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3. External Connection
Surge Protection
When connecting to digital outputs a load that may generate a voltage surge or current, for example an
inductive load such as a relay coil or incandescent lamp, suitable protection measures are required to
prevent damage to the output stage or malfunction owing to noise. The instantaneous interruption of
current flowing through a coil, including a relay, results in the sudden generation of a high-voltage pulse.
If the voltage exceeds the withstand voltage of the transistor, the transistor performance may be
degraded or the transistor may be damaged. To prevent this, be sure to connect a surge absorption
element when driving an inductive load including a relay coil. Examples of measures against voltage
surge are shown in Figure 3.9. below.
Examples of use of relay coil
+5V
Diode
Output pin
Signal common
Examples of use of lump
+5V
Output pin
Signal common
Figure 3.9. Samples of Voltage Surge Protection
CAUTION
The protection circuit must be installed less than 50 cm from the load and contact to provide
effective protection.
A Protection Function of the +5V Outputs
A protection function, which prevents excessive current flow from the +5V outputs, is attached to this
board. In case of accidental short of the +5V output and GND, for example, the function works, and
the board operation may become impossible temporarily. In such a case, you should turn the PC off
and wait for several minutes before you use the board again.
42
+5V
Relay
coil
Output pin
Signal common
External power voltage < Zener diode voltage
+5V
Output pin
Surge current
prevention
resistor
Signal common
Relay
coil
Zener diode
Resistor
DIO-1616T-PE, DI-32T-PE, DO-32T-PE
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