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indicates the amount of output current or voltage
that is available in excess of the rated output.
Although the supply can be operated in this Shaded
region without being damageci,
it
cannot be guar-
anteed to meet all of its p8riormance specifica-
tions.
However,
if
the line voltage is maintained
above 11SVac, the supply will probably operate
within its specifications.
3-14 OPTIONAL OPERATING MODES
3-15 REMOTE PROGRAMMING, CONSTANT CURRENT
3-16 Either a resistance or a voltage source can
be used to control the constant current output of
the supply.
The CURRENT control on the front
pane 1 is disabled when remote programming the
supply.
3-17 Resistance Proarammino (Fiaure 3-3).
In
this mode, the output current varies at a rate de-
termined by the remote resistance programming co-
efficient.
This coefficient is different for each
output current range, as shown in Table 1-1 of
this manual.
The programming coefficient is de-
tennined by the constant current programming cur-
rent which is adjusted to 500
±S~~
at the factory.
If greater programming accuracy is required,
it
can
be aChieved
by
changing resistor R35 as outlined
in Section V.
•
+
AO AI
A2 A3
'< - )
PROGRAMMING
~?'
RESISTOR
...-:
L-
Figure 3-3.
Remote Resistance Programming,
Constant Current
~
3-18 Use stable, low noise, low temperature co-
efficient programming resistors to maintain the
power supplies temperature coefficient and stabil-
ity specifications.
A switch may be used to set
discrete values of output current.
A rI).ake-before-
break type of switch should be used s'ince the out-
put current will exceed the maximum rating of the
power supply
if
the switch contacts open during
the switching interval.
3-3
- - - - - C A U T I O N ' - - - - -
If
the programming terminals (AD and
AI) should open at any time in the re-
mote programming mode, the output
current will rise to a value that may
damage the power supply and/or the
load.
A protection resistor (2Kn
Model 6177E or 5Kn Model 6181B)
can be connected across the program-
ming terminals to avoid the possibil-
ity; however. note that the addition of
the resistor will alter the linear pro-
gramming coefficient given in Table
1-1.
3-19
If
the negative output terminal of the supply
is grounded, care must be taken to avoid leakage
current paths from the programming source to the
negative output terminal (ground).
Shunt paths
such as this. will seriously degrade the perform-
ance of the supply,
3-20 Voltaae Proarammina (Fioure 3-4).
In this
mode. the output current varies at a linear rate
determined by the voltage programming coefficient
given in Table l-L
The entire voltage span for
the source is apprOXimately 0-1 Volt (Model 6177B)
or 0-2. 5 Volts (Model 6181B).
The programming
voltage should never exceed
1.
2 Volts (Mode 1
Sl77B) or 3 Volt. (Model 6181B).
yo!tages in ex-
cess of this will result in excessive power dissi-
pation in the instrument and possible damage.
+
AO A I A2 A3
'191<;:>1
0
1
0
1
4:tr=
VOLTAGE
~
SOURCE
F
+
Figure 3-4.
Remote Voltage Programming,
Constant Current
3-21 The 5DOllA programming current. flowing into
terminal Al from the reference supply (see sche-
matic), imposes two restrictions in the voltage
programming mode.
The first restriction is that the
voltage source must be capable of sinking (absorb-
•
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