IN6296 - Any one know about this

[KeepItSimpleStupid]

Snubberless is new to me. I doubt it existed when the charger was made. I did find this: https://www.st.com/internet/analog/subclass/124.jsp and this https://www.edaboard.com/thread256415.html and I did notice that the snubberless is a 3 quadrant device.

Snubbless means it doesn't typically require an external snubber.

Two in parallel, probably not. It would require double the gate trigger current or two triggers AND more importantly they would not share current equally. You would have to add a low value series resistor to each triac and i would create two opto trigger circuits. Not a good idea to parallel them.

 

[Quantised]

OK so I pulled the board and checked what I could with a meter and found no strange readings. Took out the triac and built the test rig in this url https://www.circuitstoday.com/how-to-test-a-triac and it shows the triac is fine, also tested the the one I pulled out a couple of days ago and shows it is fine also. Maybe the test is not good enough to show faults at higher volts or when using AC as it seems to test in one direction only.

Did notice the board was pretty black around the TVS circuit and also a bit around the pads for the triac A1 and A2.

What do you think of the test circuit - is it any good?

On the basis the charger failed and I saw 110v AC on the case which is the heat sink I have to assume the insulated triac broke down? But the meter shows it is still insulated. Bigger mystery by the day.

 

[panic mode]

i don't agree with everything that page says.
i would recommend to completely ignore their method of testing triac using multimeter (until they declare model of multimeter)

circuit below that uses lamp is common way to test SCR (thyristors) and it can be used to test Triacs as well, but the description on page is incorrect.

the testing should be:

1. connect triac or SCR to the tester, lamp should be off
2. press button S1 (or close it briefly then open if switch) lamp should turn on and - STAY ON
3. press button S2 (or open it briefly if switch) lamp should turn off and stay off

the only difference between SCR and Triac is that SCR only conducts one way (like diode) when active.
Triac conducts both ways.

if the 12V source was AC, then lamp would go out when S1 opens (would not need to open S2) because AC goes through zero 100 or 120 times per second (every halfperiod). when S1 is closed, lamp would be fully bright with Triac and about half bright with SCR.

 

[KeepItSimpleStupid]

I don't agree either. For one, the triac should stay latched until the supply is interrupted or the triac is shorted. It only tests one quadrant.

 

[Quantised]

The test does do what you say and turns off and stays on at the correct times but it obviously not a proper test as it only tests one quadrant.

I dont have 12V AC so cant do the better test.

Maybe I could rip out a transformer from a phone charger but any ideas on a circuit to build to do a full AC test on these devices.

 

[KeepItSimpleStupid]

Breakdown, you really can't check. The gate needs 50 mA and that circuit supplies 66. Whoops, maybe not. There is at least one diode drop in there. e.g. (12-0.6)/RThe idea is that the polarity of the supply has to be able to be reversed. You can do that with a DPDT switch AND the gate polarity has to be reversed. One way to do the gate is to use another battery such as a D cell for the gate.

If your below the minimum gate current or minimum load, the TRIAC won't latch. A lot of times there are different specs for each quadrant.
Sensitive gate triacs use a few mA rather than 50. You can think of a triac as back to back SCR's. Back to Back SCR's are actually preferable, but triggering is different.

You cannot detect breakdown without a voltage source high enough. Remember that a lot of tests test for bad things, but not good things. I had a few fuses in my day that passed an ohmmeter test, but flunked a load test. Drove me nuts the first time. The second time I knew better.

 

[Quantised]

OK got the parts, used a BT139 instead as it has some features more like the original. Added extra cooling area on the TVS and insulated the triac from the frame, even though it is insulated inside it seemed a good idea.

Also connected the power to and from the triac with wire so the copper does not carry the whole load.

A result I must say. The humm is much less so the new triac fits the snubber circuit better, powers up and runs nicely after a day of testing.

So many thanks to Keepitsimplestupid for such good advice and helping me to understand triacs.

Thanks all

Q

 

[KeepItSimpleStupid]

Glad it all worked out. I remember this 1000 W external lamp ignitor (40 kV pulse to start, 22 VDC, 45 A operating voltage). The manufacturer couldn't get it right. Just a little re-arranging of the wiring made it a lot more reliable. Eventually the manufacturer moved the ignitor inside the lamp housing at nearly no charge. Then the power supply acted up and I found a 10 A bridge rectifier in it and wasn't happy. Again, the retrofit (new transformer and rectifier assy) was free. I'm like "Who was the bozo who put a 10 A rectifier for a 45 A load?", but didn't say it that way.