TM 11-6625-2980-14
to the mainframe transistor used as the series pass
element, until the inverting and non-inverting inputs are
approximately equal. At this condition, the series pass
transistor drops the voltage from the raw supply until the
output is +5.2 V. Current limiting is provided by R1215.
When the current from the supply exceeds
approximately 1.1 A, the regulator provides no further
base drive current to the series pass element and
current limiting occurs.
The +33.5 Vdc from the mainframe is the raw supply
for the regulated +15 Vdc. The 3-terminal voltage
regulator, U1205, performs the entire regulating
function. Current limiting occurs within U1205.
The -33.5 Vdc from the mainframe is the raw supply
for the regulated -15 Vdc. As in the +15 Vdc supply a 3-
terminal voltage regulator, U1335, provides the
regulating function. However, due to additional load
considerations, the raw supply is pre-regulated to
decrease power dissipated by the integrated circuit. A
shunt current path to the load is furnished by VR1330
and R1330. The zener voltage is also used to maintain
base drive to the series pass mainframe transistor. This
transistor is used as a pre-regulator to drop the voltage
across U1335 to approximately 3.6 V Current limiting is
also provided by the regulator, U1335.
The dual tracking supplies provide the positive and
negative voltages required by the output amplifier. The
voltage at the base of Q1255 varies from 0 V to +5.2 V
depending on the setting of the HIGH LEVEL control.
When the voltage at the base of Q1255 varies from 0 V
to +2.6 V, the voltage at the collector of the series pass
transistor is +6 V. As the voltage at the base of Q1255
varies from +2.6 V to +5.2 V, the voltage at the collector
of the series pass transistor varies from +6 V to +26 V.
Transistor Q1255 and Q1270 form a differential
comparator. The voltage at the base of Q1270 is
referenced between the +5.2 V supply, ground and the
output voltage. As the HIGH LEVEL control is moved in
the positive direction, the collector of 01255 goes
negative This increases current flow through Q1280 and
therefore the series pass transistor in the mainframe
which raises the + tracking supply voltage to the output
amplifier Feedback to the differential comparator is
provided by R1275. Transistor 01265 prevents the +V
tracking supply from going lower than about +-6 V. The
base of Q1265 is set at about 2.6 V. When the base of
01255 goes more negative than about 2 6 V, Q1265
comes into conduction holding the common emitter
circuit at one diode drop from the base of 01265. If the
base of 01255 is lowered further, Q1255 looses control
of the circuit and the supply voltage remains at the level
determined by 01265, t6 V.
Current limiters for this circuit are Q1285, Q1290 and
Q1300 A differential comparator is formed by Q1285
and 01290. If the load on the 4 V supply exceeds the
maximum current allowed for the voltage supplied, the
voltage drop across R1282 becomes great enough that
Q1285 comes into conduction. This action increases
conduction in Q1270 reducing the current flow in Q1255.
Finally, the conduction through the series pass transistor
is limited to a safe value. The current through 01300 is
determined by the actual supply output voltage.
Therefore, the current limit varies proportionally with the
supply voltage In most overload conditions, the supply
folds back to minimum current. Diode CR1310 conducts
should the -V supply go more negative than ground.
The V supply operates in the same manner as the +V
1supply. Only the polarities are reversed. Transistors11
01355 and 01370 are the basic comparator transistors
The base of Q1355 varies between 0 V and +5.2 V The
-V output is prevented from going more positive than
about -6 V by Q1365 The series pass transistor is driven
by Q1380. The comparator transistors for the current
limiting circuitry are Q1385 and Q1395. The current
source for the current comparator is Q1400. Diode
CR1410 prevents the -V output from going more
positive than ground.
2-7/(2-8 blank)
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