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'[PICLIST] [EE] Triacs and AC power'
2002\04\06@063720 by Anand Dhuru

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Hi folks,

I have built a circuit around a 16F628 that drives a Triac directly (PIC - 220 ohms - gate) and it works fine with incandescent lamps / bulbs. Since I am not interested in controlling the phase angle as such (the load is to be on, or off, the intensity is not to be controlled) I am not pulsing the gate of the triac; the pin driving the gate is always either on, or off.

Now, my question is, can this setup be used to switch heavier loads such as an air-conditioner, if I use a triac of an appropriate rating?

Which brings me to the second question! Even triacs rated at 12 Amps, 400 volts come in a TO220 package. Can these devices really control the load of an air-conditioner without blowing up? Would a heat sink be required?

Incidentally, I have 230 volts AC in my country, and the AC I'm interested in controlling would be 1.5 tons.

Any advice here would be greatly appreciated, folks!

Thanks and regards,

Anand Dhuru

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2002\04\06@073059 by Byron A Jeff

face picon face
On Sat, Apr 06, 2002 at 04:21:26PM +0530, Anand Dhuru wrote:
> Hi folks,
>
> I have built a circuit around a 16F628 that drives a Triac directly (PIC - 220 ohms - gate) and it works fine with incandescent lamps / bulbs. Since I am not interested in controlling the phase angle as such (the load is to be on, or off, the intensity is not to be controlled) I am not pulsing the gate of the triac; the pin driving the gate is always either on, or off.
>
> Now, my question is, can this setup be used to switch heavier loads such as
>an air-conditioner, if I use a triac of an appropriate rating?

There are multiple immediate issues. First is that the AC has inductive
elements.  The second as you mentioned is current rating. The third is that at
that load will cause significant power loss across the triac. Also there's
a good chance you'll blow the PIC because there's no isolation between line
level and the PIC. Usually in this circumstance I'll use a optoisolated
triac drive like a MOC3010 to isolate the control circuitry from line level.

Many moons ago I asked a very similar question in the DC arena about driving
DC motors for a robot. Roman Black, who I just realized that we haven't heard
from in the last month or so, helped tremendously. Also Fr. Thomas McGahee
contribited a thought or two. First your questions then their thoughts.


>
> Which brings me to the second question! Even triacs rated at 12 Amps, 400 volts come in a TO220 package. Can these devices really control the load of an air-conditioner without blowing up? Would a heat sink be required?
>

It won't work without a snubber network to help manage the inductive load.
A heat sink would definitely be required.

> Incidentally, I have 230 volts AC in my country, and the AC I'm interested in controlling would be 1.5 tons.
>
> Any advice here would be greatly appreciated, folks!

Here's the advise I received:

1) Use a relay. Actually at this load you'd probably need a contactor. Reasons
are pretty simple. You're not trying to pulse the load. The relay will be
minimally affected by the inductive load, and the power loss in operation
is negligible, and gives control circuit isolaton..  Thanks Roman,
wherever you are.

2) A hybrid system can assist in the one area where relays have issues, making
and breaking contact. When a relay makes contact, there's often arcing because
the switchover isn't done at the zero crossing. This damages the contacts
of the relay over time. Fr. McGahee described a system where a triac is
used in conjunction with a relay to help save the contacts from arching.
Basically you wire the triac and relay in parallel. So switch the load on you
first switch the triac, which turns on the load without arcing. Once the
load comes up to speed kick in the relay and drop out the triac. The relay
then carries the load. At dropout do the reverse. I actually found that thread
in the archives. I cannot believe that it was THREE years ago! Here it is
(NOTE!!! PASSWORDED SITE. Both login and password is 'piclist'):

http://www.infosite.com/~jkeyzer/piclist/1999/May/0958.html

A read of that thread can give you some other thoughts on this exact same
subject.

Good Luck. And use a relay.

BAJ

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2002\04\06@174738 by Jim Paul

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1.5 tons of AC.  This must be in a small house or building.   My house is
about 1800 sq ft,
and we have a 3 ton condenser unit.  So 1.5 tons must be less than a 1000 sq
ft, correct?
And as far as the TO220 package handling the power yes it will, but yes you
will need a
heat sink.   And a rather large one at that.  12 Amps and 400 Volts is 4800
watts.  Without
a eatsink, this triac would be toast in a few seconds.  Of course, it may
only be rated at say
2000 watts though.  The current and voltage ratings are max values.  The
parameter you
really need to look at is the power dissipation value.


Regards,


Jim
{Original Message removed}

2002\04\07@095637 by Sean H. Breheny

face picon face
Hi Jim,

What do you (and the original poster) mean by "tons" of AC?

Sean

At 09:51 AM 4/6/02 -0600, you wrote:
>1.5 tons of AC.  This must be in a small house or building.   My house is
>about 1800 sq ft,
>and we have a 3 ton condenser unit.  So 1.5 tons must be less than a 1000 sq
>ft, correct?

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2002\04\07@101616 by Rick C.

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A ton is 12,000BTU

http://www.howstuffworks.com/ac3.htm

Rick


"Sean H. Breheny" wrote:

{Quote hidden}

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2002\04\07@103107 by Chris Loiacono

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In the world of refrigeration, one ton is the amount of heat absorbed in
melting one ton of ice in 24 hours. At 144 BTU's per pound that equates to
288,000 British Thermal Units.
The common use of BTU's is BTUH, or per hour. 1.5 tons = 18,000 BTUH. This
may handle the heat load for approximately 750 to 1,000 sq. ft., depending
upon the climate and construction type. Another way to look at it is that
small wall or window AC units are typically sized at 6,000 BTUH. SO, 18,000
BTUH. or 1.5 tons will generally cool 3 small rooms.

Chris

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2002\04\07@111933 by Anand Dhuru

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Thanks for the valuable inputs, Byron, Jim.

>  Also there's
> a good chance you'll blow the PIC because there's no isolation between
line
> level and the PIC. Usually in this circumstance I'll use a optoisolated
> triac drive like a MOC3010 to isolate the control circuitry from line
level.

I think this issue is put to rest, as I have succesfully tested the circuit
with mains operated (but lighter, no pun!) loads. I indeed do not have
isolation between the mains and the PIC, but I am using a transformerless
power supply for the PIC, so I have already sacrificed that anyway. Which is
also the reason I'm reluctant to use a relay; the power supply can give a
few mA, at best.

> Many moons ago I asked a very similar question in the DC arena about
driving
>
> 1) Use a relay. Actually at this load you'd probably need a contactor.
Reasons
> are pretty simple. You're not trying to pulse the load. The relay will be
> minimally affected by the inductive load, and the power loss in operation
> is negligible, and gives control circuit isolaton..  Thanks Roman,
> wherever you are.
>
> 2) A hybrid system can assist in the one area where relays have issues,
making
> and breaking contact. When a relay makes contact, there's often arcing
because
> the switchover isn't done at the zero crossing. This damages the contacts
> of the relay over time. Fr. McGahee described a system where a triac is
> used in conjunction with a relay to help save the contacts from arching.
> Basically you wire the triac and relay in parallel. So switch the load on
you
> first switch the triac, which turns on the load without arcing. Once the
> load comes up to speed kick in the relay and drop out the triac. The relay
> then carries the load. At dropout do the reverse. I actually found that
thread
> in the archives. I cannot believe that it was THREE years ago! Here it is
> (NOTE!!! PASSWORDED SITE. Both login and password is 'piclist'):
>
A very elegant solution, I feel. I inadvertantly left out the fact in my
message, that I have tried to do something similiar with the Triac in that
the gate is always switched on ONLY during a mains zero-crossing. This I
feel would reduce the arcing that one would otherwise have to contend with.
I'm hoping this strategy would also take care of the initial surge current
of a 'cold' load.


> A read of that thread can give you some other thoughts on this exact same
> subject.
>
> Good Luck. And use a relay.
>
> BAJ
>

Thanks again, folks, I appreciate your help.

And Jim, in my country it is very rare to find houses with central air
conditioning. Therefore, the tonnage of an AC is no indication of the size
of the house. More to do with the size of the room it is fitted in.

Regards,

Anand

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2002\04\07@123514 by Sean H. Breheny

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Thanks for the explanation. I didn't know that, but in addition, what added
to my confusion is that I thought "AC" in this email referred to
alternating current, not air conditioning :-)

Sean

At 10:16 AM 4/7/02 -0400, you wrote:
{Quote hidden}

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2002\04\07@123716 by Sean H. Breheny

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Thanks, Chris, for the good explanation.

Sean

At 10:30 AM 4/7/02 -0400, you wrote:
{Quote hidden}

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2002\04\07@141707 by Bob Barr

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On Sun, 7 Apr 2002 12:32:54 -0400, "Sean H. Breheny" wrote:


>Thanks for the explanation. I didn't know that, but in addition, what added
>to my confusion is that I thought "AC" in this email referred to
>alternating current, not air conditioning :-)
>

Well, in the case of tons of alternating current, wouldn't you just
calculate the total weight of the elecrons flowing and convert it to
tons? :=)


Regards, Bob

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2002\04\07@151607 by Sean H. Breheny

face picon face
Wow, THAT would be a LOT of current! If I recall correctly, there are about
100,000 coulombs of electrons in 1 mole of electrons. 1 mole of electrons
weighs 1/1836 gram. So, 1 (Imperial) ton per second would be
100,000*1,836*907,000 (grams/ton) = 168 trillion (10^12) amps!!!!! Now
THAT's a heavy load! Consider that the entire U.S. power consumption, if
considered at 120V, would correspond to only about 4 billion amps!

Sean

At 11:09 AM 4/7/02 -0700, you wrote:

{Quote hidden}

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2002\04\07@163647 by Peter L. Peres

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Anand,

imho you are looking for trouble switching an A/C with a triac. You can
get triacs in stud-mount cases for 35A and up but that is not your
problem. Your problem is that the A/C compressor has a starting current
easily 10 times the run current, and you can't limit it (it won't start).
This current is required for 0.3-4 sec depending on how big the motor is
mechanically (inertia etc). Most major makers use relays or contactors to
switch these loads (and so do I when needed). Provide ample spark/surge
suppression on the contactor coil (and/or the triac if you use one). Maybe
you have a more expensive unit that starts the compressor with no load and
has inherent current limiting (I don't think so).

hope this helps,

Peter

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2002\04\12@170103 by Jesse Lackey

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Hi - I'm trying to do something similar - 16f877 pic turning on/off a
triac that switches a bit of an unusual AC waveform - AC, but not a sine
wave, 4Khz / 120V approximately.  Very low power - a few milliamps at most.

I haven't used triacs before and I'm getting nothing but grief.  I have
a bag (100 of) MAC228A8 - motorola "sensitive gate" triacs, but what is
happening is that the triac switches on when the gate is positive or
negative - its only off when the gate is floating.

Do you use some kind of zero-crossover detect as part of your circuit ?
I'd rather not build such, I really only need on/off right now.

I will be building many of these, as in 24 triac switches on one board
with the PIC, and keeping the component count to a minimum for both cost
and space savings is desirable...

Any help most gratefully appreciated.
Jesse


Anand Dhuru wrote:
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2002\04\12@173443 by Spehro Pefhany

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At 05:00 PM 4/12/02 -0400, you wrote:
>Hi - I'm trying to do something similar - 16f877 pic turning on/off a
>triac that switches a bit of an unusual AC waveform - AC, but not a sine
>wave, 4Khz / 120V approximately.  Very low power - a few milliamps at most.
>
>I haven't used triacs before and I'm getting nothing but grief.  I have
>a bag (100 of) MAC228A8 - motorola "sensitive gate" triacs, but what is
>happening is that the triac switches on when the gate is positive or
>negative - its only off when the gate is floating.

Issues:

1)      Commutation time  (the triac doesn't have time to turn off
       completely)

2)      Holding current (if you are using pulse drive)- at only a few
        mA the triac may or may not stay on until the next pulse.

I will be building many of these, as in 24 triac switches on one board
>with the PIC, and keeping the component count to a minimum for both cost
>and space savings is desirable...

Can you say a little more about the load you are using and the
AC waveform? Possibly some other kind of switching device might be more
appropriate (probably).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2002\04\12@174205 by M. Adam Davis

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A note you might think about:

Many triacs will pass low currents, and only turn off when they are
loaded by a small resistance.  Hooking up a neon bulb to a regular 2 amp
triac, for instance, will result in a neon that will never turn off
unless it's connected in parallel with another larger load.  I don't
know if this has to do with leakage current or the ability of the triac
to turn off under very small loads.

If your load is small (few mA) you may be able to use a MC3010 or
similar optoisolator as your triac.  It has a small triac inside that
can handle some current (I don't know the rating - look it up) but I
suspect that you'll find it's more responsive to your small current
needs.  You can get them with built in zero crossing circuits if you
need it.

That's from experience, I can't tell you whether it applies to the
specific triac you're using.

-Adam

Jesse Lackey wrote:

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2002\04\12@204243 by Jesse Lackey

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I knew you were going to ask that...  :)
Basically I want to build:

http://www.elwire.com/faq/seq/seq5/index.html

But I don't have a schematic nor the thing itself to examine.  EL wire
glows then you put a 120v current thru it; 4-8khz is the brightest, but
60hz will produce some light.  What you normally do it get a "driver"
(battery to 120vac / someKhz, they vary) and connect the EL wire to it.
 The aforementioned circuit uses a little PIC to switch the connected
driver's output to one of five EL wires using triacs.

I looked up the triac specs ("L201E3" into google) and it seems more or
less identical to the one I'm using.  It looks like the triacs are being
driven directly by the PIC pins thru 470 ohm resistors.  So I wired up
what I think is the equivalent circuit (I have EL wire and a driver, not
the same as theirs, but its 120vac at 1Khz) and a triac and no go.

In their circuit I don't understand what the diode is for (polarity
protection for the DC to power the pic?).

It looks so simple yet I can't get the equivalent to work at all and I'm
running out of time and getting kind of frantic about it (10 days before
an art exhibition happens) ...

Anyone?  Anyone?

Should I just order a bunch of optoisolator triac drivers (MC3010) and
be done with it?

All I want is for when the PIC output line is low, triac off.  When
high, triac on.  Seems simple enuf and clearly the aforementioned
circuit works this way.  I need to be able to switch rapidly, and I'd
like to have dimming based on PWM (which I have working with LEDs) so
relays are out.

Help...help....  :(
Jesse



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2002\04\12@205903 by 859-1?Q?Alexandre_Guimar=E3es?=

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Hi,

> It looks so simple yet I can't get the equivalent to work at all and I'm
> running out of time and getting kind of frantic about it (10 days before
> an art exhibition happens) ...
>
> Anyone?  Anyone?

   Here goes some points that might be woth considering:

   They might have zero crossing detection directly at the pic pins.

   The diodes may be there to make sure the triacs are just driven in some
quadrants.

   Why not using a couple of cheap high Voltage transistor such as the
MPS92 and MPS42 ? It would make swithing much more predictable than with
triacs.

> Should I just order a bunch of optoisolator triac drivers (MC3010) and
> be done with it?

   I am not sure if those would be fast enough ! Sometimes the turn off
time with optos can be so long that you would be in the next cycle of your
AC signal. They are usually made thinking about regular 60 hz. Take a look
at the datasheet and check the on and off time specs.

> All I want is for when the PIC output line is low, triac off.  When
> high, triac on.  Seems simple enuf and clearly the aforementioned
> circuit works this way.  I need to be able to switch rapidly, and I'd
> like to have dimming based on PWM (which I have working with LEDs) so
> relays are out.

   Think about the transistor switch, might be much simpler to work and
also make PWM easier.

Best regards,
Alexandre Guimaraes

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2002\04\12@210741 by M. Adam Davis

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The show the bottom of the circuit board.  You could derive the circuit
from that, and the parts are shown clearly enough to get the part
numbers and equivilant parts.

I've run wall EL strips off the moc3010 (hook the optoisolators up to an
LED bar graph chip with its input coming from an audio source - looks
nice on the dj stand) so you could do that, but the current draw is
likely higher.  I chose that route mainly for reasons of isolation as I
was deriving the EL driving power directly from the 120v mains, and
there was the possibility of connecting it to other devices (audio
input).  Since your power supply won't supply a large current it may not
be that much of an issue.

You may try floating the pin as well as driving it high or low - that
may be their trick.

-Adam

Jesse Lackey wrote:

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2002\04\12@234652 by Spehro Pefhany

picon face
At 08:40 PM 4/12/02 -0400, you wrote:
{Quote hidden}

Yes, that's all. It's just in series with the input to the regulator.


>It looks so simple yet I can't get the equivalent to work at all and I'm
>running out of time and getting kind of frantic about it (10 days before
>an art exhibition happens) ...

One problem right off- the triacs spec'd on that web page are guaranteed
to trigger at 3mA in ALL 4 QUADRANTS. It looks like the circuit uses the
"tough" 4th quadrant (gate +ve MT2 -ve). The Motorola/Onsemi "sensitive gate"
triacs need 3.3 times as much current to trigger (10mA) in that quadrant
and 5mA in the other quadrants. You could reduce the gate resistor and
consider changing it so the gate gets -ve drive. The +5 would then be
the common for the high voltage supply and you'd supply a negative voltage
to power the unit. Low would be ON, high OFF. This is the preferred way
to drive a triac, as it avoid Q4. I haven't looked at this in a lot of detail,
so be  careful. That would reduce the current requirements to only 5mA,
and you could simply use 240R resistors rather than the 470R. The PIC
should be able to drive the 10mA too, but you might have to fiddle with
the  resistor value to get it close enough to right, and there are issues
with triac gates under some conditions.

This way of using a triac is a little odd, but I think I see what they
are doing.

>Anyone?  Anyone?
>
>Should I just order a bunch of optoisolator triac drivers (MC3010) and
>be done with it?

You'd still have to pay attention to the drive current. If the isolation
is worth something to you , the extra cost might be worth it, otherwise
there isn't much advantage that I can see.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2002\04\13@031406 by Jesse Lackey

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Thanks Spehro for the info.  Your help is much appreciated.

But let me back up a bit ... I need to be able to crawl before walking...

Could you correct me here?  I'm clearly not understanding something.  I
haven't used triacs (or SCRs) before and am really dumb about this stuff
(digital is definitely more my game).

Here goes.

My circuit has 80VAC, and +5VDC.
Following the aforementioned sequencer circuit, where the AC is switched
by the triac with the gate connected to the PIC pin thru a resisor, I
would have thought something like:

 ---------------------
 |                   |
 |         470     (V^) (triac)
 |    +5v-/\/\/\---/ |
(AC)                 |
 |                   |
 |               [EL Wire]
 |                   |
 ---------------------

Would cause the EL wire to always be on, and connecting the gate to
ground (thru the 470 ohm resistor) would cause the EL wire to always be
off.  What I get instead is kind of weird and depends on the driver (AC
source) I'm using, but generally I get "flashes" as I tap the +5V line,
as well as flashes when tapping the ground line.

I think part of my problem is that the +5v comes via regulated
wall-wart, and the AC comes from a battery powered standalone driver.
I've tried tying the negative of the battery to my "system" ground, and
I've tried tying one of the two AC driver outputs to "system" ground.

In the first case I get the "flickery" behavior, and in the second I get
maybe what is correct behavior: connect gate (thru resistor) to +5.
Nothing.  Disconnect to float: wire on, at least for a little while
(anywhere from very briefly to several seconds).  Same when connecting
to ground.  However driving from the PIC does nothing - always off.
Changing resistor to 280ohms - no difference.

I still don't see why connecting the gate to +5v thru the 470ohm
resistor doesn't turn the triac steady on, and to gnd turn the triac
steady off...  do they just not work this way???

Without a clue,
jesse






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2002\04\13@041947 by Jesse Lackey
2002\04\13@162413 by Bob

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Yes, you will have to sync to the AC zero crossings to run a triac for dimming
control, and some sort of ZC detect is usually used for on/off control.  You
don't need to PWM the gate, unless your load is inductive (ST Micro has some
docs on that).

As I recall, you said that your AC was 4khz?  At that rate, that is 8hz in half
cycles (you turn on triac once each half cycle, it turns off at end of 1/2
cycle), and you'll only have about 125us between the start and end of each half
cycle.  That's 125 instructions at 1mhz code speed (4mhz chip).  If your able to
have a pretty close AC sync, and you have a timer automatically turning on a
port (read hardware), you'll have a granularity of 125 "possible" turn on points
in each 1/2 cycle, probably less.  If using an interrupt, you'll have some code
overhead, and some loss or gain in timing each half cycle.  Not exactly
conducive for dimming control.

The way most triacs work, you have to hold the gate on for at least 10 to 15us,
depending on how many Ma your feeding it (until it "latches"), and it must be
off again before the end of the 1/2 cycle (or the triac will be full on for the
next 1/2 cycle).  For on/off control, I could see using a PWM to run a 15us
pulse at the beginning of each 1/2 cycle, if you can sync it with ZC's.  I'm not
sure if you'd burn up the gate if you just left it on all the time or not.  Of
course, you could for-go the ZC detector for the PIC, and just use a ZC triac
opto instead.  Leaving the gate on shouldn't be a problem then, and the ZC
circuit in the triac optocoupler should keep you from getting that nasty
transient noise.

Also, at that high of a frequency (4khz), especially on a non-sinusoidal
waveform (like a square or sawtooth), you need to watch that you don't exceed
the triac's dv/dt ratings, or you'll get false triggerings (read "snubber").

For on/off control triacs could work, but I don't know how well it would work
for dimming at that frequency....




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