What is special about a wall wart transformer

** The big one is user safety.

Wall wart transformers have no safety ground so must be designed and built to class 2 ( double insulation) standards.

The isolation between primary and secondary winding must survive any possible overload and other known events that might damage the insulation and render the secondary live at AC supply voltages. These days, the use of extra fire resistant insulation and suitable, internal thermal fuses connected in the primary circuit is sufficient - along with more than usual clearance and creepage distances across and through insulation.

Compared to some diabolical SMPS designs on sale, they are extremely safe.

.... Phil

I suspect that at least some are also intentionally built with some leakage inductance or high-resistance secondaries, to allow for safe short-circuit operation.

Oh, I'm sure that if the world still wanted big clunky wall-warts then the Chinese would figure out how to carve out 1/20 of a penny of the cost by making them unsafe.

--
Tim Wescott 
Control systems, embedded software and circuit design 
I'm looking for work!  See my website if you're interested 
http://www.wescottdesign.com

You make it sound like it's a plot to destroy democracy. It's not like crappy, unsafe goods were never made here.

--

Rick C

Like every "All American Five" radio sold, the old timers called them "suicide boxes"

The approved ones from good makers in China are extremely good- I have bought thousands of 9V/200mA UL/CSA linear adapters. Every material and component is specified and approved. Facilities are inspected by UL and you can get third party inspections for shipments.

Of course if you buy something unapproved from Ali or eBay you get what you get and it just might kill you.

--sp

--
Best regards,  
Spehro Pefhany

Some wall warts are iron core transformers - but they're going out of fashion fast.

Most are a very compact SMPSU with much better regulation than an iron core.

Either way - very few have a safety earth, and must have a "double insulated" rating.

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** Inherently short circuit proof transformers exist, but are not seen in common wall wart supplies. They have poor regulation and cost more to make. ** Garbage, the Chinese have made hundreds of millions of transformer wall warts that are all very safe. The same cannot be said of SMPS types.

Regulators in Europe and most places have effectively banned DC output, transformer wall warts on a false pretext.

You need to get out more .....

...... Phil

Design wise, if you are making a big TV set or 200 WPC audio amp, you simpl y must design your own power supply. Wall warts simply cannot handle it usu ally.

This entails that when designing the layout you must consider what happens if the thing gets run over by a bus, flooded with seawater and all sorts of things. That is for the UL in the US, which is not mandatory, but if your house burns down and they find that a non-approved piece of equipment did i t there will be hell to pay. I Europe it is the CE and it might be mandator y, I don't know.

You have to think if your SMPS board breaks this way or that way, at all co sts do not let the hot touch the cold. This comes down to where you place t he components on the board, and even where you can put the mounting screws.

But when all you need is 2 volts at 1 amp, it is much cheaper and easier to use a wall wart. You have no worries with the UL or CE, just design your c ircuit. You don't have to worry about ground faults or any of that. And if you need a split supply, like +/-5 or whatever, there is circuitry for that and voltage conversion is getting cheap.

ply must design your own power supply. Wall warts simply cannot handle it u sually.

s if the thing gets run over by a bus, flooded with seawater and all sorts of things. That is for the UL in the US, which is not mandatory, but if you r house burns down and they find that a non-approved piece of equipment did it there will be hell to pay. I Europe it is the CE and it might be mandat ory, I don't know.

costs do not let the hot touch the cold. This comes down to where you place the components on the board, and even where you can put the mounting screw s.

to use a wall wart. You have no worries with the UL or CE, just design your circuit. You don't have to worry about ground faults or any of that. And i f you need a split supply, like +/-5 or whatever, there is circuitry for th at and voltage conversion is getting cheap.

12 volts

The TLE2426 "Rail Splitter" provides a virtual ground and can source or sink about 20 mA.

Thank you,

--
Don Kuenz KB7RPU

A TCA0372 can source or sink over an amp, and is cheaper than the TLE2426. You do need an extra couple of resistors. ;)

It would sure be nice if they had a single version of it in a DPAK.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

some new Samsung TVs are powered by an external lap top like brick.

Seems like a cost effective way to deal with regulatory issues re safety and EMI.

m

you mean iron core transformer types, or also SPS types?

what was the false pretext, energy efficiency?

m

In crappy, unsafe factories. Those jobs were all exported to China, and we want them back!

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com 

I'm looking for work -- see my website!

** Iron core, of course.

** It was off load power consumption.

The standards were deliberately set so almost no iron transformer could comply while allowing recent SMPS types to do so by essentially shutting down when off load.

They had to make an exception for AC output transformers which have no off load rule.

The better safety, life span and reliability of iron transformer types was never considered.

... Phil

** Nothing new in that idea, early Sanyo flat screens had remote, 15V SMPS.

** Dunno about the cost advantage, but the most troublesome part of the TV is then user replaceable. That has goota be a good thing.

.... Phil

s never considered. "

That figures the way "they" think. They wrecked flourescent lights here. We had 40 watt tubes, they were more efficient and lasted along time but they wanted to get it down to 32 watts. Now they don't last for shit, they flic ker when cold and sometime won't even start so I can't use them in the gara ge because it gets cold here.

An electronic starter can work wonders. The landlords f****it electrician put the wrong ballast in the bog light, it was very reluctant to start from day one. After a month; it was switch on and go make a cuppa while I wait for it to strike.

With the electronic starter, it just didn't come on for a while then blinked on with no flickering.

When I spotted the wrong ballast, I ordered a new tube and an electronic ballast - the damaged tube lasted another year on the electronic ballast, the new tube went in a few years ago and is still going fine.

--
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