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Increasing the high frequency galn of the amplifier
Ql. RC 'network C4, Rl3, and Rl4 Introduce neg-
~tl ve feedbacii< In Ql to eliminate 'oscillation.
Rl3 Is select~d to eliminate ringing and minimize
overshoe,! for load transient recovery time, dis:-'
cusse1, ~n Paragraph 5-73.
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4-25 CURRENT COMPARISON AMPLIFIER
, /
I
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4-26 Thls circuit Is similar In appearance and
., operation to 'the voltage comparison amplifier. It
'consists basically of current programming resistor
. R9, current sampling resistor R53, and stage QB.
4-27 The current ~omparlson'ampllfier continu-
ously monitors the voltage r,lrop across currez;it
sampling resistor R53. When a preset voltage I~
,
exceeded,' the amplifier produces·an error voltage,
, which fo!"~arl biases CRB. The remaining stages
1
In the fe,;,dback loop function to maintain the drop .
across "!.he current sampllng resistor and',. 'iconse~
quent:f, the output current at a constant value.
RC- network R47'and C23 provide negative feedback
to stab'lllze the current comparison nmi:,llfler and
the feedback loop.
4-28 GATING CIRCUIT
4-29 Transistor,
Q3
draws current from the SCR
regulator control circuit (capacitor C25). The mag-
nitude of this current ls determined by either the
'voltage
or
current' comparison amplifier. For con-
stant wltage·operatlon, dlode CR7 Is forward
biased to permit the voltage circuit to drive
Q4;
diode CRB ls reverse biased to Inhibit the Input
from the curr~nt Input circuit. For constant current
operation., the re~rse occurs ..
,).
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4-30 To prevent transients In the de output wl]en
the power supply ls turned-on, the tum-on of Q4
ls delayed by capacitor C24 which charges through
. R57 and CR15. When C24 charges sufficiently to
, ,reverse blas CRIS, all the current through R57
., flows to the collector of Q4 to tum It on. Base
current ls controlled by the vo'ttage or current cir-
cults 'via CR7 or CRB, respectively. .For example,
during 'constant voltage operation the collector
voltage of QI (voltage lnput) forward b,lases CR7'
(CRB reverse biased by QB), the current through
CR7 will vary as QI collector voltage varies and
thus vary Q4 base current; therefore, the·collector
current of Q4 ls controlled by the voltage Input.
In a similar manner, the current Input circuit con-
trols the collector current of Q4 during constant·
current operation.
4-:iI SCR REGU!ATOR CONTROL (Refer to Figure
4-3, SCR Control Timing Diagram.)
4-3'2 The SCR regulator control
lR
basically a
blocking oscillator (Q7 and T3) that applies pulses·
4-4
Flg•1re 4~3. SCR Regulator Control, Timing Diagram
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to the SCR regulator In response to error signals
detected by the voltage or current comparison cir-
cuit. When transistor Q7 conducts, i~e pulse
developed In winding 1-2 of transformer T3 ls. .
.
coupled to the base of Q7 (positive feedback) and . ' ,
, and to the SCR regulator (CR17 and CRIB). Capac-
itor C27 charges In opposition to the feedback
voltage and cuts off Q7 •. The charge time of C27
determines the pulse duration In the collector of,
Q7 (approximately 20 microseconds). The 32Vdc
bias supplies current thro~gh R52, CR46, and CR44
to discharge C27 after
Qi
stops conducting.
4-33 Gate Input. Throughout the 'operation of the
blc,cklng oscillator, capacitor C25 supplies most
of the collector current for Q4 In the gating circuit'
(refer to Paragraph 4-30). The amount of current
pulled from C25 by,Q4 Is determfned by the Input
(from the voltage or current comparison clrcult)'to
the gating circuit. As a result of.this current flow
from'C25, the voltage across C25 increases neg-
atively with respect to the +O. 7V bias and has a
waveshape that approximates a linear ramp. Thus,
the slope of this ramp Is determined by the volt-
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