TM 11-6130-247-14-1
network R33 and C13. Resistor R36 maintains
and filter circuit C1, CR1 through CR4, and C2.
a minimum load across the preregulator output.
There are three secondary windings of trans-
former T2. One secondary winding (pins 10, 12,
b. Current Overload Protection. If a series reg-
and 14) supplies bias to the Darlington connec-
ulator passing stage develops a short circuit, a
tion of series switch transistors Q10 and Q9.
heavy load or short circuit at the output of the
The second secondary winding (pins 6, 7, and
power supply will result in a significant increase
8) of transformer T2 supplies back bias to the
in the current through the series switch. This
Darlington connection of Q15, Q14 and Q13. The
increase in current is sensed by resistor R28.
third secondary winding (pins 4, 5 and 15) of
The voltage drop across R28 increases and for-
transformer T2 supplies power to the auxiliary
ward-biases transistor A4Q38 which then applies
power supply consisting of differential amplifier
a positive voltage to the Schmitt trigger input,
A3Q25 and associated circuitry, second different-
shutting it off. The reaction time of this circuit
ial amplifier A3Q23, A3Q24 and associated cir-
is in microseconds. If the transient or short cir-
cuitry and series regulator circuit A3Q22, A3Q21
cuit persists, capacitor A4C41 begins charging.
and associated circuitry. The output of the full-
When the positive charge across A4C41 reaches
wave rectifier is used to supply operating voltage
the breakdown voltage of Zener diode A4CR32,
to the preregulator by applying the rectified volt-
the zener diode allows this positive voltage to be
age to zener diode A4CR29 and resistor A1R90
applied to the control gate of silicon-controlled
in series. This produces a 15-volt dc potential to
rectifier A4CR31, allowing it to conduct. A4CR31
be used by the preregulator without disturbing
then shorts out the preregulator, removes all cur-
the full output voltage of the rectified dc. Resistor
rent from series switch transistors Q9 and Q10,
A4R2 provides bias for unijunction transistor
and drops the output voltage and current to zero.
A4Q1 which will be used as an oscillator. Re-
The only way A4CR31 can be reset is to remove
sistors A4R3 and A4R4 and capacitor A4C4
input power.
produce a charging time constant to the gate of
A4Q1. As the positive charge on A4C4 increases,
a point is reached which forward biases A4Q1.
ply output voltages is sensed by voltage divider
Capacitor A4C4 then discharges through A4Q1
R59A and R59B, which are the front panel VOLT
which reduces the positive charge of capacitor
ADJ controls, and A3R60. This divided-down
A4C4. Transistor A4Q1 turns off and the cycle
sample of the output voltage is applied to A3Q-
is repeated. Resistor A4R4 is used to vary the
36, which is one-half of a differential amplifier.
time required for A4C4 to charge to the forward
The other half, A3Q35, is supplied with a con-
bias point. This sawtooth output of capacitor
stant reference voltage. The bases of transistors
A4C4 is coupled through resistor A4R5 to emit-
A3Q35 and A3Q36 receive a constant current
ter-follower transistor A4Q2 and its associated
supply from transistor A3Q34 and associated cir-
circuitry. The signal output across resistor A4R7
cuitry. Any error sensed by the differential amp-
is coupled to the mixer amplifier circuitry by
lifier is applied to a second differential amplifier
capacitor A4C7. Mixer amplifiers A4Q3 and A4-
composed of A3Q32, A3Q33 and associated cir-
Q4 and associated circuitry provide a means of
cuitry. Capacitors A3C24 and A3C25 are used
injecting a dc bias, proportional to detected error
to insure that the differential amplifier will not
in output voltage or current; to control the time
oscillate under any line of load conditions. Varia-
required for the dc signal combined with the
tions in A3Q32 collector current are coupled via
sawtooth signal, to fire the Schmitt trigger com-
A3Q31 into the base of Q15. The base bias of
posed of A4Q5, A4Q6, and associated circuitry.
Q15 is constant current generator A3Q30 and its
The output frequency of the Schmitt trigger will
associated circuitry. Transistor A3Q31 operates
remain constant (that is, same as the sawtooth
in the saturated condition during voltage mode
frequency), but the pulse width will vary. The
operation and has no affect on Q15 bias. The
Schmitt trigger output pulses are amplified by
change in Q15 bias controls the drive current for
transistor A4Q7 and applied to driver transistor
the Darlington connection linear series regulator,
A4Q8 which will switch Darlington-connected
changing the impedance of Q13. This provides
series switch transistors Q10 and Q9 on and off.
instantaneous correction of an existing error, and
As the on time of the series switch transistors
thus holds the output voltage constant. To pro-
increases, the output voltage and current in-
vide proper voltage drop across series pass reg-
crease. The switched output is filtered by in-
ulator Q13 without excessive heating, it is neces-
sary to maintain the Q13 voltage drop essentially
ductor L1 and series resistance-capacitance (rc)
4-3
