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K Series
DC-DC Converters >100 Watt
Rugged Environment
Edition 4/4.99
12/31
MELCHER
The Power Partners.
Output Protection
Each output is protected against overvoltages which could
occur due to a failure of the internal control circuit. Voltage
suppressor diodes (which under worst case condition may
suppressor diodes are not designed to withstand externally
applied overvoltages. Overload at any of the outputs will
cause a shut-down of all outputs. A red LED indicates the
overload condition.
Parallel or Series Connection of Units
Single or double output units with equal nominal output
voltage can be connected in parallel without any precau-
tions using option T.
With option T (current sharing), all units share the current
approximately equally.
Single output units and/or main and second outputs of dou-
ble output units can be connected in series with any other
(similar) output.
Note:
– Parallel connection of double output units should always
include both, main and second output to maintain good
regulation of both outputs.
– Not more than 5 units should be connected in parallel.
– Series connection of second outputs without involving
their main outputs should be avoided as regulation may
be poor.
– The maximum output current is limited by the output with
the lowest current limitation if several outputs are con-
nected in series.
Thermal Considerations
If a converter is located in free, quasi-stationary air (con-
vection cooling) at the indicated maximum ambient tem-
perature
TA max (see table: Temperature specifications) and
is operated at its nominal input voltage and output power,
the temperature measured at the
Measuring point of case
temperature TC (see: Mechanical Data) will approach the
indicated value
TC max after the warm-up phase. However,
the relationship between
TA and TC depends heavily on the
conditions of operation and integration into a system. The
thermal conditions are influenced by input voltage, output
current, airflow and temperature of surrounding compo-
nents and surfaces.
TA max is therefore, contrary to TC max,
an indicative value only.
Caution: The installer must ensure that under all operat-
ing conditions
TC remains within the limits stated in the
table
Temperature specifications.
Notes: Sufficient forced cooling or an additional heat sink
allows
TA to be higher than 71°C (e.g. 85°C) if TC max is not
exceeded.
For -7 or -9 units at an ambient temperature
TA of 85
°C with
only convection cooling, the maximum permissible current
for each output is approx. 40% of its nominal value as per
figure.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
50
60
70
80
90
100
Io/Io nom
TA [°C]
0.9
1.0
Forced cooling
05089
TA min
TC max
Convection cooling
Fig. 7
Output current derating versus temperature for -7 and -9
units.
Thermal Protection
A temperature sensor generates an internal inhibit signal
which disables the outputs if the case temperature exceeds
TC max. The outputs are automatically re-enabled if the tem-
perature drops below this limit.
It is recommended that continuous operation under simul-
taneous extreme worst case conditions of the following
three parameters be avoided: Minimum input voltage,
maximum output power and maximum temperature.
Uo1d
t d
Ur
t
Uo2d
<10
s
<10
s
Uo1
Uo2
Io1/Io1 nom
0
0.5
1
Io2/Io2 nom
05072
Fig. 8
Typical dynamic load regulation of Uo1 and Uo2