Relay protection on power failure

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#41
The types having a discharge circuit included can drive a MOS directly, and the tlp3906 seems to fall into that category.
However, I do not know the behaviour of the discharge circuit when it is subjected to large Miller-effect currents caused by a large D-S AC voltage. I guess you need to test that in reality.
I am not certain either that the opto can be included in the power-detection circuit and give the same results regarding speed.
Italso has to be tested in the real world .
Here is another Toshiba document
https://toshiba.semicon-storage.com/info/docget.jsp?did=65308
 
#42
Hi Humbledeer,
I first tried the 12VAC relays, and they turned out to be noisy, and started exhibiting a higher than normal resistance. Well, the approach I am exploring now is to shunt the amplifier output on a power failure, using SSRs. This way, there are no relays in the audio path in normal scenario.
 
#43
HumbleDeer said:
I'm seeing a lot of designs in the earlier parts of this topic that rely on the supply voltage that powers the relays to be the one that collapses. But now I'm thinking, why is that necessary? Why complicate your own situation by introducing a race for time?

Simply sensing the AC dropping out could act as a trigger, and if you're fine with a little bit of power loss, an opto can be put directly on mains with a resistor of suitable size, as far as I know, that's how many HVAC systems do their MainsPresence sensing, albeit higher power transistors used. It is more expensive, but often worth the solid performance and predictable turn off time for relatively low power systems (eg, not huge power amps.)

On topic of the last posts, I agree with Elvee. Just use the TLP as it was mostly intended to be used. Using it in any odd less common configuration is likely to cause these weird behaviours to pop up.
Click to expand...
Yes,it's getting complicated, but an you please simplify?
Sensing AC power supply loss is exactly what is being used, unless I'm missing something. As I mentioned earlier, I'm using a shunt approach on a power loss. Please contribute with your alternate designs to help this discussion.
I'm not sure what you're agreeing with Elvee, as the TLP3906 is meant to drive Mosfets in a SSR. Please educate me if my understanding is wrong,
 
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