Siemens S7-400 Suppression for DC-Operated Coils, Suppression with Diodes / Zener Diodes

Assembling and Installing Systems

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.

With varistor	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.

Automation System S7-400	Hardware and Installation	A-31
A5E00850741-01