Siemens S7-400 Installation Manual page 283

Suppression for DC-Operated Coils
DC-operated coils are interconnected to diodes or Zener diodes.
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-
Figure A-9
Suppression with Diodes / Zener Diodes
Suppression with diodes or Zener diodes exhibits the following characteristics:
• Switching overvoltages can be avoided entirely. A Zener diode has a higher
turn-off voltage.
• High turn-off delay (6 to 9 times higher than without suppressor circuits)
The Zener diode switches off more quickly than a diode circuit.
Suppression with AC-Operated Coils
AC-operated coils are suppressed with varistors or RC elements.
With varistor
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Figure A-10
Suppression with a varistor exhibits the following characteristics:
• The amplitude of the switching overvoltage is limited but not attenuated.
• The steepness of the surge voltage remains the same.
• Low turn-off delay.
Suppression with an RC element exhibits the following characteristics:
• The amplitude and steepness of the switching overvoltage are reduced.
• Low turn-off delay.
S7-400 and M7-400 Programmable Controllers Hardware and Installation
A5E00069481-04
With diode
Suppression for DC-Operated Coils
Suppression with AC-Operated Coils
Assembling and Installing Systems
With Zener diode
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-
With RC element
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A-31