3.5 Power supply
3.5.1 General description
The supply voltage for the PROTECT-PSC is 24 volt DC. The safe/operational I/O
modules can be supplied with power from the power supply unit for the pow-
er/booster module or from their own power supply unit.
The power/booster has an internal DC/DC transformer that generates the neces-
sary 3.3 volt operating voltages for the logic parts from the 24 volt DC supply. The
logic parts of the remaining modules are supplied via the back plane BUS..
All existing and generated power voltage is monitored internally for overvoltage
and undervoltage. A detailed description of voltage monitoring is provided in Chap-
ter 3.7.5.
3.5.2 External power supply units
The power supply units used for power supply must comply with IEC 61000-6-2
and one of the following requirements:
• Safety mains transformer to IEC 61558/VDE 0570 Part 2-6: ‘Special Re-
quirements on Safety Transformers for General Applications (IEC 61558-2-
6:1997)’
• Switch mode power supply to IEC 60950-1: ‘Information Technology Equip-
ment – Safety’ and to IEC 50178: ‘Electronic Equipment for Use in Power In-
stallations’. Furthermore, the power supply unit must suitably supply its
SELV circuits to IEC 60950-1.
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