HP 6268B Operating And Service Manual

f. Reset crowbar by returning OVERVOLTAGE
ADJUST control to its maximum clockwise position and
turning off the supply. On turning the supply back on,
the voltage should be the same value as was set in step (d).
g. To check the constant current circuit, first turn off
the supply, connect a short across the output bus bars
(see Figure 3-2), and turn it back on.
h. Adjust COARSE and FINE CURRENT controls (7)
until ammeter (8) indicates desired output current or
current limit. (The VOLTAGE controls must be set for
a greater-than-zero output to obtain the output current
programmed.)
i. Turn off the supply, remove the short from its out¬
put, and read the remainder of these operating instructions
before connecting the supply to an actual load.
3-3 OPERATING MODES
3-4 This power supply is designed so that its mode of
operation can be selected by making strapping connections
between terminals on its rear panel. The following para¬
graphs first describe normal operation using the normal
strapping pattern as it is connected at the factory. Later
paragraphs cover some optional operating modes including
remote voltage sensing, remote programming, and some
methods of operating these power supplies in combinations
of two or three.
3-5 The DC Power Supply Handbook, Application
Note 90A, is a useful source of additional information on
using regulated power supplies effectively. This 138-page
handbook includes chapters on operating principles, ac
and load connections, optional operating modes, and
performance measurements and is available at no charge
from your local HP sales office. The address of your local
sales office can be found in the back of this manual.
3-6 NORMAL OPERATING MODE
3-7 This power supply was shipped with the proper
rear panel strapping connections made for constant-voltage/
constant-current operation with local sensing and local
programming. This strapping pattern is illustrated in
Figure 3-2. By means of the front panel voltage and current
controls, the operator selects either a constant-voltage or a
constant-current output. Whether the supply functions in
the constant-voltage or the constant-current mode depends
on the settings of the voltage and current controls and on
the resistance of the output load. For values of load resis¬
tance greater than a critical crossover value equal to the
voltage setting divided by the current setting, the supply
operates in the constant-voltage mode. With a load resis¬
tance smaller than this critical value, it operates in the
constant-current mode. The transition occurs automati¬
cally; no switches need to be operated or connections
changed.
EXT.
CROWBAR
TRIGGER
' + - ' AI A2 A3 A4 A5 A6 A7 A8 fS -S A9
i
IE 3E
p 0
r t-i
5
-OUT
-0
+ OUT
Figure 3-2. Normal Strapping Pattern
3-8 Constant Voltage Operation
3-9 To adjust the supply for constant voltage operation:
a. Turn on supply and, with output terminals open,
adjust the VOLTAGE controls for the desired output
voltage. Then turn power off.
b. Connect a short across the rear panel output terminals,
restore power, and adjust the CURRENT controls for the
desired maximum output current. Then remove the short.
If a load change causes this current limit to be exceeded,
the supply automatically crosses over to constant current
operation at this preset current limit and the output voltage
drops proportionately. In setting the current limit, make
an adequate allowance for high peak currents that could
cause unwanted crossover. (Refer to paragraph 3-77.)
3-10 Constant Current Operation
3-11 To adjust the supply for constant current operation;
a. Connect a short across the rear output terminals, turn
the power on, and adjust the CURRENT controls for the
desired output current.
b. Open the output terminals and adjust the VOLTAGE
controls for the desired maximum output voltage. If a
load change causes this voltage limit to be exceeded, the
supply automatically crosses over to constant voltage opera¬
tion at this preset voltage limit and the output current drops
proportionately. In setting the voltage limit, make an
adequate allowance for high peak voltages that could cause
unwanted crossover. (Refer to paragraph 3-77.)
3-12 Overvoltage Trip Point Adjustment
3-13 The crowbar trip voltage is adjusted by using the
screwdriver control on the front panel. The approximate
trip voltage ranges are listed in Table 1 -1. When the crowbar
trips, an SCR shorts the output and the amber OVER¬
VOLTAGE indicator on the front panel lights. Rotating
the control clockwise sets the trip voltage higher. (It is set to
maximum at the factory.) Paragraph 5 108 contains instruc¬
tions for completely disabling the crowbar, if this is desired.

HP 6268B Specifications

General

Brand	HP
Model	6268B
Category	Power Supply
Language	English