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Theory of Operation-DC
50 1 0
pulse amplifier to direct the current flow to the selected relay
coil. This causes the relay to change state and latch.
The Darlington transistors, Q1121 and Q1120 (with as-
sociated circuitry), are used to drive the relay coils, K1612
(K1632, Channel B), that provide for the Common Separate
channel input function (see Diagram 1).
POWER SUPPLIES-DIAGRAM
@
The four main supplies derive power input (through the
instrument's two rear interface connectors) from the
TM 5000-Series power module. These primary supplies are
the +12 V and +5 V, located on the Auxiliary board, and
the other +5 V and a
-
12.2 V, located on the Digital board.
They are individually fused and current limited. The four sup-
plies are referenced to the
+2.5
V
(Master Reference) preci-
sion voltage reference supply on the Auxiliary board.
The secondary supplies include the +2.7 V (ECL Termi-
nation), +5.7 V (derived from the
+
12 V supply), -5 V
(three-terminal regulator derived from the
-
12.2 V supply),
and the
+
18 V (three-terminal regulator derived from the
+26 V from the power module) that is used in the Option 01
timebase only (see Diagram 5).
--
The
+
12 V supply (located on the Auxiliary board
-
Dia-
gram 8) is derived from the unregulated +26 V dc power in
the power module. The
+
12 V regulator circuit consists of
U1420 and associated components. Load current for this
supply passes through resistor R1425 (current limit sensing
component) and the PNP series-pass transistor located in
the power module. The
+
12 V supply is regulated within
design limits by varying the voltage on the base of the se-
ries-pass transistor via P I 600 pin 11 A. The Zener diodes,
VR1410 and VR1411, reduce the voltages to appropriate
levels for U1420. Should the load current exceed 0.4 A, the
voltage drop across R1425 becomes great enough to cur-
rent limit U1420. This voltage is sensed at U1420 (pins 2
and 3) and reduces the base-to-collector voltage of the se-
ries-pass transistor. Feedback signals for voltage regulation
of the +12 V supply appear on pin 4 (U1420) and are com-
pared with the +2.5 V reference voltage on pin 5. Capacitor
C1310 provides for frequency compensation.
Emitter follower Q1330 uses pin 6 ( V , , )
of U1420 to pro-
vide an input voltage for the precision voltage reference,
U1223. The +2.5 output voltage is used for all major sup-
plies and is a master reference source for the DIA's.
The +5 V supply (located on the Auxiliary board) is de-
rived from the unregulated +8 V dc power in the power
-
-
module. The +5 V regulator circuit consists of U1320 and
associated components. Load current for this supply
passes through current limit sensing resistor R1426 and the
NPN series-pass transistor (located in the power module).
This supply is also regulated by varying the voltage on the
series-pass transistor base (PI600 pin 6A). If the load cur-
rent is exceeded, the voltage drop across R1426 will cause
U1320 to limit this current. This voltage (sensed at pins 2
and 3 of U1320) causes the series-pass transistor to even-
tually turn off. The feedback signal for the voltage regulator
occurs on pin 4 (U1320) and is compared to the reference
voltage on pin 5. Capacitor C1320 provides for frequency
compensation.
The other +5 V supply (located on the Digital board) is
identical in operation to the +5 V supply just discussed. It
consists of the regulator, U1720 and associated compo-
nents, and an NPN series-pass transistor (located in the
power module). An additional filter network consisting of
C1022 and L1020 provides the display power and isolates
its noise from the rest of the instrument.
The -5 V supply (located on the Auxiliary board) con-
sists of a three-terminal regulator, U1330, that provides reg-
ulated -5 V from the
-
12.2 V input.
The +2.7 V supply (located on the Auxiliary board) is the
ECL termination supply and is used as a terminating supply
for all the pull-down resistors located in the ECL circuits on
the Analog board (see Diagrams 3 and 5). The +2.7 V sup-
ply is derived from the +5 V supply and consists of an error
amplifier, (2133, an amplifier stage, Q1331, an emitter-fol-
lower output stage, Q1332, and associated components.
The
-
12.2 V supply (located on the Digital board) is de-
rived from the unregulated -26 V dc power in the power
module. This supply consists of error amplifier Q1723 and
Q1722, error signal amplifier Q1721, current limit sense am-
plifier Q1720, and associated components. The reference
voltage on the base of (21723 is approximately
0
V. Diode
CR1620 provides temperature compensation for the error
amplifier circuit. This supply is regulated within design limits
by varying the voltage on the base of the PNP series-pass
transistor, located in the power module, via the collector of
Q1721. An excessive load current through current limit re-
sistor R1718 causes (21720 to increase conduction and the
bases of Q1723 and Q172l to go more negative. The PNP
series-pass transistor base goes more positive, thereby re-
ducing the load current below the design limit.
PROCESSOR AND DlSP AY
DRIVERS-DIAGRAM
9
6
Introduction
The DC 5010 is a digital counter based on a micro-
computer system. The microprocessor, U1301 (located on
REV OCT 1981
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