Mitsubishi Electric MELSEC-L Series User Manual page 28

(4) Precautions for using the triac output module
Because of characteristics of a triac, a sudden change of voltage or current may cause unstable operations of a
triac used for the triac output module.
Whether the voltage or current change causes a problem differs depending on an individual part (each triac), thus
check the following when using the triac output module.
(a) Checking of the load current
When the current consumption is equal to or smaller than the minimum load current and the margin is low by
using an inductive load such as a solenoid valve, a triac may not turn on or off properly. In that case, an action
such as connecting a bleeder resistance is required.
For detail on actions, refer to the following.
Page 75, Section 8.2
(b) Precautions on a full-wave rectifier load
The load current of a full-wave rectifier load forms waves similar to rectangular waves as shown below.
Output module
A triac may not operate properly if the current forms rectangular waves associated with sudden current
changes. To avoid it, use a load with which the load current does not form rectangular waves.
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Load
Circuit current wave