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MELSEC-Q
11 I/O MODULE TROUBLESHOOTING
Table 11.2 Output Circuit Problems and Corrective Actions (Continued)
Condition Cause Corrective action
Example 3
The load
does not
turn off.
(triac
output)
• If the load current is insufficient (lower than
25mA), the triac does not operate, causing the
load current to flow into a phototriac as shown
below.
If an inductive load is connected in this
condition, the load may not turn off because
surge at the time of off is applied to the
phototriac.
• Connect a resistor to both ends of the load so
that the load current of approx. 100mA flows
and the triac operation is stable.
Resistance value ≤ Voltage across the load /
100mA
(Example)
When using 100VAC (output voltage), for
instance, calculate the resistance value from
the formula below.
100VAC / 100mA = 1kΩ
Resistance value = 1kΩ
(To the next page)
Triac
Surge suppressor
Phototriac
QY22
Control
circuit
Load
Load
Resistor
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