Programming Overcurrent Protection; Unregulated Operation - HP 654 A Series Operating Manual

Programming Overcurrent Protection
When enabled, overcurrent protection removes the power supply output whenever it goes
into CC operation. This prevents the supply from indefinitely supplying the full programmed
current to the load.
Setting the OCP Protection
To activate overcurrent protection, press
(ocp
]. The OCP annunciator will come on and power
supply will continue to operate normally until it is forced into CC operation. If that occurs,
the power supply will remove its output.
Checking OCP Operation
The easiest way to check this operation at any specified current is to place a short across the
output. If the supply is connected to a HP Electronic Load, press its
f^on On)
key. The power
supply output will then drop to zero and the Prot annunciator will come on.
There is now no power supply output due to an overcurrent condition. To verify this, press
[ Protect 1
and observe that the display indicates
DC.
Clearing the OCP Condition
With the OCP tripped, return to the meter mode and try to clear the condition by pressing
(Prot Clear).
Nothing will appear to happen because the reason for the condition has not
been removed. Thus, as soon as the circuit is cleared, it trips again. You can clear the OC
condition by:
■ increasing the load resistance to lower the output current below the programmed current
value,
■ or by reusing the programmed current to a value above that required by the load.
In this example, the easiest way to clear the OCP fault is by removing the short from across
the output. After doing this, you clear the OVP circuit by pressing
[Prot Gear].
The Prot
annunciator will go off and the power supply output will be restored to normal.
If desired, you can also restore the output by disabling the OCP function (press focFl to turn
off the OCP annunciator. This restores the output but does not clear any condition that may
have caused OCP to trip.
Note
Under certain conditions, the OCP circuit may fail to clear because
load demand occurs before the power supply has time to build up the
required output current capacity. In such cases, disable the output (press
(Output Qn/Offl)
before clearing the OCP circuit. After OCP is cleared, then
enable the power supply output.
Unregulated Operation
If the power supply goes into a mode of operation that is neither CV nor CC, the Unr
annunciator will come on. An unregulated condition limits the output current to a value that
safe for the supply. Some unregulated states occur so briefly that they do not turn on the Unr
annunciator. One condition that can cause a noticable unregulated state is low ac line voltage.
Overcurrent Protection
Front Panel Operation 5-7