TRIAC Question

Thread Starter

drjackool

Joined May 23, 2021
34
Hi







Does exist a TRIAC with 220v AC gate voltage?I want use a Triac to On/Off an appiliance butTriacs i found on Internet them gate voltage is low

thanks
 

Ian0

Joined Aug 7, 2020
9,667
Hi

Does exist a TRIAC with 220v AC gate voltage?I want use a Triac to On/Off an appiliance butTriacs i found on Internet them gate voltage is low

thanks
A triac is current triggered. The gate-MT1 junction looks like two diodes in inverse parallel, so the gate voltage will always be <1V.
What are you trying to switch it with? Could you use an opto-triac?
 

Dodgydave

Joined Jun 22, 2012
11,284
A triac has three terminals, if you're using mains,the Live goes to the MT2 via the Load, Neutral to MT1 and Gate gets the trigger voltage between MT1 and Gate, , as long as the Gate gets the same phase as MT2 it will trigger.
 

Ian0

Joined Aug 7, 2020
9,667
A triac has three terminals, if you're using mains,the Live goes to the MT2 , Neutral to MT1 and Gate gets the trigger voltage between MT1 and Gate, , as long as the Gate gets the same phase as MT2 it will trigger.
If you connect Live to MT2 and Neutral to MT1, then trigger it, it will blow up. You need to connect a load somewhere!

I would recommend Live to MT1, Load between MT2 and neutral. Otherwise the load is switched on its neutral making it live when it is off. Gate current does not need to be the same phase as MT2, it will always trigger with Gate negative of MT1.
Most triacs will trigger in all four quadrants, but some (generally "snubberless" types) will not trigger with gate positive and MT2 negative.
 

Dodgydave

Joined Jun 22, 2012
11,284
If you connect Live to MT2 and Neutral to MT1, then trigger it, it will blow up. You need to connect a load somewhere!

I would recommend Live to MT1, Load between MT2 and neutral. Otherwise the load is switched on its neutral making it live when it is off. Gate current does not need to be the same phase as MT2, it will always trigger with Gate negative of MT1.
Most triacs will trigger in all four quadrants, but some (generally "snubberless" types) will not trigger with gate positive and MT2 negative.
I said earlier the load goes in the MT2 path, and the MT1 goes to Neutral...
 
Last edited:

Thread Starter

drjackool

Joined May 23, 2021
34
I
A triac is current triggered. The gate-MT1 junction looks like two diodes in inverse parallel, so the gate voltage will always be <1V.
What are you trying to switch it with? Could you use an opto-triac?
I want to create a circuit like Start/Stop with contactors (to protected the appliance when power comeback after AC lose), but instead the Contactor or the Relay I want use Triac or a SSR (Solid Relay)?
Which you recommend?
 

Ian0

Joined Aug 7, 2020
9,667
Relays has flyback voltage, in this circuit can flyback voltage damage to my appliance?!
If the current is interrupted by the "off" button being pressed the relay is one side of the open contacts and the appliance is at the other, so it is hard to see how any flyback voltage could actually get to the appliance.
Secondly, a 230V 16A relay has a 0.75VA coil with an impedance of 38kΩ+188H and a current of 3mA. The stored energy is about 1.6mJ. I can't imagine any appliance being damaged by that little energy. Bear in mind that a tiny switched-mode supply will have a smoothing capacitor of about 10uF/325V which stores 500mJ.
 

Reloadron

Joined Jan 15, 2015
7,501
Hi

Does exist a TRIAC with 220v AC gate voltage?I want use a Triac to On/Off an appiliance butTriacs i found on Internet them gate voltage is low

thanks
A Google of Triac Circuits should bring up a dozen hits on using mains voltage to control a Triac. You only need add a resistor between MT2 and the Gate. Next it may be easier to just buy an inexpensive SSR designed for mains voltage control, these are pretty common. If you want to roll your own then give this a read.

Ron
 

Thread Starter

drjackool

Joined May 23, 2021
34
،اث قثمشغ
If the current is interrupted by the "off" button being pressed the relay is one side of the open contacts and the appliance is at the other, so it is hard to see how any flyback voltage could actually get to the appliance.
Secondly, a 230V 16A relay has a 0.75VA coil with an impedance of 38kΩ+188H and a current of 3mA. The stored energy is about 1.6mJ. I can't imagine any appliance being damaged by that little energy. Bear in mind that a tiny switched-mode supply will have a smoothing capacitor of about 10uF/325V which stores 500mJ.
The relay will off by AC power lose not a button.
 

Ian0

Joined Aug 7, 2020
9,667
،اث قثمشغ

The relay will off by AC power lose not a button.
There may be all sorts of spurious voltages on the mains at the point it fails, due to wiring inductance and fuses failing upstream. The tiny amount of stored energy in the relay coil would be the least of your worries.
 

Reloadron

Joined Jan 15, 2015
7,501
I want to create a circuit like Start/Stop with contactors (to protected the appliance when power comeback after AC lose), but instead the Contactor or the Relay I want use Triac or a SSR (Solid Relay)?
Which you recommend?
If you want to control something be it an appliance or whatever for a load you want a latching relay circuit or similar latching circuit based on your description. Press a N/O button the circuit latches on, Press a N/C button or if power fails the circuit is off until you press the start button again. Anyway it sounds like you want a latching relay circuit.

Ron
 
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