a little help with capacitive power supply values

[Dennis]

Hi all

I would like to incorporate a transformer-less capacitive power supply in the project I am busy with.
I found this app note on the microchip site
[HTML]http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf[/HTML]

What's confusing me is deriving the values for a 220V 50Hz supply.

I can't seem to fugure out where the values for R1 and C1 are initially derived...are the just assumed and we calculate the rest from there?

Also hat is not clear is the WATTAGE for R2 1M in figure 10 nor for VR1 or the MOV.

I hope someone can offer some help here

Kind regards
Dennis

[Pic_User]

Hi all

I would like to incorporate a transformer-less capacitive power supply in the project I am busy with.
I found this app note on the microchip site
[HTML]http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf[/HTML]

What's confusing me is deriving the values for a 220V 50Hz supply.

I can't seem to fugure out where the values for R1 and C1 are initially derived...are the just assumed and we calculate the rest from there?

Also hat is not clear is the WATTAGE for R2 1M in figure 10 nor for VR1 or the MOV.

I hope someone can offer some help here

Kind regards
Dennis

Hi Dennis,

Transformerless Power Supplies are extremely dangerous and discussed in many threads.
http://www.picbasic.co.uk/forum/showthread.php?t=3265
http://www.picbasic.co.uk/forum/showthread.php?t=3898

Most here would advise against them.
-Adam-

[Dennis]

Hi Adam

Thanks for the advice and heads-up !.. I promise to wear rubber gloves and have lots of back-up components for the smoked ones and will keep a fire-extinguisher handy.

It's gotta be more fun that flying a kite in the rain with a key attached to the string and waiting for the odd lightening bolt though :-)

Kind regards
Dennis

PS .. Adam ...what interesting posts !
thanks for pointing them out to me ...and I too was confused by the App Note author's use of ground and circuit ground ..especially regarding the 3-wire system.

What I would like to accomplish is a PIR/LDR controlled security light switch using a PIC , the PIC ciruit is powered from the mains and on 'sensing ' movement or light supplies mains to the light.
Something like this

MAINS ------------|PIC circuit| ----|LOAD
| PIC port
|
Live |__________-----_________|LOAD
Neutral |_______________________|LOAD

[Pic_User]

Something like this? LOL
http://www.picbasic.co.uk/forum/show...0&postcount=33

[Dennis]

That's pricless :-)
Fell really sorry for the goldfish though ! Although I'm not sure if it's the first shock ... smelly feet or the second shock .. the high voltage :-) Well I guess they could always recover from the first :-)

Wish me luck :-)

Kind regards
Dennis

[Byte_Butcher]

You laugh....

Back in the day when electricians were REAL men (and human life was cheaper than a voltmeter...) THIS is how it was done...

http://www.weirdstuffwemake.com/swee...ages/aeh66.jpg




steve

[mackrackit]

DO NOT TRY IT !!!

Life is to short the way it is...

Buy a transformer.

[Dennis]

Steve...

Ah yes the tongue tip taste !! There is something tantalizing (addictive perhaps) about the tongue tip taste for a battery (up to 9volts DC) not so ?

And then there's something thats very off-putting like the shock delivered working older monitors and some TV's and getting a nice belt from the LOPT or finding out from the other side of the room as an apprentice with your mentor laughing at you afterwards about the fact that the chasis of one such monitor was live.
Something so different between a shock from DC and one from AC.

Many years back I heard about an incident at a nearby college where a student had used the tongue tip test on a PC PSU (when they still had live coming to the front power switch)...they lived but couldn't do anything but mutter and waffle for quite a while afterwards !

We were always taught to use things like the right hand rule and have a friend nearby (some lecturer's actually joked about it and said the friend was there to laugh at your stupidity or have them test the circuit first :-))

Dave ...
How does one learn without experimenting ?

Keep well

Kind regards

Dennis

[dhouston]

...and I too was confused by the App Note author's use of ground and circuit ground ..especially regarding the 3-wire system.

What's the potential of the neutral line when it's tied to earth ground?

X-10 has used capacitive power supplies in nearly all of its billions of 120V and 230V modules for 40+ years without frying too many of its customers. You can check Ido Bartana's website for 120V to 230V conversions to get values for R & C.

• http://www.idobartana.com/hakb/

If you read the Microchip app note carefully, you will find that it explains how to size R1 and C1.

Or you can Google using transformerless power supply or capacitive power supply and find suggested circuits for both 120V/60Hz and 230V/50Hz.

If the very limited current capacity is insufficient, there was a recent thread showing a design capable of 1A.

[Melanie]

> What's the potential of the neutral line when it's tied to earth ground?

Actually it can be several volts.

Consider a few kW load at the end of the wire (very easy if you consider the kind of loads encountered in a building). The wire has a Resistance depending on it's material and cross-section and length.

If you connect your DVM between the Neutral Line and Earth at your wall socket with no load on that circuit (remembering it could be connected to several outlets), then you probably will get no voltage, but as soon as you start to switch on appliances you will begin to register a voltage. Now load up with a few kW (say an electric room heater) and report back with what you find...

[Dennis]

Hi guys

Dave .. thanks a million for the extra info :-) , it is the appnote which is confusing me .. The values for R1 and C1 seem to arrive out of nowhere, unless I'm reading it wrong ?

Melanie .. thanks for the extra info too !
There ain't now way I'm gonna be measuring much after I've done the right calculations especially not when under a real load :-) ....or should I .. have you ? Have you taken pics? Video ?
And as for switch on , I will do it using a push-button and a broomstick ;-)

Kind regards

Dennis

[Pic_User]

This is an interesting idea.
Transformerless Power Supply of 1A at 5Volts!
Thanks to Ioannis!
http://www.picbasic.co.uk/forum/showthread.php?t=12249
-Adam-

[Dennis]

Adam Thanks for that :-)
Saw it when it was first posted ... I don't want to use a bride rectifier or transformer and 1 amp is way more that I need :-)

All I want the pic to be able to do is act as and intelligent switch

AC IN --->> PIC >>> LOAD

Make sense ?

Kind regards

Dennis

[amgen]

the capacitor reactance (resistance for ac voltage) is
1/(2 X pi X freq X Cap(micro-farad)) ohms,

for 50MA from power supply, 220V/.050 = 4400 ohms....
the required resistance provided by cap for 50HZ at 220V.

then,
Cap= 1/(314 X 4400) equal aprox .7 micro-farad cap (>250 VAC rated)
works out to about .15 micro-farad per 10MA.
See attached diag.

[Dennis]

Amgen

Thank you that's exactly what I'm asking for !

I have been through the appnote and what's confusing me is how you got he value for the resistor R1 ??
You said ....

the capacitor reactance (resistance for ac voltage) is
1/(2 X pi X freq X Cap(micro-farad)) ohms,

For 50MA from power supply, 220V/.050 = 4400 ohms....
the required resistance provided by cap for 50HZ at 220V.

How did you get the value for this ...

Cap(micro-farad)) ohms

Kind regards
Dennis

[Melanie]

Just Transpose the formula that you've got... if...

Xc=1/(2 pi F C)

then...

C=1/(2 pi F Xc)

Xc is the AC Resistance (Reactance) that you want in Ohms, C=Capacitance in Farads and F is the Frequency in Hertz.

Say you wanted 50mA at 110v 60Hz (way too high for driving a PIC and a TRIAC say for Lamp Control - more like 15mA required), then V/I=R (where in our case R is actually Xc)...

110/0.05=2200

So we know that Xc must equal 2200... therefore applying the transposed formula...

1/(2 x 3.14 x 60 x 2200) = 1.2uF

Theoretically, that's great... but practically you'll discover that Capacitors don't come in all the myriad of values that Resistors come in, so you probably only have easilly available 0.1uF, 0.22uF, 0.47uF and 1uF. Work out which one best suits your current requirements and design your circuit to match it. I would strongly discourage you from desgining Transformerless Power Supplies with Supply Capacitor values greater than 1uF.

[Byte_Butcher]

Melanie pretty much said it all, but there's schematics and math formulas for transformerless supplies in this Microchip appnote:

http://ww1.microchip.com/downloads/e...tes/00954A.pdf



steve

[Dennis]

Hi all

Thanks to everyone for their help so far ..

Steve for the tongue-tip-test tip and for the latest one
but I am already referring to that document in post number 1 in this thread .. and that's the source of the confusuion.

Amgen thanks for the bridge-rectifier based sketch and formulae !

Dave Houston I will remain eternally grateful for the X-10 info pages and other links.

Adam those links you pointed me to where a great read and it seems I may have opened a can of worms with this thread ??

Dave, Mackrackit aka "CODE EYES" thanks for the forewarning and all the help thus far.

Melanie not only did you clear up my confusion regarding the calculation but have also given some fantastic tips to take into consideration which also triggered some more thoughts/questions.

So far I have the following calculated.

For 220V @ 50Hz to drive a MAX load of 30mA, I would need the following values (or have I messed up somewhere and is it just under 15mA?)

MOV(VDR1) = 275V
C1 = .47uF (suggested is X2 rated 275VAC based on other forums posts and internet sources)
R1 = 100 OHM (1/2 Watt)
D1 = IN4007

C2 = 470uF 25V (electrolytic)
D2 = 5V1 Zener

If all is correct, this output a half-wave rectified, smoothed 5V supply, right? If full wave were required I would need to a
If there are any further suggestions/changes I would appreciate them.

Is it true to say that the circuit ground 'hovers'(for lack of a better word) below HOT/LIVE and is not reference to EARTH GROUND and this is why all the warnings and danger signs ?

My questions are ...
(And while I ask I am busy reading/checking up on the following)

1.Whats happens when the circuit wants to draw more than max Ohms ?
2.How do I check the current draw of my PIC (assuming the PIC is standalone and not connected to anything other than power ?)
3. Once I start connectinng things like a push-button or triac or relay and perhaps an LED and maybe a POT for dimming, what would the ball-park usage start looking like and why ?
4.Which component is taking the most strain as the circuit draws current, is it C1 ?
5.Is C1 the current limiting factor of this circuit ?
6. I was thinking of using a BT139 Triac (since I have quite a few lying around), is it a good choice? I read that
7.What should the value for R3 be if I am to drive a triac ?
8. Is it feasible/possible to add a wireless TX module to the PIC circuit and if so what safegaurds (if any) like noise reduction should I put in place and where ?
9.In post #14 here amgen points out that we are looking at 0.15UF per 10MA and this seems to run true for both bride rectifier (full-wave) based as well as for the non-bridge based (half-wave) supplies. So the question is why choose to use a rectifier or not ? Is it cost ? Less of a smoke factor ? Space ?
10.To test the voltage on the output side could I just pop my good old Fluke meter on 5V and circuit GND with it set to read DC volts.
(and yes I will make sure I am insulated - rubber sole shoes, no jewellery, rubber gloves - hell I will wear a rubber suit if needs be!)
11. Are there any tips for connecting things up on the PIC side ?
12.And for taking measurements on the PIC side ? Apart from the app note SAFETY PORTION which refers to using an isolation tranformer.
Anyone have a schematic/block-diagram for measurements please?
13. Unless I am planning to use zero-crossing point to control the triac (can't think of a use right now, can you ? ) ,should I be concerned about zero-crossing issues as I have read somewhere that this circuit may cause slight delays in switching the load on or off based on Wattage and type either resistive or inductive) because the zero-crossing signal is phase shifted from the actual zero-crossing?

Oh and last but not least I can think of at least two applications that might be a no-no
1.Touch-sensitive pad(s)
2.ICSP
But what about things like USB or Connection to the PC serial port?
What sort of buffering or isolation would be required if is possible.

Apologies for the lengthy post and any questions which may seem obvious or silly to anyone reading this post (and the other posts too!)


Thanks once again

Kind regards

Dennis

[amgen]

Dennis,
Very through work !, and good questions.
Your diag had diodes in wrong places.
1) too much current draw will drop voltage to PIC to a point of no-operation,
thats why my ckt had 12V ZD and 5V reg, it provides smoother supply.
2)you have to insert DC ammeret (can be digital meter) in wire supplying PIC and other circuit.
3)Probably getting toward your 30MA, keep draws as small as possible, example---2MA led
4) C1 drops most voltage but most all parts are critical for operation
5)C1 is the current limiter, could use 600VAC rated part which is larger than say 250V part
-R1 developes heat by the amount of -- Current squared times Resistance
- also Z diode makes a little heat -----Z voltage times current through it (can measure or estimate
6) use an OPTO triac driver then any triac of the amps you need is OK
7) use 200 to 500 ohm to drive the triac driver depending on the opto chosen
8) consider added power used (more current) by added parts, within range of designed supply components
9) full-wave bridge makes use of pos and neg cycle of ACV, where 2 diodes only uses 1/2 cycle and the other 1/2 cycle is just wasted. bridge rectifiers come in dip package up to 1000 volts.
10,11,12,13,1,2))) If not using Z crossing, you could hook 10 or 20 volts from an ac or dc supply to test,adjust, ICSP then after all working hook to 110/220 power.
I think touch-sense sw's would be possible shock hazzard due to lack of higher voltage isolation, at some point Transformer isolation makes more sence.

I made some push-button 110V fan timers with this circuit, fits in wall switch box, never skipped a beat or burned one up, so I was addressing the same issues as you.

good luck,
don
amgen

[mackrackit]

Dennis,

Glad to see you are not jumping into this without asking the questions.
But by asking the questions I see you are not familiar with high voltage.
So it is a "catch 22" to learn how to handle it. This is one of the places where "self experimentation" could get you in trouble.

Make sure you have a low value fuse in the system.

I do not want you to end up looking like my avatar

Yes, I am getting to be an "old fuddy duddy"

[Dennis]

Hi guys :-)

Don thanks for the reply and update :-)

Your diag had diodes in wrong places.

Which diode is in the wrong place ??

Dave ....
Thanks for the tip .. just curious though ..fast blow low current fuses ?

Kind regards
Dennis

[Melanie]

Happy New Year Boys...

That's a very dangerous circuit you've posted Dennis.

What you've got is Vdd at LIVE potential, and Vss is just -5v below it. You've put all your voltage drop in the NETURAL rail. That means your ENTIRE low-voltage PIC circuitry is actually referenced against your HIGH VOLTAGE LIVE. Yes it will work, but there is no margin for error anywhere, because GROUND is (more than) 250 volts away...

If you look at other half-wave rectified circuits (posted on this forum), you'll notice that Vss (0v) is sitting at NEUTRAL, with Vdd +5v above it (with all the voltage drop being done in the LIVE rail). So, in that instance most of your PIC circuit is close to GROUND (since NETURAL and GROUND 'should' be connected together somewhere along the Power Grid to your Wall Socket). This makes it a damn sight 'safer' if you really want to play with mains. I use the word 'safer' cautiously - because playing with supply mains for folks that don't know what they're doing is not safe at all.

All the above is negated by the fact that some countries Power Systems allow users to plug appliances in either way around.

Now I'm going to get serious here. Your questions highlight the fact that you don't know what you're doing and you're asking the forum for advice on values of components and such. Read the Datasheets for the components you're using and determine if what you are doing is correct for the purpose intended. For example, the TRIAC Datasheet should tell you what Gate current it requires (your R3 question) to switch on. Because if ANYONE gives advice on a particular component or value, and you end up killing yourself, the liability falls onto the person that gave you the advice.

[amgen]

I would like to take a step back.........and agree with Melanie about this power supply danger.
Any possible touching or contacting of any parts of this circuit can cause serious injury!!! Leaving this circuit available for any person to contact in any way would be very negligent. Only persons with strong electronic knowledge should be working with this type of circuit.
Never want to see someone hurt.
df
amgen

[Dennis]

Hi All (Happy new year by the way :-) I hope it's a good and prosperous one for everyone!)

Melanie thanks for the clarity and tips again ,

So if we are using a 3 prong plug, (Three wire system)
then Brown wire is LIVE
and Blue is NEUTRAL
and YELLOW/GREEN is EARTH

The measured voltages are as follows
At the time I measured

Between LIVE and EARTH = 227.5 V (Readings may vary 235 to 225V (Varies based on time of day load etc) )

Between NEUTRAL and EARTH = < 1 V (May vary too!)

Between LIVE and NEUTRAL = 227.1 V

In most AC driven appliances where a mechanical SWITCH is used to switch
Either one of two switches are used (not so ?)
1.
ON-OFF
Single Pole, Single Throw = SPST

A simple on-off switch. This type can be used to switch the power supply to a circuit.

When used with mains electricity this type of switch must be in the live wire, but it is better to use a DPST switch to isolate both live and neutral.

2.
Dual ON-OFF
Double Pole, Single Throw = DPST

A pair of on-off switches which operate together (shown by the dotted line in the circuit symbol).

A DPST switch is often used to switch mains electricity because it can isolate both the live and neutral connections.

In at two wire system (2 prong plug) we are using LIVE and NEUTRAL


So....

In for the example of a PIR security light controller, the circuit draws its power from the mains , when the PIR detects a movement (PIC pin goes high) it opens the power to the load , in this instance it switches the light on (the light draws from the same mains power that the circuit draws from)
See the attached diagram..

So without creating a dangerous circuit how does one draw from the very same power that you are switching on and off (or dimming for that matter) ???

Melanie, what exactly are you suggesting to make it safe ?
You said ...

What you've got is Vdd at LIVE potential, and Vss is just -5v below it. You've put all your voltage drop in the NETURAL rail. That means your ENTIRE low-voltage PIC circuitry is actually referenced against your HIGH VOLTAGE LIVE. Yes it will work, but there is no margin for error anywhere, because GROUND is (more than) 250 volts away...

I agree it would be better to be 5V away from ground than 5v away from 250V :-)
You also said ...If you look at other half-wave rectified circuits (posted on this forum), you'll notice that Vss (0v) is sitting at NEUTRAL, with Vdd +5v above it (with all the voltage drop being done in the LIVE rail).
[/QUOTE]
What keywords did you search on ? I tried transformerless and transformer-less as well as half-wave, and didn't find very much :-(
I did find some that you had suggested to others ...
Like this onehttp://www.picbasic.co.uk/forum/atta...9&d=1213285761
and this one
http://www.picbasic.co.uk/forum/atta...1&d=1139474240

In the cuits I have seen, not many actually depict how the PIC is to be wired for various operations.

You aslo said ...

So, in that instance most of your PIC circuit is close to GROUND (since NETURAL and GROUND 'should' be connected together somewhere along the Power Grid to your Wall Socket). This makes it a damn sight 'safer' if you really want to play with mains. I use the word 'safer' cautiously - because playing with supply mains for folks that don't know what they're doing is not safe at all.

I totally agree here
But how do you suggest I change the circuit to do that ?

Please check the attached (but no yet complete) updated diagram , what's missing here is the value for R2, R3 and the TRIAC stage (I plan to use a BT139F (see attached diagram) ..Is 01A correct ?
I did raise a question about it being correct.

I do understand the risks of the circuit and have been shocked before and why I am raising all these questions is because I would like to cover all the bases and not just dive into the deep-end.

And regarding the calculations and so forth , I last used most of them 20 years ago when I was studying electronics (and sadly it is not my full-time career!) so please forgive me for being a little rusty.
Electronics and PIC programming are a really fond hobby of mine which I recently re-kindled after a nearly 4 or 5 year break !

As regards the safety aspects ... thanks to everyone who has issues warnings here and all have been noted and considered.
I have a question though .. did you all encounter the dangers first-hand by a shock or was it from a warning from others ?
Was it that feeling of total shock and frustration (at yourself) when you opened the equipment to work on or look inside while ignoring the DANGER and HIGH-VOLTAGE warning stickers ?


I look forward to your responses be they critical, analytical or other :-)

Kind regards

Dennis

[Dennis]

Just to throw a 'spanner in the works' , if I do eventually use a transformer based supply like the dimmer attachment, what would be the smallest footprint 220V to 9V/5V transformer I could use ?

Kind regards
Dennis

[Dennis]

My questions ....

Are they perhaps profane , not correctly formulated, without direction , off-the beaten track, stupid ?

I realise there is google, encyclopedias, textbooks, etc. , but nothing can replace the power of human thoughts and minds !!

Is not our very nature to question how a system works and why ? When new technology is built or invented don't we find ourselves asking how it works ? How did someone think of that ?

Don't questions and discussions prompt new thoughts and ideas ?

In this instance I am asking for advice, information and thoughts regarding how others power PIC's and their circuitry.
I have not even attempted to build any such circuit yet and I have been researching this particular topic for two weeks already, gathering info.

Did the inventors of X10 and the likes of know all the odds before they started dabbling ?

What was life like before transformers?

Are there alternatives to transformers ?

I thank you all once again for answering some or most of my questions as well as for your concern for my safety !

I apologize for my lack of knowledge BUT I have a desire to learn more and I have found this forum to be the most interesting in this field thus far! Hats off to all of you !! THANK YOU!

So I have two options .. I recede back into cyberspace and lurk around in the shadows silently OR I summon the courage to ask the questions that other may/may not have thought of or asked before !

Thank you

Kind regards
Dennis

[Pic_User]

Hi Dennis,

Please continue to ask questions on this forum.

-Adam-

[dhouston]

Just to throw a 'spanner in the works' , if I do eventually use a transformer based supply like the dimmer attachment, what would be the smallest footprint 220V to 9V/5V transformer I could use ?

One alternative would be to use a switchmode wall transformer that supplies regulated +5V. That way, it's external to your device and has minimal effect on the footprint.

[dhouston]

Did the inventors of X10 ... know all the odds before they started dabbling ?

I'm sure they did as they had designed many other products before X10. They chose a capacitive supply because it cost less and had a smaller footprint. Their devices are enclosed in plastic cases so there's no shock potential. They also chose to make neutral their hot lead because they thought there was less noise near ZC (where they do their signalling) that way.

What was life like before transformers?

DC all the way. That's how Edison started out. Tesla was the one who pushed AC.

[Byte_Butcher]

Just to throw a 'spanner in the works' , if I do eventually use a transformer based supply like the dimmer attachment, what would be the smallest footprint 220V to 9V/5V transformer I could use ?

Kind regards
Dennis

Dunno what the smallest available size would be, but I like these quite a lot for only $2.67USD each in 10 quantity:
http://ww2.pulseeng.com/products/dat.../LT2007_04.pdf

I use 6 volt output... rectified and filtered it's perfect for powering a LDO to get 5 volts at up to 80mA.

Size is 22mm x 23mm x 19mm.

Small, cheap, safer than transformerless supplies, and able to produce plenty of current for powering a PIC + accessories.

For circuits where an "external" power supply (wall wart) is acceptable, I use these or something similar:
http://search.digikey.com/scripts/Dk...P6P-ND&stock=1



steve

[Dennis]

Adam ..will do , thank you!

Dave thanks again definitely checking out the switch mode stuff too.
And agrred on the Edison and Tesla facts :-)

Steve.. thank you will check asap!
>> I think these look awesome .. so tiny ! Thank YOU

Melanie/Amgen(Don) , please check the updated Capacitive Transformerless AC-DC PSU diagram attached. Common neutral this time (correct me if I am wrong!)

So now the circuit should be floating 5 Volts ABOVE NEUTRAL and not 5 Volts below LIVE right ?

Kind regards

Dennis

[anonymouse]

Adam ..will do , thank you!

Dave thanks again definitely checking out the switch mode stuff too.
And agrred on the Edison and Tesla facts :-)

Steve.. thank you will check asap!
>> I think these look awesome .. so tiny ! Thank YOU

Melanie/Amgen(Don) , please check the updated Capacitive Transformerless AC-DC PSU diagram attached. Common neutral this time (correct me if I am wrong!)

So now the circuit should be floating 5 Volts ABOVE NEUTRAL and not 5 Volts below LIVE right ?

Kind regards

Dennis

Dennis no its not safe, never never put a fuse in the neutral leg when it is at zero potential to earth. The fuse may blow the appliance looks like it is dead, somebody opens it up touches the phase/neutral, they could be dead. Try a transformer, that way you can sleep at night without worrying about the device killing somebody or smouldering away and catching fire.
all the best

[Byte_Butcher]

Yep, like anonymouse said, fuse in the neutral is bad!

If you really *must* build a transformerless supply, goto the document I referenced in post #17, scroll down to page 10, figure 10 and build it just like that. They've already figured out the right way.

Correctly designed transformerless supplies are plenty safe, especially since the commercial devices that usually contain them are invariably well sealed in a well insulated (plastic) housing to keep curious fingers away. Lots of insulation between the device and the user is the key.

But most of my projects involve a lot of testing, fiddling, finger poking, and experimentation (with the guts open and exposed), so most of the time I much prefer a good isolated supply.
I buy little transformers 10 at a time for under $3 each and don't have to worry about what parts are "hot" when I connect my 'scope ground or poke at a part with my finger.

If the size and weight of your project is REALLY critical (but if you're sending it up in a rocket, it probably won't be mains powered), or if you're building a product by the 1000's where saving $1 worth of parts becomes a pretty big deal, then maybe xformerless is the way to go. But for most applications (especially hobbiest) I have to ask... Why? What's to be gained that offsets the risks?

So... why do you want a xformerless supply? What benefits does it have for your project?


steve

[Melanie]

You're getting there...

Loose the Neutral Fuse as suggested.

Your Triac isn't completely wired... it's a three legged device. The LIVE goes through the TRIAC from the Supply Connector and goes out to the LIVE pin on the LOAD Connector. The NEUTRAL is common between the Supply and the Load, correct as you have it.

For those keeping an eye on this thread, if you use an isolated Supply for the PIC, it's low-voltage side will become LIVE the moment you connect it to the TRIACs gate. If you want your PIC to be isolated, then you will need an Opto-Isolator (or Pulse Transformer) of some sort between the Gate and the PIC.

Again, going back to an earlier question, yes, zero-cross is important - for many reasons (even if it's just to keep the peace with your neighbours). Go read up about it.

[dhouston]

If you really *must* build a transformerless supply, goto the document I referenced in post #17, scroll down to page 10, figure 10 and build it just like that.

Steve, isn't that the same document Dennis referenced in post #1 of this thread?

[dhouston]

Dennis,

You might also find Microchip AN236 helpful. It has a capacitive supply, a ZC detector and a triac.

• http://www.microchip.com/stellent/id...pnote=en012050

And there are more schematics of X10 modules on NASA engineer Dr. Ed Cheung's site.

• http://www.edcheung.com/automa/circuit.htm

[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