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Specifications of Basic I/O Units Appendix A
Load Short-circuit Protection for CJ1W-OD204/OD212/OD232/MD232
Output Units
As shown below, normally when the output bit turns ON (OUT), the transistor will turn ON and then output cur-
rent (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 Figure 2 below. When the junction temperature (Tj) of the output
transistor reaches the thermal shutdown temperature (Tstd), the output 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 tem-
perature (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.
Figure 1: Normal Condition
Figure 2: Overload or Short-circuit
Operating Restrictions for the CJ1W-OD204/OD212/OD232/MD232
These Units are provided with short-circuit protection, these are for protecting internal circuits against momen-
tary short-circuiting in the load. As shown in Figure 2 below, the short-circuit protection is automatically
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.
Restrictions
If a short-circuit occurs in an external load, immediately turn OFF the corresponding output and remove the
cause. An an alarm output bit that corresponds to the external load output number is turned ON. There is an
alarm output bit for every common.
When an alarm output bit turns ON, use a self-holding bit for the alarm in the user program and turn OFF the
corresponding output.
The alarm output bit is allocated in the Basic I/O Unit Information Area (A050 to A069) for every Unit mounting
slot.
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
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