M-Family
DC-DC Converters <100 W
Rugged Environment
7 - 6
Edition 2/96 - Melcher AG
MELCHER
The Power Partners.
7.1
Functional Description
The input voltage is fed via an input fuse, an input filter, a
rectifier 3 and an inrush current limiter 4 to the input capaci-
tor. This capacitor sources a single transistor forward con-
verter. Each output is powered by a separate secondary
winding of the main transformer. The resultant voltages are
rectified and their ripples smoothed by a power choke and
an output filter. The control logic senses the main output
voltage
Uo1 and generates, with respect to the maximum
admissible output currents, the control signal for the pri-
mary switching transistor. This signal is fed back via a cou-
pling transformer.
The auxiliary outputs
Uo2 and Uo3 are individually regulated
by means of secondary switching transistors. Each aux-
iliary output's current is sensed using a current transformer.
If one of the outputs is driven into current limit, the other
outputs will reduce their output voltages as well because all
output currents are controlled by the same control circuit.
Fig. 1b
DC-DC (AC-DC) converter block diagram,
class II equipment (double insulation)
1 Transient suppressor (VDR) in C/D/E/F/LM and C/D/LMZ
2 Transient suppressor diode in A/B/C/FM and CMZ types
3 Bridge rectifier in LM/LMZ, series diode in EM types
4 Inrush current limiter (NTC) in C/D/E/LM and C/D/LMZ types
(option E: refer to the description of option E)
5 Single output modules A...LM 1000 and C/D/LMZ 1000 with
feature R
Fig. 1a
DC-DC (AC-DC) converter block diagram, class I equipment
Input
filter
Output 1
filter
Output 3
filter
Output 2
filter
Control
circuit
Main control circuit
Control
circuit
1
2
Fuse
P
29
11
8
23
5
26
32
17
14
20
2
14
17
4
3
Forward
converter
approx.
70
kHz
5
Y
MKT
Input
filter
Output 1
filter
Output 3
filter
Output 2
filter
Control
circuit
Main control circuit
Control
circuit
1
2
Fuse
P
29
11
8
23
5
32
17
14
20
2
14
17
4
3
Forward
converter
approx.
70
kHz
5
Y