A-117
Appendices
CJ2 CPU Unit Hardware User’s Manual
A-6 Load Short-circuit Protection and Line Disconnection Detection for Basic I/O Units
App
A-6-2 Load Short-circuit Protection for CJ1W-
OD204/OD212/OD232/MD232
As shown below, normally when the output bit turns ON (OUT), the transistor will turn ON and then out-
put current (Iout) will flow. If the output (Iout) is overloaded or short-circuited exceeding the detection
current (Ilim), the output current (Iout) will be limited as shown in second figure below. When the junc-
tion temperature (Tj) of the output transistor reaches the thermal shutdown temperature (Tstd), the out-
put will turn OFF to protect the transistor from being damaged, and the alarm output bit will turn ON to
light the ERR indicator. When the junction temperature (Tj) of the transistor drops down to the reset
temperature (Tr), the ERR indicator will be automatically reset and the output current will start flowing.
Normal Operation
Operation for Overload or Short Circuit
These Units are provided with short-circuit protection, these are for protecting internal circuits against
momentary short-circuiting in the load. As shown in Figure 2, the short-circuit protection is automati-
cally released when the Tj equals to Tr. Therefore, unless the cause of short-circuit is removed,
ON/OFF operations will be repeated in the output. Leaving short-circuits for any length of time will
cause internal temperature rise, deterioration of elements, discoloration of the case or PCBs, etc.
Therefore, observe the following restrictions.
A-6-2 Load Short-circuit Protection for CJ1W-
OD204/OD212/OD232/MD232
Operating Restrictions for the CJ1W-OD204/OD212/OD232/MD232
OUT
ON
OFF
I
OUT
ON
OFF
ERR
ON
OFF
OUT: OUTPUT instruction
I
OUT
: Output current
ERR: Alarm output, ERR indicator
I
lim
: Detection current
Tj: Junction temperature of transistor
Tstd: Thermal shutdown temperature
Tr: Reset temperature
OUT
ON
OFF
I
OUT
ON
OFF
ERR
ON
OFF
I
lim
Tj =Tstd Tj =Tr
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