Power Supply
3-
34
When Q1310 is off, the current ramps
down
while flowing
in
through the
freewheel diode CR1310. Preregulator
01310
varies the
duty
cycle of
conduction of Q1310, so that the voltage
on
filter capacitor C1311 is a
nominal 3
7V.
The network ofR1310, R1316, R1317, R1319
and
CR1311 monitors
the
voltage across Q1314,
and
if
that voltage is lower
than
the nominal 1.4V,
01310
increases
the
voltage across C1311 until Q1314 has
the
correct
voltage.
If
Q1314 is open circuited,
CR1311
clamps the lower
supply
voltage to 31V.
If
Q1314 is short circuited, the ratio ofR1316
and
R1317 across R1319
together
with
R1310
is
so that the maximum voltage across C1311 is 41V.
So the preregulator supplies a sensible output
under
all conditions of the
circuitry
that
it drives except during an overload condition. In this situa-
tion, the voltage developed across the current-sense resistor R1322 reaches
the offset voltage developed by R1321
and
R1315 and
01310
current limits
the output.
Series Pass
The
function of the series pass transistor Q1314 is to reject ripple current
having a frequency of twice the power-line frequency.
The
nominal
de
voltage across it is only 1.4V. Base current is supplied to Q1314 via R1323,
CR1313
and
CR1312 in
the
absence of drive from Q1320
when
the instru-
ment
is first turned
on.
Transistor Q1314 is driven by both halves of 01311
through Q1320. The output at
pin
7 serves to reject
hum
on
the
37V supply
by comparing the output of potential divider R 1330
and
R1331 with the
voltage across reference diode
VR1330.
The output at
pin
1 ofO1311
slightly varies the value
of
the reference as seen at
pin
6 via attenuator
resistors R1334
and
R1335. This variation maintains
the-8.6V
supply
at the
value set
by
the -8.6V set potentiometer R1337.
Inverter
Inverter oscillator 01350 is driven via Q1313, R1341, Q1315, Q1316,
R1346, C1363 and R1372
at
the same frequency as 01310.
The outputs of U1350 are two non-overlapping complementary square-
wave signals to Q1350
and
Q1353. These transistors are
in
feedback loops,
one of which is formed
by
the filter R1361, CR1350, reservoir capacitor
C1356 and level shifter VR1351. The feedback is
such
that the base
of
Q1351 is adjusted to drive Q1352 sufficiently
hard
that the emitter swings
to within 3V of ground,
but
not hard enough to saturate it.
The
output
voltages of transformer T1350 secondary windings are full-wave rectified.
The 100V
supply
is derived from an auto-transformer
winding
in
series
with the primary winding. Resistors R1368
and
R1369 feed a sample of the
37V supply voltage into
the
error amplifier connected to
pins
1
and
2 of
U1350. If the 37V supply should go high, U1350 will
shut
down.
Theory
of
Operation
To Next Page
Loading...
Need help?
General
