trying to get a triac to work, but unsuccessful

[Gibson486]

I am trying to get a triac to work so it can purposefully blow a fuse (ie crow bar circuit)

My first attempt is a no go. I am using this guy:

https://www.st.com/content/ccc/resource/technical/document/datasheet/67/06/bc/c9/35/8e/4f/ea/CD00002265.pdf/files/CD00002265.pdf/jcr:content/translations/en.CD00002265.pdf

Yeah, it is beefy as hell.

I started by applying a voltage to the gate pin (9V to start).

Then I applied 12V to A1 and GND to A2 (both GNDs are connected from the 2 supplies)

Well...that did not work. Out of the gate, everything just shorts. The gate side shorts as well  and I cannot get the triac to shut off.

Can I not test it this way? I did get it to work by just using one supply and moving the wire that connects the gate from 12V (turns it off) to 0V (turns it on).

What am I doing that is incorrect? 

[bob91343]

I didn't look at your attachments but the way to test a triac or SCR is to apply a current limited voltage to the anode and then apply a voltage to the gate.  That should start conduction, which usually won't stop until you remove the anode potential.

Some units will stop conduction with a change in gate drive but mostly you need to stop anode conduction first.

If the conduction current doesn't reach a high enough level, the anode current will shut off with removal of drive, as there is a minimum anode current required.

Read the data sheet for more information; if there is a test circuit you can reproduce that.

[soldar]

A schematic would help. There are plenty of circuits if you just search.

[Gibson486]

I was just going to use the application circuit in the LM431 datasheet. I made a boo boo in ordering parts, though. The voltage threshold for the triac I ordered has a 1.3 volt gate voltage, while the LM431 regulates to around 2.5V. As a result, I had to test the triac separately.

 I attached a separate file to show the schematic of the triac. I varied the 9V line, but it did not matter since it was shorting.

[RoGeorge]

I cannot get the triac to shut off.

That's expected.

The anodes A1 A2 must be connected at all times, the Gate pin G is a control pin that can only turn on the triac.  The G can not turn off a triac.  Once the current through the triac is turned ON, it will stay ON (like a latch) until the current passing through anodes A1 A2 is zero.

In other words, if you use a triac for DC, once turned ON, only blowing the fuse will turn the triac off again.  Same for thyristors.

[Gibson486]

I cannot get the triac to shut off.

That's expected.

The anodes A1 A2 must be connected at all times, the Gate pin G is a control pin that can only turn on the triac.  The G can not turn off a triac.  Once the current through the triac is turned ON, it will stay ON (like a latch) until the current passing through anodes A1 A2 is zero.

In other words, if you use a triac for DC, once turned ON, only blowing the fuse will turn the triac off again.  Same for thyristors.

Awww man...that helps a lot! Thanks.