Hi,
In a dishwasher machine main board we have used 107NN0 TRIAC for controlling ac loads such as valves, pumps, dispenser, etc. In about 2 to 3 percent of products sold to customers, one of TRIACs that has a parallel RC equivalent load is half-burned (TRIAC is short-circuited in one direction) when the machine gets plugged in. Here’s the schematic of a single TRIAC on mainboard. All 8 TRIACs have the same configuration. One TRIAC has RC load and others have inductive load. Surprising point is that we couldn’t reproduce the fault in lab under different test conditions such as Surge or EFT noise, input voltage connection in different angles of sine wave. We’re glad if anyone can help us about this problem.
triac half burn - Page 1 has the link to Mahdi’s schematic. If it were me, I’d check the 47 ohm and 10 nF on the failed units, and make sure there is appropriate protection on the input to the whole machine. And escalate to the vendor of the Z-107NN0.
There’s a 100nf cap from BC817 emitter to Null… Perhaps the 100nF cap is there to slow the turn-on down?
But, any noise, surge, burst or notches on Null will have an easy path through the 100nF to emitter of BC817, and possibly also gate of triac. You would need to have a varistor or eq across phase/null
Also 1k for gate is a quite high value. Normally that is 10 times lower to avoid spurious turn-on.
The drive is very slow, could case turn on losses or failures
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Snubber resistor and capacitor are ok on failed units.
there is a VARISTOR and EMI filter on the input of main board and also an extra EMI filter on input plug.
And the reason for the 100nF capacitor? And slow turn on?
I think (because I haven’t designed the circuit) it is intended to prevent noises on NULL from false triggering the TRIAC.