.
Common 3 V converted from the H8V line and
regulated by the VDD3R3 regulator circuit
VDD3R3
(IC21). The voltage is applied to the LOGIC unit
via the J821, pin 3.
DESCRIPTION
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