Brochure/Catalogue

With RC modules, voltage peaks
are compensated via a capacitor.
Thanks to its special characteristics
during charging and discharging
the interference pulses are already
filtered out during the voltage rise
and not only when the breakdown
voltage (U
RC
) is reached.
Advantage:
• Suitable for DC and AC voltage
• Slightly extended switch off process
Disadvantage:
• Exact dimensioning required
• High inrush current
• Low effect on the service
life of the contact
U
RC
Last
+
–
(∼)
(∼)
R
C
U
S
12
t
Varistors
U
VDR
Last
+
–
(∼)
(∼)
VDR
U
S
12
t
Free-wheeling diodes
U
D
Last
+
–
U
S
12
t
Free-wheeling diodes are used to
protect against overvoltages caused
by self-induction when an inductive
DC voltage load is switched off (e.g.
solenoid valves or electric motors).
They ensure that the voltage peaks
that occur are reduced to the value
of the diode forward voltage (U
D
).
However, this leads to a delay in
the voltage drop and thus in the
switch-off process of the load.
Advantage:
• Uncritical dimensioning
• Very positive effect on the
service life of the contacts
Disadvantage:
• Significantly extended
switch off process
• Only suitable for DC voltage
The functional principle of varistors
is also based on breakdown voltages
(U
VDR
). High energies can be dissipated,
but this causes the component to
aging. Therefore, the breakdown
voltage is reduced over time and
the leakage current is increased.
Advantage:
• Uncritical dimensioning
• Suitable for DC and AC voltage
• Slightly extended switch off process
Disadvantage:
• Complex and expensive
with increasing power
• Low effect on the service
life of the contact
RC modules
In order to implement a protective circuit tailored to the load, suitably dimensioned protective circuits
are available as accessories from many manufacturers of inductive loads such as contactors or solenoid
valves. This enables simple integration of the protective circuit on the load.
A.112737920000
Selection guide
A
Selection criteria for protective circuits of inductive loads