Triac efficiency

Efficiently (maybe 2-3% loss) at full ON. Near-OFF, the percent is higher.

Losses are higher near off, or efficiency is higher?

Thanks,

Michael

Losses are lower, but percent losses are higher. Efficiency of something that's nearly off, is nearly irrelevant.

There are three issues. Whatever the voltage drop it is when on, what the l eakage current when off,, and the power dissipated during the turnoff. (the last is usually the most significant in high speed circuits because there are more turnoffs per unit of time)

MOSFETS and BJTs alog with other devices (capable of somewhat linear operat ion usually require base/gate drive optimization for efficiency. Thrysistor s do not suffer that need. (to any great degree)

Thyristors turn themselves off near the zero-current point, so there's not much opportunity for excess dissipation then.

Triacs being four-quadrant devices, if you try anything too fancy when optimizing the gate drive, you just wind up turning it on in the other direction. (There are also three-quadrant triacs, so this isn't always true.)

I haven't used a triac in roughly forever, but ISTR the main issue is the volt or so of drop across the device in operation. At 60 Hz, the turn-on transient would have to be pretty slow to have much effect on the efficiency.

Cheers

Phil Hobbs

It does it by switching on and off really fast, most of the unwanted energy is blocked. (and not consumed, it "stays in the power line")

There's a 1.5 volt ineficiency (ballpark figure) added by the triac, so if you're running a 10A load at full power the triac will get about

Triacs are used in variable speed hand-tools (mains powered) and incandescent lamp dimmers (amongst other uses) feel free to probe the outside of these devices with a heat-sensitive finger :)

As opposed to an 'insensitive' one? Will that reduce the mains VAC sensation?

I thought it was obvious that defective equipment should be avoided,

a numb finger will tell you nothing.

Should be none of that on the user-facing surfaces

It could at least be repaired and put back into operation.