Tektronix 7623, Инструкция по эксплуатации

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Circuit Description— 7623/R7623 Service
of Q909. Then Q909 takes over conduction of the
comparator. The collector current of Q909 increases the
voltage drop across R896 to reduce the conduction of
Q896 in the —50 V Feedback Amplifier and limit the
conduction of Q903. Q910 is connected as a constant­
current source for Q908-Q909.
Fig. 3-23. Schematic illustrating voltage drop between power
supply output and load due to resistance of interconnecting wire.
—15-Volt Supply
Basic operation of all stages in the —15-V Supply is the
same as for the —50-Volt Supply. Reference level for this
supply is established by divider R945-R946 between
ground and the —50 V Sense voltage. The divider ratio of
R945-R946 sets a level of -15 volts at the base of Q943A.
The level on the 50 V Sense line is held stable by the
-50-Volt Supply as described previously. The -15 V Sense
voltage is connected to the base of Q943B through R940.
Any change at the output of the —15-Volt Supply appears
at the base of Q943B as an error signal. The output voltage
is regulated in the same manner as described for the
-50-Volt Supply.
—50 Volts adjustment R881 determines the divider ratio
to the base of Q886B and thereby determines the feedback
voltage. This adjustment sets the output level of the supply
in the following manner: If R881 is adjusted so the voltage
at its variable arm goes less negative (closer to ground), this
appears as an error signal at the base of Q886B. In the same
manner as described previously, this positive-going change
at the feedback input of the differential amplifier increases
the conduction of the -50 V Series Regulator to produce
more current to the load, and thereby increase the output
voltage of this supply. This places more voltage across
divider R880-R881R882 and the divider action returns the
base of Q886B to about - 9 volts. Notice that the feedback
action of this supply forces a change in the output level
which always returns the base of Q886B to the same level
as the base of Q886A. In this manner, the output level of
the —50-Volt Supply can be set to exactly —50 volts by
correct adjustment of R881.
The —50 V Current Limiting stage Q908-Q909 Q910
protects the - 50-Volt Supply if excess current is demanded
from this supply. All of the output current from the
—50 Volt Supply flows through R903. Transistor Q908
senses
the voltage at the collector of the -50 V Series
Regulator Q903 and compares it against the -50 V output
level at the base of Q909 which is obtained from the other
side of R903. Under normal operation, Q908 is held in
conduction and Q909 is off. However, when excess current
is demanded from the -50 V Series Regulator due to a
short circuit or similar malfunction at the output of this
supply, the voltage drop across R903 increases until the
base of 0908 goes more negative than the level at the base
+5-Volt Supply
Basic operation of the +5-Volt Supply is the same as
described for the previous supplies. The +5 V Current
Limiting and +5 V Feedback Amplifier (except for Q985) is
made up of a five-transistor array U973. Notice that both
U973C and Q985 in the +5 V Feedback Amplifier are
connected as emitter followers, since inversion is not
necessary in the feedback path for positive output voltages.
Reference voltage for the +5 V Feedback Amplifier stage is
established by divider R970-R971 between the +5 V Sense
and - 50 V Sense feedback voltages. This divider establishes
a quiescent level of about 0 volt at the base of U973E.
+ 15-Volt Supply
The + 15-Volt Supply operates in the same manner as
described for the previous supplies. The unregulated
+ 15 Volt Supply provides the source voltage for the
High-Voltage Oscillator stage in the CRT circuit through
fuse F814 and P870.
+50-Volt Supply
Operation of the +50-Volt Supply is the same as
described for the previous supplies. The unreg50
volts, from 50 V Rectifier CR808, is used to provide a
positive starting voltage for the -50-Volt Supply.
3-30