HP 6038A Service Manual

3-34 OVP Reset. To reset OVP locally, turn the LINE switch
off and then back on. OVP can also be reset via HP-IB by
sending RST. The cause of the overvoltage must be removed
before the OVP circuit is reset or the circuit wiif trip again
immediately. If the OVP circuit trips continuously check the load
and the trip voltage.
3-35 Foldback Protection
3-36 In some applications either CV or CC mode may be
regarded as an error condition. The foldback protection feature
protects sensitive loads by disabling the power supply output
If the unit switches to the prohibited mode.
3-37 in local control, foldback protection Is toggled on or
off by the FOLDBACK pushbutton switch. The output will be
disabled if the power supply switches from whichever mode
(CV or CC) is in operation when foldback is enabled to the other
mode, in addition to turning foldback protection on and off,
the FOLDBACK pushbutton switch also resets the foldback pro¬
tection circuit if it has tripped. The conditions which caused
foldback should be corrected before the circuit is reset, or the
foldback protection circuit will trip again after reset. To turn
off foldback protection if the foldback protection circuit has
tripped, press the FOLDBACK switch twice in rapid succes¬
sion, once to reset the foldback protection circuit and the se¬
cond time to turn off foldback protection.
3-38 The green FOLDBACK ENABLED LED tights to in¬
dicate that foldback protection is enabled; the yellow
FOLDBACK LED lights to indicate that the foldback protection
circuit has tripped. Note the ERROR will light if an attempt is
made to turn on foldback protection while the power supply
is not in CV or CC mode.
3-39 When enabled via HP-IB foldback protection can be
enabled for either mode, regardless of the operating state of
the power supply when the command is received.
3-40 Remote Voltage Sensing
3-41 Because of the unavoidable voltage drop developed
in the load leads, the strapping pattern shown in Figure 3-4 will
not provide the best possible voltage regulation at the load. The
remote sensing connections shown in Figure 3-6 improve the
voltage regulation at the load by monitoring the voltage there
instead of at the supply's output terminals. Remote sensing
allows the power supply to automatically increase the output
voltage and compensate for the voltage drops in the load leads.
This improves the voltage regulation at the load, and is especially
useful for CV operation with loads that vary and have signifi¬
cant load-lead resistance. Note that with remote sensing,
voltage readback is at the load. Remote sensing has no effect
during CC operation. When using remote sensing, turn off the
power supply before changing the rear-panel straps, sense
leads, or load leads. Connect the unit for remote voltage sens¬
ing by connecting load leads from OUT and - OUT terminals
to the load, disconnecting straps between -f Out and -f S and
between -Out and -S, and connecting sense leads from the
+ S and -S terminals to the load as shown in Figure 3-6.
Sensing is independent of other power supply
functions; either local or remote sensing can be
used regardless of how the power supply is
programmed.
Figure 3-6. Remote Voltage Sensing
3-42 The load leads should be of the heaviest practical wire
gauge, at least heavy enough to limit the voltage drop in each
lead to 0.5 volts. The power supply has been designed to
minimize the effects of long load-lead inductance, but best
results will be obtained by using the shortest load leads practical.
Remote voltage sensing compensates for a
voltage drop of up to 0.5 V in each lead, and there
may be up to a 0.12 V drop between the -output
terminal and the internal sensing resistor, at
which point the OVP circuit is connected.
Therefore, the voltage sensed by the OVP circuit
could be as much as 1.12 V more than the voltage
being regulated at the load. It may be necessary
to readjust the OVP trip voltage when using
remote sensing.
3-43 Because the sensing ieads carry oniy a few
miiliamperes, the wires used for sensing can be much lighter
than the load leads. Each sense lead should have no more than
0.2 ohms resistance. Use the resistivity columns in Table 3-2
to determine the minimum wire size for the length of sense leads
being used. The sense ieads should be a shielded, twisted pair
to minimize the pickup of external noise. Any noise picked up
on the sensing leads will appear at the supply's output, and
CV load regulation may be adversely affected. The shield should
be grounded at the power supply end only, and should not be
used as one of the sensing conductors. The sensing ieads
should be connected as close to the load as possible.
3-8

HP 6038A Specifications

General

Brand	HP
Model	6038A
Category	Inverter
Language	English