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Connecting a BTA40 triac

David Wheeldon

Mar 14, 2011
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Mar 14, 2011
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HI anyone.

I have to use an existing triac with a new pulse width control of different design to the previous type. The diagram is the centre one on the attached PDF. Not being familiar with the use of triacs and the symbols used in the data sheet I want to know what value of resistor I use between the gate and terminal 1.
The supply and load are at 240V ac 50 Hz as is terminal 1. Are there any other rules with triacs that would affect performance/life?

I have also attached the relevant ST data sheet.

David Wheeldon
 

Attachments

  • BTA40 Datasheet.pdf
    62 KB · Views: 157
  • Mona Vale Hotel Controls.pdf
    61.5 KB · Views: 164

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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I see no resistor between the gate and terminal 1.

I see a resistor between the "load" pin of the triac and neutral. And that resistor is your load (i.e. the device being controlled).
 

David Wheeldon

Mar 14, 2011
3
Joined
Mar 14, 2011
Messages
3
Steve I mistakenly may have replied to the email my post generated.

There should be something between terminal 1 on the control and the gate on the triac. That's what I'm looking for.

The attachment shows the original (and now obsolete0 configuration -at least the working 240V bit. I am at a loss to know the function of the two low value resistors. They are too small to reduce the voltage significantly and I cannot find a typical circuit that might explain them.

David Wheeldon
 

Attachments

  • Mona Vale Hotel Original Control.pdf
    88.7 KB · Views: 197

Resqueline

Jul 31, 2009
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The 47 ohm resistor is a peak inrush gate current limiter, specified by the datasheeet of the optotriac. The new controller datasheet may specify one if needed.
In the new diagram the pilot light will always be on btw.
The 130 ohm resistor may be recommended by either the optotriac datasheet or the triac datasheet, but there's already an in-built resistor there in the triac (~33 ohm).
It's there to ensure the gate is kept off until there's a significant trigger current.
 
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