Tektronix 7834 - Converter;Rectifiers

Theory of Operation-7834
Line Input
CONVERTER/RECTIFIERS
3- 5 2
POWER
ON
The Converter/Rectifiers circuit
provides the operating
power for this instrument from an ac
line-voltage source .
This circuit includes a
LINE VOLTAGE SELECTOR switch,
located on the rear panel
. Figure 3-40 shows a detailed
block diagram of the
Converter/Rectifier circuit . A schema-
tic is provided on diagram 11
in the Diagrams section of
this manual .
Power is applied through Line
Filter FL1200, line fuse
F1200,
POWER
switch
S1200, and Line Selector switch
S1212 .
The Line Filter is designed to keep powerline inter-
ference from entering the instrument and to keep the
approximate 25 kilohertz Inverter signal from
entering the
power line . Components R1205, C1205, and
C1206 sup-
press reverse-recovery transients of CR1215
.
LINE
TRIGGER
TO PLUG-IN
COMPARTMENTS
Figure 3-40
.
Detailed block diagram of Converter/Rectifiers circuit .
Line Selector switch
S1212 allows the instrument to oper-
ate from either a 115 volt
nominal or a 230 volt nominal
line-voltage source . In the
115 volt position, rectifier
CR1215 operates as a
full-wave doubler with energy-storage
capacitors C1216
and C1217, so the voltage across the
two
capacitors
in series will be the approximate peak-to-peak
value of the line voltage .
For 230 volt operation, CR1215
is connected as a bridge
rectifier and the voltage across
C1216 and C1217 will be the
approximate peak value of
the line voltage . Thus, the do
voltage applied to the Inverter
stage is about the same for
either 115 volt or 230 volt
operation .
Thermistors
RT1209 and RT1213 limit the surge
current
when the power supply is first turned on
. After the instru-
ment is in operation, the resistance of these
thermistors
drops so that it has little effect on the
circuit
.
When the
instrument is turned off, the Inverter
control stage turns
off the Inverter which prevents
it from discharging C1216
SEMI-REGULATED
VOLTAGESTO
LOW-VOLTAGE
REGULATORS