Circuit For Coils Operated With Dc Voltage - Siemens SIMATIC S7-300 Hardware And Installation Manual

Circuit for coils operated with DC voltage

The figure below shows DC-operated coils equipped with diode or Zener diode
circuit.
Figure 12-9 Circuit for coils operated with DC voltage
Diode/Zener diode circuits have the following characteristics:
• Opening surge voltage can be totally avoided.
The Zener diode has a higher switch-off voltage capacity.
• High switch-off delay (6 to 9 times higher than without protective circuit).
The Zener diode switches off faster than a diode circuit.
Circuit for coils operated with AC voltage
The figure shows coils operated with AC voltage and varistor or RC circuit.
Figure 12-10
The characteristics of varistor circuits are:
• The amplitude of the opening surge is limited rather than attenuated.
• The surge rise-ratio remains the same
• Short off-delay.
The characteristics of RC circuits are:
• Amplitude and steepness of the opening surge are reduced.
• Short off-delay.
S7-300 Programmable Controller Hardware and Installation
A5E00105492-02
with diode
+
-
with varistor
~
~
Circuit for coils operated with AC voltage
Appendix
with Zener diode
+
-
with RC element
~
~
12-29