3. PANEL DESIGN
3.3.8.2. Circuit with Diode and Zener
The circuit with zener diode is used when the circuit off time with diode is excessive. As the circuit with diode, it can only
be used in DC. The zener diode voltage must be higher than the power supply peak voltage and the current at least the same as
the load.
Figure 36: Zener diode circuit
3.3.8.3. Circuit with Varistor
The circuit with VDR (Voltage Dependent Resistor) limits the inductive circuit voltage almost the same as the zener diode.
Its conduction voltage is often higher than a zener diode and it’s bidirectional, allowing its use in DC or AC where is most
used. It must be selected according to the power source maximum voltage, load energy storage and desired lifetime.
ATTENTION:
It is imperative the complete reading of the Technical Characteristics of the products used
prior to installation or use thereof. For choosing the type of suppressor to be used, it should
be checked the type of load (DC or AC) and the voltage levels supported by the module
chosen for the project
Figure 37: Varistor circuit
3.3.8.4. RC Circuit
The RC protection circuit (resistor connected in series with a capacitor) can be assembled parallel to the contact or the
load. The parallel assembly with the contacts is recommended to DC powered loads and the parallel assembly with the load is
recommended to DC or AC powered loads. The RC circuits are more efficient when used in voltages higher than 100V.
In order to select the R and C values, it’s recommended the resistor to have 0.5 to 1 Ohm for each 1V and the capacitor 0.5
to 1µF for each 1A. For instance, in a load connected to 220V/1A a 220 Ohms resistor and a 1 µF capacitor can be used (the
capacitor model must meet the load voltage level).
Figure 38: RC circuit parallel with contacts
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