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the programming resistors have been adjusted s o
that the supply i s yielding the desired output
voltage.
Further assume that the (-) s i d e of the
supply i s ground (common) and that the output
voltage instantaneously r i s e s (goes positive) due
to a variation in the external load circuit.
4-9
Note that the change may be in the form of a
slow r i s e in the output voltage or a positive going
a c signal. An a c signal i s coupled to the base of
Q1 by capacitor C1 and a d c voltage i s coupled by
R21.
4-10
The instantaneous r i s e in output voltage
c a u s e s the base of Q1 to go positive.
Q1 now in-
c r e a s e s i t s conduction and i t s collector voltage
goes negative.
The negative going error voltage
is amplified and inverted by Q2 and Q4, and
coupled to the gate of CR10. The negative going
input c a u s e s CRlO to decrease i t s conduction s o
that i t drops more of the filtered dc, and reduces
the output voltage to i t s original level.
4-11 If the external load resistance i s decreased
to a point where the load current exceeds the
value selected by the current limit potentiometer
R24, the negative voltage on the collector of Q1
forward biases CR7.
Thus, the collector of Q7 i s
clamped a t the negative voltage on the arm of
potentiometer R24 and the output current i s main-
tained a t a constant safe maximum. Any further
decreases in load resistance causes the output
voltage to decrease proportionally.
The range of
potentiometer R24 enables current limiting be-
tween 5 and 10 +1
mA.
4-12
MAIN DC SUPPLY
4-13 The 0-1 600 Vdc output is generated by the
main dc supply which consists of five low voltage
supplies in series.
The five supplies are CR31-
CR34 (205V), CR11-CR13 (380V), CR12-CR14
(380V), CR15-CR17 (380V), CR16-CR18
(
380V).
The negative side of the 205 volt supply i s con-
nected to the regulator CR10, and four positive
voltages, +585, +965, +1345, and +I725 volts are
connected through the VOLTAGE RANGE switch S2
to the (+) output terminal.
By switching the output
voltage in four s t e p s , the voltage across series
regulator CRlO never exceeds 585 volts.
Diode
CR28 protects the supply when the output i s short
circuited.
When the supply in delivering greater
than 585 volts and the output i s shorted, the
anode of CR28 becomes more positive than +585V.
Load current flows through CR28 and R33; and
depending on the position of S 2 , current may flow
through R30, R31, or R32. Resistor R33 determines
the maximum short circuit current that flows
through CR28.
4-1 4 SERIES REGULATOR
4-15 The conduction of the series regulator i s
controlled by the feedback voltage obtained from
the driver.
The conduction i s varied to provide a
voltage drop, which i s subtracted from the main
dc supply that results in the selected voltage
available a t the output terminals.
Silicon Con-
trolled Rectifier CRlO
is
a standard SCR used in a
reverse bias configuration, referred to a s a remote
base transistor. The name i s derived from the ap-
plication and mechanical structure of the device.
The gate lead in an SCR i s one junction removed
from the anode.
4-16 In this reverse bias configuration the SCR is
always conducting and the characteristics are
similar to a high voltage transistor with l e s s than
unity gain.
4-17 Diode CR8, connected across the series reg-
ulator, protects i t against reverse voltages that
could occur during parallel operation, if one supply
i s turned on before the other.
4-1 8 CONSTANT VOLTAGE INPUT CIRCUIT
4-1
9
This circuit (Q1 and Q2) continuously com-
pares a fixed voltage received from the reference
circuit with a portion of the output voltage and, if
a difference e x i s t s , produces an error voltage
whose amplitude and phase i s proportional to the
difference.
4-20
Diode CR1 prevents the emitter of Q1 from
going more positive than circuit common (-S).
This condition occurs when the output voltage i s
turned down (down programmed) rapidly.
Diode
CR3 prevents the base of Q1 from exceeding -0.7V
i n the negative direction. When the output volt-
a g e is turned up rapidly i t drives the b a s e of Q1
negative.
Network C3 and R18 provid'e some neg-
ative feedback from collector to base to eliminate
the posibility of oscillations.
4-2 1 DRIVER CIRCUIT
4-22 This circuit receives inputs from either the
voltage input circuit or the current limit circuit.
In constant voltage mode, driver Q4 maintains
CRlO a t the correct conduction level s o that CRlO
drops a sufficient voltage to hold the output con-
stant.
However, when the output current exceeds
the current limit setting, the voltage a t the arm of
R24 forward biases CR7 and applies a negative
voltage a t the base of Q4.
Transistor Q4 and CRlO
are held in steady conduction until the external
load i s removed.
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