HP 6269B Operator’s, Organizational, Direct Support And General Support Maintenance Manua L page 30

output. When A4CR110 is fired, overvoltage lamp
A5DS2 is tuned on, completing a path for a + 11V
unregulated holding current through A5DS2. This
current holds A4CR110 on even after the output
voltage has fallen. A4 CR110 will remain in conduc-
tion until the supply is turned off. R92 supplies the
holding current if lamp A5DS2 should open. R106
protects A4CR108 and A4CR110 from the large surge
current that occurs when A4CR110 is first fired.
CR93 damps out positive overshoot in the trigger
pulse.
4-53 The firing of SCR A4CR110 biases Q90 into
conduction, placing approximately +11 volts on the
cathode of CR74 in the preregulator control circuit
and thus reverse biasing CR74 and CR75. This
action, by preventing transistor Q 72 from turning
off, prevents the generation of any trigger pulses
and turns off the preregulator. This prevents the
series regulator from experiencing a full-voltage,
full-current condition.
4-54 The crowbar circuit creates an extra current
path during normal operation of the supply, thus
changing the current that flows through the sam-
pling resistor. Diode CR92 keeps this extra current
at a fixed level for which compensation can then be
made in the constant current comparator circuit.
4-55 A slaving arrangement of crowbar circuits in
more than one unit is made possible by an extra
secondary winding (terminals 5 and 6) on transfor-
mer T90. Terminals on the rear barrier strip (±EXT.
CROWBAR TRIGGER) allow easy connection to this
winding. Connecting these windings in parallel
when operating in a multiple-supply configuration
will result in all the crowbars being activated if
one of the crowbars is tripped. To reset the crow-
bars in this arrangement, all of the units must be
turned off and then on. Correct polarity must be
observed when connecting the windings in parallel.
Figures 3-10 and 3-11 (Auto-Parallel and Auto-
Series ) demonstrate these connections.
4-56 TURN-ON CONTROL CIRCUIT
4-57 This circuit is a long time-constant network
which protects the triac and the series regulator
from possible damage during turn-on. When the
supply is first tuned on, C35 provides a positive
voltage to the anodes of CR35 and CR36. The volt-
age from CR35 is connected to the cathode of diode
CR74 in the preregulator control circuit to ensure
that it is initially reverse biased. After C35 be-
comes sufficiently charged, diode CR35 becomes
reverse biased and the preregulator control circuit
is permitted to fire the triac.
4-58 Diode CR36 performs a similar function for
the series regulator. CR36 initially couples a pos-
itive voltage to Q41 where it is inverted and ap-
plied to the series regulator. This negative voltage
keeps the regulator cut off untill C35 charges up.
Diode CR37 provides a discharge path for C35 when
the supply is turned off.
4-59 REFERENCE REGULATOR
4-60 The reference circuit is a feedback power
supply similar to the main supply. It provides
stable reference voltages used throughout the unit.
AH the reference voltages are derived from dc ob-
tained from full wave rectifier CR61-CR62 and filter
capacitor C61. The total output of the reference
circuit is 18.6V. Zener diodes VR60 and VR61 es-
tablish moderately well regulated potentials of
+6.2V and -6.2V respectively from the common point
+S, while the regulator circuit establishes a very
well regulated potential of +12.4 volts from +S.
Resistor R63 limits the current through the Zener
diodes to establish an optimum bias level.
4-61 The regulating circuit consists of s cries reg-
ulating transistor Q60, driver Q61, and differential
amplifier Q62 and Q63. The voltage across Zener
diode VR60 (+6.2 volts with respect to +S) and the
voltage at the junction of divider Z2L-R69B and Z2J
are compared, and any difference is amplified by
Q 62 and Q63. The error voltage thus appearing at
the collector of Q62 is amplified by driver stage
Q61 and applied to series regulator Q60 in the cor-
rect phase and amplitude to maintain the +12.4 volt
output at a constant level.
4-62 Diode CR60, connected from voltage divider
R66 and R67 to the base of Q61, serves as a turn-
on circuit for series regulator transistor Q60. When
the supply is first turned on, CR60 biases driver
Q61 on, thus turning on the series regulator. When
the reference supply reaches normal output, the
base voltage of Q61 is sufficient to reverse bias
CR60, thus effectively removing it from the circuit.
Capacitor C60, connected across the output of the
reference supply, removes spikes and stabilizes
the reference reguIator loop.
4-63 Unregulated 11Vdc is supplied from a sepa-
rate winding on transformer A3T2 by diodes CR53
and CR54 and filter capacitor C44. Additional light-
ly regulated reference voltages of -4V and -2.4V are
provided by diodes CR45-CR46 and CR47-CR48-CR49
respectively. Diode CR43 prevents reverse current
flow from damaging the main supply series reguIator
transistors. Diode CR7, shown in the schematic
near the current pullout resistors (R3, R4, and RS),
protects the Zener diodes in the reference circuit
by providing a path for surge currents which occur
during rapid down programming.
4-64 METER CIRCUIT
4-65 The meter circuit provides continuous indica-
4-7
TM 11-6625-2958-14&P