HP 6268B Operating And Service Manual

3-58 Figures 3-1 2 and 3-13 show the rear panel and
circuit board interconnections required to operate two or
three supplies in the auto-series mode. This mode of
operation allows two or three series-connected supplies to
be simultaneously programmed by the voltage and current
controls of a master supply. The master supply must always
be the one at the positive end of the series combination.
The output voltage of each slave supply varies in direct
proportion to that of the master and the ratio of each slave's
output voltage to the master's is established by the settings
of the slave supplies' voltage controls. The resulting
combination of two or three supplies behaves as if it were
a single constant-voltage/constant-current supply. The
supply with the lowest current rating limits the maximum
output current of the combination. Any of the supplies
included in this manual can be used as an auto-series slave,
and any well-regulated variable output supply can be used
as the master.
3-59 In applications where coordinated positive and
negative voltages are required, grounding the center tap of
an auto-series combination of supplies allows simultaneous
proportional control of both supply voltages.
3-60 Determining the Value for R^. Each slave supply
has an external resistor R x associated with it that supplies
its voltage programming current. If the temperature
coefficient and stability specifications of the supplies are
to be maintained, these must be stable, low noise resistors
with a temperature coefficient of less than 30ppm per °C
and a power rating at least 30 times what they will actually
dissipate. The proper value for R x (when using two units
in auto-series) or for R X1 (for the first slave when using
three units) is calculated by first finding the voltage pro¬
gramming current of the slave supply. This is calculated by
referring to Table 1-1 for the remote voltage programming
resistance control coefficient and taking its reciprocal. For
example, the voltage programming current in the Model
6259B is 1/(200fi/V) or 5mA. Next, divide this current
into the maximum voltage rating of the master supply to
determine R x for the first slave. If our master supply were
a zero-to-25-volt unit, for example, R x or R x ^ would be
25V/5mA = 5000 ohms.
3-61 When operating three supplies in auto-series, find
R X 2 by dividing the voltage programming current of the
second slave, calculated as in paragraph 3-60, into the
maximum voltage expected from the first slave.
3-62 Setting the Voltage Controls. The voltage each
slave supply contributes is determined by its voltage control
setting. The output voltage of the first slave supply tracks
the voltage of the master, and the voltage of the second
slave (if used) tracks the voltage of the first slave. For this
reason, the voltage of the master must be adjusted to
maximum, and then each slave, in turn, must be set to the
corresponding voltage desired during initial setup of the
auto-series combination. Once this has been done, the total
voltage of the combination can be controlled by the voltage
controls of the master supply or it can be remotely program
med through the master supply.
3-63 Setting the Current Controls. Auto-series opera¬
tion leaves the current controls of all supplies operative,
but the supply whose current control has the lowest setting
determines the point at which automatic crossover to
constant current operation begins to tower its output volt¬
age and thus that of the series combination. The constant
current circuit of a supply has no effect on the outputs of
the supplies connected in a more positive position in the
series combination, but it does affect its own output and
the outputs of the supplies connected in a more negative
position. If the current controls of one of the slave supplies
are set the lowest, then an overload or short circuit at the
output will cause the master supply (or the master and the
first slave) to force current through the reverse voltage
protection diodes at the outputs of the downstream slaves.
Because this current could be excessive either for the diodes
EXT
CROWBAR
TRIGGER
' + - ' Al A2 A3 A4 A5 A6 A7 A6 +S ~$ A9
Figure 3-11. Auto-Parallel Operation of Three Units
3-9

HP 6268B Specifications

General

Brand	HP
Model	6268B
Category	Power Supply
Language	English