Danfoss VLT 3032 Service Manual page 7

LOGIC TO POWER
INTERFACE
The logic to power interface isolates the high voltage components of
the power section from the low voltage signals of the logic. This is
accomplished by use of the interface board. All communication between
the control logic and the rest of the unit passes through the interface
board. This communication includes: feedback from the current sensors,
input from the heatsink temperature sensor, line voltage monitoring,
DC Bus voltage monitoring, control of the fans , control of the input
thyristor rectifiers and control of the gate drive firing signals. Also on
the interface board is the power supply which provides the unit with
low voltage power such as 24VDC, 16VDC, 13VDC and 5VDC. The
power supply is a Switch Mode Power Supply (SMPS). The switch
mode type supply is used due to its efficiency and linearity. Another
benefit of the switch mode supply is that it obtains its power from the
DC Bus; in the event of a power loss the power supply remains active
for a longer period of time versus conventional power supplies.
During the troubleshooting process it is important to determine whether
the interface board is receiving or sending the signal that appears to
be at fault. For example, the loss of a gate-drive signal is a waveform
generated by the interface board and conversely a heatsink over-
temperature fault is a result of the interface board receiving an input
from the heatsink temperature sensor. If the signal is of the later type
(received), it is then necessary to isolate the fault to either the sending
device or the interface board. It is generally assumed that a component
within the unit is usually at fault; and although this may in fact be the
case, it is critical to check all possibilities to avoid costly errors and
lengthy downtime. In any case, the interface board is a relatively quick
and easy assembly to exchange; and so if it is suspect, a quick exchange
will prove the assumption.
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