C
Cursitor Doom
Guest
On Mon, 05 Jun 2023 11:04:03 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:
<jlarkin@highlandSNIPMEtechnology.com> wrote:
Well, you got me there!
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C
Cursitor Doom
Guest
On Mon, 05 Jun 2023 11:01:33 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:
Seriously, I\'m not seeing 15A relays on Digikey for less than around
15 dollars. Where do you get 60 cents from ??
<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.
Seriously, I\'m not seeing 15A relays on Digikey for less than around
15 dollars. Where do you get 60 cents from ??
F
Fred Bloggs
Guest
On Sunday, June 4, 2023 at 5:34:08â¯PM UTC-4, Cursitor Doom wrote:
No.
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.
No.
L
Lasse Langwadt Christensen
Guest
mandag den 5. juni 2023 kl. 20.45.03 UTC+2 skrev Cursitor Doom:
https://www.digikey.dk/en/products/detail/amphenol-anytek/AHQSH112LM1F00G/16721973
60 cent if you buy 250, 90cent if you buy one
On Mon, 05 Jun 2023 11:01:33 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
On Mon, 05 Jun 2023 18:54:16 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 05 Jun 2023 18:50:38 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 05 Jun 2023 09:21:32 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
On Mon, 5 Jun 2023 12:10:05 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:
On 2023-06-04 23:05, John Larkin wrote:
On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <c...@notformail.com
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. :-(
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.
Seriously, I\'m not seeing 15A relays on Digikey for less than around
15 dollars. Where do you get 60 cents from ??
https://www.digikey.dk/en/products/detail/amphenol-anytek/AHQSH112LM1F00G/16721973
60 cent if you buy 250, 90cent if you buy one
F
Fred Bloggs
Guest
On Sunday, June 4, 2023 at 6:13:39â¯PM UTC-4, John Larkin wrote:
If you ever look at a comprehensive thyristor handbook, you will see they have these devices categorized by application. They have the 60 Hz line of products for mains switching, and they have the switching line for all the advanced inverter/ converter/ resonator applications imaginable. Triacs have pretty sizeable I2t ratings, as in HUGE, they can take a lot of abuse. Supposedly the main failure mode is due to excessive dI/dt, which is too much current density before the entire conduction junction area turns fully on to support it. That\'s more of an external circuit design issue than a gate drive. I\'ve seen quite a few consumer applications for switching the line onto a load, and they usually use something on the order of a 10KHz square wave ac-coupled to the gate via capacitor or transformer. 50us is plenty of time to fully turn on the gate most of the time. The square wave usually runs continuously while the triac is on.
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.
If you ever look at a comprehensive thyristor handbook, you will see they have these devices categorized by application. They have the 60 Hz line of products for mains switching, and they have the switching line for all the advanced inverter/ converter/ resonator applications imaginable. Triacs have pretty sizeable I2t ratings, as in HUGE, they can take a lot of abuse. Supposedly the main failure mode is due to excessive dI/dt, which is too much current density before the entire conduction junction area turns fully on to support it. That\'s more of an external circuit design issue than a gate drive. I\'ve seen quite a few consumer applications for switching the line onto a load, and they usually use something on the order of a 10KHz square wave ac-coupled to the gate via capacitor or transformer. 50us is plenty of time to fully turn on the gate most of the time. The square wave usually runs continuously while the triac is on.
E
ehsjr
Guest
On 6/5/2023 2:44 PM, Cursitor Doom wrote:
Digikey qty ! forty eight cents:
J1071AS5VDC.36
RELAY GEN PURPOSE SPST N.O. 15A
Plus a bunch more
https://www.digikey.com/en/products/filter/power-relays-over-2-amps/188?s=N4IgjCBcpgLGAGKoDGUBmBDANgZwKYA0IA9lANrgCsABAIIgC6xA
DgC5QgCqAdgJZsA8ugCy%2BTLgCuAJ3wgAvvOIA2ZCD4ATTgFpEEVh0ggQxNgE8
WcoxLSKgA
Ed
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.
Seriously, I\'m not seeing 15A relays on Digikey for less than around
15 dollars. Where do you get 60 cents from ??
Digikey qty ! forty eight cents:
J1071AS5VDC.36
RELAY GEN PURPOSE SPST N.O. 15A
Plus a bunch more
https://www.digikey.com/en/products/filter/power-relays-over-2-amps/188?s=N4IgjCBcpgLGAGKoDGUBmBDANgZwKYA0IA9lANrgCsABAIIgC6xA
DgC5QgCqAdgJZsA8ugCy%2BTLgCuAJ3wgAvvOIA2ZCD4ATTgFpEEVh0ggQxNgE8
WcoxLSKgA
Ed
F
Fred Bloggs
Guest
On Sunday, June 4, 2023 at 8:29:49â¯PM UTC-4, Phil Allison wrote:
Right- was gonna say. A diac is also a thryistor. It\'s a breakover device almost always used to discharge a capacitor into the gate. Controlling the charge time of the capacitor controls the conduction phase angle.
Breakover device is not like a zener. When voltage hits breakover, the device goes high conductivity and its voltage collapses to zero theoretically.
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.
Right- was gonna say. A diac is also a thryistor. It\'s a breakover device almost always used to discharge a capacitor into the gate. Controlling the charge time of the capacitor controls the conduction phase angle.
Breakover device is not like a zener. When voltage hits breakover, the device goes high conductivity and its voltage collapses to zero theoretically.
...... Phil
C
Cursitor Doom
Guest
On Mon, 5 Jun 2023 12:12:24 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:
Okay, thanks, Lasse, I got \'em now. They\'re a bit more expensive in
Yurp, but not by much. Well, I stand corrected, then.
<langwadt@fonz.dk> wrote:
mandag den 5. juni 2023 kl. 20.45.03 UTC+2 skrev Cursitor Doom:
On Mon, 05 Jun 2023 11:01:33 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
On Mon, 05 Jun 2023 18:54:16 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 05 Jun 2023 18:50:38 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 05 Jun 2023 09:21:32 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
On Mon, 5 Jun 2023 12:10:05 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:
On 2023-06-04 23:05, John Larkin wrote:
On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <c...@notformail.com
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. :-(
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.
Seriously, I\'m not seeing 15A relays on Digikey for less than around
15 dollars. Where do you get 60 cents from ??
https://www.digikey.dk/en/products/detail/amphenol-anytek/AHQSH112LM1F00G/16721973
60 cent if you buy 250, 90cent if you buy one
Okay, thanks, Lasse, I got \'em now. They\'re a bit more expensive in
Yurp, but not by much. Well, I stand corrected, then.
J
John Larkin
Guest
On Mon, 05 Jun 2023 19:32:40 +0100, Cursitor Doom <cd@notformail.com>
wrote:
Please do not go the the Digikey site. The shock may be harmful to
your health.
wrote:
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.
Please do not go the the Digikey site. The shock may be harmful to
your health.
J
John Larkin
Guest
On Mon, 5 Jun 2023 12:21:36 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:
A hard fast-rise gate pulse turns the whole chip on all at once.
A slow trigger rise can create a hot spot that spreads slowly and may
fry the silicon before it does.
If the load is inherently current-rise limited, like an inductor
maybe, it\'s usually OK.
There must be app notes about this.
<bloggs.fredbloggs.fred@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.
If you ever look at a comprehensive thyristor handbook, you will see they have these devices categorized by application. They have the 60 Hz line of products for mains switching, and they have the switching line for all the advanced inverter/ converter/ resonator applications imaginable. Triacs have pretty sizeable I2t ratings, as in HUGE, they can take a lot of abuse. Supposedly the main failure mode is due to excessive dI/dt, which is too much current density before the entire conduction junction area turns fully on to support it. That\'s more of an external circuit design issue than a gate drive. I\'ve seen quite a few consumer applications for switching the line onto a load, and they usually use something on the order of a 10KHz square wave ac-coupled to the gate via capacitor or transformer. 50us is plenty of time to fully turn on the gate most of the time. The square wave usually runs continuously while the triac is on.
A hard fast-rise gate pulse turns the whole chip on all at once.
A slow trigger rise can create a hot spot that spreads slowly and may
fry the silicon before it does.
If the load is inherently current-rise limited, like an inductor
maybe, it\'s usually OK.
There must be app notes about this.
J
John Larkin
Guest
On Mon, 5 Jun 2023 12:08:41 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:
Yes.
<bloggs.fredbloggs.fred@gmail.com> wrote:
On Sunday, June 4, 2023 at 5:34:08?PM UTC-4, 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?
CD.
No.
Yes.
P
Phil Hobbs
Guest
John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
Sorta. A triac is going to drop a good volt whenever itâs on, so you canât
do too much about the losses.
It also has a fair amount of silicon for its dissipation, so its datasheet
power rating will be reasonably honest, unlike your average FETâs. (Weâre
looking at you, IR.)
As JL said, itâs dI/dt that kills them, and soft triggering makes that much
worse.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
On Mon, 5 Jun 2023 12:08:41 -0700 (PDT), Fred Bloggs
bloggs.fredbloggs.fred@gmail.com> wrote:
On Sunday, June 4, 2023 at 5:34:08?PM UTC-4, 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?
CD.
No.
Yes.
Sorta. A triac is going to drop a good volt whenever itâs on, so you canât
do too much about the losses.
It also has a fair amount of silicon for its dissipation, so its datasheet
power rating will be reasonably honest, unlike your average FETâs. (Weâre
looking at you, IR.)
As JL said, itâs dI/dt that kills them, and soft triggering makes that much
worse.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
F
Fred Bloggs
Guest
On Monday, June 5, 2023 at 4:39:09â¯PM UTC-4, John Larkin wrote:
There are and I\'ve studied them. The gate junction is negligibly small compared to the main terminal junctions. It\'s the main terminal junctions that, when triggered by the small gate current, fully turn on the device high current junctions, gate current does not turn on the full conduction area. Sprague at one time manufactured triac trigger transformers with slow current rise times, specifically to avoid the dI/dt failure.
Of course, my source material is quite dated, so things may have changed in the interim.
On Mon, 5 Jun 2023 12:21:36 -0700 (PDT), Fred Bloggs
bloggs.fred...@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.
If you ever look at a comprehensive thyristor handbook, you will see they have these devices categorized by application. They have the 60 Hz line of products for mains switching, and they have the switching line for all the advanced inverter/ converter/ resonator applications imaginable. Triacs have pretty sizeable I2t ratings, as in HUGE, they can take a lot of abuse. Supposedly the main failure mode is due to excessive dI/dt, which is too much current density before the entire conduction junction area turns fully on to support it. That\'s more of an external circuit design issue than a gate drive. I\'ve seen quite a few consumer applications for switching the line onto a load, and they usually use something on the order of a 10KHz square wave ac-coupled to the gate via capacitor or transformer. 50us is plenty of time to fully turn on the gate most of the time. The square wave usually runs continuously while the triac is on.
A hard fast-rise gate pulse turns the whole chip on all at once.
A slow trigger rise can create a hot spot that spreads slowly and may
fry the silicon before it does.
If the load is inherently current-rise limited, like an inductor
maybe, it\'s usually OK.
There must be app notes about this.
There are and I\'ve studied them. The gate junction is negligibly small compared to the main terminal junctions. It\'s the main terminal junctions that, when triggered by the small gate current, fully turn on the device high current junctions, gate current does not turn on the full conduction area. Sprague at one time manufactured triac trigger transformers with slow current rise times, specifically to avoid the dI/dt failure.
Of course, my source material is quite dated, so things may have changed in the interim.
C
Cursitor Doom
Guest
On Mon, 5 Jun 2023 20:59:10 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
And a circuit like this is the very epitome of \'soft triggering\' but
you see them all over the place. I guess they\'re okay for low power
control:
XU1 N002 N004 0 2N5568
R_variable N001 N003 1k
C1 N003 0 0.47µ
V1 N001 0 SINE(0 230 50) Rser=4
R_load N001 N002 28
R3 N004 N003 100
D1 0 N004 1N750
..model D D
..lib C:\\users\\bruno\\Documents\\LTspiceXVII\\lib\\cmp\\standard.dio
..SUBCKT 2N5568 1 2 3
* CONNECTIONS: MT2 G MT1
QN1 5 4 3 NOUT
QN2 11 6 7 NOUT
QP1 6 11 3 POUT
QP2 4 5 7 POUT
DF 4 5 DZ OFF
DR 6 11 DZ OFF
RF 6 4 40MEG
RT2 7 1 52.8M
RH 6 7 75
RGP 8 3 54.5
RG 8 2 26.4
RS 4 8 52.6
DN 9 2 DIN
RN 9 3 27.8
GNN 6 7 9 3 38.8M
GNP 4 5 9 3 51.2M
DP 2 10 DIP
RP 3 10 16.2
GP 7 6 10 3 26.1M
..Model Din D (IS=53.5F)
..Model Dip D (IS=53.5F N=1.19)
..Model Dz D (IS=53.5F N=1.5 IBV=10u BV=400)
..Model Pout PNP (IS=53.5F BF=5 CJE=235P TF=25.5u)
..Model Nout NPN (IS=53.5F BF=20 CJE=235P CJC=46.9P TF=1.7u)
..ENDS
..tran 0 1.2s 1s 1m
* Value of C1 is largely irrelevant. R1 needs to be a 20k pot in
series with a 1k fixed resistor to give the full power range.
..backanno
..end
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
On Mon, 5 Jun 2023 12:08:41 -0700 (PDT), Fred Bloggs
bloggs.fredbloggs.fred@gmail.com> wrote:
On Sunday, June 4, 2023 at 5:34:08?PM UTC-4, 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?
CD.
No.
Yes.
Sorta. A triac is going to drop a good volt whenever its on, so you cant
do too much about the losses.
It also has a fair amount of silicon for its dissipation, so its datasheet
power rating will be reasonably honest, unlike your average FETs. (Were
looking at you, IR.)
As JL said, its dI/dt that kills them, and soft triggering makes that much
worse.
And a circuit like this is the very epitome of \'soft triggering\' but
you see them all over the place. I guess they\'re okay for low power
control:
XU1 N002 N004 0 2N5568
R_variable N001 N003 1k
C1 N003 0 0.47µ
V1 N001 0 SINE(0 230 50) Rser=4
R_load N001 N002 28
R3 N004 N003 100
D1 0 N004 1N750
..model D D
..lib C:\\users\\bruno\\Documents\\LTspiceXVII\\lib\\cmp\\standard.dio
..SUBCKT 2N5568 1 2 3
* CONNECTIONS: MT2 G MT1
QN1 5 4 3 NOUT
QN2 11 6 7 NOUT
QP1 6 11 3 POUT
QP2 4 5 7 POUT
DF 4 5 DZ OFF
DR 6 11 DZ OFF
RF 6 4 40MEG
RT2 7 1 52.8M
RH 6 7 75
RGP 8 3 54.5
RG 8 2 26.4
RS 4 8 52.6
DN 9 2 DIN
RN 9 3 27.8
GNN 6 7 9 3 38.8M
GNP 4 5 9 3 51.2M
DP 2 10 DIP
RP 3 10 16.2
GP 7 6 10 3 26.1M
..Model Din D (IS=53.5F)
..Model Dip D (IS=53.5F N=1.19)
..Model Dz D (IS=53.5F N=1.5 IBV=10u BV=400)
..Model Pout PNP (IS=53.5F BF=5 CJE=235P TF=25.5u)
..Model Nout NPN (IS=53.5F BF=20 CJE=235P CJC=46.9P TF=1.7u)
..ENDS
..tran 0 1.2s 1s 1m
* Value of C1 is largely irrelevant. R1 needs to be a 20k pot in
series with a 1k fixed resistor to give the full power range.
..backanno
..end
C
Cursitor Doom
Guest
On Mon, 05 Jun 2023 13:32:08 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:
Whereas Mouser is harmful to my wealth. Nothing to choose from there
at all for under 15 bux.
<jlarkin@highlandSNIPMEtechnology.com> wrote:
On Mon, 05 Jun 2023 19:32:40 +0100, Cursitor Doom <cd@notformail.com
wrote:
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.
Please do not go the the Digikey site. The shock may be harmful to
your health.
Whereas Mouser is harmful to my wealth. Nothing to choose from there
at all for under 15 bux.
J
John Larkin
Guest
On Mon, 05 Jun 2023 23:00:29 +0100, Cursitor Doom <cd@notformail.com>
wrote:
My very first search hit:
https://www.mouser.com/ProductDetail/Amphenol-Anytek/AWHSH112DM00G?qs=rSMjJ%252B1ewcRkINR7MLX27w%3D%3D
They also stock several 20 amp relays under $3.
wrote:
On Mon, 05 Jun 2023 13:32:08 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:
On Mon, 05 Jun 2023 19:32:40 +0100, Cursitor Doom <cd@notformail.com
wrote:
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.
Please do not go the the Digikey site. The shock may be harmful to
your health.
Whereas Mouser is harmful to my wealth. Nothing to choose from there
at all for under 15 bux.
My very first search hit:
https://www.mouser.com/ProductDetail/Amphenol-Anytek/AWHSH112DM00G?qs=rSMjJ%252B1ewcRkINR7MLX27w%3D%3D
They also stock several 20 amp relays under $3.
W
whit3rd
Guest
On Sunday, June 4, 2023 at 9:07:55â¯PM UTC-4, Wanderer wrote:
That\'s why \'incandescent only\' labels are used. With non-resistive loads, turnon also is problematic.
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.
That\'s why \'incandescent only\' labels are used. With non-resistive loads, turnon also is problematic.
L
Lasse Langwadt Christensen
Guest
mandag den 5. juni 2023 kl. 20.01.47 UTC+2 skrev John Larkin:
yeh, this one looks nice at 8A, until you look at figure 2
https://files.seeedstudio.com/wiki/Grove-Solid_State_Relay/res/S208t02_datasheet.pdf
On Mon, 05 Jun 2023 18:54:16 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 05 Jun 2023 18:50:38 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 05 Jun 2023 09:21:32 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
On Mon, 5 Jun 2023 12:10:05 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:
On 2023-06-04 23:05, John Larkin wrote:
On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <c...@notformail.com
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. :-(
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.
yeh, this one looks nice at 8A, until you look at figure 2
https://files.seeedstudio.com/wiki/Grove-Solid_State_Relay/res/S208t02_datasheet.pdf
R
Ricky
Guest
On Monday, June 5, 2023 at 11:03:19â¯AM UTC-4, Wanderer wrote:
I don\'t see your circuit.
Yeah. Luck beats skill any day. You just don\'t know which days those will be.
--
Rick C.
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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
I don\'t see your circuit.
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.
Yeah. Luck beats skill any day. You just don\'t know which days those will be.
--
Rick C.
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R
Ricky
Guest
On Monday, June 5, 2023 at 3:12:28â¯PM UTC-4, Lasse Langwadt Christensen wrote:
Interesting. It is rated to switch DC too! What will they think of next?
--
Rick C.
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mandag den 5. juni 2023 kl. 20.45.03 UTC+2 skrev Cursitor Doom:
On Mon, 05 Jun 2023 11:01:33 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
On Mon, 05 Jun 2023 18:54:16 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 05 Jun 2023 18:50:38 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 05 Jun 2023 09:21:32 -0700, John Larkin
jla...@highlandSNIPMEtechnology.com> wrote:
On Mon, 5 Jun 2023 12:10:05 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:
On 2023-06-04 23:05, John Larkin wrote:
On Mon, 05 Jun 2023 00:03:20 +0100, Cursitor Doom <c...@notformail.com
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. :-(
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.
Seriously, I\'m not seeing 15A relays on Digikey for less than around
15 dollars. Where do you get 60 cents from ??
https://www.digikey.dk/en/products/detail/amphenol-anytek/AHQSH112LM1F00G/16721973
60 cent if you buy 250, 90cent if you buy one
Interesting. It is rated to switch DC too! What will they think of next?
--
Rick C.
+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209