Shockingly piss-poor USB power supply

[mikeselectricstuff]

A switchmode mains supply with one transistor.... guess how well it performs...?

[firewalker]

A killer PSU, ftw. 

Alexander.

[EEVblog]

I was pleasantly surprised at how bad it actually was! 

Dave.

[Psi]

My guess would be that, to save money, the manufacture reused a plastic case made for some other unit.
Either that or they ran out of the correct case so used whatever they had available

So it ended up with the wrong specs on it.

That would also explain why the pcb doesn't fit very well and doesn't use the proper guide rails in the case.

Sadly all they really care about is that it has enough current for the product they ship it to run.

[Bored@Work]

Nice dissection.

Such Chinese power supplies regularly show up in the weekly reports of the EU's "rapid" alert system for non-food products (RAPEX). And you can be sure when even the EU bureaucrats manage to regularly pick up some that the problem is actually epidemic. The criminals really don't care if they kill people.

[ciccio]

Years ago I designed some 2-3 W switching power supplies using 3 transistors to power panel meters and controllers, and they were light years better than this one. The industrial cost was about 20 cents higher (not accounting for filter components needed to pass emission tests).
I don't know how much the manufacturer ask for such an horror, but it's too much, in any case...
I have some Christmas tree LED lights here, that are built with the same mentality: Next week I will dissect one of them and post the results.

[mikeselectricstuff]

Sadly all they really care about is that it has enough current for the product they ship it to run.

In this case, not even that. It  literally will  do little more than light the LED on the hub.

[Psi]

Sadly all they really care about is that it has enough current for the product they ship it to run.

In this case, not even that. It  literally will  do little more than light the LED on the hub.

oh, my mistake, i miss-heard that bit as powering the hub leds normaly.

[Fraser]

Mike,

Thanks for opening my eyes to the crap PSU's that come with some Cheap products. I just gutted a China sourced PSU that recently arrived with a DVB-T adapter and what I found didn't impress me either. The SMPSU uses more components and very slightly better design than your unit but the isolation provided by the transformer still looks suspect.

I will be going through my "cheap & cheerful" plugpack PSU's and giving my bin a good feed !  Unfortunately many small SMPSU plugpacks have welded cases so are very difficult to inspect. I will look at the cheap far East sourced units with great suspicion in the future !

Thanks again for a great video.

[johnmx]

Thanks for opening my eyes to the crap PSU's that come with some Cheap products. I just gutted a China sourced PSU that recently arrived with a DVB-T adapter and what I found didn't impress me either. The SMPSU uses more components and very slightly better design than your unit but the isolation provided by the transformer still looks suspect.

At least the regulator of your board has a feedback node.

[The_Penguin]

A switchmode mains supply with one transistor.... guess how well it performs...?

Wow what a P O S!
Thanks for sharing. I was thinking of maybe re-using 1 or 2 we got with USB hubs at work, but you've cured me of that idea.

[hacklordsniper]

The more interesting fact is that usually this cheap hubs will connect their external power supply parallel to the USB supply of your PC, frying your PC if the power supply is something like in this topis (or worse).

This product remebers me about car starting cables we bought some time ago, thick like thumb when looking the insulation outside and inside there is 2-3 strands of speaker wire.

[Bored@Work]

Thanks for opening my eyes to the crap PSU's that come with some Cheap products. I just gutted a China sourced PSU that recently arrived with a DVB-T adapter and what I found didn't impress me either. The SMPSU uses more components and very slightly better design than your unit but the isolation provided by the transformer still looks suspect.

At least the regulator of your board has a feedback node.

And a fuse. Almost a high-end PSU by chinese standards.

[don.r]

Excellent dissection work on the transformer. 

We should have expected this given the "quality" of some of the Chinese bench equipment being posted here. At least things like the Atten hot air station and some of the bench PSUs are repairable to a point of being both useable and safe. This unit is not even worth saving for the parts.

[Greg J]

Like I commented under the video, you get what you pay for.

I am not shocked about performance of the unit - because we all saw how little there is to actually do anything.

I'm shocked to see how much power is lost in the cable.
It doesn't look that thin, and I have similar looking cables going to motors in my little robots. Each engine draws good 0.5A when busy - and I don't see much of a drop on em.

What I am trying to say, is that the cable might be looking solid - but it must be made of pure quality materials too.

[amyk]

It probably would've been able to do its rated output with beefier components (like the small-signal glass body diodes(!) replaced with 1N4001s) and wire. It's just a simple oscillator circuit (like a Joule thief) but with a secondary step-down winding.

[mikeselectricstuff]

It probably would've been able to do its rated output with beefier components (like the small-signal glass body diodes(!) replaced with 1N4001s) and wire. It's just a simple oscillator circuit (like a Joule thief) but with a secondary step-down winding.

Maybe but wthout feedback, if it could do 1A at 5V, the n-load voltage would be excessively high

[Jon Chandler]

I'm a big advocate of using 5 volt cell phone chargers to power circuits.  I can usually pick these up at the local thrift store for a buck a piece which is far cheaper than I can build anything and the name-brand ones seem to be well engineered.

I'll working on a project where I need to embed a 5-volt supply, so I looked at disassembling the wall wart and using its circuit board inside my enclosure.  I took several of these chargers apart to evaluate the feasibility of doing this.  What really surprised me was comparing a number of Samsung chargers.  All in the same enclosure, all the same ratings, and no two boards alike!  Here are some of the pictures I posted at Digital-DIY.

The First Victim









Looks like it's probably a reasonable circuit and it's a well-made board.

The Second Victim

From outward appearances, this should be the same charger.







The circuit board and circuit are completely different.


The Third Victim

Again, the same outward appearance.






The Fourth Victim

This is another Samsung charger in a slightly different package.





Different circuit boards and different implementations.  They'll all different, but all seem to be nicely built.


As a comparison, here's a Nokia charger.  I should note that the Samsung chargers are screwed together and can be opened without much trouble.  The Nokia charger was glued together and required a brute-force approach to open it.  After looking at the circuit board, this may be more than a coincidence!

[mikeselectricstuff]

I bet that last one was made by neither Nokia or Astec.

[IanB]

Of the first two, one was made in China and one was made in Korea. Therefore I am not surprised they are different inside. Each was most likely made by a different company to a different design.

[caroper]

The first 2 have different model numbers too. I can't make out the numbers on the rest.

[Mechatrommer]

i have this thing lying around, took apart, exact circuit as shown. mike said about fuse resistor, its actually a bleed resistor for the half bridge cap. yes its using half bridge rectifier. isolation is through the small (hi freq?) transformer, but not sure inside i havent watch mike's video to the end. fuse? i think the whole circuit is a fuse, or some random (weakest) component.

about the half bridge rectifier, the adapter only pulling power when the mains is on +ve side, zero load on -ve. my recent testing using Uni-T UT202 clamp Aac meter registered different current reading from the mains when using between full and half bridge rectifier, same switching volt-regulation circuit, same Adc output reading, same transformer, only different bridge. half bridge showing less efficient power from calculation/comparison, i'm not sure why though, my circuit (different bridge will give different result/output/efficiency?) or the clamp meter that cannot register half loaded mains correctly.

i dont see any problem with the china adapter circuit, in fact i like the design... simple, i would say this is a cheap PS, not crappy (what do you expect from a small and light transformer and cheap product?), or maybe i'm on the low standard side the only ridiculous thing is the spec written on the product, mine showing INPUT 220-240V 50Hz 350mA, OUTPUT: 5.1V-5.5V, 500mA±50mA, its like the adapter will draw min 5.1V which proved to be a bullshit from Mike's video. but mine is more humble on the current spec, at least it can do 700+mA on short circuit and not blowing to the face right away

just checked the noise, its around 50-200mV on open circuit and 1Vpp at short circuited iirc (i've pulled the output wire apart unintentionally cant do the retest again for more accurate figure, late nite GTG)

[alm]

about the half bridge rectifier, the adapter only pulling power when the mains is on +ve side, zero load on -ve. my recent testing using Uni-T UT202 clamp Aac meter registered different current reading from the mains when using between full and half bridge rectifier, same switching volt-regulation circuit, same Adc output reading, same transformer, only different bridge. half bridge showing less efficient power from calculation/comparison, i'm not sure why though, my circuit (different bridge will give different result/output/efficiency?) or the clamp meter that cannot register half loaded mains correctly.

If the clamp meter does not report the true RMS value, you should expect it to be wrong for non-sinusoidal currents like those drawn by rectifier/smoothing cap combinations, switch-mode power supplies or half-wave rectification.

[RJSC]

I'm a big advocate of using 5 volt cell phone chargers to power circuits.  I can usually pick these up at the local thrift store for a buck a piece which is far cheaper than I can build anything and the name-brand ones seem to be well engineered.

I'll working on a project where I need to embed a 5-volt supply, so I looked at disassembling the wall wart and using its circuit board inside my enclosure.  I took several of these chargers apart to evaluate the feasibility of doing this.  What really surprised me was comparing a number of Samsung chargers.  All in the same enclosure, all the same ratings, and no two boards alike!  Here are some of the pictures I posted at Digital-DIY.

Is the nokia also a one transistor power supply?  Or does it have surface mount components on the back?

[Jon Chandler]

Is the nokia also a one transistor power supply?  Or does it have surface mount components on the back?

What you see is the entire circuit.