Operation Beyond Rated Output - HP 6236B Operating And Service Manual

Figure 3-2. line Voltage Selector (Set for 120 Vac)
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 line voltage
selector switch for the desired line voltage (see Figure 3-2).
2. Check the rating of the installed fuse and repla-
ce 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 3-19). 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 (
outputs may be left floating. Loads can be connected
separately between each of the 0 to 20V output terminals
and the COM terminal, or between the -20V and the +20V
terminals for a 0 to 40V output.
3-8 Tracking Ratio Control
3-9 With the TRACKING RATIO control in the FIXED
position, the voltage of the -20V supply tracks that of the
+20V supply within 1% for convenience in varying the
symmetrical voltages needed by operational amplifiers
and other circuits using balanced positive and negative
inputs. Turn the TRACKING RATIO control counterclock-
wise out of the FIXED position to set the voltage of the -
20V supply lower than that of the +20V supply. The
negative supply can be set from a minimum of less than
0.5 volts to a maximum within 10% of the +20V
supply's output. Once this is done, the ±20V VOLTAGE
control still controls both outputs and maintains a
constant ratio between their voltages.
in Figure 3-1 ), or all
3-2
3-10 Overload Protection Circuits
3-11 ±20-Volt Current Limit. The +20V and -20V
outputs are individually protected against overload or short-
circuit damage by separate current limit circuits adjusted
at the factory to limit the output current to 0.55A ±5%.
(This is 110% of the maximum rated output.) 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 deterioration 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.
3-12 +6V Current Foldback (Model 6236B). The over-
load and short-circuit protection circuit for the +6V output
of the Model 6236B 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 output is 6 volts. At lower output voltages, the circuit
reduces the maximum obtainable output current linearly
until 1A ±15% flows when the output is shorted.
The shortcircuit current cannot be adjusted, but R46 can be
set to limit the maximum current at 6V to 2.75A ±5%.
(See paragraph 5-47 for current limit calibration instruction.)
3-13 +18Volt Current Limit (Model 6237B). The +18-
volt output of the Model 6237B is protected by a fixed cur-
rent limit circuit that operates at 1.1 A (110% of its maxi-
mum rated output). The circuit is similar to the ones in the
±20-volt supplies. (See paragraph 5-47 for calibration
instructions.)
3-14

Operation Beyond Rated Output

3-15 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
damage 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.
3-17 Connect each load 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 supply.
Load wires must be of adequately heavy gauge to maintain
satisfactory regulation at the load. Make each pair of
connecting wires as short as possible and twist or shield