Author Topic: Improving small unregulated power supplies  (Read 5113 times)

0 Members and 1 Guest are viewing this topic.

Offline soldarTopic starter

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Improving small unregulated power supplies
« on: September 22, 2019, 07:15:57 pm »
I have crates full of these old wall warts and similar PSUs. While I have many SMPS fail the old transformer-diode bridge - capacitor type seem to last forever.

The main objection is that they are unregulated and they are a pain to match to the load. If the load is not stable the voltage can be all over the place.

I often end up using a PSU with a lower nominal voltage because at the current I need the voltage it outputs is higher than the nominal voltage. Testing each time I need one is a pain.

Series regulation is not easy or convenient because there is really not enough headroom.

I have used in the past parallel regulation with a zener diode or zener plus transistor. It is a waste of energy but the amount is very small and the addition can be placed in the output cable or receptor without needing to open the enclosure which sometimes cannot be done without breaking it and there is no space anyway.

I am playing with a small transformer which I guess we could call "12 V , 200 mA". The following table gives the voltages at different currents.

Code: [Select]
mA	V
0 19.4
10 18.9
15 18.6
20 18.4
30 17.9
50 17.0
75 16.0
100 15.0
125 14.1
150 13.3
175 12.6
200 11.9
225 11.3
250 10.8

So, let's say I want to limit the voltage to 14 V max. I would need to sink 125 mA @ 14 V which is a bit under 2 W.  A zener and transistor can handle that easily.

This prevents up to 20 V building up in the capacitor and being dumped suddenly into whatever device is connected.

I'd like to hear thoughts and ideas on this topic.

BTW, I actually measured a number of points but then I put them into Excel and I obtained the following equation

V = 19.359 - 0.0492 I(mA) + 0.00006 I(mA)^2

So the table is an idealized table.

« Last Edit: September 23, 2019, 08:09:58 am by soldar »
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 21611
  • Country: us
Re: Improving small unregulated power supplies
« Reply #1 on: September 22, 2019, 07:20:11 pm »
I typically just build a switching regulator into the project and then use whatever old wall wart is reasonably suitable. My broadband router for example has a switching regulator inside it and originally came with a 12V switching type wall wart. I think I went through 2 or 3 of those before I replaced it with an old unregulated transformer type and it has been fine for years. They are not the most efficient things but they are much more reliable than the low cost switchmode ones.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 20363
  • Country: gb
  • 0999
Re: Improving small unregulated power supplies
« Reply #2 on: September 23, 2019, 03:09:53 pm »
I've not noticed a significant difference in reliability. I've hardly had any problem with switched mode wall warts failing and I've also had the old transformer type fail.

My advice would be to simply ditch the old transformer type of supply, especially in equipment which is left on all the time. Even if it is slightly less reliable, it will probably work out cheaper, due to the amount of power saved. If you keep having problems with switched mode power supplies failing, then it's a problem with high voltage spikes.
 

Online Ian.M

  • Super Contributor
  • ***
  • Posts: 13217
Re: Improving small unregulated power supplies
« Reply #3 on: September 23, 2019, 04:05:13 pm »
I really wouldn't advise shunt regulation - if the mains supply voltage rises, something is likely to burn up and if the PSU doesn't have a thermal fuse in series with its primary, it could literally catch fire.
Needing a few volts extra headroom is the cost of doing business if you need to stabilise the output from a small unregulated linear PSU.


That nominal 12V unregulated PSU would make a decent feed for a 9V linear regulator.  At its nominal max load current you've got 2.9V headroom, and should still have 1.7V headroom if the mains supply is 10% low. 
 

Offline soldarTopic starter

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Improving small unregulated power supplies
« Reply #4 on: September 23, 2019, 06:33:20 pm »
I've not noticed a significant difference in reliability. I've hardly had any problem with switched mode wall warts failing and I've also had the old transformer type fail.


My experience is quite different and it makes sense. SMPS are much more complex and the components are much more stressed.

Just a few days ago my wife's Samsung's phone charger stopped working. It was the second one to stop working. They are tiny and have some complex charging system with two voltages. Since she spends a lot of time in the car she's just decided to charge it while she's driving and not buy a new charger for the time being.  Maybe a non-Samsung, non-fancy fast charging, just regular more bulky USB would last longer. She had the same experience with her earlier tiny Apple chargers. Did not last.  I have them in a box with the idea of looking into repairing them but they are tiny and it's not worth it.

I wish they would make things more substantial and not try to miniaturize everything to the point where it has to fail. One of these small SMPS should be eternal.

About a year ago I was woken up in the middle of the night by a small explosion in my room.  A SMPS wall wart had exploded. No fire, nothing. Just a small explosion and the thing was dead.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline Gyro

  • Super Contributor
  • ***
  • Posts: 10174
  • Country: gb
Re: Improving small unregulated power supplies
« Reply #5 on: September 23, 2019, 07:05:46 pm »
My advice would be to simply ditch the old transformer type of supply, especially in equipment which is left on all the time. Even if it is slightly less reliable, it will probably work out cheaper, due to the amount of power saved. If you keep having problems with switched mode power supplies failing, then it's a problem with high voltage spikes.

I wouldn't bin them all. Keep some for projects needing 'quiet' supplies and ones where Y-cap leakage from SMPS types is a pain (isn't that most of them!  :()

7.5 - 9V bricks were typically intended for 7805 regulation to 5V and tend to have good enough regulation  to keep regulator dissipation relatively constant. The higher voltage ones are good for audio stuff.

I have similar experience with reliability, or at least longevity. If properly rated, they tend to last forever.
« Last Edit: September 23, 2019, 07:08:02 pm by Gyro »
Best Regards, Chris
 

Offline soldarTopic starter

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Improving small unregulated power supplies
« Reply #6 on: September 23, 2019, 07:10:30 pm »
I really wouldn't advise shunt regulation - if the mains supply voltage rises, something is likely to burn up and if the PSU doesn't have a thermal fuse in series with its primary, it could literally catch fire.

I have used shunt regulation for very small power supplies and never had a problem. I have never seen serious overvoltage here. If it did happen I bet a lot of appliances would be damaged and my small circuits would be the least of my worries.  A very small transformer has substantial output resistance and just a zener works well. It only conducts during a very small part of the cycle and dissipates little power. Again, this is for very small transformers with high output resistance. I am talking about, say, under 12 V 200 mA. It does not make any sense once you get into higher power.


Needing a few volts extra headroom is the cost of doing business if you need to stabilise the output from a small unregulated linear PSU.
Well, I totally agree and if I design anything from scratch I will do it that way.

The most common nominal voltage of the PSUs and of the devices is 12 V. I could stabilize the PSUs to a lower voltage but I do not have that much need for lower voltages.  The issue is that I have several crates of the old transformer type power supplies and I try to use them but every time it is a pain having to measure currents and voltages and trying to get something that matches.

The ideal receptor has stable current consumption and an unregulated PSU can be matched but if the receptor's use varies then you need an active regulator. In the past I have had this issue with circuits that switch relays and the coil of the relay uses much more current than the controlling circuit.

As I say, I am mainly trying to use the PSUs I already have; not trying to design or build new ones.




All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 20363
  • Country: gb
  • 0999
Re: Improving small unregulated power supplies
« Reply #7 on: September 23, 2019, 08:30:02 pm »
I've not noticed a significant difference in reliability. I've hardly had any problem with switched mode wall warts failing and I've also had the old transformer type fail.


My experience is quite different and it makes sense. SMPS are much more complex and the components are much more stressed.
Not necessarily. A properly designed switched mode power supply can be more reliable than the old transformer type, because it won't run as hot. It will also have over current protection/limiting, so won't overheat, like the old transformer types do resulting in the single shot thermal fuse failing.

Quote
Just a few days ago my wife's Samsung's phone charger stopped working. It was the second one to stop working. They are tiny and have some complex charging system with two voltages. Since she spends a lot of time in the car she's just decided to charge it while she's driving and not buy a new charger for the time being.  Maybe a non-Samsung, non-fancy fast charging, just regular more bulky USB would last longer. She had the same experience with her earlier tiny Apple chargers. Did not last.  I have them in a box with the idea of looking into repairing them but they are tiny and it's not worth it.
That sounds very strange. I thought all modern phones just worked at 5V?

Quote
I wish they would make things more substantial and not try to miniaturize everything to the point where it has to fail. One of these small SMPS should be eternal.
Just stick to decent branded USB chargers and you should be fine. The 12V ones used to power routers, I've also found to be very reliable.

Quote
About a year ago I was woken up in the middle of the night by a small explosion in my room.  A SMPS wall wart had exploded. No fire, nothing. Just a small explosion and the thing was dead.
That was probably the smoothing capacitor and there's one of those in the old transformer type of power supplies too. I've not experienced it myself, but I've heard stories about old transformer power supplies melting down. Probably because they had too little iron and copper and didn't conform to the appropriate safety standards i.e. the lack of a thermal fuse. Cheap, poorly designed junk won't last long irrespective of what technology it's based on. One of the best old transformer wall warts I've had was a Tandy/Radioshack brand. It was the one with the voltage selector switch and had a resettable bi-metal strip thermal cut-out, for safety, as well as reliability.

My advice would be to simply ditch the old transformer type of supply, especially in equipment which is left on all the time. Even if it is slightly less reliable, it will probably work out cheaper, due to the amount of power saved. If you keep having problems with switched mode power supplies failing, then it's a problem with high voltage spikes.

I wouldn't bin them all. Keep some for projects needing 'quiet' supplies and ones where Y-cap leakage from SMPS types is a pain (isn't that most of them!  :()

7.5 - 9V bricks were typically intended for 7805 regulation to 5V and tend to have good enough regulation  to keep regulator dissipation relatively constant. The higher voltage ones are good for audio stuff.

I have similar experience with reliability, or at least longevity. If properly rated, they tend to last forever.
Yes, I suppose the old transformer power supplies still have their uses. A low drop-out regulator can be used for minimal power dissipation. The AC output type are also very handy because they can be used with a voltage doubler circuit to get a dual rail supply for powering op-amp circuits.

One issue I've found is the smoothing capacitor is almost always far too small. It's often something stupid like 2200μF in for a 1A unit, which will result in a huge ripple. I slap in a 4700μF capacitor before the regulator in anything run from one of those old transformer PSUs and the capacitor should be rated to 25V, for reliability's sake.
 

Offline rcbuck

  • Frequent Contributor
  • **
  • Posts: 355
  • Country: us
Re: Improving small unregulated power supplies
« Reply #8 on: September 23, 2019, 08:36:04 pm »
I would just use a resistor, zener, and capacitor on the base of the transistor and run it in pass mode. That has the advantage of the transistor multiplying the effective capacitor filtering value.
 

Offline Gyro

  • Super Contributor
  • ***
  • Posts: 10174
  • Country: gb
Re: Improving small unregulated power supplies
« Reply #9 on: September 23, 2019, 09:32:25 pm »
One issue I've found is the smoothing capacitor is almost always far too small. It's often something stupid like 2200μF in for a 1A unit, which will result in a huge ripple. I slap in a 4700μF capacitor before the regulator in anything run from one of those old transformer PSUs and the capacitor should be rated to 25V, for reliability's sake.

Oh yes, I place a premium on the ones that have case fixing screws rather than being ultrasonically welded shut. Quite a surprising number (of UK ones) do. Always worth checking when scanning ebay.
« Last Edit: September 23, 2019, 09:34:06 pm by Gyro »
Best Regards, Chris
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 21611
  • Country: us
Re: Improving small unregulated power supplies
« Reply #10 on: September 23, 2019, 09:32:35 pm »
Most of the small consumer grade switching wall warts are not what id call "properly designed", they work ok but they rarely last me more than a couple years in 24/7 service and they tend to be RF bombs. Yes some are ok, but far from all of them.

I have had probably a dozen of them fail over the last decade compared to zero failures of the iron transformer type in my lifetime. These days I save all the transformer ones because they're hard to get anymore.
 
The following users thanked this post: Ian.M

Offline soldarTopic starter

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Improving small unregulated power supplies
« Reply #11 on: September 23, 2019, 10:44:36 pm »
A properly designed switched mode power supply can be more reliable than the old transformer type, because it won't run as hot. It will also have over current protection/limiting, so won't overheat, like the old transformer types do resulting in the single shot thermal fuse failing.

I disagree. The old type are simpler and more rugged. I have linear power supplies that have been going for decades. It seems your experience is unusual.

I have no doubt SMPS can be built to last but the small ones are not built like that, they are built to minimize size and budget. The public prefers a tiny charger even though unreliable to a bulkier but reliable one.

That sounds very strange. I thought all modern phones just worked at 5V?

Um, no. https://www.digitaltrends.com/mobile/how-does-fast-charging-work/

Now, build a complex SMPS and make it this size and it is a recipe for unreliability.

Just stick to decent branded USB chargers and you should be fine.

The ones that failed were original Samsung and Apple. Again, look at the design and size of the thing.

Your experience that SMPS warts are more reliable seems to be contrary to everybody elses's, inclusing mine.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 20363
  • Country: gb
  • 0999
Re: Improving small unregulated power supplies
« Reply #12 on: September 24, 2019, 11:26:14 am »
One issue I've found is the smoothing capacitor is almost always far too small. It's often something stupid like 2200μF in for a 1A unit, which will result in a huge ripple. I slap in a 4700μF capacitor before the regulator in anything run from one of those old transformer PSUs and the capacitor should be rated to 25V, for reliability's sake.

Oh yes, I place a premium on the ones that have case fixing screws rather than being ultrasonically welded shut. Quite a surprising number (of UK ones) do. Always worth checking when scanning ebay.
I'm talking about the unregulated type. No need to open it up, just put the capacitor on the PCB of the device you're designing.

Your experience that SMPS warts are more reliable seems to be contrary to everybody elses's, inclusing mine.
I'd hardly call a thread with a few people commenting concrete proof either type of PSU being more reliable. It's anecdotal evidence which means nothing. To prove one way or another, we need hard, reliable, mean time before failure data.

Quote
The public prefers a tiny charger even though unreliable to a bulkier but reliable one.
It's probably more to do with energy saving legislation. The old transformer PSUs have too higher idle current to meet the current EU regulations, hence why switched mode power supply power supplies are now the norm.
Quote
The ones that failed were original Samsung and Apple. Again, look at the design and size of the thing.
I've no experience with Samsung, but with Apple it tends to be the cable which fails, nothing to do with the actual power supply; I've had that happen to me several times.
Quote
Your experience that SMPS warts are more reliable seems to be contrary to everybody elses's, inclusing mine.
No, I didn't say that. I've found modern switched mode power supplies to be no better, nor no worse, than the old transformer type. In my experience they are equal, reliability wise.
 

Offline soldarTopic starter

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Improving small unregulated power supplies
« Reply #13 on: September 24, 2019, 01:11:59 pm »
I'd hardly call a thread with a few people commenting concrete proof either type of PSU being more reliable. It's anecdotal evidence which means nothing. To prove one way or another, we need hard, reliable, mean time before failure data.

Right now I got in my hand something hard, reliable and mean telling me all I need to know.


Quote
The public prefers a tiny charger even though unreliable to a bulkier but reliable one.
It's probably more to do with energy saving legislation. The old transformer PSUs have too higher idle current to meet the current EU regulations, hence why switched mode power supply power supplies are now the norm.

I was not comparing SMPS with old style. What I meant is that I have no doubt they could design and build a SMPS for a phone which would last for many years. What is apparent is they cannot do that and make it fit in a one inch cube and between reliability and miniaturization they choose the one that sells.


I've no experience with Samsung, but with Apple it tends to be the cable which fails, nothing to do with the actual power supply; I've had that happen to me several times.

Nope, I have fixed many cables but I have a few "one inch cube" SMPS which failed. I don't know why I keep them because I am pretty sure I will never attempt to repair them. 
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 21611
  • Country: us
Re: Improving small unregulated power supplies
« Reply #14 on: September 26, 2019, 05:29:03 am »
Efficiency regulations is the reason the iron transformers have gone away. The small iron wall warts are not very efficient, only about 50% IIRC, they are "impedance protected" by having thin wire windings that cannot supply enough energy to catch fire if there is a short but this also leads to high losses and significant sag under load.
 

Offline basinstreetdesign

  • Frequent Contributor
  • **
  • Posts: 466
  • Country: ca
Re: Improving small unregulated power supplies
« Reply #15 on: September 26, 2019, 07:04:14 am »
The biggest problem for me is the absence of ground out of the WW.  This has caused me problems in making small signal generators for the bench.  For instance I made a ovenized 10 MHz source a couple of years ago and used what I thought was a good WW to power it.  It did power it well since the design had 7X05/7X12 inboard.  The problem was that the output signal had some 60 Hz added to it that when connected to other equipment would bleed 60Hz and harms into my counter/scope/audio spec an. etc.
Now I am making a synthesized signal generator to replace it and will use a 3-wire grounded cord and a linear supply with Xfrmr to try to avoid that.
It bugs me that I cannot justify using up a spare WW even when I have one with suitable V/I output and I have about 25 lbs of the things in a box doing nothing. :palm:
STAND BACK!  I'm going to try SCIENCE!
 

Offline soldarTopic starter

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Improving small unregulated power supplies
« Reply #16 on: September 26, 2019, 07:50:51 am »
Efficiency regulations is the reason the iron transformers have gone away. The small iron wall warts are not very efficient, only about 50% IIRC, they are "impedance protected" by having thin wire windings that cannot supply enough energy to catch fire if there is a short but this also leads to high losses and significant sag under load.

I do not think "efficiency regulations" have much, if anything, to do with it.  The losses in very small units, say under 5 or 10 W, are negligible. More powerful units get too big and heavy. A 50 or 100 W SMPS is very manageable but it would be too heavy with a mains transformer.

In the very small units range I believe the main reason is economic. SMPS are cheaper and provide stable regulated output. If you want to add a linear regulator to a conventional PSU then it gets too big, too heavy and too expensive.

Another point in favor of SMPS is wide range voltage input.

In summary, in the very small power range, say under 10 W, I believe market forces are the reason SMPS have replaced conventional PSUs and not any regulations (which I have not seen or heard of).
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline soldarTopic starter

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Improving small unregulated power supplies
« Reply #17 on: September 26, 2019, 07:53:16 am »
The biggest problem for me is the absence of ground out of the WW. 

I do not understand this. Adding a ground to a floating PSU is trivial. Am I missing sumpting?
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline Gyro

  • Super Contributor
  • ***
  • Posts: 10174
  • Country: gb
Re: Improving small unregulated power supplies
« Reply #18 on: September 26, 2019, 09:00:03 am »
One issue I've found is the smoothing capacitor is almost always far too small. It's often something stupid like 2200μF in for a 1A unit, which will result in a huge ripple. I slap in a 4700μF capacitor before the regulator in anything run from one of those old transformer PSUs and the capacitor should be rated to 25V, for reliability's sake.

Oh yes, I place a premium on the ones that have case fixing screws rather than being ultrasonically welded shut. Quite a surprising number (of UK ones) do. Always worth checking when scanning ebay.
I'm talking about the unregulated type. No need to open it up, just put the capacitor on the PCB of the device you're designing.

I disagree, there's no point in losing an unregulated PSU brick just because its cheap overstressed internal electrolytic (is about to) spill its guts. You can put snubber caps on the rectifiers too - although I've found that most reputable ones already have them fitted.

Also, you have the opportunity to convert them to AC/AC, sometimes centre tapped.
Best Regards, Chris
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 20363
  • Country: gb
  • 0999
Re: Improving small unregulated power supplies
« Reply #19 on: September 26, 2019, 04:03:12 pm »
Gyro, I see your point, but it's not worth my time or effort opening up a linear wall wart to replace the capacitor.

The biggest problem for me is the absence of ground out of the WW.  This has caused me problems in making small signal generators for the bench.  For instance I made a ovenized 10 MHz source a couple of years ago and used what I thought was a good WW to power it.  It did power it well since the design had 7X05/7X12 inboard.  The problem was that the output signal had some 60 Hz added to it that when connected to other equipment would bleed 60Hz and harms into my counter/scope/audio spec an. etc.
Now I am making a synthesized signal generator to replace it and will use a 3-wire grounded cord and a linear supply with Xfrmr to try to avoid that.
It bugs me that I cannot justify using up a spare WW even when I have one with suitable V/I output and I have about 25 lbs of the things in a box doing nothing. :palm:
Was it the transformer type or SMPS? Presumably the latter, in which case, it sounds like you've had problems with the leakage through the Y capacitor. This shouldn't be an issue for low impedance nodes, but can be a problem for low level high impedance stuff. The easiest way to resolve this is to connect the 0V of the circuit you're powering from the wall wart, to the other devices connected to its output. It does surprise me you had problems with a signal generator, because the wall wart's ground would normally go the the output ground, which would be connected to the device under test.
 

Offline soldarTopic starter

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Improving small unregulated power supplies
« Reply #20 on: September 26, 2019, 07:41:49 pm »
Oh, I forgot to mention that I have used a few transformer PSUs to build simple battery chargers. Provide a battery holder and a resistor and you have a battery charger. I have built a few of these for friends when they complained their fast & furious & intelligent chargers were damaging their batteries. A simple slow charger is much better.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 21611
  • Country: us
Re: Improving small unregulated power supplies
« Reply #21 on: September 27, 2019, 06:25:51 pm »
I do not think "efficiency regulations" have much, if anything, to do with it.  The losses in very small units, say under 5 or 10 W, are negligible. More powerful units get too big and heavy. A 50 or 100 W SMPS is very manageable but it would be too heavy with a mains transformer.

In the very small units range I believe the main reason is economic. SMPS are cheaper and provide stable regulated output. If you want to add a linear regulator to a conventional PSU then it gets too big, too heavy and too expensive.

Another point in favor of SMPS is wide range voltage input.

In summary, in the very small power range, say under 10 W, I believe market forces are the reason SMPS have replaced conventional PSUs and not any regulations (which I have not seen or heard of).

It is absolutely about regulations, at least in the USA. The old iron transformer type is typically around 50% which is not compliant.

https://www.eesi.org/articles/view/new-energy-efficiency-standards-for-small-power-adapters-will-make-a-big-di
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 20363
  • Country: gb
  • 0999
Re: Improving small unregulated power supplies
« Reply #22 on: September 27, 2019, 08:18:56 pm »
 

Offline soldarTopic starter

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Improving small unregulated power supplies
« Reply #23 on: October 13, 2019, 09:20:06 am »
I am seriously thinking of buying a bunch of these regulators I saw mentioned in another thread and just making them into regulated PSUs at whatever voltage each one can handle.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 20363
  • Country: gb
  • 0999
Re: Improving small unregulated power supplies
« Reply #24 on: October 15, 2019, 11:17:47 am »
I am seriously thinking of buying a bunch of these regulators I saw mentioned in another thread and just making them into regulated PSUs at whatever voltage each one can handle.
What about reliability?
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf