a little help with capacitive power supply values

[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]

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.

[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.

[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