Triac Efficiency...

[Cursitor Doom]

Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.

 

[John Larkin]

On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <cd@notformail.com>
wrote:

Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.

Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

 

[Ricky]

On Sunday, June 4, 2023 at 6:13:39 PM UTC-4, John Larkin wrote:

On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[Cursitor Doom]

On Sun, 4 Jun 2023 15:45:44 -0700 (PDT), Ricky
<gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, June 4, 2023 at 6:13:39?PM UTC-4, John Larkin wrote:
On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.

I thought diacs were sometimes used because triacs don\'t fire
symetrically, but I could be wrong.
So, as regards AC drive, is a higher frequency drive signal a safer
bet? Also, the load is AC too, so the thing will turn off at every
zero-crossing point, which makes life more complicated. :-(

 

[Ricky]

On Sunday, June 4, 2023 at 7:03:27 PM UTC-4, Cursitor Doom wrote:

On Sun, 4 Jun 2023 15:45:44 -0700 (PDT), Ricky
gnuarm.del...@gmail.com> wrote:
On Sunday, June 4, 2023 at 6:13:39?PM UTC-4, John Larkin wrote:
On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.
I thought diacs were sometimes used because triacs don\'t fire
symetrically, but I could be wrong.
So, as regards AC drive, is a higher frequency drive signal a safer
bet? Also, the load is AC too, so the thing will turn off at every
zero-crossing point, which makes life more complicated. :-(

Diacs are used with SCRs as well. The idea it the Diac lets very little current flow until the voltage is fairly high. Then it conducts suddenly, just what works best for the triac/scr.

I don\'t know why you are lamenting the turn off at each zero crossing. That\'s fundamental to how they work. Every half cycle you get to time the next turn on. What\'s hard about that?

Do you know anything about using triacs? There is plenty of reference material on the web. Data sheets are not a bad place to start.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[John S]

On 6/4/2023 4:34 PM, Cursitor Doom wrote:

Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.

How do you want to use it? Is it just a switch that you turn on like a
light switch, or do you want to phase control the AC into your load?

And another question is, what kind of load? An inductive load might need
a long gate pulse. Maybe even continuous.

Tell us about your project for maximum help.

 

[Cursitor Doom]

On Sun, 4 Jun 2023 18:40:25 -0500, John S <Sophi.2@invalid.org> wrote:

On 6/4/2023 4:34 PM, Cursitor Doom wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.

How do you want to use it? Is it just a switch that you turn on like a
light switch, or do you want to phase control the AC into your load?

And another question is, what kind of load? An inductive load might need
a long gate pulse. Maybe even continuous.

Tell us about your project for maximum help.

No project in mind. No particular type of load either. Just a question
that came to mind, nothing more.

 

[Phil Allison]

Cursitor Doom wrote:

-----------------------------------

Tell us about your project for maximum help.

No project in mind. No particular type of load either. Just a question
that came to mind, nothing more.

** See: https://www.electronics-tutorials.ws/power/triac.html

The schem headed \"Triac Switching Circuit \" is commonly used where a physically small switch must control a large mains current.

Diacs come to the fore if phase control of a load is needed.



....... Phil

 

[Wandere]

On Sun, 4 Jun 2023 16:27:46 -0700 (PDT), Ricky <gnuarm.deletethisbit@gmail.com> wrote:

I don\'t know why you are lamenting the turn off at each zero crossing.
That\'s fundamental to how they work. Every half cycle you get to time the next turn on.
What\'s hard about that?

The problem is they don\'t turn off unless you use the zero-crossing or a phase-crossing.
I\'m no expert on triacs but the two times I ended up redesigning circuits with them,
they wouldn\'t turn off. Once someone had pulse width modulated a triac. The other time
someone had it run into an end switch. The circuit would almost always work but when
conditions were just right they would stay on and burn up. You have to make sure they are
turned off when they want to be turned off.

 

[Ricky]

On Sunday, June 4, 2023 at 9:07:55 PM UTC-4, Wanderer wrote:

On Sun, 4 Jun 2023 16:27:46 -0700 (PDT), Ricky <gnuarm.del...@gmail.com> wrote:
I don\'t know why you are lamenting the turn off at each zero crossing.
That\'s fundamental to how they work. Every half cycle you get to time the next turn on.
What\'s hard about that?
The problem is they don\'t turn off unless you use the zero-crossing or a phase-crossing.
I\'m no expert on triacs but the two times I ended up redesigning circuits with them,
they wouldn\'t turn off. Once someone had pulse width modulated a triac. The other time
someone had it run into an end switch. The circuit would almost always work but when
conditions were just right they would stay on and burn up. You have to make sure they are
turned off when they want to be turned off.

Sorry, I don\'t understand what you are talking about, \"they don\'t turn off unless you use the zero-crossing or a phase-crossing\". When the current in the triac goes to zero, it turns off. If your gate signal is still above the threshold, it won\'t turn off, but that\'s because you are telling it to stay on.

Did you ever get your circuits working? What was wrong?

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[John Larkin]

On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <cd@notformail.com>
wrote:

On Sun, 4 Jun 2023 15:45:44 -0700 (PDT), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, June 4, 2023 at 6:13:39?PM UTC-4, John Larkin wrote:
On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.

I thought diacs were sometimes used because triacs don\'t fire
symetrically, but I could be wrong.
So, as regards AC drive, is a higher frequency drive signal a safer
bet? Also, the load is AC too, so the thing will turn off at every
zero-crossing point, which makes life more complicated. :-(

With an AC load, an AC gate drive is probably OK. The triac will turn
on before the voltage gets too high, so the spreading damage mechanism
won\'t happen much.

The bad case is when there\'s a lot of voltage across the device with a
lot of instantaneous current behind it, and it gets a slow, wimpy
trigger.

Post your proposed circuit and we can discuss it.

I still call the terminals anode, gate, cathode. I can never remember
what\'s MT1 and MT2. Top and bottom would be OK too.

 

[Jasen Betts]

On 2023-06-04, Cursitor Doom <cd@notformail.com> wrote:

Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

Assuming 50Hz operation use a much higher frequency like 100KHz
to drive the gate.

--
Jasen.
🇺🇦 Слава Україні

 

[Wandere]

On Sun, 4 Jun 2023 19:29:27 -0700 (PDT), Ricky <gnuarm.del...@gmail.com> wrote:
Sorry, I don\'t understand what you are talking about, \"they don\'t turn off unless you
use the zero-crossing or a phase-crossing\". When the current in the triac goes to
zero, it turns off. If your gate signal is still above the threshold, it won\'t turn
off, but that\'s because you are telling it to stay on.

Did you ever get your circuits working? What was wrong?

Here\'s a link.

https://resources.pcb.cadence.com/blog/why-your-triac-wont-turn-off

In short, this means we can see a few instances where the triac fails to totally turn off,
even if the gate terminal bias has been removed:

1. The triac continues to have DC bias after the gate terminal bias is removed
2. There is some phase difference between current and voltage (reactive load)
3. The edge rate of the switched AC signal is too fast

Did I fix it? I think I did. Sustaining work. Mfg is getting returns. They want me to fix the problem without changing anything so they can use existing stock. I can\'t reproduce the problem. Using app notes and books, I change the zero crossing circuit, the triac and add a snubber network. My circuit works but the old circuit works. We rework the boards and we don\'t get returns. I probably just got lucky.

 

[Phil Hobbs]

On 2023-06-04 23:05, John Larkin wrote:

On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Sun, 4 Jun 2023 15:45:44 -0700 (PDT), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, June 4, 2023 at 6:13:39?PM UTC-4, John Larkin wrote:
On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.

I thought diacs were sometimes used because triacs don\'t fire
symetrically, but I could be wrong.
So, as regards AC drive, is a higher frequency drive signal a safer
bet? Also, the load is AC too, so the thing will turn off at every
zero-crossing point, which makes life more complicated. :-(

With an AC load, an AC gate drive is probably OK. The triac will turn
on before the voltage gets too high, so the spreading damage mechanism
won\'t happen much.

The bad case is when there\'s a lot of voltage across the device with a
lot of instantaneous current behind it, and it gets a slow, wimpy
trigger.

Post your proposed circuit and we can discuss it.

I still call the terminals anode, gate, cathode. I can never remember
what\'s MT1 and MT2. Top and bottom would be OK too.

The triac is one of those parts where folks get confused by fossilized
analogies.

A triac is a bidirectional thyristor, but it does not behave like two
SCRs in antiparallel. SCR triggering only works in one quadrant, for a
start, so two antiparallel SCRs would be a two-quadrant device, whereas
triacs trigger in all four quadrants.

The triggering also isn\'t that symmetrical, because the structures
aren\'t--the second and fourth quadrant triggering mechanisms are fairly
different, and the four-layer stacks aren\'t well separated, as they
would be in two SCRs.

Triacs are also very slow even compared with SCRs, which are pretty poky
devices by modern standards.

Someplace I have a paper that goes into the details of real triac
operation--iirc it\'s a good read, but I\'m not laying my hands on it at
the moment.

(I haven\'t actually used a triac since I was a teenager, so this is just
out of general interest.)

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
http://hobbs-eo.com

 

[John Larkin]

On Mon, 5 Jun 2023 12:10:05 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-06-04 23:05, John Larkin wrote:
On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Sun, 4 Jun 2023 15:45:44 -0700 (PDT), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, June 4, 2023 at 6:13:39?PM UTC-4, John Larkin wrote:
On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.

I thought diacs were sometimes used because triacs don\'t fire
symetrically, but I could be wrong.
So, as regards AC drive, is a higher frequency drive signal a safer
bet? Also, the load is AC too, so the thing will turn off at every
zero-crossing point, which makes life more complicated. :-(

With an AC load, an AC gate drive is probably OK. The triac will turn
on before the voltage gets too high, so the spreading damage mechanism
won\'t happen much.

The bad case is when there\'s a lot of voltage across the device with a
lot of instantaneous current behind it, and it gets a slow, wimpy
trigger.

Post your proposed circuit and we can discuss it.

I still call the terminals anode, gate, cathode. I can never remember
what\'s MT1 and MT2. Top and bottom would be OK too.


The triac is one of those parts where folks get confused by fossilized
analogies.

A triac is a bidirectional thyristor, but it does not behave like two
SCRs in antiparallel. SCR triggering only works in one quadrant, for a
start, so two antiparallel SCRs would be a two-quadrant device, whereas
triacs trigger in all four quadrants.

The triggering also isn\'t that symmetrical, because the structures
aren\'t--the second and fourth quadrant triggering mechanisms are fairly
different, and the four-layer stacks aren\'t well separated, as they
would be in two SCRs.

Triacs are also very slow even compared with SCRs, which are pretty poky
devices by modern standards.

Someplace I have a paper that goes into the details of real triac
operation--iirc it\'s a good read, but I\'m not laying my hands on it at
the moment.

(I haven\'t actually used a triac since I was a teenager, so this is just
out of general interest.)

Cheers

Phil Hobbs

I haven\'t designed in a triac for maybe 15 years now. I used a couple
of triacs to soft-start a giant power supply that had a 60 Hz power
transformer. Switch in a giant resistor on the primary side, wait a
second, then short it out. That was hard on resistors but prevented
the occasional 1000 amp startup surge. And allowed a little C&K power
switch on the front panel.

The customer insisted that we not use a switching power supply!

Real relays are usually cheaper than triacs, easier to drive, and
don\'t need heat sinks.

 

[Cursitor Doom]

On Mon, 05 Jun 2023 09:21:32 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Mon, 5 Jun 2023 12:10:05 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-06-04 23:05, John Larkin wrote:
On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Sun, 4 Jun 2023 15:45:44 -0700 (PDT), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, June 4, 2023 at 6:13:39?PM UTC-4, John Larkin wrote:
On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.

I thought diacs were sometimes used because triacs don\'t fire
symetrically, but I could be wrong.
So, as regards AC drive, is a higher frequency drive signal a safer
bet? Also, the load is AC too, so the thing will turn off at every
zero-crossing point, which makes life more complicated. :-(

With an AC load, an AC gate drive is probably OK. The triac will turn
on before the voltage gets too high, so the spreading damage mechanism
won\'t happen much.

The bad case is when there\'s a lot of voltage across the device with a
lot of instantaneous current behind it, and it gets a slow, wimpy
trigger.

Post your proposed circuit and we can discuss it.

I still call the terminals anode, gate, cathode. I can never remember
what\'s MT1 and MT2. Top and bottom would be OK too.


The triac is one of those parts where folks get confused by fossilized
analogies.

A triac is a bidirectional thyristor, but it does not behave like two
SCRs in antiparallel. SCR triggering only works in one quadrant, for a
start, so two antiparallel SCRs would be a two-quadrant device, whereas
triacs trigger in all four quadrants.

The triggering also isn\'t that symmetrical, because the structures
aren\'t--the second and fourth quadrant triggering mechanisms are fairly
different, and the four-layer stacks aren\'t well separated, as they
would be in two SCRs.

Triacs are also very slow even compared with SCRs, which are pretty poky
devices by modern standards.

Someplace I have a paper that goes into the details of real triac
operation--iirc it\'s a good read, but I\'m not laying my hands on it at
the moment.

(I haven\'t actually used a triac since I was a teenager, so this is just
out of general interest.)

Cheers

Phil Hobbs

I haven\'t designed in a triac for maybe 15 years now. I used a couple
of triacs to soft-start a giant power supply that had a 60 Hz power
transformer. Switch in a giant resistor on the primary side, wait a
second, then short it out. That was hard on resistors but prevented
the occasional 1000 amp startup surge. And allowed a little C&K power
switch on the front panel.

The customer insisted that we not use a switching power supply!

Real relays are usually cheaper than triacs, easier to drive, and
don\'t need heat sinks.

Yes, but you can\'t fire them on and off anything like as fast and they
don\'t have the same longevity AFAIK.

 

[Cursitor Doom]

On Mon, 05 Jun 2023 18:50:38 +0100, Cursitor Doom <cd@notformail.com>
wrote:

On Mon, 05 Jun 2023 09:21:32 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Mon, 5 Jun 2023 12:10:05 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-06-04 23:05, John Larkin wrote:
On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Sun, 4 Jun 2023 15:45:44 -0700 (PDT), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, June 4, 2023 at 6:13:39?PM UTC-4, John Larkin wrote:
On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.

I thought diacs were sometimes used because triacs don\'t fire
symetrically, but I could be wrong.
So, as regards AC drive, is a higher frequency drive signal a safer
bet? Also, the load is AC too, so the thing will turn off at every
zero-crossing point, which makes life more complicated. :-(

With an AC load, an AC gate drive is probably OK. The triac will turn
on before the voltage gets too high, so the spreading damage mechanism
won\'t happen much.

The bad case is when there\'s a lot of voltage across the device with a
lot of instantaneous current behind it, and it gets a slow, wimpy
trigger.

Post your proposed circuit and we can discuss it.

I still call the terminals anode, gate, cathode. I can never remember
what\'s MT1 and MT2. Top and bottom would be OK too.


The triac is one of those parts where folks get confused by fossilized
analogies.

A triac is a bidirectional thyristor, but it does not behave like two
SCRs in antiparallel. SCR triggering only works in one quadrant, for a
start, so two antiparallel SCRs would be a two-quadrant device, whereas
triacs trigger in all four quadrants.

The triggering also isn\'t that symmetrical, because the structures
aren\'t--the second and fourth quadrant triggering mechanisms are fairly
different, and the four-layer stacks aren\'t well separated, as they
would be in two SCRs.

Triacs are also very slow even compared with SCRs, which are pretty poky
devices by modern standards.

Someplace I have a paper that goes into the details of real triac
operation--iirc it\'s a good read, but I\'m not laying my hands on it at
the moment.

(I haven\'t actually used a triac since I was a teenager, so this is just
out of general interest.)

Cheers

Phil Hobbs

I haven\'t designed in a triac for maybe 15 years now. I used a couple
of triacs to soft-start a giant power supply that had a 60 Hz power
transformer. Switch in a giant resistor on the primary side, wait a
second, then short it out. That was hard on resistors but prevented
the occasional 1000 amp startup surge. And allowed a little C&K power
switch on the front panel.

The customer insisted that we not use a switching power supply!

Real relays are usually cheaper than triacs, easier to drive, and
don\'t need heat sinks.

Yes, but you can\'t fire them on and off anything like as fast and they
don\'t have the same longevity AFAIK.

Plus a relay capable of switching 16A is going to be a hog, take up
loads of space compared to a triac and cost a hell of a lot more, I
would imagine.

 

[John Larkin]

On Mon, 05 Jun 2023 18:54:16 +0100, Cursitor Doom <cd@notformail.com>
wrote:

On Mon, 05 Jun 2023 18:50:38 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Mon, 05 Jun 2023 09:21:32 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Mon, 5 Jun 2023 12:10:05 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-06-04 23:05, John Larkin wrote:
On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Sun, 4 Jun 2023 15:45:44 -0700 (PDT), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, June 4, 2023 at 6:13:39?PM UTC-4, John Larkin wrote:
On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.

I thought diacs were sometimes used because triacs don\'t fire
symetrically, but I could be wrong.
So, as regards AC drive, is a higher frequency drive signal a safer
bet? Also, the load is AC too, so the thing will turn off at every
zero-crossing point, which makes life more complicated. :-(

With an AC load, an AC gate drive is probably OK. The triac will turn
on before the voltage gets too high, so the spreading damage mechanism
won\'t happen much.

The bad case is when there\'s a lot of voltage across the device with a
lot of instantaneous current behind it, and it gets a slow, wimpy
trigger.

Post your proposed circuit and we can discuss it.

I still call the terminals anode, gate, cathode. I can never remember
what\'s MT1 and MT2. Top and bottom would be OK too.


The triac is one of those parts where folks get confused by fossilized
analogies.

A triac is a bidirectional thyristor, but it does not behave like two
SCRs in antiparallel. SCR triggering only works in one quadrant, for a
start, so two antiparallel SCRs would be a two-quadrant device, whereas
triacs trigger in all four quadrants.

The triggering also isn\'t that symmetrical, because the structures
aren\'t--the second and fourth quadrant triggering mechanisms are fairly
different, and the four-layer stacks aren\'t well separated, as they
would be in two SCRs.

Triacs are also very slow even compared with SCRs, which are pretty poky
devices by modern standards.

Someplace I have a paper that goes into the details of real triac
operation--iirc it\'s a good read, but I\'m not laying my hands on it at
the moment.

(I haven\'t actually used a triac since I was a teenager, so this is just
out of general interest.)

Cheers

Phil Hobbs

I haven\'t designed in a triac for maybe 15 years now. I used a couple
of triacs to soft-start a giant power supply that had a 60 Hz power
transformer. Switch in a giant resistor on the primary side, wait a
second, then short it out. That was hard on resistors but prevented
the occasional 1000 amp startup surge. And allowed a little C&K power
switch on the front panel.

The customer insisted that we not use a switching power supply!

Real relays are usually cheaper than triacs, easier to drive, and
don\'t need heat sinks.

Yes, but you can\'t fire them on and off anything like as fast and they
don\'t have the same longevity AFAIK.

Plus a relay capable of switching 16A is going to be a hog, take up
loads of space compared to a triac and cost a hell of a lot more, I
would imagine.

It\'s easy to look up. Digikey has 15 amp relays starting around 60
cents.

The triac will need a heat sink, which will be big and cost more than
the triac.

 

[John Larkin]

On Mon, 05 Jun 2023 11:01:33 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Mon, 05 Jun 2023 18:54:16 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Mon, 05 Jun 2023 18:50:38 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Mon, 05 Jun 2023 09:21:32 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Mon, 5 Jun 2023 12:10:05 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-06-04 23:05, John Larkin wrote:
On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Sun, 4 Jun 2023 15:45:44 -0700 (PDT), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, June 4, 2023 at 6:13:39?PM UTC-4, John Larkin wrote:
On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.

I thought diacs were sometimes used because triacs don\'t fire
symetrically, but I could be wrong.
So, as regards AC drive, is a higher frequency drive signal a safer
bet? Also, the load is AC too, so the thing will turn off at every
zero-crossing point, which makes life more complicated. :-(

With an AC load, an AC gate drive is probably OK. The triac will turn
on before the voltage gets too high, so the spreading damage mechanism
won\'t happen much.

The bad case is when there\'s a lot of voltage across the device with a
lot of instantaneous current behind it, and it gets a slow, wimpy
trigger.

Post your proposed circuit and we can discuss it.

I still call the terminals anode, gate, cathode. I can never remember
what\'s MT1 and MT2. Top and bottom would be OK too.


The triac is one of those parts where folks get confused by fossilized
analogies.

A triac is a bidirectional thyristor, but it does not behave like two
SCRs in antiparallel. SCR triggering only works in one quadrant, for a
start, so two antiparallel SCRs would be a two-quadrant device, whereas
triacs trigger in all four quadrants.

The triggering also isn\'t that symmetrical, because the structures
aren\'t--the second and fourth quadrant triggering mechanisms are fairly
different, and the four-layer stacks aren\'t well separated, as they
would be in two SCRs.

Triacs are also very slow even compared with SCRs, which are pretty poky
devices by modern standards.

Someplace I have a paper that goes into the details of real triac
operation--iirc it\'s a good read, but I\'m not laying my hands on it at
the moment.

(I haven\'t actually used a triac since I was a teenager, so this is just
out of general interest.)

Cheers

Phil Hobbs

I haven\'t designed in a triac for maybe 15 years now. I used a couple
of triacs to soft-start a giant power supply that had a 60 Hz power
transformer. Switch in a giant resistor on the primary side, wait a
second, then short it out. That was hard on resistors but prevented
the occasional 1000 amp startup surge. And allowed a little C&K power
switch on the front panel.

The customer insisted that we not use a switching power supply!

Real relays are usually cheaper than triacs, easier to drive, and
don\'t need heat sinks.

Yes, but you can\'t fire them on and off anything like as fast and they
don\'t have the same longevity AFAIK.

Plus a relay capable of switching 16A is going to be a hog, take up
loads of space compared to a triac and cost a hell of a lot more, I
would imagine.

It\'s easy to look up. Digikey has 15 amp relays starting around 60
cents.

The triac will need a heat sink, which will be big and cost more than
the triac.

Relays don\'t need isolated gate drivers, TVS/MOV protection, or
snubbers either.

 

[Cursitor Doom]

On Mon, 05 Jun 2023 11:01:33 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Mon, 05 Jun 2023 18:54:16 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Mon, 05 Jun 2023 18:50:38 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Mon, 05 Jun 2023 09:21:32 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Mon, 5 Jun 2023 12:10:05 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-06-04 23:05, John Larkin wrote:
On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Sun, 4 Jun 2023 15:45:44 -0700 (PDT), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

On Sunday, June 4, 2023 at 6:13:39?PM UTC-4, John Larkin wrote:
On Sun, 04 Jun 2023 22:34:00 +0100, Cursitor Doom <c...@notformail.com
wrote:
Greetings, gentlemen,

As we all know, to get maximum efficiency out of a MOSFET, it needs to
be driven hard and fast and spend as little time between fully on and
fully off as possible. Does that same principle extend to Triacs? And
if so, how can that best be implemented when one has to use AC to
drive the gate?

CD.
Once a triac fires, the gate drive doesn\'t matter any more.

But they do need a hard, fast drive to fire properly, long enough to
let the drain current rise above the latch limit.

AC gate drive will be slow-rise, which could just possibly damage the
triac if the load current is high.

That should be on the data sheets.

I believe that is why a diac is typically used in the control circuit.

I thought diacs were sometimes used because triacs don\'t fire
symetrically, but I could be wrong.
So, as regards AC drive, is a higher frequency drive signal a safer
bet? Also, the load is AC too, so the thing will turn off at every
zero-crossing point, which makes life more complicated. :-(

With an AC load, an AC gate drive is probably OK. The triac will turn
on before the voltage gets too high, so the spreading damage mechanism
won\'t happen much.

The bad case is when there\'s a lot of voltage across the device with a
lot of instantaneous current behind it, and it gets a slow, wimpy
trigger.

Post your proposed circuit and we can discuss it.

I still call the terminals anode, gate, cathode. I can never remember
what\'s MT1 and MT2. Top and bottom would be OK too.


The triac is one of those parts where folks get confused by fossilized
analogies.

A triac is a bidirectional thyristor, but it does not behave like two
SCRs in antiparallel. SCR triggering only works in one quadrant, for a
start, so two antiparallel SCRs would be a two-quadrant device, whereas
triacs trigger in all four quadrants.

The triggering also isn\'t that symmetrical, because the structures
aren\'t--the second and fourth quadrant triggering mechanisms are fairly
different, and the four-layer stacks aren\'t well separated, as they
would be in two SCRs.

Triacs are also very slow even compared with SCRs, which are pretty poky
devices by modern standards.

Someplace I have a paper that goes into the details of real triac
operation--iirc it\'s a good read, but I\'m not laying my hands on it at
the moment.

(I haven\'t actually used a triac since I was a teenager, so this is just
out of general interest.)

Cheers

Phil Hobbs

I haven\'t designed in a triac for maybe 15 years now. I used a couple
of triacs to soft-start a giant power supply that had a 60 Hz power
transformer. Switch in a giant resistor on the primary side, wait a
second, then short it out. That was hard on resistors but prevented
the occasional 1000 amp startup surge. And allowed a little C&K power
switch on the front panel.

The customer insisted that we not use a switching power supply!

Real relays are usually cheaper than triacs, easier to drive, and
don\'t need heat sinks.

Yes, but you can\'t fire them on and off anything like as fast and they
don\'t have the same longevity AFAIK.

Plus a relay capable of switching 16A is going to be a hog, take up
loads of space compared to a triac and cost a hell of a lot more, I
would imagine.

It\'s easy to look up. Digikey has 15 amp relays starting around 60
cents.

Yeahbut I don\'t want to order a million of them to get that price.

The triac will need a heat sink, which will be big and cost more than
the triac.