Triac efficiency

[mrda...@gmail.com]

Hi everyone,

When regulating the power to a motor or light, does the triac do so efficiently or does it dump the unwanted power as heat, as a linear voltage regulator does?

Thanks,

Michael

[whit3rd]

On Thursday, December 14, 2017 at 4:49:49 PM UTC-8, mrda...@gmail.com wrote:
> Hi everyone,
>
> When regulating the power to a motor or light, does the triac do so efficiently or does it dump the unwanted power as heat, as a linear voltage regulator does?

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

[mrda...@gmail.com]

Losses are higher near off, or efficiency is higher?

Thanks,

Michael

[whit3rd]

On Thursday, December 14, 2017 at 9:24:50 PM UTC-8, mrda...@gmail.com wrote:
> Losses are higher near off, or efficiency is higher?

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

[jurb...@gmail.com]

There are three issues. Whatever the voltage drop it is when on, what the leakage 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 operation usually require base/gate drive optimization for efficiency. Thrysistors do not suffer that need. (to any great degree)

[Phil Hobbs]

On 12/15/2017 06:30 AM, jurb...@gmail.com wrote:
> There are three issues. Whatever the voltage drop it is when on, what
> the leakage 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)

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

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

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

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
https://hobbs-eo.com

[Jasen Betts]

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
15W of heat.

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 :)

--
This email has not been checked by half-arsed antivirus software

[bruce2...@gmail.com]

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

[Jasen Betts]

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

[Jasen Betts]

On 2017-12-20, bruce2...@gmail.com <bruce2...@gmail.com> wrote:

a numb finger will tell you nothing.

> Will that reduce the mains VAC sensation?

Should be none of that on the user-facing surfaces

[bruce2...@gmail.com]

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