SIEMENS
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Siemens KT 10.1 · 2016
15
Technical information and configuration
Series connection to increase the voltage
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Overview
Series connection to increase the voltage
To generate a load voltage of e.g. 48 V DC, two 24 V SITOP
power supplies of the same type can be connected in series.
The SITOP outputs "+" and "–" are isolated up to at least 60 V DC
against PE (creepages and clearances as well as radio interfer-
ence suppression capacitors on "+" and "–" against PE), so that
with this type of series connection (see Figure), the following
points can be grounded:
•
"–" of the lower power supply (results in +48 V DC against PE)
•
Midway "+"/ "–" between both power supplies (results in ±24 V
DC against PE)
•
"+" of the upper power supply (results in -48 V DC against PE)
Series connection of two SITOP power units to double the voltage
Note:
If two devices are connected in parallel, it cannot be guaranteed
that the voltage will remain below the maximum permissible
SELV voltage of 60 V DC in the event of a fault.
The purpose of diodes V1 and V2 is to protect the electrolytic
output capacitor integrated in the power supply against reverse
voltages > 1 V. As a result of the not absolutely simultaneous
power-up (even when a common mains switch is used for
switching on, differences of a few tens of milliseconds can occur
between the various startup-up delays), the power supply which
starts up more quickly supplies current from output "–" of the
slower power supply whose output electrolytic capacitor is then
theoretically impermissibly discharged.
The internal LC filter causes the internal rectifier diode on the
secondary side of the slower-starting power supply to accept
this current a few milliseconds later; this means that the external
diode connected with its anode to "–" and cathode to "+" is es-
sential on each power supply. These diodes are, however, only
loaded dynamically so that the 8.3 ms surge current loading ca-
pability (specified in the data sheets for suitable diodes) can be
used as a basis for dimensioning and it is not usually necessary
to cool the diodes using heat sinks.
Example:
Two 1-phase SITOP power supplies with 10 A rated output cur-
rent (Article number: 6EP1334-1AL12) should be connected in
series to increase the voltage. They supply approximately 35 A
dynamically for 700 ms on power-up in the short-circuit case or
also, for example, with loads with a high-capacity input capaci-
tor that momentarily act as a short-circuit at the start.
Suitable diodes for V1 and V2 are, for example, of Type SB 340
1)
(Schottky diode in axially wired enclosure DO-201AD with
approximately 5.3 mm diameter and approximately 9.5 mm
length of body).
40 V are permissible as the blocking voltage, and the stationary
direct current load capacity
I
F AV
is 3 A. The dynamic surge cur-
rent loading capacity
I
F SM
important in this case is sufficient for
the selected SITOP power supply at more than 100 A for 8.3 ms.
For SITOP power supplies with a lower rated output current, this
diode can also be used, but it is over-dimensioned.
1)
We do not accept any liability for this diode recommendation.
SITOP power
+
-
SITOP power
+
-
G_KT01_EN_00059
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© Siemens AG 2016