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MELSEC-Q
1 GENERAL SPECIFICATIONS AND PRECAUTIONS FOR USE
(8) 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 Section 11.2.
(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.
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.
(c) Measures for connecting an inductive load
To connect an inductive load, take measures to reduce noise to the side where
the load is connected as shown below.
Circuit example Method for selecting elements Remarks
Varistor method
Select a cut voltage (Vc) for
the varistor to meet the
following condition.
• Vc > Power supply voltage
1.5(V) √2
This method is not effective
when the Vc is too high.
The recovery time delays
slightly.
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