Consideration for Inrush Current from Built-in Output
When connecting a transistor to an output device with a high inrush current (such as an incandescent
lamp), steps must be taken to avoid damage to the output transistor.
Use either of the following methods to reduce the inrush current.
l
Countermeasure 1
Draw about 1/3 of the current consumed by the load.
0Vn
Cn(+V)
OUT
L
OUT
Cn(0V)
R
L
+
NPN (sinking) type
Output
terminal block
Output
terminal block
PNP (sourcing) type
l
Countermeasure 2
Mount a limiting resistor.
0Vn
Cn(+V)
OUT
L
R
OUT
Cn(0V)
+
L
NPN (sinking) type
Output
terminal block
Output
terminal block
PNP (sourcing) type
In countermeasure 1, the current consumption from I/O power supply is increased although the
voltage supplied to the load L is not decreased.
In countermeasure 2, the voltage supplied to the load L is decreased although the current con-
sumption from I/O power supply is not increased.
Select the appropriate countermeasures according to the operating conditions.
Cn(0V) and Cn(+V) in the figure represent the common terminals, and 0Vn represents the terminal
of the power supply to drive the output circuit. Refer to Output Terminal Block
on page 3-15 under
3-1-4 Terminal Blocks on page 3-12 for details.
5 Installation and Wiring
5-68
NX-series NX1P2 CPU Unit Hardware User’s Manual (W578)
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