Icom IC-211 Instruction Manual page 34

11. POWER SUPPLY CIRCUIT
Regardless of whether the transceiver is switched to the receive mode or not, power is
always supplied from a constantly activated source to the receiver AF amplifier, AGC,
the transmitter microphone amplifier circuits and also to the CW monitor. BFO and
VXO circuits are supplied through the mode switch. This power source supplies current
through R144, D33 and zener diode D32, producing a regulated voltage of about 9.6V.
This corresponds to the reference voltage of D32's cathode, and is applied to the base of
Q37, resulting in a regulated voltage of about 9.5V which is taken out at the emitter of
Q37.
The power source which is operative during reception supplies voltage to the RF am-
plifier, mixers, SSB IF amplifier, and FM IF circuits through the mode switch. Similar
to the constantly activated source in the receive mode power circuit, current flows
through R138, D26, and D32. A reference voltage is supplied to the base of Q34 and
regulated voltage is taken from the emitter of Q34.
The power source which is in operation during transmit supplies power to the 10.7MHz
oscillator, transmit mixer, IF amplifier, driver bias circuit, and APC control circuit.
Similar to the receive mode power circuit, in the transmit mode power circuit current
flows through R143, D31, and D32. A reference voltage is supplied to the base of Q35,
and regulated voltage is taken out from the emitter of Q35.
The ALC control circuit, exciting amplifier, power amplifier, AF power amplifier and
noise blanker circuits are supplied directly with 13.8V DC.
056 is provided to retain memory of the up-down counter inside the PLL LSI. If a DC
power source is connected, and the memory switch is ON, the operated frequency is
retained irrespective of the power switch position.
If the power supply is connected with polarity reversed, the equipment is protected.
Since D34 becomes forward biased, a large current flows and causes the fuse in the
external power supply cord to blow.
During reception, since the microphone push-to-talk (PTT) switch is OFF, there is no
flow of current through D27, D28, receive power supply becomes operative, and receive
+9V is obtained. Also, since D29 is OFF, voltage is supplied through R140 to the base
of Q36 and turns 036 ON. The base of Q35 is connected to ground through 036 and
D30, and so the transmit power supply is inoperative, and the transceiver is set in the
receive mode.
During transmission, the PTT switch is ON, Q34's base is connected to ground through
D27, and output voltage of the receive power supply becomes zero.
D28 connected to
the emitter of Q34 rapidly discharges voltage stored in the receive circuit capacitor to
prevent receiver and transmitter from functioning simultaneously during switching. At
the same time, Q36 is turned OFF, as its base is connected to ground through D29, and
so the D32 reference voltage is applied to the base of Q35, 49V is obtained from the
transmit power supply, and the transceiver will transmit.
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