Load Short-Circuit Protection - Omron NX-ID3343 User Manual

7 Digital Output Units
7-4-3

Load Short-circuit Protection

Purpose
This function is used to protect the output circuits of the Digital Output Units when an external connec-
tion load short-circuit occurs.
Details on the Function
As shown in the figure below, normally when the output bit (OUT) turns ON, the transistor turns ON and
then output current (Iout) will flow.
The transistor of the Transistor Output Units generates heat when output current (Iout) flows.
ON
OUT
OFF
ON
Iout
OFF
If an overload or short-circuit occurs, causing the output current (lout) to exceed the maximum value of
load current as shown in the figure below and the junction temperature (Tj) of the transistor to reach the
thermal shutdown temperature (Tstd) in which a load short-circuit protection operates, the output will
turn OFF to protect the transistor from being damaged.
When the junction temperature (Tj) of the transistor drops down to the reset temperature (Tr), the out-
put OFF will be automatically reset and the output current will start flowing.
ON
OUT
OFF
ON
Iout
OFF
7 - 18
Maximum load
current
Tj = Tstd
Maximum load
current
OUT : Output bit
Iout : Output current
Tj = Tr
Tj = Tstd
OUT : Output bit
Iout : Output current
Tj : Junction temperature of transistor
Tstd : Thermal shutdown temperature
Tr : Reset temperature
NX-series Digital I/O Unit User's Manual (W521)