TM 11-6625-486-14&P
5-8 . Regulated
Power
Supply
and
Voltage
b. Ac Line Operation.
Distribution Circuit
(1) With the FUNCTION SW in any position
except OFF, ac line voltage is applied through front panel
receptacle P701, (through filter Z701 (AN/USM-159B
The unit power supply operates from self-contained
only)) fuses F701 and F702, and line ballast lamp DS703
flashlight batteries that supply 9 volts dc or 115 to 250
to T701. The ballast lamp limits the current in the T701
volts ac external power. Automatic switchover from
primary circuit. The secondary voltage is applied to full-
batteries to ac is accomplished internally. A plunger-type
wave rectifiers CR601 and CR602. Negative dc voltage
interlock switch, connected in series with the batteries on
is taken from the center tap of T701 and applied through
the front panel, prevents battery drain when the unit front
deocupling resistor R601 to the regulator and T501. With
cover is closed. The front panel voltmeter monitors power
this voltage, Q601 operates in the same manner as
supply output voltage for either battery or ac operation.
described for battery operation (a (1) above). The
The power supply provides regulated and unregulated
unregulated voltage is filtered by C703.
voltages for all circuits in the meter. Power supply
(2) The entire power supply output voltage is
operation for batteries or ac line power is explained in a
impressed on the anode of diode CR603 and, since the
and b below.
polarity of this voltage is opposite to that required for
a. Battery Operation.
conduction, CR603 cannot conduct. This diode is used to
(1) During battery operation, 9 volts dc is
switch from battery power to ac line power while the
applied through battery interlock switch S702 (closed
batteries remain connected in the circuit. Regardless of
when front cover is removed) and switch S701A to diode
ac or battery operation, battery voltage is impressed on
CR603. This negative voltage passes through CR603
the cathode of CR603 and would normally pass through
and is applied to the collector of emitter-follower regulator
the diode. The main difference between ac and battery
Q601. Unregulated voltage is taken from this point and
operation is that with ac operation, the negative voltage
directed to transformer T501. All other voltages are
on the anode of CR603 us equal to, or slightly greater
regulated by Q601. Transistor Q601 is connected as a
than, that applied to the cathode side. Diode CR603 acts
series regulator with unregulated voltage applied to the
like an open switch and cannot conduct.
collector and regulated voltage taken from the emitter.
(3) The power supply output voltage is also
Resistor R602 provides forward base bias and Zener
directed through resistor R605 to resistor R604 and
diode CR604 sets the level and regulating range.
voltmeter M701. Resistor R605 drops the voltage to 9
(2) If emitter load current increases, the output
volts which is the same as the battery voltage. Although
voltage will drop (become less negative) in proportion to
this voltage is added to the battery voltage from switch
the voltage drop across Q601. This voltage drop is
S701A, it has no affect on the batteries since the battery
sensed by the base as a decrease in forward bias and
voltage is also 9 volts. Voltmeter M701 is basically a 0- to
causes Q601 to increase its internal resistance. The
1- milliampere meter converted to measure 10 volts full-
transistor then conducts less and tends to hold a constant
scale with multiplier resistor R604. This panel meter
output voltage. If emitter load current drops (output
provides a relative indication of battery voltage or. power
voltage decreases), the increase in forward base bias
supply rectified voltage. The meter has red and green
causes Q601 to decrease its internal resistance and
scale divisions, with the red section starting at zero and
increase voltage. The regulated output voltage is filtered
the green section starting at 6.5 volts. Normal indication
by C704 and applied directly to the audio amplifier circuit
is approximately three-fourths of the green section. In
and through switch S701A to the crystal oscillator. The
variable frequency oscillators receive voltage through
desired, the power cable must be unplugged from either
decoupling resistor R603 and switch S703D. In all
the panel receptacle or the ac power source; otherwise,
positions of the FUNCTION SW, except MOD, Zener
either the panel receptacle or the ac power source;
diode CR605 regulates the vfo voltage. With the switch
otherwise, the unit will operate on ac power instead of
set to MOD, the vfo voltage is modulated at 900 Hz rate.
batteries.
5-16
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