Maker Pro
Maker Pro

Driving Triac Directly with 555 Output?

S

SMS

Jan 1, 1970
0
Several circuits I've seen use an opto-isolator or a transistor between
the 555 output and the triac gate, i.e.
<http://www.circuitstoday.com/wp-content/uploads/2008/03/lamp-flasher12.jpg>
or
<http://www.electro-tech-online.com/images/projects/triac_light_flasher.gif>.

The triac I'm using has a 50mA gate current and the 555 can sink and
source 200mA. The triac will be controlling a non-inductive AC load
where the AC voltage will not exceed 18V (coming from a bicycle dynamo),
so there is no shock hazard here.

Can anyone think of a reason I need that extra component between pin 3
of the 555 and the triac gate? I was just going to put in a current
limiting resistor of 10 ohms or so.
 
J

Jamie

Jan 1, 1970
0
SMS said:
Several circuits I've seen use an opto-isolator or a transistor between
the 555 output and the triac gate, i.e.
<http://www.circuitstoday.com/wp-content/uploads/2008/03/lamp-flasher12.jpg>
or
<http://www.electro-tech-online.com/images/projects/triac_light_flasher.gif>.


The triac I'm using has a 50mA gate current and the 555 can sink and
source 200mA. The triac will be controlling a non-inductive AC load
where the AC voltage will not exceed 18V (coming from a bicycle dynamo),
so there is no shock hazard here.

Can anyone think of a reason I need that extra component between pin 3
of the 555 and the triac gate? I was just going to put in a current
limiting resistor of 10 ohms or so.
You won't get both sides of the wave with a simple direct hook up like
that. Current must flow in both directions with the polarity of the
AC.. This is one reason why optical are used and those that like to use
OP-Triac's to drive the larger triac. The OP-Triac can get pulsed
on with a single ended source, the 555. And the internal emitter will
forward bias both photo's at the same time but only one will fire
depending on the polarity.


Jamie
 
P

Phil Allison

Jan 1, 1970
0
"SMS"
Several circuits I've seen use an opto-isolator or a transistor between
the 555 output and the triac gate, i.e.
<http://www.circuitstoday.com/wp-content/uploads/2008/03/lamp-flasher12.jpg>
or
<http://www.electro-tech-online.com/images/projects/triac_light_flasher.gif>.

The triac I'm using has a 50mA gate current and the 555 can sink and
source 200mA. The triac will be controlling a non-inductive AC load where
the AC voltage will not exceed 18V (coming from a bicycle dynamo), so
there is no shock hazard here.

Can anyone think of a reason I need that extra component between pin 3 of
the 555 and the triac gate? I was just going to put in a current limiting
resistor of 10 ohms or so.

** It will work fine.

The resistor should be chosen to limit current to about 60mA - the exact
value depends on the 555's DC supply voltage minus the gate voltage of the
triac, about 1.2 volts.


...... Phil
 
P

Phil Allison

Jan 1, 1970
0
Jamie is a FUCKWIT RADIO HAM !!!!!!!!!!!

Real ID = Maynard A. Philbrook, KA1LPH

You won't get both sides of the wave with a simple direct hook up like
that. Current must flow in both directions with the polarity of the
AC..

** ROTFLMAO !!!!!!!!

Wot ABSOLUTE BOLLOCKS !!!!!!!!!!!!!!!!

Go look up a data sheet - fuckwit !!!!

Find out what the four "quadrants" are.



..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"John Larkin"
Most triacs are spec'd to trigger in three quadrants. The one they are
usually not specified for is q4, negative MT2 and positive gate.

** Write your point down - asshole.

Show how it relates to the OP's question and my comments.

Is the ham radio guy right or not ???


..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Greegor"

** Wot a fucking scumbag.

This gutless, anonymous, psychopathic **** should be reported to the police.




..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"John Larkin"
Use your brain, dingbat.


** So the bullshitting, autistic pig has no relevant point.

Cept the one on top of his pointy head.




..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"SMS"

** That schem is wrong and dangerous.

D2 should connect to the active (after the fuse) and one never links
neutral to ground.

Q1 etc is totally superfluous.


** Not a good one either - that 330nF, 400V cap is gonna fail pretty quick
with 220V AC across it .

It needs to be a special 250 VAC rated X1 or X2 class type.

BTW:

There is a little publicised trap when using opto-isolators like the
OC3021 - the holding voltage of the internal SBS is sometimes lower than
that of the triac on voltage, resulting in failure to switch off as
expected. The issue is more likely to crop up when the triac is hot.

One fix is to add inverse parallel diodes in series with the SBS.

Motorola once made special range of triacs to go with their MOC isolators -
for the above reason I suspect.


..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Greegor"

** Wot a fucking scumbag.

This gutless, anonymous, psychopathic **** should be reported to the police.





..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Greegor"

** Wot a fucking scumbag.

This gutless, anonymous, psychopathic **** should be reported to the police.

Or shot dead - which ever is easier.



..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Robert Baer" <
Have you never heard of FOUR QUADRANT triacs?


** The prick is a RADIO HAM !!!!

All the retard knows about are rubber duckies ....




..... Phil
 
S

SMS

Jan 1, 1970
0
You won't get both sides of the wave with a simple direct hook up like
that. Current must flow in both directions with the polarity of the
AC.. This is one reason why optical are used and those that like to use
OP-Triac's to drive the larger triac. The OP-Triac can get pulsed
on with a single ended source, the 555. And the internal emitter will
forward bias both photo's at the same time but only one will fire
depending on the polarity.

Hmm, so the triac won't turn on on the negative half of the sine wave.

Well, in any case, I now realize that this won't work at all anyway
because the load is not resistive. The load is an MR16 LED lamp that
operates on AC (because internally it has a rectifier and controller).
So I'll need to drive it with DC when it's in strobe mode (which is what
I had been planning to do originally). I wanted to see if I could
directly control the AC into it to minimize losses (since the dynamo is
only 500 mA at 6 to 9V). I could use a mechanical relay but these are
rated for only 10 million or so cycles which would not be enough for
more than a few years of use.
 
P

Phil Allison

Jan 1, 1970
0
"SMS"
Hmm, so the triac won't turn on on the negative half of the sine wave.

** Ignore Jamie - the man is complete fool.

Well, in any case, I now realize that this won't work at all anyway
because the load is not resistive.

** No need for it to be.
The load is an MR16 LED lamp that operates on AC (because internally it
has a rectifier and controller). So I'll need to drive it with DC when
it's in strobe mode

** Really - why do you say that ?

Once triggered, triacs do not switch off unless the current falls to near
zero - so operation in DC circuits is generally not possible.


..... Phil
 
J

Jamie

Jan 1, 1970
0
Phil said:
Jamie is a FUCKWIT RADIO HAM !!!!!!!!!!!

Real ID = Maynard A. Philbrook, KA1LPH





** ROTFLMAO !!!!!!!!

Wot ABSOLUTE BOLLOCKS !!!!!!!!!!!!!!!!

Go look up a data sheet - fuckwit !!!!

Find out what the four "quadrants" are.



.... Phil
You better look again Phil before putting your
foot into your mouth, again.

Jamie
 
P

Phil Allison

Jan 1, 1970
0
Jamie is a FUCKWIT RADIO HAM !!!!!!!!!!!

Real ID = Maynard A. Philbrook, KA1LPH

You better look again Phil ....


** Piss off to HELL

- you fucking IGNORANT WANKER !!
 
J

Jamie

Jan 1, 1970
0
Phil said:
"John Larkin"



** Write your point down - asshole.

Show how it relates to the OP's question and my comments.

Is the ham radio guy right or not ???


.... Phil

Hang on Phil. It's going to get bumpy...

Jamie
 
P

Phil Allison

Jan 1, 1970
0
"Jamie"
Sure I have, made a few nice little trinkets with them.


** You are a fucking LIAR !!
Still does not change any reasoning for what I said.

** What you said was CRAP.

On top of that, it's most likely a 4Q isn't being used


** Triacs will work fine with + DC drive on the gate.

Never come across one that did not.

**** you - asshole.


...... Phil
 
J

Jamie

Jan 1, 1970
0
Robert said:
Have you never heard of FOUR QUADRANT triacs?

Sure I have, made a few nice little trinkets with them.

Still does not change any reasoning for what I said.

If you are able to fully absorb what the circuit is that its
being implemented in, you may then understand how I think...

On top of that, it's most likely a 4Q isn't being used and if it
was, it wouldn't make any difference in this case.

Maybe you've never heard of Latchup issues in Triacs.

Jamie
 
P

Phil Allison

Jan 1, 1970
0
"John Larkin is Bullshit Artist "
Most triacs are not spec'd to fire in quadrant 4.

** John is determined to beat this dead donkey till it moves.

Hee haw, hee haw ....


.... Phil
 
J

Jamie

Jan 1, 1970
0
John said:
---
The circuit at:

http://www.circuitstoday.com/wp-content/uploads/2008/03/lamp-flasher12.jpg>
can't work because there's no supply for the 555, unless I'm missing
something.

The other circuit needs the optoisolator because there's no common
ground between the dynamo, the 555, and the TRIAC's MT1.

It also has some extra stuff that's not needed for your application,
and I'll post a schematic for you some time today.
Yes, that circuit is bogus, I am sure its just a mistake...

One point that I must make here is this, it was asked about
driving the Gate directly from the output of the timer. And
unless I am over looking something here, it looks like a
Q3 operation.. When the timer is on, you'll get gate current
in both directions how ever, when off the 555 goes into a
sink operation, I see a problem here.


Jamie
 
Top