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Model 7754A/7414A
4-41. Regulator/Oscillator.
442. The Regulator/Oscillator Assembly includes a +5V, a
+12V and a -12V voltage regulator, a 200 kHz oscillator
with a stabilizing regulator, and the timing circuits for the
timed marker stylus. The relationship of these circuits is
shown in Figure 4-10.
443. +5-VOLT REGULATOR. The +5 volt regulated sup-
ply is used in the timing generator, and in the signal inter-
ruption circuit of each driver amplifier. It is derived from
the +20 volt unregulated supply with an integrated circuit
voltage regulator that has an independent voltage reference.
A resistor in series with the regulator absorbs some of the
power dissipated in the regulation process, thereby reducing
the amount of heat generated in the regulator.
444. +12-VOLT REGULATOR. The +12 volt supply is
derived from +20 volts with an integrated circuit regulator
used as a regulator-driver. Since the IC is not capable of
handling the required power, an external power transistor,
Q6, acts as the series regulator. The IC regulator incorpor-
ates a ±5% voltage reference. To adjust the voltage (within
100 millivolts), the circuit uses potentiometer R2 to refer-
ence ground. Resistor R15, one ohm in series with regu-
lating transistor Q6, provides short circuit protection and
has a current-sensing function. R4 and Cl form an RC net-
work that improves the stability of the operational ampli-
fier that drives Q6.
445. -12 VOLT REGULATOR. The -12 volt supply is
derived from the -20 volt unregulated output. The -12
volt regulator is another operational amplifier, with the
driven, series regulating element as Q5. Q1 and Q2 are the
differential components of the amplifier. Q1 base is
returned to ground via R5, and the reference input, derived
from -12 volts through R12 and R13, is connected to Q2.
The amplifier output drives Q5, and is returned to the
refer~
ence input via feedback resistor RIO. Current limiting is
provided by R8 and Q4 (not shown in diagram), and RC
network R6, C3 aids stability.
446. 200 kHz OSCILLATOR. The high frequency excita-
tion signal, used in the galvanometer position capacitive
transducer, is generated by L-C Oscillator Q9 and its associ-
ated circuitry. Random conductance in Q9 sets up currents
in Tl which are fed back, in phase, to the base of Q9
through CI3. Since feedback is greater than unity gain,
oscillation amplitude is controlled only by saturation of
Q9, and reaches nearly the power supply voltage. Oscillator
frequency is determined by C15 and the external loading
capacitance across the transformer primary together with
Tl inductance. Filter choke Ll, with C14 (not shown),
decQuples the oscillator and its harmonics from the -12
07754-1
Section IV
Principles of Operation
volt supply. A step-up winding, connected to CI8, increases
the oscillator output voltage by about 7 to 1.
4-47. OSCILLATOR REGULATION CIRCUIT. Since the
position transducers are an important factor in recorder
accuracy, the 200 kHz oscillator must remain extremely
stable in operation. An indication of oscillator stability,
both in frequency of oscillation and ill amplitude, can be
obtained by detecting the product of frequency and output
voltage, and comparing the results with a reference voltage.
The L-C oscillator circuit, by nature, exhibits frequency
changes with variations in load. The oscillator regulation
circuit varies the oscillator supply voltage to compensate
for loading, which stabilizes the output.
4-48. To do this, the oscillator output detector generates a
voltage proportional to frequency and amplitude of the
200 kHz component being removed by C11. This voltage is
compared in differential amplifier U2 to a reference voltage
(+4.23 volts), derived from the +12 volt supply through
voltage divider RI8-RI9. The comparator output drives a
series regulator transistor, part of U2, in such a way that
the oscillator will maintain a constant output amplitude,
and therefore a constant frequency.
4-49. Marker Circuits.
4-50. The Recorder includes two monopolar markers, one
of which is timed, and the other actuated with a front panel
or remote pushbutton. The timing circuits for the timed
marker are located on the Regulator/Oscillator Assembly,
and operate by dividing 50 or 60 Hz ac input to generate
one-second pulses, and then dividing these pulses to obtain
pulses at one-minute intervals. The selected set of pulses is
then amplified to drive the timed marker.
4-51. Line frequency ac voltage at 24 Vac is obtained from
the power transformer and filtered to remove transients and
high-frequency noise. Then a threshold detector circuit,
QI3-QI4, generates a train of spike waveforms at line fre-
quency to drive the divider TTL logic circuitry. Integrated
circuit U3 divides by 5 or 6, and then U4 divides by 10 to
achieve a 50: I or 60: 1 division. The seconds output is
routed to switch Q16, and also to the minutes divider,
which divides by 60 in the same way, using IC's U5 and U6.
The minutes output is routed to transistor switch Q15.
4-52. MARKER SWITCHES. When the circuit is off, both
switches are grounded, stopping conduction in QI5 and
Q16 and permitting Q17 to conduct steady-state. When
either minute or second marking is selected, the ground is
removed from one switch, which conducts and connects the
base of Q17 to ground. Once each minute or second, the
timing circuit cuts off the switch, thereby restoring the base
4-11
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