HP 6268B Operating And Service Manual

3-46 With zero ohms connected across the programming
terminals, the output current of the supply may be set to
exactly zero either by installing and adjusting R11 7 as
described in paragraph 5-91 or, if the instrument is equipped
with Option 021 or 022, by adjusting potentiometer R11 9
as discussed in paragraph 5-93.
-CAUTION-
Do not allow programming terminals A4 or
A 6 to become open-circuited while resistance
programming the output current. If they do
open, the supply's output current rises to a
value that may damage the supply or the
load. If in the particular programming con¬
figuration used there is a chance that the
terminals might open, we suggest that a
200 ohm resistor be connected across the
programming terminals. Of course, when this
resistor is used, the resistance value actually
programming the supply is the parallel
combination of the remote programming
resistance and the resistor across the
programming terminals. Like the program¬
ming resistor, this resistor should be a low
noise, low temperature coefficient type.
The load on the programming voltage source is less than 20
microamperes. The programming voltage required to obtain
maximum rated current from these supplies is about 500
millivolts. An input greater than 600mV may damage the
instrument through excessive power dissipation. Impedance
matching resistor R^ is required to maintain the temperature
coefficient and stability specifications of the supply. To
adjust the output current to exactly zero with a zero pro¬
gramming voltage, follow the same instructions as are referred
to in paragraph 3-46.
3-48 Constant Current Output, Voltage Input (Variable
Gain). In the remote programming arrangement shown in
Figure 3-9, the series combination of external voltage
source Eg and reference resistor Rp replaces the supply's
internal current programming source. As a result, the volt¬
age this external current source develops across gain
control Rp becomes the reference against which the voltage
drop across the output current sampling resistor is compared
by the constant-current comparator. The relationship
between Eg and the supply's output current depends on
the resistance ratio Rp/Rp and on the constant-current
programming coefficient (Kp) of the supply. (These
coefficients are given in paragraph 3-47.) The relationship
between input voltage and output current is
iQyy (Eg x Rp)/( K p x Rp).
3-47 Constant Current Output, Voltage Input (Fixed
Gain). The rear panel connections shown in Figure 3-8
allow the output current to be varied by using an external
voltage source to program the supply. The constant-current
programming coefficients for the supplies included in this
manual are as follows (±10%):
Model 6259B 10.OmV/ampere
6260B 5.0mV/ampere
6261B lO.OmV/ampere
6268B 16.7mV/ampere
6269B 10.OmV/ampere
Figure 3-7. Resistance Programming of Output Current
3-49 When using this programming technique, select
a value for Rp that is less than 10k ohms and that would
conduct at least 2.5 milliamps if connected across the
programming voltage source with its voltage at the maximum
value of input voltage to be used. Once the value for Rp
is selected, multiply it by Kp x Iq^j (max)/Eg (max) to
find Rp. (|f desired, the power supply's front panel current
controls can be used in place of external gain control R p
by deleting the external gain control from the circuit and
strapping together terminals A5 and A6.)
Figure 3-8. Voltage Programming of Output Current
(Fixed Gain)
3-7

HP 6268B Specifications

General

Brand	HP
Model	6268B
Category	Power Supply
Language	English