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Reverse Current Protection (RCP)
The standard output modules use synchronous rectification in the output stages to achieve high efficiency and, as a result, the
outputs can both source and sink current. The sink current is internally limited to approximately -6% of the maximum rated
current. However, in applications where the output modules are connected to external power sources, such as batteries or
other power supplies, certain precautions must be observed to prevent damage to the unit.
The outputs should never be directly connected to to external power sources without some form of reverse current protection
such as an external diode or controlled MOSFET. If protection is not used, large reverse currents which will ultimately result in
damage to the unit will occur, especially when the AC mains is disconnected.
Output Module Average and Peak Power
All modules have an average and peak power rating. The average power of each unit must at all times remain below its
specified limit. However, each output can deliver up to 150% of its average power rating for a maximum of 5 seconds at 50%
duty-cycle, subject to the current limit not being exceeded and subject to the overall average power drawn from that section
being less than the specified average power rating (including any input de-rating due to temperature or line voltage). The
available peak power is a function of the output voltage and maximum current for each module. Full peak power is only
possible when the output voltage is adjusted to V
MAX
and the maximum current is drawn from the module. Note that both
average and peak power ratings are subject to the same temperature de-rating as the input section (de-rate by 2.5% per °C
above 50°C), but are not subject to any line de-rating.
Start up and Shut down
All outputs are designed to have a regulated monotonic start-up
with a rise time of approximately 3 ms as shown in the diagram
right. The power good signal stays low until the voltage exceeds
the power good threshold (
≈90%).
Where multiple output modules are used, in each section, the
default start up scheme is ratio-metric with all outputs starting
at the same time as shown in the diagram right. External
control circuits may be used to implement tracking or
sequenced start up if necessary.
The outputs are not designed to start into a pre-biased load and
may discharge any externally capacitance before beginning to
ramp the output voltage up in the normal way.
At shut-down the outputs enter a high impedance state. Where
no external load is present it may take some time for the
voltage to decay. When driving inductive loads, care must be
taken to limit the voltage at the output terminals so as to
prevent damage to the unit.
Synchronisation
All output modules in the same section of the power unit are synchronised. The typical operating frequency is 260 kHz and
paralleled/seriesed modules will not produce beat frequencies.
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