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SL.AV£
Figure 3-9. Auto-Series, Two and Three Units
3-39 In order to maintain the temperature coeffi-
cient and stability specifications of the power sup-
ply, the external resistors
(Rx)
shown in Figure 3-9
should be stable, low noise, low temperature coef-
ficient {less than 30ppm per degree centigrade) re-
sistors. The value of each resistor is dependant on
the maximum voltage rating of the "master" supply.
The value
of
Rx
ls this voltage divided by the volt-
age programming current of the sla11e supply (l/Kp
where Kp is the voltage programming coefficient).
The voltage contribution of the sla11e is determined
by its voltage control setting,
3-40 When the center tap of an Auto-Series combi-
3-5
nation is grounded, coordinated positive and nega-
tive voltages result. This technique is commonly
referred to as "rubber-banding" and an external ref-
erence source may be employed lf desired.
.Any
change in the internal or external reference source
(e.g.
drift,
ripple) will cause an equal percentage
change in the outputs of both the master and slave
supplies. This feature can be of considerable use
in analogue computer and other applications, where
the load requires a positive and a negative power
supply and is less susceptible to an output voltage
change occurring simultaneously in both supplies
than to a change in either supply alone.
3-41 PARALLEL OPERATION
3-42 Normal Parallel Connections (Figure 3-10).
Two or more power supplies can be connected in
parallel to obtain a total output current greater than
that available from one power supply. The total
output current is the sum of the output currents of
the individual power supplies. The output CURRENT
controls of each power supply can be separately
· set. The output voltage controls of one power sup-
ply should be set to the desired output voltage: the
other power supply should be set for a slightly larger
output VC?ltage. Tbe supply set to the lower output
voltage will act as a constant voltage source; the
supply set to the higher output will act as a con-
stant cuiTent source, dropping its output voltage
until it equals that of the other supply. The con-
stant voltage source will deliver only that fraction
of its total rated output current which is necessary
to fulfill the total current demand.
Figure 3-10. Normal Parallel
3 -43 Auto-Parallel. The strapping patterns for
Auto-Parallel operation of two and three power sup-
plies are shown
in
Figure 3-11. Auto-Parallel oper-
ation permits equal current sharing under all load
conditions, and allows complete control of output
current from one master power supply, The output
current of each slave is approximately equal to the
master• s. Because the output current control"s of
each slave are operative. they should be set to
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