The protection circuit is made up of CRl16, U144C. Kl01,
and associated resistors. The purpose of these components is
to make s.ure that erroneous and possible dangerous voltages
do not appear at the voltage scwrce output during power up.
For example, if the Model 617 power is briefy turned off and
then back on, the voltage swrce output might otherwise be at
some undetermined value because of random data appearing
on the DAC inputs. The protection circuit eliminates this
potential problem by briefly opening up the contacts of KlOl
under these circumstances.
6.8 POWER SUPPLIES
The Model 617 has numerous power supplies which are used
to power the analog, digital, and voltage sauce circuits.
Diagrams of these supplies may be found on drawing
numbers 617-106, page 1 and 617-166.
The power supplies are essentially divided into two groups:
one group powers the digital and voltage swrce circuits,
while a second group of supplies is used to power the input
circuits. Each group of supplies has its own power supply
transformer. This configuration is used to maintain proper
isolation between the voltage source and digital circuits, and
sensitive analog circuitry.
AC power is applied to JlOll, which is the power connector
located on the rear panel of the instrument. SlOl is the
POWER switch located on the front panel, while 5102 is the
line voltage selection switch. When 5102 is in the 115V posi-
tion, the primary windings are connected in parallel: when
S102 is in the 230V position, the TlOl windings are placed in
series.
TlOl has three secondary windings, which are used to supply
the kllOV, +15V, and +5V supplies. The tllOV and
k 15V sources supply the voltage source, and the + 5V sup-
ply is used for the digital circuitry.
The +llOV supplies consist of half-wave rectifier diodes
(CR108 and CR107) and filter capacitors (Cl09 and CllO).
Each of the ?z 15V supplies has a similar half-wave rectifica-
tion scheme (CR101 and Cl03 for the - 15V supply, CR109
and Cl08 for the +15V supply). Regulation for these supplies
is performed by Ul14 and U115, which are IC regulators.
The third winding of TlOl supplies the t5V sxrce that is
used to power the digital circuits. Rectification is done by
elements of CR110, while filtering is performed by ClOl. The
supply voltage is regulated by UlOl, which is a standard 7805
IC regulator.
The same secondary of TlOl that supplies the +5V digital
scurce also supplies power to the primary of the electrometer
section power transformer, T301. This transformer supplies
power to all the DC supplies that power the analog circuits.
The +21OV supplies, which are used to power the pre-
amplifier output circuit, are generated by one secondary win-
ding of T301 and two voltage-doubling circuits. CR301,
CR303, C301, and C304 perform the rectifier and filtering
functions for the f210V supply, while CR302, CR304, C302,
and C303 are similar components in the -210V supply. The
&21OV supplies are not regulated and are referenced to
analog and signal common.
Another secondary winding on T301 feeds power to com-
ponents that generate the +5V analog and -9V analog sup-
plies. The +5V supply is used to power the ranging amplifier,
A/D converter and other components (such as U301) located
in the analog section, while the -9V supply powers the -2V
reference source. +5V supply components include CR311,
which rectifies AC input, C305 for filtering, and Q309,
VR302, and U306 for regulation. Elements of CR311 also pro-
vide rectification for the -9V supply, while C306 filters, and
VR303 regulates the output voltage. Both of these supplies are
referenced to analog and signal common.
The *5V sources supply power to much of the input
preamplifier section. These two supplies, which are refer-
enced to bootstrap common, utilize half-wave rectification
and IC regulators. CR320, C316, and U308 are associated
with the +5V supply, and CR319, C315, and U307 perform
similar functions for the -5V supply. R344 and R345 are in-
tended to trim the -5V supply voltage to a precise value.
The &24V sources supply power to the preamp output stage
when the circuit is configured for amps or coulombs. Each
supply is a simple half-wave rectifier, filter capacitor pair,
with CR323 and C317 supplying +24V, and CR322 and C311
performing the same functions in the -24V supply. Both
these supplies are referenced to the preamplifier output.
6-14
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