K-Family
DC-DC Converters >100 W
Rugged Environment
8 - 8
Edition 2/96 - Melcher AG
MELCHER
The Power Partners.
8.1
Input Fuse
A fuse mounted inside the converter protects the module
against severe defects. This fuse may not fully protect the
module when the input voltage exceeds 200 V DC! In appli-
cations where the converters operate at source voltages
above 200 V DC an external fuse or a circuit breaker at sys-
tem level should be installed!
Table 5: Fuse Specification
Module
Fuse type
Fuse rating
AK 1
fast-blow
Little fuse 314
30.0 A, 125 V
BK 1
fast-blow
Little fuse 314
25.0 A, 125 V
CK 2
slow-blow
SPT
12.5 A, 250 V
DK 2
slow-blow
SPT
8 A, 250 V
EK 2
slow-blow
SPT
4 A, 250 V
FK 2
slow-blow
SPT
16 A, 250 V
LK 2
slow-blow
SPT
4 A, 250 V
1 Fuse size 6.3
× 32 mm
2 Fuse size 5
× 20 mm
Input Transient Protection
A suppressor diode or a VDR (depending upon the input
voltage range) together with the input fuse and a symmetri-
cal input filter form an effective protection against high input
transient voltages which typically occur in most installa-
tions, but especially in battery driven mobile applications.
Nominal battery voltages in use are: 12, 24, 36, 48, 60, 72,
110 and 220 V. In most cases each nominal value is speci-
fied to a tolerance of –30 %/+25%.
In certain applications, surges according to RIA 12 are
specified in addition to those defined in IEC 571-1. The
power supply must not switch off during these surges and
since their energy can not practically be absorbed an ex-
tremely wide input range is required.The EK input range for
110 V batteries has been designed to meet this requirement
and is available upon customer request.
Input Under-/Overvoltage Cut-out
If the input voltage remains below approx. 0.8
Ui min or ex-
ceeds approx. 1.1
Ui max, an internally generated inhibit sig-
nal disables the output(s). When checking this function the
absolute maximum input voltage rating
U i abs should be
considered!
Inrush Current Limitation
The C/D/E/LK modules of the versions -7, -6, -5 incorpo-
rate a NTC resistor in the input circuitry which - at initial turn
on - reduces the peak inrush current value by a factor of
5...10 to protect connectors and switching devices from
damage. Subsequent switch-on cycles within short periods
will cause an increase of the peak inrush current value due
to the warming-up of the NTC resistor. See also option E.
Inrush Current Peak Value
The inrush current peak value/initial switch-on cycle) can
be determined by following calculation: (See also Input In-
rush Current Characteristic)
Ui source
Iinr p = ––––––––––––––––
(
Rs ext + Ri + RNTC)
Rs ext
Ri
RNTC
Iinr p
Ui source
+
Ci int
Fig. 4
Equivalent circuit for input impedance
Input Inrush Current Characteristic
1
23
t [ms]
0
50
100
Ii inr [A]
150
CK
EK, LK
DK
Fig. 5
Typical inrush current versus time at Ui max, Rext = 0.
For AK/BK and FK as well as for application related val-
ues use the formula given in section "Inrush Current Peak
Value" to get realistic results.