TM 11-6625-2980-14
Period Generator
This circuitry generates the internal period timing
waveform. In this mode, U140B operates as an a stable
multivibrator. When either input of U140B is high, pin 7
is high and pin 6 is low. The switched timing
capacitances are connected from pin 7 to pin 11. These
capacitors are switched by the period range switch. The
period variable control, R190, varies the resistance in
the negative feedback loop.
To start the period cycle, assume pin 7 of U140B goes
high and pin 6 low. This positive step, at pin 7, is
coupled through the period timing capacitor to pin 11. As
the timing capacitor discharges through the resistances
connected from pin 11 to pin 6, the voltage at pin 11
decays at a rate determined by the timing capacitor and
these resistances. When the switching level
(approximately 4 V) is reached, pin 7 goes low and pin 6
goes high. The negative step, at pin 7, is coupled
through the timing capacitor, and appears at pin 11. The
capacitor now charges through the resistances until the
switching level is reached, and the period cycle repeats
The symmetry adjustment compensates for the bias
current through pin 11.
When the PERIOD switch is in any position other than
EXT TRIG (MAN), switch S200-2 is opened. This lowers
pin 10 of U140B and permits the period generator to
operate during the external gate on time. During the
time of the external gating signal pins 4 and 2 of U 140A
are low. Pin 3 is high. As transistors Q150 and Q160
form a comparator, with their bases connected to pins 3
and 1 of U140A respectively, the collector of 0150 is low
causing the emitter of Q175 to be low, as well as pin 11
of U140B. This allows the period generator to operate.
During the gated off time this action reverses. Pin 11 of
U140B rises and inhibits the period generator.
Resistor R170 and R165 adjust the lock up voltage at
pin 11 of U140B so that, at turn on, the first period
generated is identical in time with subsequent periods.
Resistor R 165 is switched into the circuit only on the 20
ns range. Components R177 and C177 form a time
constant to help compensate for first period error.
Delay Generator
This circuitry provides the delay for delayed or paired
pulse operation. As the signal from the period generator
of the external trigger input goes from high to low at pin
7 of U270B, pin 3 goes high. This causes pin 5 of
U270A to go high and pin 2 low. Pin 13 of U270D and
pin 9 of U300B go low. Pin 15 of U270D goes high but
pin 10 of U300B does not follow until about 10 ns later,
due to the delaying action of R275 and C275. When pin
9 of U300B goes low pin 6 goes high, assuming pin 11 is
already low Pin 6 stays high until pin 10 goes high as
described above. This action provides the delay
generator with about a 10 ns trigger pulse under all input
conditions
The positive-going trigger pulse, at pin 5 of U300A,
causes pin 3 to go low and pin 2 high. Positive feedback
through R300 and C300 causes pin 4 to go high. The
low at the base of 0320 turns 0320 off. The emitter of
Q320 goes negative at a rate determined by the timing
capacitor and current source 0342, with its variable
emitter resistances. As the emitter of 0320 goes
negative, it pulls the base of 0294 negative which lowers
pin 4 of U300A. When pin 4 reaches the switching
threshold (=4.0 V) pin 2 goes low and pin 3 high. The
timing capacitor is now discharged through 0320. The
monostable delay generator is now reset for the next
trigger pulse. Transistor Q290 provides a constant load
for the power supplies irrespective of the current flowing
through Q294.
Components R304, R306 and C304 provide a delay line
for the CONTROL ERROR light. The output from the
delay generator is connected to pin 13 of U300C. Pin 15
of U300C is high during the delay time and pin 14 low.
Gates U360B and D provide a positive-going trigger at
pin 15 of U360D when the delay time ends. Gates
U360A and C provide a positive-going trigger at pin 14
when the delay time starts. As the delay time starts, pin
4 of U360A goes low as does pin 11 of U360C. Pin 10 of
U360C is low as the anode of CR378 is grounded
through the UNDLY switch. The low at pin 11 of U360C
allows pin 14 to go high Pin 14 stays high until the
propagation time through gate U360A and the delaying
action of R364 and C366 allow the high generated in
U360A, from pin 2, to reset U360C through pin 10. This
causes pin 14 to return to its low state. The width of the
output trigger pulse is about 6 ns.
To obtain the delayed trigger, the anode of CR378 is
connected to +5 V disabling gate U360C. The anode of
CR382 is grounded through the DLY switch. Gates
U360B and U360D now operate in exactly the same
manner as U360A and C A positive trigger pulse
appears on pin 15 of U360D when the delay time ends
(pin 6 of U360B goes from high to low). In the paired
pulse mode both gates operate. Gate U360C provides a
positive-going trigger at the start of the delay time and
U360D a positive trigger at the end of the delay time.
Duration Generator
This circuitry generates the duration times. Gate U400B
accepts the delayed or undelayed positive triggers from
the delay generator. The result is a positive-going pulse
at pin 5 or U400A. This triggers the duration generator
which operates in the same manner as the delay
generator. Refer to the discussion under the heading
Delay Generator for a description of the duration
generator operation. Gate U400C is an output buffer Pin
2-2
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