Digital modules
3.5 How to protect digital modules from inductive overvoltage
S7-300 Module data
62 Manual, 06/2017, A5E00105505-AJ
Configuration of coils operated with direct current
Coils operated with direct current are shown in the following diagram and configured with
diodes or Z diodes.
Figure 3-2 Configuration of coils operated with direct current
Properties of the diode/Z diode circuit:
● Cut-off currents can be avoided. Z diode withstands a higher cut-off voltage.
● High cut-off delay (6 to 9 times higher compared to non-protective cid´rcuits).
Faster cut-off of the Zener diode compared to the diode circuit.
Connection of AC-operated coils
The operation of AC coils with varistors or RC elements is shown in the diagram.
Figure 3-3 Connection of AC-operated coils
Properties of a circuit with varistor:
● The amplitude of the cut-off current is limited but not attenuated.
● The steepness of the overvoltage remains the same.
● Low cut-off delay.
Properties of acircuit with RC elements:
● Reduction of the amplitude and steepness of the cut-off current.
● Low cut-off delay.
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