INPUT VOLTAGE
--
ABSORBED
VOLTAGE
PASSING
STAGE:
\
r-
---r
-'
-
I
I
..
-
�
CONTROL
Figure 4-3 Passing Stage Principle
To illustrate circuit operation, assume an increase in the T2 (Figure 6-4) supply
output. Pin 2 of !Cl will become more negative, and the output at pin 6 more
positive, tending to turn Ql off. The reduction in drive current increases the
impedance of Ql, and consequently its absorbed voltage, resulting in
precise
regulation of reference supply output.
Several other bias supplies are used to power the control circuitry:
1.
2.
3.
4.4.2
+20
volts from CRS. Note that there is no filtering on this
20
volt out
put. (See waveforms in Figure 6-1). This signal is used as a time
reference to the ac line. The
+20
volt source is then gated through
CR6, and filtered by C2 to provide the
+20
Vdc primary operating
power for the control PCB.
CR23 and R51 utilize the +16 Vdc, derived from R35 and CRl 7, to gen
erate and precisely regulate the + 11. 7V for the current amplifier ref
erence voltage.
+30 Vdc unregulated (CR3 and CR4 on the overall schematic) is used to
operate the current/voltage mode lamps.
Voltage Mode Section
Primary components of this circuit include constant voltage error amplifier IC2,
variable reference voltage programmer IC3, and emitter follower stage QS. The
circuit functions as follows:
Pin 3 of IC3 is- connected to plus - sense. Front panel voltage controls Rl0/Rll
function as variable feedback resistances from IC3 pin
6
to pin 2. The negative
12 .4 volt reference through R28/29/30 establishes the desired programming
current range, such that from O to 10 volts is obtained at pin 6 of IC3.
Theory of Operation
4-4
Rev B (6/84)
