HP 6826A - Page 20

parallel. These connections are employed whenever it is re¬
quired to extend the voltage/gain or current capability be¬
yond one supply. For auto-series operation, the output volt¬
age of each slave supply varies in accordance with that of
the master supply. For auto-paraliel operation, complete
control of the output current from one master is allowed.
Diagrams are included for the strapping connections re¬
quired between master and slaves for both auto-series and
auto-parallel operations. In either case, the master must be
in the power supply or variable gain amplifier mode and the
slaves must be in the fixed gain amplifier mode. Also, for
auto-series or parallel operation, the master supply's Local/
Auto switch A2S1 {see Figure 3-9) must be in the Local pos¬
ition and each slave supply must have its Local/Auto switch
in the Auto position. The diagrams show the master strapped
for local programming and with an external signal applied to
the amplifier input terminals. However, the same auto-series
or auto-parallel connections could be used with the master
strapped for remote programming. Also, with the master
supply in the power supply mode, the external signal applied
to the A1 and A2 terminals is internally disconnected.
3-59 Auto-Series Operation. Two or more BPS/A's can
be connected in an auto-series arrangement to obtain a high¬
er output voltage than that available from a single supply.
Figure 3-12 illustrates the auto-series connections for three
supplies. When this arrangement is used, the output voltage
of each slave supply varies in accordance with that of the
master supply; thus, the total output voltage of the combin¬
ation is determined by the master supply's front panel
VOLTAGE control (or remote programming input). The
front panel CURRENT controls (or remote programming
inputs) of all three units are operative and the current limit
is equal to the lowest setting. The slave units must be floated
off ground. Instruments can be operated floating up to
300 volts off ground whether operated singlely or in series.
This limits model 6826A (±50V @ 1.0A)vto six units in
series and model 6827A (±100V @ 0.5A) to three units in
series.
3-60 For instantaneous equal voltage sharing, resistors
R-j, R2, or R3 must be equal. Since any variation in
R2, or R3 will result in a change in the voltage divider ratio
and hence the output of the slave supply, it is important
that these resistors be stable, low temperature coefficient
(20 ppm/°C or better). Also, they should have power rating
of at least 10X, their actual power dissipation. The resis¬
tors should be selected at the normal operating voltage
levels so that the current through them is about 1 to 2mA.
3-61 Auto-Parallel Operation. Two or more BPS/A's
can be connected in auto-parallel arrangement to obtain an
output current greater than that available from a single sup¬
ply. Figure 3-13 illustrates the auto-parallel connections
for three supplies to allow increased output current in con¬
stant voltage operation. When this arrangement is used,
current sharing under all load conditions is permitted under
control (front panel CURRENT control or remote program¬
ming) of the master supply. Because the CURRENT con¬
trols (or remote programming) of each slave are operative,
they should be set to a maximum to prevent the slave re¬
verting to constant current operation; this could occur if
the master output current setting exceeded the slave’s. For
equal current sharing, the leads from Rfy] to the load and
to the (—) terminals should be approximately equal in length.
To maintain instrument accuracy and stability, R|yj should
be a stable, low temperature coefficient resistor of sufficient
rating to prevent any appreciable self-heating (typically 1£2,
8W, ±20 ppm/°C, ±1%).
3-11