a little help with capacitive power supply values

[Dennis]

Hi All
I'm still busy trying to get my head around all the valuable info you have offered and definitely am taking the time to read through as much as my already overloaded mind can take !

Melanie and anonymouse thanks for the tip regarding the fuse on the NEUTRAL line :-) , I have updated the schematic to reflect only a single fuse on the LIVE line !
And thanks again Melanie for the info regarding the OPTO and the TRIAC,
the reason the TRIAC is open ended is because I have not decided what value to use for the TRIAC, since I think this may be dependent on the choice of PIC (and PORT) ? The designs I have seen so far seem to indicate somewhere between 470R and 1000R for the TRIAC resistor (R3 in my diagram).
Two things should me taken into consideration here :
1. the TRIAC gate currents (MIN and MAX)
2. the PIC pin allowable current
PLEASE CORRECT me if I am wrong!
In the meantime I am reading through this as a start!
http://www.microchip.com/stellent/id...pnote=en011202

What's of concern is that Microchip have made no mention (that I can see) of the differences between a COMMON NEUTRAL or COMMON LIVE design in the appnotes !!

Steve,thanks again for the tip especially for the transformer info ... READ the posts to date very carefully please... we have already established that the Microchip design is a COMMON LIVE design which 'floats' 5V below either 120VAC or 220/230/240VAC and that it would be a whole lot 'safer' to rather 'float' 5V above NEUTRAL, hence the changed design thus far.
Also as Dave pointed out, I did mention in post 1 that I would like to use a transformer-less PSU.

Dave .. thanks so much for the continuous valuable x10 references as well as the tips thus far.
That appnote sure has a lot of info and someone went through a huge amount of work to setup the application to get it to that stage I'm sure (especially looking at the section for the tuned circuit replacement of the usual x10 120KHz tuned transformers), is that mains injection being done purely with a resistor and a cap ?
I saw a project a few days ago where the designer is injecting a 135KHz pulse into the carrier and was wondering if that could be done with the pulsin pulsout command instead? Will see if I can find it for you since I think it may interest you as well.

Dave and Melanie (and anyone else)... regarding a zero-crossing sensor (which may be needed for dimming), where would you best situate it in this circuit ?
I have seen various designs indicating it in different places, and most have one of the PIC pins connected with a resistor in series directly to

For all those following this thread, please note that nothing has been built as yet and the attached schematics are merely used for the discussion.
Please also take note of ALL the safety warnings!

Thanks to everyone for all the info so far!

Kind regards

Dennis

[Dennis]

I have been reading through this appnote http://ww1.microchip.com/downloads/e...tes/40171a.pdf and noticed the presence of two extra capsacitors namely C1 and C2 in the appnote schematic ..what is the function of these in this instance?

I have updated my design (see attached file) to include a zero-crossing sensor and have connected the TRIAC.
My concern is the value of the TRIAC resistor and that's the reason for the ???.
If there are any suggestions/concerns or changes to be made please let me know.

Kind regards

Dennis

[Dennis]

Forgot to attach the update.

While checking out various design for PSU's I noticed one person remarked that he might move the Varistor put the varistor after the 47R, so it doesnt have to short out the power station on spikes, same with the 20M resistor.
He also suggested he would not use a 20M but a rather an attenuator, say/guess 220K and 5k to ground.
Any thoughts around this statement ?

PLEASE NOTE - I have also added a WARNING for anyone who might stumble across this !!

Kind regards

Dennis

[Dennis]

Trying to attach the schematic again (renamed this time)


Dennis

[dhouston]

I saw a project a few days ago where the designer is injecting a 135KHz pulse into the carrier and was wondering if that could be done with the pulsin pulsout command instead?

Search the forum for Anand Dhuru's posts on building his own X10 modules for 230V. I believe he is using the hardware PWM to generate 120kHz. Also, Darrel Taylor made some modifications to the PBP XOut command that might be of use.

[Dennis]

Hi all

Dave .. thanks once again for the extra info and tips :-) they always provide good reads and info :-)

Melanie,Steve and anoymouse...

While re-reading the Microchip appnotes, this one in particular

I noticed some interesting points...
Firstly this one regarding the current draw,

The PIC12/16/17 microcontrollers draw a maximum of 10 mA, even at the highest frequency and voltage of operation, therefore low current availability is not an issue. AC line voltage isolation can be addressed by using MOVs or transient suppressors on the PIC12/16/17.

and then something strange about the FUSE on the NEUTRAL LINE ???

In most applications, the output voltage should be reg-
ulated. Figure3 shows a diagram for a practical circuit
where a +/- 5V regulated output is generated. Note that
the neutral is connected to ground through a fuse. This
+5V
would guard against improper AC wiring.

Any comments on these statements?

Kind regards
Dennis

[mackrackit]

Where did you get the second quote? The one about the neutral.

Have you checked your local electrical codes about the proper way to wire something for the system you have? Might clear up the neutral thing for you. Here the ground and neutral are "bonded in the box" not at the device. I can not see yours being any different, I am sure you have a transformer with a center tap providing power to you.

BTW, you never said why you want to do this or what you think the benefit will be.

[Dennis]

Hi Dave

Thanks for tip, I was going to get eyes in on the local sub-station but will do so tomorrow ;-) and update as soon as possible :-)

The quotation is actually from a Microchip appnote TB008 , the paragraph is just above figure 3. in the appnote. [HTML]http://ww1.microchip.com/downloads/en/AppNotes/91008C.pdf[/HTML]

Ok the project is for the PIR-sensor based security lights, I need to tap into the PIR and replace the existing LDR and sensor circuit which are also transformer-less and triac controlled. Each sensor light PIC transmit back to a central PIC.

Given the space I have I cannot fit a transformer based supply into the housing or wall point (someone did a good job installing them) and there is no way I can mount the circuit externally.
So transformer-less it is !
I have seen circuits aplenty on the web yet it seems most are common live and also mainly for 120VAC it seems.
Some even with dual fuses (one on LIVE and one on NEUTRAL!)

So it seems there is quite a lot of confusion in this arena and for good reason I suppose, fear of death being the ultimate reason people shy away and of course once bitten twice shy(being shocked into submission certainly shys people away).

So my quest was to research the topic of transformer-less supplies before I dive into anything like building one only to encounter serious injury and the possibility of my circuit frying !

Nothing I have seen out on the web quite explains how one should wire things up on the pic if you're using a transformer-less PSU.
So appnotes are created and design note etc ... but the very simple steps seem to be missing, the questions (FAQ's) and their solutions.

So how do we find news ways of doing things if we are stuck designing only in the confines of a transformer-based supply.

In the early years I remember learning about the effects of capacitive, inductive and resistive circuits.
For example :

With a CAPACITIVE circuit, A current will flow through the circuit, first in one direction, then in the other.
No current actually flows through the capacitor. Electrons build up on the one plate and are drained off from the other plate in very rapid succession, giving the impression that the current flows through the insulator separating the plates.
However, a capacitor in an AC circuit does offer resistance to the overall current flow. We define a quantity called the CAPACITIVE REACTANCE, Xc,

In the designs I have seen, people place and swop around the components as the desire almost as though it's a little slap-dash design which may or may not work and your mileage may vary.

For example, I changed my original circuit design around to make it safer (which was a copy and make-up of the Microchip appnotes (or close to it ) , why would they suggest such an unsafe circuit I wonder ?
Then I keep getting told to use the Microchip designs ... yes I would love to but are they the safest ? And most if not all of them are for 120VAC without worked examples for 220V or 230V.
You may have already noted that there COMMON HOT(LIVE) and COMMON NEUTRAL transformer-less supplies.
So after having changed the initial part of the circuit to make it a common neutral supply , this raised more questions
what then? , what else needs to be changed ?
Are the diodes and other components correctly setup and placed the correct way around ?

And as regards the benefits... well
1. it is space saving,
2. is cost (the tiny transformers are extremely expensive here) and
3. is that I can go extremely small if I use SMD components not so ?

I have to put the same circuit in about 15 lights.
If you do manage to see a mistake please let me know.

Anyways that it from me.. I hope that exaplins it so far :-

Kind regards

Dennis

[Dennis]

Check out this power supply ..take particular note of the input side..
[HTML]http://www.redcircuits.com/Page134.htm[/HTML]

Dave Houston this is the 135KHz injector I was referring to [HTML]http://www.redcircuits.com/Page56.htm[/HTML]

Enjoy

Dennis

[Melanie]

Back in Post #2 of this Thread you were directed to posts which had schematics. The discussion also continued as to what I thought of Microchips App Notes! The product had a production run of several thousand and many hundreds were installed in Hospitals (this I thought was a great idea, since if anything did go wrong, the punter was already in the right place to get assisstance). To my knowledge, in the intervening years, nobody's died and niether has the product, since we never did get any back for service. Looking at the schematic of that product, one end of the TRIAC was tied to NEUTRAL, the other went through the LOAD through a second FUSE (the first Fuse was on the Capacitive Supply to the PIC) to LIVE (you'll note the board had two Fuses). My Gate Resistor from the PIC to the TRIAC was 1K8 - but yours will depend on what your TRIAC's Datasheet tells you.

So how do we find news ways of doing things if we are stuck designing only in the confines of a transformer-based supply.

You go to school and learn the theory of what components can and can't do. You learn the math behind calculating component values. Then, and only then, you will have armed yourself with the knowledge that should stop you from doing something stupid. I've said this before - Darwin had a great theory of "Natural Selection", unfortunately every now and again, good people are also lost along the way.

3. is that I can go extremely small if I use SMD components not so ?

Prime example of lack of knowledge. SMD parts seldom come in high voltage ratings. By reducing the size you reduce the separation between adjacent connections... as a rough guide you need 1mm per 100v. Go pull the Datasheet on an 0805 series Resistor and tell me what the maximum voltage rating is!