Transformerless Power Suppply

[ERIK]

Hi there,

Despite the obvious safety issues etc, I am very interested in building a transformerless power supply for my PICs. I am in New Zealand where the power is 240VAC @ 50Hz so most of the App Notes/Tech briefs on the web aren't quite appropriate for these conditions. I've been using rectifier diodes and or bridge rectifiers, a Zener, and some heavy duty resistors and caps. I've asked my friend who is an electrical engineer to have a think about it and he begrudgingly agreed so I'll see what he reckons. I was just wondering if anybody else out there has built a good/simple transformerless power supply to run on 240VAC @ 50Hz?

[muddy0409]

Silicon Chip had a project about a light dimmer. That had a method of scourcing power DIRECTLY off the mains. I'll have a look for the mag and post the details if I can find it.
From memory, this small module was fitted inside a lamp with no transformer or anything else, other than direct connection to the Active mains power for its supply.

[Melanie]

Why no transformer?

A transformer is there for good reason (whether it's a conventional iron cored item or a high-frequency switcher), apart from the obvious in dropping the incoming mains supply down to something safe to play with, it also provides ISOLATION from the supply mains which is a very important feature. Without that ISOLATION your circuit is LIVE regardless what voltage you play with.

[muddy0409]

Ahh....there we are....

SILICON CHIP October 2005. You can get a reprint from their website www.siliconchip.com.au for a small reasonable price...

Hmmmmm.............I was wrong, it's a fan controller, not a dimmer.

Yes Mel, you are correct ( as always ) but in this case, built into a plastic box with no easy access, once installed in the roof, there shouldn't be a problem. I may even try this for a couple of projects at sometime in the future.
Anyway, read and see what you think.]

[Melanie]

If you must... here's part of a circuit I designed (coincidentally for a fan controller for Hospitals)... total disclaimer if you die whilst playing with it - it is LIVE - you have been warned! No big dropper Resistors (R1 is a standard 0.25W), no heat disspation problems...

The only real justification for using a circuit like this is space... The total physical real-estate a circuit like this requires is a fraction of that taken by an iron cored transformer or a switcher.

[ERIK]

Thanks for those. Yes space is exactly why I don't want a tranny. I'll try your's Mel it looks good. And I'll make sure it is well housed. I was getting some heat disspation problems as you mentioned by using all the ones with the big dropper resistors. Nice looking fan controller by the way.

[ERIK]

Hey Mel, sorry about going back to this dreaded topic again but I was wondering a couple things about your transformerless power supply circuit.

1 - What sort of 470nF 400V cap did you use? I can't seem to find a suitable one down here in my funny little country.

2 - Is the voltage dependant resistor an integral part of the circuit or a somewhat optional component?

No more questions on this subject after this I promise.

[Melanie]

Ask as many questions as you want... that's what the forum is here for.

Only C1 (10nF X2 type) is surplus. This PSU was part of a Fan Controller which used a Triac controlling the Fan. C1 was there for noise surpression and in your case can be removed.

C2 is either an X2 grade capacitor, or, any 400vDC rated Capacitor. Look for metalised polypropylene or metallised polyester. Typical manufacturers are Dachs-Kondel, Arcotronics, BC Components (Vishay), LCR and TruCap.

VDR1 (11v) is a safety component. My original design was going into Hospitals... if Zener D2 failed and there is negligable power consumption by the target circuit, the voltage at the junction of D3 and C3 would rise rapidly towards supply mains level destroying the Regulator and every low-voltage component (ie the PIC) downstream. The Zener is the weak spot... if it fails, basically everything is toast. That VDR is sufficient to keep the supply from rising much above 18v, still well within the parameters (30v) for the Regulator. My PIC had additional circuitry (two Resistors as a potential divider to an ADC pin) that detected that the Input DC supply to the Regulator Q1 had risen above 14v and flashed an LED to tell maintenance engineers that the unit is broke. Omit VDR1 at your risk.

PM me off-list if you have trouble finding suitable parts and I'll see what I can do.

[sayzer]

Hi ERIK,

Is your current (I) always the same or it changes? In terms of mA, what is the current of the entire PIC circuit at its max and min ?

Also, how is the stability of the power lines in your city? Is it always 240V or increases on holidays and decreases on working days? If not stable, how much is the change?

I may come up with a different solution!

[Melanie]

I'm always interested in alternatives and to see how other engineers approach problems, as I'm sure others on this forum are... try this spec... Input supply 220-250vAC 50/60Hz. Output 5vDC (regulated), operating current range 0-30mA (total), short-circuit proof. Which is roughly the specification of the circuit I've submitted. The important features are (a) that there must be minimal heat dissipation... so high wattage dropper Resistors or high voltage Regulators like the VB409 which require heatsinks are out... and (b) minimal size both physically and in PCB real-estate usage.

[sayzer]

On Microchip's WEB site, there is a Transformerless Power Supply concept similar to Melanie's.

The file name is TB008.pdf and attached here.


---------

[Melanie]

I have mentioned before that some of Microchips Application Notes are downright dangerous... and that is one of them.

Connecting Neutral and Earth together will trip most ELCB's a small fact that the author of that AN seems to have overlooked. Not fusing the Live is plain stupidity (as is any power distribution system that allows users to plug appliances in either way around)!

[NavMicroSystems]

I have mentioned before that some of Microchips Application Notes are downright dangerous... and that is one of them.

Connecting Neutral and Earth together will trip most ELCB's a small fact that the author of that AN seems to have overlooked. Not fusing the Live is plain stupidity (as is any power distribution system that allows users to plug appliances in either way around)!

I absolutely agree !

Unfortunately DO most european systems allow users to plug in appliances in either way around.

Hey Mel, you must be lucky living on an island with some better system!

There is one thing in addition I would like to mention:

Guess what happens if your mains is only "kind of" 50Hz sine?

Do you see where I'm going?

I have had several portable devices on my bench for repair.
Some of them had poor designed low-cost transformerless PSUs.

i.e. coffee (or espresso) makers a.o.

Users had thought it would be nice to use that coffee maker in their caravan
and hooked it up to one of those low-cost power inverters.
The output of most of the low-cost inverters is not even kind of sine, it is actually square, so all the transformerless PSU did was saying goodby by generating smoke.

You'll wonder what strange ideas users come up with...

[Melanie]

It's a 3-pin ONLY system in the UK. Yes you can get continental 2-pin shaver adaptors, but I'm told you men like to live dangerously in the bathroom.

Let's just look at TB008 for a moment... and just consider...

Neutral is grounded at the Power Station, and at the substation, and probably at the Building incommer... Here we have a fuse between Neutral and Earth... why? It's completely USELESS!!! If the fuse wasn't there (or it blows for whatever reason), you STILL have a FULL conductive path between LIVE and EARTH. Actually he's (I'm assuming 'he' as a girl I'd expect to know better *smiles*) even using EARTH as a return path of his circuit. Plug that circuit into most properly wired homes and the first thing that happens is the ELCB breaker trips! The author of TB008 should be prosecuted for the most dangerous suggestion you could possibly think of!!!

I'm well aware of the square wave inverters... still... the great unwashed (general public) hasn't got a clue... which is why you can market complete crap and they'll still pay good money for it.

[NavMicroSystems]

I'm not using any transformerless PSU's at all.

Some time ago I could get hold of a large number of well designed switching PSU-units at about $0,50 each (stock/production overhead)

They provide well regulated 7,5V @ 600mA
and are very small in size.
(Actually not more in PCB-Space than a good transformerless design would require since they are fully SMD)

I could not even design and build any transformerless PSU at comparable cost.

Why develop/build something that is already available on the market at lowest cost?

OK,
for someone selling 10thousands of units per year it is a different story,
but if you are selling "only" several hundreds of units I still feel it is a good option to search the web for those stock overheads.

The only rule is:
get a sample before your bulk order and test it carefully.
If the sample is OK (meets or exceeds the requirements):
order a quantity that lasts at least to the planned production/life-cycle of your product.

That way I have saved a lot of time & money.

[NavMicroSystems]

... still... the great unwashed (general public) hasn't got a clue... which is why you can market complete crap and they'll still pay good money for it.

Mel, I doubt you would risk your reputation by marketing crap just to make money.
(please correct me if I'm wrong)

[Melanie]

You just have to walk down any High Street in any Town, anywhere in the world to see what I mean...

[NavMicroSystems]

You just have to walk down any High Street in any Town, anywhere in the world to see what I mean...

I'm almost sure I know what you mean and hope you haven't taken my comment too serious ;-)

[nomada]

Hi,

Be carefull, be very carefull, when using a power supply without transformer is like walking in the wire without the net underneath...

Atached you can see the circuit I use to put some power ... in PICs and other stuff. I found this circuit some years ago when I bought a kit (K6713)from Velleman, its a IR receiver to switch on/off a load connected to mains trough a relay.

One more advise, if by any chance you are planning to use this circuit in a touch sensor or similar do not forget to use two resistors in series for the sensor, the contour voltage for a regular 1/4W is less than 200V, unless you like to get a curly hair...

regards

[Melanie]

If you're still looking for components, attached PIC I've taken gives you an idea of what to look for... The 11V VDR is pretty small (VDR2 in this pic) - and also laying alongside with a view of a typical Capacitor you can use. If it's an X2 type you're OK, otherwise you'll have to fit one with a 400vDC rating. It's a real good idea to absolutely and positively mark the PCB that it's LIVE... even if it's just for yourself. Some time in the future you'll forget and it'll bite you.

[ERIK]

Thanks Mel, I have finally got some 275V X2 caps and some VDR's (I had to buy 100 of them but thats OK). So I'll sort out a PCB (well marked, and well housed) and let you know how it goes...

[sayzer]

Hi Melanie,

Going back to this post,

Would that be too much to ask for your complete fan controller schematic?
and, if possible, for the code also?

I am having a similar inquiry and would like to see your approach.
Or if there is anyone else who had a similar design.

Regards

[Melanie]

Hi Sayzer

This product is still in volume production (about 1000/month), and I'm treading on thin ice just posting the PCB view (a couple of posts above) and some snippets out of the PSU schematic - the remainder if you're clever you can figure from most of the components in use and eliminating those I've already revealed... a licence for the complete Software and Schematics would cost... I envisage around $5K.

Melanie

[sayzer]

May be, I can support that thin ice, so it will not crack.

Since you already have it in production, I may need not to work on it;

This is of course if you are able to sell it to other customers. Are you?

Should I PM to you?

[Melanie]

Sure, continue this by email, as I can then send you the product Datasheet so you can see if it fits your requirements.

[sayzer]

Upon the discussion with Melanie, attached is the capacitor value table for the current (mA) that your circuit draws.

Table is quite simple to figure out.

Table is for 110V@60Hz and 220V@50Hz.

Example: If your circuit draws 12mA, and your power line is 110V 60Hz, then, you use 0.289uF (290nF) for C2 in the circuit that Melanie posted here.

Of course you will have to adjust D2 and VDR accordingly.

If this table is any help to anyone!


Regards

[Melanie]

Nice table, but if you limited the Capacitor values to those dozen or so X2 values available (eg 10n, 22n, 47n, 100n, 220n etc, etc), you'll be able to pick the one closest to your current requirement. No point in having a 290n value when you can't buy one, and putting heaps in parallel negates the advantages (cost, size and weight) of a transformerless design to start with.

[sayzer]

Yes, of course.

Just as in your design, C2 is 470nF but in the table the nearest value is 477nF.

I am sure 330nF can also be used there although is not a near value.

Similar to this example, one can look at the table and pick a range.

I will try to make this table as an active WEB page so the user can enter the values of Frequency and Current then have an info for the capacitor range that "can" be used.

-----------------

[psdayama]

I have seen in many posts that Melanie is asking to use X2 capacitors.
For the requirement of circuit the value posted in tb008 is correctly just
470n 400V type. These are available at half price than X2 types because
X2 are required for special protection function and 'never short' across the
mains requirement.
Also the resistor across this capacitor can be 220k 1/4 W instead of 100K
1Watt. This resistor is for discharging capacitor when ckt is not in use and
not for providing resistive current. Those who are having 110V/60Hz should
double value and save money.
If one is not finding proper value of capacitor then it is not good that
one should have much higher value available. If used then low voltage regulators (zener or series type ) will dissipate much more power and may
burn out. Consider that this ckt is constant current generator and that when no load is there it will be dissipated in zener. It is better that shunt type
voltage regulators are designed with proper wattage rating so that there is
no problem later.
( I had been manufacturing X2 and normal plastic film capacitors for more than 12 years in India)

[Melanie]

There is a reason I specify X2... and you said it yourself... "they (are specified to) never short accross". If in a Transformerless Power Supply the Capacitor DID short accross it would be very bad news!!! If you don't fit X2's, then yes, your costs are very much reduced, but do you want to take the risk?

[dhouston]

I have mentioned before that some of Microchips Application Notes are downright dangerous... and that is one of them.

Connecting Neutral and Earth together will trip most ELCB's a small fact that the author of that AN seems to have overlooked. Not fusing the Live is plain stupidity (as is any power distribution system that allows users to plug appliances in either way around)!

Melanie,

This may be accurate when talking about UK or European wiring but your advice is both inaccurate and dangerous when it comes to North American wiring. The fuse between neutral and ground shown in FIGURE 3 and FIGURE 4 of TB008 is a safety feature as the authors of the app note state.

Here's a URL which briefly explains the 3-wire system used here for many, many years. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/bregnd.html
Circuits which might be plugged in either way around will not have the ground wire and thus will not have the fuse and will also require double-insulated, non-conductive enclosures. In fact, the only way to plug a North American two-wire appliance in either way around is to file down the wider neutral prong of the polarised plug.

You might also read...http://en.wikipedia.org/wiki/Double_insulated

[Melanie]

You are kidding me!

Neutral and Ground are basically one and the same. In many buildings all over the world (including in the US) the NEUTRAL incommer is tied to the Building GROUND (just as it is at the generating plant).

Go remove that fuse from the NEUTRAL line in figure 3 of TB008. Then stick your finger in the HOT terminal with one hand (or the 1uF Capacitor), and go grip a Water pipe in the other and tell me if you feel anything! They don't label that terminal LIVE for fun.

Oh, btw... I've a whole heap of US plugs and sockets that have the Neutral and Live EXACTLY the same size. So the Neutral terminal being the larger must be a recent innovation for the US.

The Transformerless Power Supply is not designed for portable equipment that can be connected either way around, but more suitable for fixed plant where the installer wires LIVE to LIVE.

[dhouston]

I suggest you actually take the time to read the URLs I cited.

We've had polarized plugs and wall sockets from even before the time the 3-wire system was implemented. I live in a 60+ year old building that predates the 3-wire system and all of the wall outlets are polarized. My memory is a bit fuzzy but I believe the 3-wire system was required from about 1960.

If you have non-polarized plugs and sockets they are likely be for IEC Class II use which you might have grasped had you bothered to read the URLs I cited.

Transformerless power supplies have been used by X-10 in their plug-in modules (some 3-wire, some 2-wire, all polarized) and switches since 1976 or so.

[Melanie]

We'll have to disagree on this one. However I've not killed anybody yet (on the basis it's bad for business) and my designs are used internationally - many with UL certification, so either I'm lucky or I must be doing something right. *smiles*

[Luciano]

Hi,

Ground Fault Circuit Interrupters (GFCI)

A GFCI will trip under a shorted Neutral-Ground condition even
if no load is connected to the circuit -- that is, no load
other than the short between neutral and ground.

Here in Italy the GFCI will trip because of this fuse between
neutral and ground. (See figure 3 and 4 Microchip TB008).

http://img6.picsplace.to/img6/22/fig3tb008.PNG (http://picsplace.to/)

Best regards,

Luciano

[dhouston]

The circuit shown is probably not intended to be plugged into a CFGI nor into any power grid other than in North America.

Here, ground and neutral are not necessarily at the same potential. Recent changes in the National Electric Code call for the ground lead to connect to the center-tap of the utility transformer and for neutral to connect to earth ground at the entrance panel.

I haven't said that fuse should be used in the UK or Europe nor have I, in any way, been critical of Melanie's design skills.

[Luciano]

Here, ground and neutral are not necessarily at the same potential.

The fuse will like that!

Best regards,

Luciano

[Melanie]

Actually Dave you quoted me as "both inaccurate and dangerous".

I challenge that.

I don't care what part of the world you're in, the Fuse in Figure 3 of TB008 is a complete waste of time, offering NO protection - let's repeat that in case anyone missed it first time around - offering NO protection to the User of that circuit. If that Fuse is in or out, the circuit will be LIVE. Microchip have dropped a bollock on this one - so let's direct the "inaccurate and dangerous" where it's needed - the author of TB008.

[Pic_User]

Hi All,

There seems to be a great deal of confusion among hobbyists and new professionals concerning ground and circuit ground.

I stopped calling the “common” connections in electrical / electronic circuits, “ground”, 30 years ago. Most of us, have worked out the dual meaning of ground. On one hand we actually mean earth ground, next we simply mean a common connection in our circuit.

This dual meaning is okay most of the time, but sometimes it causes misunderstandings and even dangerous situations. Transformerless power supplies are a common battle ground for the semantics of the term, “ground”. This is because, the misunderstandings lead to safety problems. Problems that cannot be ignored.

Melanie, as usual is the voice of reason and spot on. The TB008 application note, is right out of the twilight zone. The author, obviously has some confusion about “ground” and “common”.

I post this diagram to help illustrate what Melanie already pointed out.
http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1174&stc=1&d=1163215395

[Luciano]

Hi,

What I have in my house.
http://img10.picsplace.to/18/thumbs/myhouse.PNG (http://img11.picsplace.to/img10/18/myhouse.PNG)
(Click to enlarge).

Best regards,

Luciano

[Acetronics2]

Hi, Luciano

Seems not only for the Englishmen ...

3 Phases ... Your home really is a Castle !!!

Alain

[Luciano]

Hi Alain,

This is what we get here.
Only this option is available.

Our milking machines use three-phase motors.

Best regards,

Luciano

PS: En réalité j'habite dans un petit village au
sud des Alpes. Avec nos amis et voisins italien
on partage la langue et la culture. Ciao!

[sayzer]

...offering NO protection to the User of that circuit. If that Fuse is in or out, the circuit will be LIVE...


In this case, the circuit will protect itself but kill the user !


--------------------------

[JIM A]

The big difference between ground and "common" or "neutral" is the voltage drop that is developed on the neutral wire due to the fact that it has the same current flow as the line conductor (What goes out must return) (Load current x DC resistance of neutral conductor between receptacle and breaker box= Voltage difference between neutral and ground at the receptacle). Normally the voltage drop is neglible except in long circuit runs with higher current loads. The neutral and ground wires are normally connected together (bonded) at the breaker box. I totally agree that the fuse definitely needs to be in the "hot" or "line" or "mains" line to perform a safety function.

[psdayama]

There is a reason I specify X2... and you said it yourself... "they (are specified to) never short accross". If in a Transformerless Power Supply the Capacitor DID short accross it would be very bad news!!! If you don't fit X2's, then yes, your costs are very much reduced, but do you want to take the risk?

This whole thread, I think, is on the brink of veering off!
When U are choosing a very low cost alternative there are many conditions
which are subject to be adhered. first being a circuit a "live" it is not to be
used as any run of mill usage like powering something which can get body
contact. Secondly if "safety" being prime concern then why use "transformerless " supply at all? If I have to get 'risk' of capacitor shorting
eliminated I would rather use a double wound txr and add the cost to safety
of supply!!! Some people are just attached to fancy of some components and
don't look at overall concept of a circuit or device.
How nice it will be if everyone should consider to buy a Merc or BMW as
it won't let U down in middle of road like small car?
For Melani's information we men like to live dangerous but do consult
our purse before risking our reputation in hotel or pub !

[psdayama]

Hi All,

There seems to be a great deal of confusion among hobbyists and new professionals concerning ground and circuit ground.


I post this diagram to help illustrate what Melanie already pointed out.
http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1174&stc=1&d=1163215395

Nice to see the modified diagram but U have missed a vital component.
There should be small resistor like 22 Ohm( Ur LAW) to 47 ohm in serries
with 1uf/250V capacitor ( Melani wont approve of this ).Otherwise in few
days that capacitor will be reduced to open circuit (if of metallised film
type) or get short (if Film foil type) and whole ckt will go up in smoke.
The resistors should be atleast 1/2 watt type ( 1watt better). A high value
resistor like 220K is better placed across capacitor to protect user if he
accidently touches capacitor even when ckt is disconnected from mains.

[Pic_User]

Psdayama,

Thanks for the knowledgeable input. Makes the thread valuable to anyone reading it.
http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1190&stc=1&d=1163524317
-Adam-

[Melanie]

It's not cost saving, but size too...

When this thread started, I put forward an example of a Fan Controller. This fits inside a standard size wall recess which can be as shallow as 15mm. They just don't make transformer bobbins that small - and consider you have to wind around 8,000 turns of 0.01 or 0.008mm wire for a 0.5VA transformer primary - and even then it'll run warm because you really need about 12,000 turns at that rating and you quickly discover that there are minimum sizes for sensible transformer manufacture. Wire that thin is scary stuff to work with as it's so fragile.

Cost of course is a factor. A small Capacitor, a Diode and an Opto-isolator makes for a simple 'Fuse Blown' or 'Power Fail' detect circuit. Whilst a Transformer is nice, it just takes up too much PCB space - and you can't do it for 20 cents.

Finally, my choice of X2 Capacitors is deliberate. If you correctly chose your Capacitor, series Resistors are unnescessary. In all the years I've been designing these kinds of circuits, I've never had any failures of X2 Capacitors. Actually, I can't ever recall having a defective X2 Capacitor in any circuit. Chose your components wisely from reputable sources and you'll not have any troubles.

[shahidali55]

This App note has a lot of good information on transformerless PSU's

http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf

[psdayama]

It's not cost saving, but size too...

When this thread started, I put forward an example of a Fan Controller. This fits inside a standard size wall recess which can be as shallow as 15mm. They just don't make transformer bobbins that small - and consider you have to wind around 8,000 turns of 0.01 or 0.008mm wire for a 0.5VA transformer primary - and even then it'll run warm because you really need about 12,000 turns at that rating and you quickly discover that there are minimum sizes for sensible transformer manufacture. Wire that thin is scary stuff to work with as it's so fragile.

Cost of course is a factor. A small Capacitor, a Diode and an Opto-isolator makes for a simple 'Fuse Blown' or 'Power Fail' detect circuit. Whilst a Transformer is nice, it just takes up too much PCB space - and you can't do it for 20 cents.

Finally, my choice of X2 Capacitors is deliberate. If you correctly chose your Capacitor, series Resistors are unnescessary. In all the years I've been designing these kinds of circuits, I've never had any failures of X2 Capacitors. Actually, I can't ever recall having a defective X2 Capacitor in any circuit. Chose your components wisely from reputable sources and you'll not have any troubles.

Your very first statement is exactly opposite to end one.
Check size of X2 capacitor and normal metallised film capacitor. You will
find X2 atleast 2times bigger than normal. Obivously no manufacturer can
provide X2 at same price so they are atleast 3times expensive.
Metallised film caps which are supplied by UL approved manufacturers will
NEVER short. They may become open with overload. So either way the
argument is pointless! A serries resistor costs less than a cent and it is
wise to limit inrush current.(In all situations). You may have not recieved any complaint with
X2 capacitor as they if not used properly become open circuit SLOWLY. If
anybody notices difference in EMI after 6months or years later, it will be
sheer accident!

I have designed and made a fridge controller (Blind type) with 555 and
similiar transformerless power supply some 3-4 years ago. I have used
normal 680n / 250V capacitor --( our system is 240V 50Hz) and those are
working nicely last 3-4 years and saving 100s of Rs. every month for the
users without any recall.

[sayzer]

...

I have designed and made a fridge controller (Blind type) with 555 and
similiar transformerless power supply some 3-4 years ago. I have used
normal 680n / 250V capacitor --( our system is 240V 50Hz) and those are
working nicely last 3-4 years and saving 100s of Rs. every month for the
users without any recall.


Now it would be a good time to post that schematic here.

BTW; let me remind you that Melanie has a Klingon cloaking device.


----------------------------------

[Melanie]

Take a hundred engineers and give them the same problem, and you're likely to get a hundred different solutions, and each will argue that thiers is the best approach. I think this thread has been pretty much done to death, and there's more than enough information here for anyone but the most inept to design their own. And they, through natural selection when playing directly with the supply mains, will ensure that the standards remain high for the rest of us on the forum.

[dhouston]

Now it would be a good time to post that schematic here.Just do a web search for X-10 schematics. They've been using a metallised film cap and series resistor for many years in the millions of UL approved switches and modules they've sold.http://www.edcheung.com/automa/ws467.gif
http://www.edcheung.com/automa/am486.gif
http://www.edcheung.com/automa/lm465.gif

[Luciano]

Hi,

About the resistors:
http://img6.picsplace.to/img6/23/thumbs/ps_r123.PNG (http://img6.picsplace.to/img6/23/ps_r123.PNG)
(Click to enlarge the picture).

Best regards,

Luciano

[psdayama]

Now it would be a good time to post that schematic here.

BTW; let me remind you that Melanie has a Klingon cloaking device.


----------------------------------
Hi sayzer,
well here is the schematic. Im not so good in drawing like U.
I had a fridge which had thermostat gone bust. So I made this ckt and
saved lot of energy 0.75KWHr /day instead of 5KWHr/day. I also found
that most of fridges have improper settings evenif the thermostat is OK and
there is lot of frost and they consume abt 3-4 KWHr/day. So making a
commercial unit costing Rs.400/- ( $9 appx.) have installed in abt 20-30
homes and they are all saving energy down to 1KWHr/day.
The consumption of unit is less than 05VA and there is no area even feeling
warm. I cant afford to use X2 capacitors in this as that will push cost of unit.

[mvs_sarma]

Hi all
All said and done, we have to accept that what we try to design and implement will be used by us only and that there would not a future occassion to extend the equipment using such PSU to other eqpt, which might create ground loops- a possible shock.

many times we will be pre occupied and would like forget the non isolated psu and take it for granted that we will be safe--

AS SUCH I SUUGEST THAT WE SOULD NOT PRACTICE THIS MODE AT ALL-- ok for academic interest.

[glkosec]

Melanie i was wondering if you could suggest a manufacturer of the VDR used in your design.

[Melanie]

The VDRs (aka Varistors) we use are made by Joyin Co of Taiwan. They work out between 5-15 cents (US) each depending on the flavour. If finding Joyin is a bit elusive in your neighbourhood, then push this link...

http://www.motionnet.com/cgi-bin/search.exe?a=cat&no=2149

[T.Jackson]

Early last year I designed mark II of my PC-Controlled Mains Switch. As with the original design, I opted for a transformer-less solution. 240VAC directly feed to three paralleled X2 class rated caps, then to a full wave bridge powering two shunt regs to produce 5, 12V rails respectively. The entire circuit is optically isolated from the PC at all times.

During development of the Windows-based software which drives it, one of the opto's shorted when my multimeter probe slipped. This turned out to be disastrous! It took out the entire parallel port on my notebook weighing in at the time around $3,000 !!! &*@!()K

The paramedics managed to revive me after several hours. When I came to, had a beer and faced the inevitable reality of my "accident". The notebook was sold at a bargain price to someone who wasn't terribly concerned with the absence of the parallel port.

The project was finally completed on a desktop PC and published in the Silicon Chip magazine last July. Unlike the first version, it was a complete flop. No kits were produced. Double the features but twice the price to build. The system is easily expandable - (up to 8 units can be daisy chained together) - Windows-based software to boot, undoubtedly there will be no MK III, and I'm certainly in no rush again for a cost-effective transformer less solution.

*Always take extreme care when working with mains power!

http://www.siliconchip.com.au/cms/A_107104/article.html

Best regards,
Trent Jackson

[glkosec]

Melanie,
I have tried to emulate your schematic and have found that without the 5V Regulator the ciruit provides 11.7 V, but as soon as I add the regulator or put any kind of load across the circuit it drops to almost nothing. Does anyone have any idea of why this may be happeneing?

[mister_e]

and yet another SIM victim... trust me and Melanie, it's circuit works.

Just for my own curiosity, which SIM did you used?

[T.Jackson]

Interestingly, I designed a similar circuit myself early last year. Few variations with mine. Used two TO220 regs. (LM7805 & LM7812 1 amp packages) Plus I also have a bit more available current due to full wave rectification. This arrangement also makes the circuit a little safer too. The low voltage rails are tied close the Neutral line of the 240VAC mains, so provided you connect to a correctly wired GPO (240VAC socket), most of the circuit is nominally at low potential. (*Claimed by Silicon Chip publications)

Anyhow, I discovered a whole bag full of problems with this circuit on the bench. In theory, it all should have worked. In practice, I found that the 5 & 12V regs were unable to deliver the goods. The circuit was pre-calculated and should have been good for about 1.2W of power- 100mA on the 12V rail. The 12V rail failed to provide even a third of this. I have no explanation to the problem and my thoughts are entirely inconclusive. I discovered only about 20mVPP of ripple in the raw DC rail supplying the regs. This is more than an acceptable level of AC component.

In the end I settled for two zener-based shunts to produce 5 & 12V rails respectively. Circuit works well.

Trent Jackson

[Melanie]

Off-Load the VDR clips the upper voltage from climbing too high. But if your supply is crashing, then you are trying to draw too much current - that actually is an additional safety feature. If you measure the volts across the supply Capacitor, you'll find the whole lot appearing there.

If you just put a 5v Reg (like a 78L05) in circuit and your output crashes, then (a) your Regulator is defective, or (b) your main supply Capacitor is the wrong value for the current you're drawing or itself defective.

That circuit and the values given is good for 10-30mA total. You can measure how good the circuit is by putting some Resistors in series with a meter set to mA across the 11v VDR. Put another voltmeter across the VDR. Now increase the load (ie decrease the Resistance) until the voltage just starts to drop to say to 10v. That will the the maximum (total) useable current from your PSU based on the main Capacitor you're using.

[T.Jackson]

20-30mA?, lets see...

XC = 1/ 2Pie(FC)
= 1 / 6.283185307 x (50Hz x 0.00000047F)
= 1 / 6.283185301 x 0.0000235
= 6772Ω

Now, there's a 470K bleed resistor in parallel with the cap.

XC = 1 / (1/ 6772) + (1 / 470K)
= 1 / ( 0.000147666 + 0.000002127)
= 6675Ω

As you can see the 470K only knocks about 100Ω off the total reactance.
For those who don't know, reactance in an AC circuit is like resistance.

Rectified high voltage rail from RMS value (full wave rectification)

= 240VAC x 1.414
= 339.36VDC 'Peak value, has same heating effect as 240 RMS

(half wave rectification)...

= 0.637 x 339.36VDC
= 216.17VDC Average

Absolute max current (short circuit)

= 216.17VDC / 6675Ω
= 32.38mA

There's a 5V rail being produced from a LM78L05. It's input VCC must always be at least 2.5V greater than the output in order for it to maintain adequate regulation.

Absolute max current @ 5V

= (216.17VDC - 7.5VDC) / 6675Ω
= 208.67VDC / 6675Ω
= 31.26mA

Absolute max power @ 5V

= 31.26mA x 5
= 156mW

Spot on. In the perfect World, Melanie's supply should be good for about 30mA.
Component tolerances often compromise the accuracy of calculated events. Such is life.

Trent Jackson

[T.Jackson]

Want more power from this circuit? No problem...

Clearly, the third calculation - (full wave rectified high voltage rail from RMS value) - shown in the previous post tells us that rectifying both sides of the sine wave is beneficial.

Lets see how much current we can squeeze out using full wave rectification.

XC = 1/ 2Pie(FC)
= 1 / 6.283185307 x (50Hz x 0.00000047F)
= 1 / 6.283185301 x 0.0000235
= 6772Ω

Now, there's a 470K bleed resistor in parallel with the cap.

XC = 1 / (1/ 6772) + (1 / 470K)
= 1 / ( 0.000147666 + 0.000002127)
= 6675Ω

High voltage DC rail - (full wave rectification)...

= 240VAC x 1.414
= 339.36VDC

Absolute max current (short circuit)

= 339.36VDC / 6675Ω
= 50.84mA

Absolute max current @ 5V

= (339.36VDC - 7.5VDC) / 6675Ω
= 331.86VDC / 6675Ω
= 49.71mA

Absolute max power @ 5V

= 49.71mA x 5
= 248mW

% More power

(248mW / 156mW) x 100
= 59%

That's quite a significant increase. You could also push things even further by
decreasing XC - use a larger cap or parallel a few together. Practical limitation of such a circuit is about 1W. Takes up too much real estate and defeats the cost-effectiveness of it otherwise.

All told, it's better to use a transformer...

Trent Jackson

[T.Jackson]

Short answer is because it's much safer. But there are also other advantages
as I will spell out here...

1. Cleaner power, typically around 5mVPP of ripple - (AC component) - with the usage of sufficiently sized reservoir caps. General rule of thumb: 10uF for every 5mA of current. So, at 1 Amp you want at least 2200uF.

2. Well designed transformers are extremely efficient. Typically 95% or better.

3. Power transformers are reasonably immune to interference.

4. Isolation transformers are critical for the novice for when it comes to taking
high voltage measurements on an oscilloscope. In fact, no one should really take measurements without using it.

Trent Jackson

[Melanie]

I agree that it's better for hobbyists to include a transformer, but I do disagree with some things you write...

A Transformer will RARELY hit 95% efficiency. The reality is a figure somewhere between ZERO (yes ZERO percent efficient!!!) and somewhere approaching 90%. Let me explain...

The higher the frequency, the greater the transfer ratio between the Primary and Secondary. Hence, the most efficient are Switching Power Supplies which usually run at a few tens of kHz. However at the frequencies of the incomming AC Mains Supply (ie 45-65Hz depending where on the planet you happen to be), the efficiency is governed by the amount of iron (and quality of iron) you can shove into your transformer. Generally, the more iron, the greater the transfer ratio which conversely applies the law that the smaller the transformer the more inefficient it will be.

Now for this ZERO percent efficiency (100% waste of energy) bit...

The efficiency of a Transformer is simply calculated as Power Out divided by Power In. Actually we can reduce that to just Current In viz Current Out with regard to the turns ratio. So in a 100% efficient Transformer, 1A at 12V OUTPUT should equal 50mA at 240V INPUT as there's a 20:1 reduction ratio. Sadly, take any Transformer out of your parts box, put a series Ammeter with the Primary and plug it in completely OFF-LOAD. You will have a standing current... ie you are sucking energy in, but not taking any out. All this is doing is heating up the core, and it's worse the smaller the Transformer becasue of the smaller amount of iron. So from this you can gather, that the less current we draw from a Transformer from it's optimum design point, the more inefficient it will be. If a Transformer is designed to be most efficient at say 100mA, then any current draw less than that is heading towards the ZERO efficiency point when it is completely off-load. Likewise if you exceed the optimum design point (which is usually just below the Magnetic Saturation Point of the core), you then risk driving the core into saturation and again your efficiency plumets as all you end up doing is pumping more current in which just heats up the core.

From the above, you can gather that a Transformer is really the root cause of global warming as before it was invented we didn't have the problem!

Notwithstanding that, it does give you galvanic isolation and as proof that countless hobbyists are alive today posting silly questions on internet forums that otherwise wouldn't be, is it's most commendable feature.

Finally, there is a place for everything... even the humble Transformerless design. For small current supplies, the size and cost beats the transformer every time. For a typical Washing Machine or Freezer or Cooker or Microwave or Boiler or Central Heating or Air Conditioning or ..., or... or (add your own domestic appliance to the list) controller, losing the transformer would save about 50 cents (and save some weight too), multiplied by a typical 300,000 production run for the design and you can do the math.

As for hobbyists that play with mains... well we all gotta die sometime (it's a hereditary trait), just some sooner than later...

[T.Jackson]

You will have a standing current... ie you are sucking energy in, but not taking any out. All this is doing is heating up the core, and it's worse the smaller the Transformer becasue of the smaller amount of iron. So from this you can gather, that the less current we draw from a Transformer from it's optimum design point, the more inefficient it will be. If a Transformer is designed to be most efficient at say 100mA, then any current draw less than that is heading towards the ZERO efficiency point when it is completely off-load. Likewise if you exceed the optimum design point (which is usually just below the Magnetic Saturation Point of the core), you then risk driving the core into saturation and again your efficiency plumets as all you end up doing is pumping more current in which just heats up the core.


I think you've have described the term "Eddy loss current" ?

Just having a quick flick through some of my old college notes, I have %95 written down as a typical rate of efficiency...

Trent Jackson

[T.Jackson]

Extract of taken from college notes 16/06/98

Transformers are very efficient components. Typically they boast efficiency levels of better than 95%. This means that only a mere 5% of the total power is lost. Consumed / wasted in the form of heat. Transformers work on the principle of self-induction, and because of this, there is almost perfect isolation between the primary & secondary windings. With this infinite impedance between the two windings, power transformers are deemed very safe.

By Faraday's law of magnetic induction, when an alternating current is applied to the primary windings, a voltage will be self-induced in the secondary. These windings must be close wound. Secondary power is introduced from the primary because of the changing magnetic field between the two.

When a voltage is applied to the primary a magnetic field is set up, and if the frequency is high enough the primary windings will begin to radiate its power to the secondary. The voltage that is produced on the secondary is directly proportional to the turns ratio.

In short, minus all the math, magnetism theory, that's how a transformer works.

Trent Jackson

[Melanie]

Time college lecturers got out a bit more and got dose of the real world.

In theory everything is lovely.

In practice I challenge you to take ANY transformer you've got, and plot Input Current & Output Current from off-load, thru to full rated load in say 5% steps. From that you can calculate and plot a graph of efficiency to prove my point. Enjoy the experience. Then take the efficiency graph and tell your college that life in the real world is far from theory - so far that it's not even close!

For example... let's try to prove the theory of the International Ampere (you know Amps... it's that unit of measurement all of us use every day of our lives... so really we should try to prove the definition before we use it)...

Quote from my University Notes "That constant current which when flowing down two straight parallel conductors of infinite length and negligible cross section, separated by a distance of one meter in a vacuum, produces a force between them of 2 × 10-7 newtons per meter of length."

You get full marks for reciting this like a Parrot in your exam... but let's try to prove it...

1. You go down to your local store and ask for two drums of cable of infinite length and negligible cross-section... you lug them home...

2. You borrow the space shuttle and unravel them in the (supposed) vaccum of space from planet Earth out towards infinity.

3. When you've reached infinity, you join the far ends together and come home.

4. Then you hook up the wire to your PSU with a DVM in series switched to the famous "Newtons per Metre Length" setting on the dial.

5. Take a second DVM in series and switch it to Amps.

6. When DVM No.1 shows 2x10-7 Newtons the other should be showing 1.0000 Amps (assuming it's in calibration).

Worked when I tried it...

[T.Jackson]

Unfair game here. Someone has a UNI degree...

Where's the referee?

I'm in the process of doing a degree in Applied Science In Information Technology. Only done two years of electronics in college. I'm only at trade level
with most of the theory.

Cheers

Trent Jackson

[Pic2008]

Can someone explain to me how the 240VAC after rectification can come down to +12VDC?

[financecatalyst]

Can someone explain to me how the 240VAC after rectification can come down to +12VDC?

Are you kidding me? I have enjoyed the arguments a lot, and from the first post to the third last (subtracting yours & mine of course), I have come across 2 to 4 circuits all making 12VDC. Check them out going back few posts (Remember to use X2 capacitors with mains - else Melanie would not like it - in case she comes across your circuit :eek: )

[comwarrior]

Strangely, i have a design for a transformer-less PSU in the making...
My reason for not using a transformer is because to have a transformer that drops 110V and 240V down to a more usable voltage and supply the current i need would be massive and it costs >£50 each...

I'm not going to post details of the PSU because i intend on filing for international copyright.
The reason for this is because it will handle any single phase voltage, frequency and amount of noise (or noise only) you can throw at it.
It will even operate in a brown out with sustained unstable voltages as low as 24V (maybe lower).
It can also handle stepped AC, Square wave and saw tooth signals provided it is alternating...

Also, Mel is absolutely right, that AN is written for one purpose and one purpose only... TO KILL PEOPLE!

[rmteo]

Something like this PSAA60W-120 (http://www.phihongusa.com/html/psaa60w_60w_cec_adapter.html)
http://www.phihongusa.com/assets/images/PSAA60W.jpg
AC Input Voltage Rating: 100 to 240V AC
AC Input Frequency: 50 to 60Hz
Input Current: 1.6A at 100V AC, 0.7A at 240V AC
Output: 60W
Efficiency: 85% average

[comwarrior]

transformer-less... the above has a transformer, i can tell because of the input specification.

Here in the UK the current code for mains wiring dictates the use of an ELCB.
Earth Leakage Circuit Breaker. If more than 50mA flows up or down the earth wire the ELCB will trip isolating both live and neutral.
every time I've diagnosed wiring faults, their has always been a 50 to 60 V AC difference between earth and ether neutral or live...
If you use an isolation transformer you can connect the negative after rectification to ground. This is what most PC PSU's do.

edit:
That efficiency rating is crap!