Contec AI-1604CI2-PCI, User Manual

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3. External Connection
44
AI-1604CI2-PCI
Surge Voltage Countermeasures
When connecting a load that generates surge voltages and inrush currents, such as an induction load
(relay coil) or an incandescent light bulb, to the digital output, appropriate protection must be provided
in order to prevent damage to the output stage or a malfunction due to noise. The rapid shutoff of a
coil, such as a relay, generates a sudden high-voltage pulse. If this voltage exceeds the voltage
tolerance level of the output transistor, it can cause the transistor to gradually deteriorate, or even
completely damage the transistor. Therefore, when driving an induction load, such as a relay coil, you
should always connect a surge-absorbing device. The following illustrates a surge voltage
countermeasure that can be employed:
+Common
-Common
+Common
-Common
+Common
-Common
+Common
-Common
- Examples of use of relay coil
Relay coil
External power voltage < Zener diode voltage
Zener diode
Registor
Surge current
prevention registor
Output pin
Diode
- Examples of use of lump
Output pin
Relay coil
Output pin
Output pin
Figure 3.14. Surge Voltage Countermeasure
CAUTION
In order for a protection circuit to operate effectively, it must be connected within 50cm of a load
and a contact point.