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Obviously triacs have been well known to be used in applications which don't really require a perfect sine wave to function.

However, what about say a triac to switch on and off more complicated devices such as phone/laptop chargers, TVs, audio equipment, pretty much everything else that you would find in the average household. I'm guessing it might depend on the front end of the power supply for the equipment, on its tolerance of its input voltage. However, does anyone have any practical experience with this?

What sort of waveform would you see if we switch a triac on, vs a mechanical relay switch? (i.e. triac switched on permanently)

To clarify, I mean a persistent on/off, in the way that a mechanical relay would be used to switch equipment on and off using an electrical signal. Probably a switch on the live line of the mains?

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Rather than using a triac, I suggest using a solid-state relay instead. Most solid-state relays (SSRs) switch when the AC waveform crosses the zero point, so they provide a very clean transition between on and off.

Assuming the triac has an adequate rating for the device you want to switch, you should have no trouble using it to switch pretty much anything.

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  • \$\begingroup\$ My question was actually, what would happen if you used a triac to switch these type of loads. Maybe I didn't write clearly! When you say triac has an adequate rating, is that a triac inside an ssr? (Because I've seen triac ssrs). If so how does that overcome the zero crossing problem? \$\endgroup\$ – midnightBlue Jul 18 '14 at 11:06
  • \$\begingroup\$ The reason I wanted to use triacs is because they are so cheap. Mechanical relays are expensive. Additionally, the maximum loads I am looking at are 100w. A quick search returns some very expensive "solid state relays". I might not be looking at the right thing. \$\endgroup\$ – midnightBlue Jul 18 '14 at 11:09
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The TRIAC (as well the SCR) requires a minimum current which keeps it conducting, called the holding current - \$I_H\$. After the TRIAC is turned on, a current flows through it. When the TRIAC current falls below the holding current the TRIAC is blocked and requires another gate pulse before it can turn on again - creating a non perfect sinewave on the load (harmonic issues,...).

In other words, even if you try to make it behave like a closed switch (keeping the gate voltage), the TRIAC will not act so.

Holding current

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