R6 to the collector of Q2, and less
creases to compensate for the ini-
current flows through R5 to the base
tial output voltage reduction.
of Q1. The base-to-emitter current
(c) Diode CR6 prevents a large output
and the collector-to-emitter current of
surge voltage when VOLTAGE
Q1 decrease. This limits the output
ADJUST resistor R19 is set to a
current to the value selected by
low value and the power supply is
SHORT CIRCUIT CURRENT MA
turned off. When the power supply
switch S2. Capacitors C8 and C9 sup-
is turned off, Q4 stops conducting.
ply peak currents of a very short dur-
The output voltage rises toward
ation above the setting of SHORT
+ 40 volts dc because of the low
CIRCUIT CURRENT MA switch S2
resistance path provided by R19.
when the power supply is connected
More current flows through R21,
to an external pulse-type circuit. Ca-
and the voltage drop across R21
pacitor C8 is in parallel with C9 to
increases. The voltage between
compensate for the increased series
R20, R21, and CR6 becomes posi-
resistance of C9 at temperatures of
tive. Diode CR6, now forward bi-
0C. or below. Capacitor C11 is con-
ased, starts conducting. More cur-
nected across the output terminals
rent flows through resistor R4
and provides a low internal impedance
when CR6 conducts, and more volt-
at high frequencies. Diode CR8 is
age is dropped across R4. This ap-
connected across the output terminals
plies a positive-going voltage to the
to allow a path for surge voltages
base of regulator Q1, which stops
of reverse polarity on the output ter-
conducting, thus preventing a large
minals. This prevents damage to the
output surge voltage.
circuits of the power supply.
(2) Current regulator. The current-regu-
lating circuit consists of capacitors
f. Emitter Follower. The emitter follower
C8, C9, and C11; diodes CR5 and CR8;
circuit consists of transistor Q4 diode CR7,
regulator Q1; resistors R6, R7, R8,
and resistors R22 and R23. The emitter follow-
and R11; and SHORT CIRCUIT CUR-
er samples the voltage at the negative output
RENT MA switch S2, which is con-
terminal and applies it across reverse-biased
trolled from the front panel. Switch
diode CR7. Diode CR7 maintains a constant
S2 selects the resistance of R11 neces-
voltage across itself, and establishes a constant
sary to limit the output current to
reference voltage between the negative output
the value selected. As the load cur-
terminal and the base of Q4. Emitter follower
rent increases, more current flows
Q4 repeats this reference voltage at the emit-
through R11, and more voltage is
ter, less a constant internal base to emitter
dropped across R11. The voltage be-
The
voltage drop of approximately 0.2 volt.
tween R11 and R7 becomes more neg-
voltalge at the emitter is insensitive to normal
ative. More current flows through re-
current. variations due to the low source im-
The increased
sistor R7 and R8.
pedance. The collector of Q4 is biased by resis-
voltage drop across R8 increases the
tor R22, and the base is biased by R23.
negative voltage applied to the cath-
g. Amplifier. The amplifier circuit consists
ode of diode CR5. The increased for-
of transistors Q2 and Q3, capacitors C6 and
ward bias of CR5 causes more elec-
C10, and resistors R6, R9, R10, R15, R17, and
trons to flow through CR5 and resis-
R18. The base of Q2 is biased by resistor R,10,
More voltage is dropped
tor R10.
and the collector by R6. The collector of Q3 is
across R10, and the voltage at the
biased by resistor R17, and the base by R18. Ca-
base of Q2 becomes more negative.
pacitor C10 bypasses resistor R18 at high fre-
The base-to-emitter current and the
quencies to increase the gain of Q3. Amplif ier
collector-to-emitter current of Q2 in-
Q3 compares the reference voltage of emitter
crease. More current flows through
5
