Line Voltage Option Conversion; Operation - HP 6236A Operating And Service Manual

3-4 LINE VOLTAGE OPTION CONVERSION
3-5 To convert the supply from one line voltage option
to another, the following three steps are necessary:
1. After making certain that the line cord is discon-
nected from a source of power, remove the top cover from
the supply and. set the two sections of the li:1e voltage selec-
tor switch for the desired line voltage (see Figure 3-2),
2. Check the rating of the installed fuse and replace
it with the correct value, if necessary. For Options 100 or
120, use a normal time-constant 2-amp fuse (HP Part No.
2110-0002); for Options 220 or 240, use a normal time-
constant 1-amp fuse (HP Part No. 2110-0001).
3. Mark the instrument clearly with a tag or label
indicating the correct line voltage to be used.
3-6 OPERATION
3-7 This power supply can be operated individually or
in parallel with another supply (see Paragraph 3-17). All
output terminals are isolated from ground. The ±20V and
+6V or +18V outputs use a single common output terminal.
This common (COM) terminal or anyone of the other output
terminals may be grounded to the chassis at the front panel
ground terminal (
G)
in Figure 3-1), or all outputs may be
left floating. Loads can be connected separately between
each of the 0 to 20V output terminals and the COM ter-
minal, or between the -20V and the +20V terminals for a
o
to 40V output.
3-8 Overload Protection Circuits
3-9 ±20-Volt Current Limit. The +20V and -20V
outputs are individually protected against overload or short-
circuit damage by separate current limit circuits which are
adjusted at the factory to limit the output current to 0.55A
±5%. (This is 110% of the rated maximum output of 0.5A.)
The current limits can be set by adjusting resistor R6 for the
+20V output and R26 for the -20V output. (See Paragraph
5-47 for current limit calibration instructions.) No deteri-
oration of supply performance occurs if the output current
remains below the current limit setting. If a single load is
connected between the +20V and -20V outputs, the circuit
set for the lesser current limit will limit the output.
3-10 +6V Current Foldback (Model 6236A). The over-
load and short-circuit protection circuit for the +6V output
of the Model 6236A reduces the output current limit as the
output terminal voltage decreases. (The operating region of
the +6V output is enclosed by heavy lines in Figure 3-3).
The maximum rated output current is 2.5A and the current
limit is factory-adjusted to operate at 2.75A ±5% when the
3-2
output is 6 volts. At lower output voltages, the circuit
reduces the maximum obtainable output current linearly
until 1A ±15% flows vvhen the output is shorted. The short-
circuit current cannot be adjusted, but R46 can be set to
limit the maximum current at 6V to 2.75A ±5%. (See Para-
graph 5-47 for current limit calibration instructions.)
3-11 +18-Volt Current Limit (Model 6237A). The +18-
volt output of the Model 6237 A is protected by a fixed cur-
rent limit circuit which operates at 1.1 A (110% of its max-
imum rated output of 1.0A). The circuit is similar to the
ones in the ±20-volt supplies. (See Paragraph 5-47 for
cal ibrati on instructi ons.)
3-12 Operation Beyond Rated Output
3-13
The supply may be able to provide voltages and
currents greater than its rated maximum outputs if the line
voltage is at or above its nominal value. Operation can ex-
tend into the shaded areas on the meter faces without dam-
age to the supply, but performance cannot be guaranteed to
meet specifications. If the line voltage is maintained in the
upper end of the input voltage range, however, the supply
probably will operate within its specifications.
3-14 Connecting Loads
3-15 Each load should be connected to the power supply
output terminals using separate pairs of connecting wires.
This minimizes mutual coupling between loads and takes
full advantage of the low output impedance of the power
supply. Connecting wires to the load must be of adequately
heavy gage to maintain satisfactory regulation at the load.
Each pair of connecting wires should be as short as possible
and twisted or shielded to reduce noise pickup. If shielded
wire is used, connect one end of the shield to the power
supply ground terminal and leave the other end unconnect-
ed.
3-16 If load considerations require that the output power
distribution terminals be remotely located from the power
supply, then the power supply output terminals should be
connected to the remote distribution terminals by a pair of
twisted or shielded wires and each load separately connect-
ed to the remote distribution terminals.
3-17 Parallel Operation
3-18 Two or more power suppl ies 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 voltage controls of one power supply
should be set to the desired output voltage, and the other
power supply should be set for a slightly larger output volt-