Technical data

The output voltage and current of the power supplies in this
section can be remotely controlled with either a voltage or
resistance signal. There are terminals on the rear panels of
these power supplies to facilitate this.
Resistance Programming
Programming the output voltage or current of a power supply
with resistance is simple with Agilent analog programmable
power supplies. Using the terminal strip on the rear panel for
the power supply, the front panel encoders used to control
voltage and current can be disconnected. User supplied vari-
able or fixed resistors can then be connected in their place.
The resistance values needed are stated in the specifications
for each individual power supply.
Voltage Programming
Programming of the output voltage or current of a power
supply with a voltage signal can be accomplished in any of a
few ways. Normally, the programming voltage is supplied by a
DAC. The programming technique used is dependent upon the
characteristics of the particular DAC and power supply being
used. For all the techniques, however, the connections to
the power supply are made to the terminals provided on
the rear panel.
In the specification for each power supply, the voltage
programming coefficient is given. This is the ratio of the
programming signal voltage to the resultant output voltage
or current of the power supply.
One type of power supply has scaled voltage coefficients.
This means that the full scale programming voltage required is
a specific value, for example five volts, regardless of the power
supply full scale output voltage or current. Providing a DAC
for this signal directly is a practical solution.
Constant Voltage Programming with Unity Voltage Gain
Another type of power supply has a 1v/1v voltage coefficient.
This means that the output increases one volt for each one volt
increase in the programming voltage signal. For lower voltage
power supplies, a DAC could be used directly to program the
power supply. This is called programming with unity gain and
is shown in Figure 1.
Figure 1 Voltage Programming with Unity Voltage Gain
Constant Voltage Programming with Variable Voltage Gain
In most cases, the power supply output voltage is greater than
the DAC output, so the “Variable Voltage Gain” programming
method, shown in Figure 2, must be used. This configuration
requires two external precision wirewound resistors
(Rp and Rr). As indicated by the equation in Figure 2, Rp can be
selected so that the resulting voltage gain is either less than or
greater than unity. Also note that the summing point S is made
available at external terminals on all Agilent analog program-
mable power supplies, so no internal wiring changes are needed.
Figure 2 Voltage Programming with Variable Voltage Gain
When programming the output using a remote voltage source,
the use of a zener diode across the programming terminals
will prevent the power supply output from exceeding a
predetermined limit, even though the programming source
may provide an excessively high input command. The
relationship between the zener diode and the output limit
value depends upon the power supply design and the
programming connection, but in any case can be determined
by considering the power supply as equivalent to an
operational amplifier. The zener diode must have a current
rating equal to or greater than the largest current which the
remote programming source can provide - in some cases the
power rating of the zener diode can be reduced by employing
a fixed resistance in series with the programming path.
Constant Current Remote Programming
The same principles for constant voltage programming apply
to constant current programming, since either a resistance or
a voltage may be applied to the remote programming terminals.
If the constant current programming terminals are accidently
opened, however, the current limiting protection normally
provided by the constant current setting will be lost. Particular
care must be taken to insure that no open circuit conditions
exist for even a short interval of time. Such an open circuit will
program the power supply to an output current in excess of its
rating, and would probably destroy the regulating components
of the supply. Any constant current programming mechanisms
involving switches should therefore use make-before-break
switches.
Series Regulator
External Voltage Source from DAC
or Programmer Replaces
Internal Reference Supply
Unreg.
dc
R
L
E
P
E
OUT
C
O
C
I
E
OUT
=E
P
OV
Comparison
Ampl.
S
+
+
-
-
Series
Regulator
Program Control
(External or Internal)
External
Voltage
Source
Normally Choose R
R
Such that
Unreg.
dc
R
L
R
P
E
OUT
C
O
C
I
E
OUT
= E
V
E
P
=
OV
Comparison
Ampl.
S
+
-
E
P
R
R
+
-
I
P
E
P
R
R
>
E
P
R
P
R
R
68 APPLICATIONS INFORMATION
Analog Programming Methods
Visit our web site
http://www.agilent.com/find/power
A
B
C
D
E
F
G
H
I
K
App.
Info.