HP 6269B Operator’s, Organizational, Direct Support And General Support Maintenance Manua L page 17

then proceed at a slower rate towards zero. The
actual time required for the output to fall from two
volts to zero will vary from several seconds to
several minutes, depending upon which down-pro-
gramming method is used.
3-20 OPERATION BEYOND RATED OUTPUT
3-21 The shaded area on the front panel meter face
indicates the approximate amount of output voltage
or current that may be available in excess of the
normal rated output. Although the supply can be
operated in this shaded region without being dam-
aged, it cannot be guaranteed to meet all of its
performance specifications.
3-22 OPTIONAL OPERATING MODES
3-23 REMOTE PROGRAMMING, CONSTANT
VOLTAGE
3-24 The constant voltage output of the power
supply can be programmed (controlled) from a re-
mote location if required. Either a resistance or
voltage source can be used as the programming
device. The wires connecting the programming
terminals of the supply to the remote programming
device should be twisted or shielded to reduce
noise pickup. The VOLTAGE controls on the front
panel are automatically disabled in the following
procedures.
3-25 Resistance Programming (Figure 3-3). In this
mode, the output voltage will vary at a rate deter-
mined by the voltage programming coefficient of
200 ohms/volt. The programming coefficient is de-
termined by the programming current. This current
is factory adjusted to within 1% of 5mA. If greater
programming accuracy is required, it may be
achieved by either adjusting R3 as discussed in
Paragraph 5-88, or, if the instrument is equipped
with Option 020, by adjusting potentiometer R112
as discussed in Paragraph 5-89.
Figure 3-3. Remet e Resistance Programming
(Constant Voltage)
3-26 The output voltage of the supply should be
-15mV ±5mV when zero ohms is connected across
the programming terminals. If a zero ohm voltage
closer to zero than this is required, it may be
achieved by inserting and adjusting R110 as dis-
cussed in Paragraph 5-83, or, if the instrument is
equipped with Option 020, by adjusting potentiome-
ter R113 as discussed in Paragraph 5-85.
3-27 To maintain the stability and temperature co-
efficient of the power supply, use programming re-
sistors that have stable, low noise, and low temp-
erature coefficient (less than 30ppm per degree
Centigrade) characteristics. A switch can be used
in conjunction with various resistance values in
order to obtain discrete output voltages. The switch
should have make-before-break contacts to avoid
momentarily opening the programming terminals dur-
ing the switching interval.
Figure 3-4.
Unity Gain (Constant Voltage)
3-28 Voltage Programming, Unity Gain (Figure 3-4).
Employ the strapping pattern shown in Figure 3-4
for voltage programming with unity gain. In this
mode, the output voltage will vary in a 1 to 1 ratio
with the programming voltage (reference voltage)
and the load on the programming voltage source will
not exceed 20 microampere. Impedance matching
resistor (R ) is required to maintain the temperature
x
coefficient and stability specifications of the sup-
ply .
3-29 Voltage Programming, Non-Unity Gain (Figure
3-5). The strapping pattern shown in Figure 3-5
can be utilized for programming the power supply
using an external voltage source with a variable
voltage gain. The output voltage in this configura-
tion is found by multiplying the external voltage
source by (Rp/RR).
3-30 External resistors Rp and R
ble, low noise, and low temperature coefficient
3-3
TM 11-6625-2958-14&P
Remet e Voltage Programming,
should have sta-
R