Question regarding triggering a Triac with a 555

Thread Starter

K.e

Joined May 7, 2017
81
In order to implement the phase angle control for same point in each cycle the same trigger (crossover point) has to be known.
Max.
indeed .

the peak V for the Gate on a BT137 Triac is 5v do you think for optimal operation i should saturate this gate?

removing the opto from the equation i have 4.4v~ going to it presently from the junction Vcc from output (pin3)

i'm yet to check the freq though my basic scope as i'm salvaging a cap that will fit the order. (exciting times)
 

Thread Starter

K.e

Joined May 7, 2017
81
Here is another option. A 555 makes things complicated vs just an R and C (with R being a potentiometer wired like a rheostat.

View attachment 126446
indeed ha ha that will be my fall back after the smoke clears, (jokes) - but honestly being humans half the fun is the journey right?

as i'm, a learner the 555 will help me, what can you tell me about the humble so called 'DIAC' (if you are in a teaching mood)

thanks for these attachments they will be useful.

note*

it surprises me (a little) that searching for a similar design online results in the saturation of mostly irrelevant and overly complex 'DIY' solutions (that usually involve a micro-controller) ha ha then again i guess i've seen the 'dimmer switch' solutions also.
 
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Thread Starter

K.e

Joined May 7, 2017
81
As your application uses a transformer to power both the load and the '555 you don't need to bother with the optical isolation.
re this sullivan-county.com/ele/pdf/an3006.pdf

you guys will probably know better but i think you will find that the opto is needed actually (on the rectified side)

based on my limited present knowledge of the 555 the circuit looked like it was missing some aspects related to other square wave configs i have seen.

and i may be correct because i think the tricky thing that is being done here is that the actual square wave is being generated by the opto and the 555 is being used to just control duty cycle.

i was getting the same rectified signal all the way though then hooked the (not yet complete) config up to a straight variable DC powers supply and sure enough there is no square wave (that i can see) being generated.

i'll keep building and see if i did something obviously incorrect. (unless all the NE555's i have are nonfunctional)
 

Thread Starter

K.e

Joined May 7, 2017
81

MaxHeadRoom

Joined Jul 18, 2013
28,621
i think the tricky thing that is being done here is that the actual square wave is being generated by the opto and the 555 is being used to just control duty cycle.
'Scoping the output of the H11L1 I see the positive going 720μs pulse, this is then inverted for the 555, C1,R5,VR1 just delays the pulse for the required phase point, once the 555 output goes low the MOC3023 is triggered, the rest is ignored as the Triac has turned on for that half cycle.
Max.
 

Thread Starter

K.e

Joined May 7, 2017
81
'Scoping the output of the H11L1 I see the positive going 720μs pulse, this is then inverted for the 555, C1,R5,VR1 just delays the pulse for the required phase point, once the 555 output goes low the MOC3023 is triggered, the rest is ignored as the Triac has turned on for that half cycle.
Max.
well i made it (kind of) in Easy EDA and have asked for help there also (it's public)

https://easyeda.com/forum/topic/lea...to_see_if_it_produces_a_squarewave_-PDwO60iAS

yeah the positive going pulse, see this from the AN? (attached)

the first time i built it i just got a pulse going right though, maybe i'll give it a day work on something else and see if i can see what i did wrong.

I may just go back to the 'dimmer' solution for now for the solder Iron as i really do need a new Iron and I have a good quality handle correct for the 24V transformer, i just need to make it work ha.
 

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Thread Starter

K.e

Joined May 7, 2017
81
'Scoping the output of the H11L1 I see the positive going 720μs pulse, this is then inverted for the 555, C1,R5,VR1 just delays the pulse for the required phase point, once the 555 output goes low the MOC3023 is triggered, the rest is ignored as the Triac has turned on for that half cycle.
Max.
oh wait ... are you saying perhaps it does not (and doesn't need to) produce a squarewave?

as it is just being used to trigger the top (moc3023) opto (and gate) and control duty cycle ? if so i think you are right , and maybe i just did something incorrect the first time.

what threw me off was the probe images in the AN
 

MaxHeadRoom

Joined Jul 18, 2013
28,621
Once the 555 output triggers the MOC3023, this fires the triac and the rest of the 555 pulse is superflous.
As I mentioned, in your png file of the fig 4 should be 720μs not 720ms as shown.
It is just a short pulse at each zero crossing. And the firing pulse is triggered off of that pulse After the R/C delay.
Max.
 

Thread Starter

K.e

Joined May 7, 2017
81
Once the 555 output triggers the MOC3023, this fires the triac and the rest of the 555 pulse is superflous.
As I mentioned, in your png file of the fig 4 should be 720μs not 720ms as shown.
It is just a short pulse at each zero crossing. And the firing pulse is triggered off of that pulse After the R/C delay.
Max.
ah thank you Max you have illuminated this for me ha ha

ah i see now, thank you greatly.
next i will try to make it do something : )
 

ian field

Joined Oct 27, 2012
6,536
sorry for the confusion the 555 circuit i used is the image attached not the linked image - the used circurt uses a comparator and does not utilize the 'output' pin. (can't edit due to 10 min limit)
AFAICR: a triac gate is most sensitive when pulled negative regardless of MT1 polarity.

Once or twice when MT2 is above ground; I've got away with using pin 7 to drive the gate. Output and pin 7 are in phase, so interchangeable in some situations. You have to do a bit of careful working out - its not hard to blow the discharge transistor.
 

Thread Starter

K.e

Joined May 7, 2017
81
AFAICR: a triac gate is most sensitive when pulled negative regardless of MT1 polarity.

Once or twice when MT2 is above ground; I've got away with using pin 7 to drive the gate. Output and pin 7 are in phase, so interchangeable in some situations. You have to do a bit of careful working out - its not hard to blow the discharge transistor.
ah back in the old days when my circuit worked ha ha - thanks for this yes i may move to the traditional 'dimmer' although i like the AN-3006 and am slowly understanding it.
 

Thread Starter

K.e

Joined May 7, 2017
81
AFAICR: a triac gate is most sensitive when pulled negative regardless of MT1 polarity.

Once or twice when MT2 is above ground; I've got away with using pin 7 to drive the gate. Output and pin 7 are in phase, so interchangeable in some situations. You have to do a bit of careful working out - its not hard to blow the discharge transistor.
Ok guys thanks for all the help on this one - (i'm not going to give up ha ha) I have one question that i can't let go (before moving back to the dimmer) but still working on this mystery

What is D5 all about? see attached, it actually makes no sense to me as the rectified source is going straight into D5 and there would be actually 0v potential at that point after which is supposedly the source for the H11L1 'anode'

also there is absolutely no Ref to D5 1n5248 in the AN3006 (you can search that term the only D5 that appears is in that image)

all my measurements give me 0 v at that point due to the rectifier being in the forward direction of the D5 (but i'm likely missing something i guess)

regards.
 

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Thread Starter

K.e

Joined May 7, 2017
81
P2 titled Current Limiters explains the function and formulae for the D5 12v zener switching point.
Max.
ok thanks Max this will help.

i'm making some slight progress, these are the outputs i got i just ran the bench DC across the output of the octo and probed it, seems obvious i guess but hey i'm leaning here. the others are obviously from the 10v~ trans and it's fully rectified output. (without the D5 etc)

at least i found the 'trigger' signal for the inverting trans, i guess by studying the current limiters i will learn more about the knee point as it suggests.

thanks again.
 

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