Assembling and Installing Systems
A-31
AutomationSystem S7-400 Hardwareand Installation
A5E00850741-01
Suppression for DC-Operated Coils
DC-operated coils are interconnected to diodes or Zener diodes.
+
-
+
-
With diode With Zener diode
Figure A-9 Suppression for DC-Operated Coils
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.
Withvaristor With RC element
~
~
~
~
Figure A-10 Suppression with AC-Operated Coils
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.