Power supply teardowns reveal safety issues

A power supply is an electronic device that supplies electric energy to an electrical load. Most of the power supplies you use every day are the AC-DC power supplies that convert mains AC power (typically in 100-240V range) to low voltage DC (typically 5V to 24V). In those power supplies the output will be electrically isolated from the mains; this feature is essential for user safety. Many modern power supplies (switch mode) often include safety features such as current limiting or a crowbar circuit to help protect the device and the user from harm. The power supplies also typically need to have some form of fuse in the mains side to protect against short circuit or severe over-load inside the power supply (to avoid potential fire).

Power supplies come with various specifications, built using different technologies and with varying quality (from cheap unsafe counterfeit knock-offs to good quality).  Take a look at the nearest power supply labeling. It will hopefully have a slew of marks on it that indicate what standards it abides to (or at least promises to).

But not all product do what they promise. Many finding culminate to this: An engineering/project management triangle. Pick 2 of 3!

We all love a good tear-down (at least me), so here are some interesting tear-downs of power supplies:

Sparkfun Tears Apart Power Supplies for fun and to learn. Enginursday: Supplies! article takea a look inside some common power supplies. It walks us through how the basic circuit works and then points out why various other elaborations are made, and how corners are sometimes cut, in a few power supplies that he’s taken apart.

 

Dangerous Chinese power supply article tells about a cheap, Chinese, 12V 1A power supply, designed to be used in LED lamp retrofit project. It’s marked CE (meaning it respects European norms, which essentially have to do with EMI interference), but it still has a serious safety problems. What we learn of this: Remember that the the CE marking is stamped by **the manufacter himself**, which basically means “I tell you that this product respects regulations”. But of course, that does’nt mean at all that it does. Usually this is the case with cheap chinese crap where you usually get what you pay for. To safely use this power supply several corrections/modifications needed to be done.

Cheap switch-mode power supplies video a quick look as some cheap £15 generic Chinese switch-mode universal power supplies and what is wrong with them. Quality is as expected… I wouldn’t trust this at all for anything serious!

There are many cheap bad-quality USB chargers.  I have made Safety analysis of one USB power supply  and saw something to worry about! Take a look at the separation between mains carrying parts and low voltage side: There is less than one millimeter between them (I measured shorted distances to be in 0.5-0.7 mm range). This is not how to build a safe power supply.

I also made Teardown of cheap USB charger that failed after quite short use. The power supply is built using very simple circuit (simpler than expected). There are two worrying safety issues here: The insulation distances on the circuit board are very small (less than 1 mm on several places between mains side and output). Too small to be safe! There does not seem to be any fuse in this circuit!

Autopsy of an exploded USB power supply. (With skidmark) video shows what is inside pre-detonated multi-port USB power supply. Given the isolation between the mains voltage primary windings and the low voltage secondary windings, perhaps it’s a good thing that it exploded (and did not put people in more danger).

Don’t buy a cheap replacement power supply! video warns about counterfeit batteries and power supplies. eBay and Amazon.com are loaded with cheap replacement power supplies and battery chargers for digital cameras, camcorders, laptop computers, and other devices. But as you might expect, these power supplies are built using cheap components with very bad build quality, and use no shielding and very poor filtering. This creates a tremendous amount of radio interference.

 

Why You Should NEVER Buy Generic Chinese Laptop Power Supplies by XanderDarien

Remember also this danger with adapters if you plan to use power supply with different powewer connector than you have on your wall: Deadly Chinese plug adapter

For more interesting tear-downs take a look at Teardown category on this blog.

37 Comments

  1. Tomi Engdahl says:

    Related video:

    How to open a laptop power supply and modify its output voltage
    https://www.youtube.com/watch?v=uGP6eZVaZwI

    This video provides a few tips on opening up a laptop power brick, as well as how to go about modifying its output voltage.

    Reply
  2. Tomi Engdahl says:

    Teardown: 12V AC adapters – The Horror
    http://www.edn.com/design/pc-board/4441830/Teardown–12V-AC-adapters—The-Horror?_mc=NL_EDN_EDT_EDN_today_20160420&cid=NL_EDN_EDT_EDN_today_20160420&elqTrackId=2cd037b29dec48aeaa93fdd4092a51c4&elq=1e3f2dd7a13345c4bf00fe5180b7e7de&elqaid=31925&elqat=1&elqCampaignId=27841

    In the name of science, I introduced three of the worst 12V adapters (from My kingdom for a 12V adapter) to my bandsaw. What I found may shock you.

    Yes! Can you believe it? This board used to be in another adapter housing, or more likely, in an end-product. It seems Chinese manufacturing has sunk to a new low: repackaging used and/or surplus power supplies. On the plus side…recycling.

    The board was held in place by two pieces of foam, which you’ll see is pretty high-end packaging, relatively speaking.

    Next up, the “XY1205A”, again with its fictitious approvals & specs. Nothing horrifically wrong here, unless you count the tacked-on wires and lack of mounting. Good clearance between primary and secondary sides, except where there isn’t.

    This is good quality guts paired with a botched repackaging job.
    As far as I can tell, the production date is ca. 2000-2001 (board:0093, AC rectifiers:0062). Ugh. Wonder if the board had seen service before being repackaged.

    The two blue caps at the upper left are 2.2nF parts in series, bridging primary to secondary sides in parallel with the 88MΩ of resistance. What’s the goal here?

    None of the boards have isolation slots cut in them between primary & secondary sides

    There you are. A look at a very dirty side of Chinese manufacturing. One wonders how deeply this sort of thing permeates the industry,

    Home> Community > Blogs > BenchTalk
    My kingdom for a 12V adapter
    http://www.edn.com/electronics-blogs/benchtalk/4441809/My-kingdom-for-a-12V-adapter

    Our new house is inching towards 100% LEDness, from LED “bulbs” in standard light fixtures, to custom LED lighting, to flexible LED light strips. It’s the latter I’m having some problems with.

    After some preliminary research, I decided that the only affordable sources for LED strips would be from among the numerous Shenzhen & Hong Kong mega-retailer Websites. There, you’ll find standard 5m LED strips in the $4-$20 range, instead of the $50-$100 range typical of other sources.

    After some preliminary research, I decided that the only affordable sources for LED strips would be from among the numerous Shenzhen & Hong Kong mega-retailer Websites. There, you’ll find standard 5m LED strips in the $4-$20 range, instead of the $50-$100 range typical of other sources.

    With the LEDs themselves taken care of, I turned to power sources. In the basement, I’ll probably use some centralized high current 12V power supplies..

    While I’m willing to accept some creative LED specs, I do expect a 5A adapter to be a 5A adapter. Silly me. They turned out to be more like 2A, and to add insult to injury, the output cables appeared to be vastly undersized

    Reply
  3. Tomi Engdahl says:

    Horrific USB power supply fault. (Electrocution risk.)
    https://www.youtube.com/watch?v=3Hdn0MuCK_0

    Although I’ve come across some really dodgy power supplies with poor insulation between the mains and low voltage sides, this is the first one where the USB ports have carried full mains current. (via a rectifier)
    It’s a Swees QY08-05010 with this model and style carrying various other branding as well. Oddly it does appear to be relatively sensibly designed inside, but this one has a serious manufacturing fault that suggests others from the same run may also pose a risk of serious electric shock.

    Sadly, this just reinforces my doubts about the poor separation in many of these small transformers. I’d rather have split bobbin transformers even if it meant efficiency taking a slight hit.

    Reply
  4. Tomi Engdahl says:

    Searching for USB Power Supplies that Won’t Explode
    http://hackaday.com/2016/04/27/searching-for-usb-power-supplies-that-wont-explode/

    USB power supplies are super cheap and omnipresent. They are the Tribble of my household. But they’re not all created equal, and some of them may even be dangerous. I had to source USB power supplies for a product, and it wasn’t easy. But the upside is that I got to tear them all apart and check out their designs.

    In order to be legitimate, it’s nice (but not legally required) for a power supply to have UL approval. Some retailers and offices and building managers require it, and some insurance companies may not pay claims if it turns out the damage was caused by a non-UL-approved device. UL approval is not an easy process, though, and it is time consuming and expensive. The good news is that if you are developing a low voltage DC product, you can pair it with a UL approved power supply and you’re good to go without any further testing necessary.

    Sourcing cheap electronics in large quantities usually ends up in China, and specifically Alibaba. First, we started with a how-low-can-you-go solution.

    Quality control could not be a high priority. After cutting it open, it wasn’t terrible, and it had all the necessary parts. It was surprising how much of it was through-hole, which indicates that the assembly was done mostly by people. That happens when factories are cheaper, hire inexpensive labor, don’t invest in technology, and don’t care as much about quality.

    There are certain things you should look for in a power supply to determine the level of risk:

    Isolation Distance – This is how much space there is between the primary (AC) and secondary (DC 5V) sides. UL requires a few millimeters, and often you’ll see two separate PCBs. On many single-PCB solutions you’ll see a white line meander across the board to distinguish between the two. The smaller this separation, the closer your USB power is to AC line voltage, and if the gap is bridged somehow, you’re in for a world of hurt.
    Fuse – if there is a short, a lot of current starts flowing, components heat up, and things get dangerous. A thermal cut-off (TCO) fuse (also known as a resettable fuse or a PTC) is a component that breaks the circuit when it gets too hot, like a circuit chaperon. When it cools off, the TCO resets and you can plug the device back in with no harm done. Without the fuse, the supply heats up and current keeps flowing until a component fries, sometimes explosively.
    Connectors – You don’t want bare leads hanging out in space where they could move and touch something. You don’t want the USB port to be soldered only by its four pins. You don’t want the power pins to be loose.
    Decent Label – “Adaptep”? Yes, to someone who uses a different alphabet the “P” and R are very similar characters. But still. Also, fake certifications abound. Look for the difference between the CE (China Export) and the CE (Communite Europeanne) labels. And the UL Logo should have a number. So should an FCC label.

    Check out a much more thorough analysis of this and pretty much every USB power supply cube by [Ken Shirriff]. It’s surprising how little has changed in four years with these supplies, and his analysis goes into how the circuits behind these supplies work, identifying each component and its purpose.

    Tiny, cheap, and dangerous: Inside a (fake) iPhone charger
    http://www.righto.com/2012/03/inside-cheap-phone-charger-and-why-you.html

    Reply
  5. Tomi Engdahl says:

    Water damage
    http://jeelabs.org/2016/04/water-damage/

    Water and electricity don’t mix
    http://jeelabs.org/article/1616a/

    Scary stuff! – if you look closely, you can see that the USB adapter was cracked open, probably by the pressure released as it finally gave up and let out the magic smoke

    It has obviously been going on for a long, long time – that amount of corrosion couldn’t possibly have been caused by just a few hours of moisture!

    Reply
  6. Tomi Engdahl says:

    Cheap bench power supply tear-down (it’s bad!)
    https://www.youtube.com/watch?v=tL12onTZMzA

    cheap MCH-K305D 30V, 5A 150W switching bench supply
    the current limiting has never worked so I figured I’d tear it down and take a look inside. It’s *awful*

    EEVblog #828 – Siglent SPD3303X Precision Lab PSU Teardown
    https://www.youtube.com/watch?v=mdOauVzY9OU

    Reply
  7. Tomi Engdahl says:

    Test of bare eBay 12V 1A PSU module, including safety tests.
    https://www.youtube.com/watch?v=Pa-bPlZikfE

    There are a few of these little power supply modules on ebay, so I thought I’d get one and give it a thorough test. Voltage holds relatively well, with just a slight drop under overload conditions, and the module layout and filtering is actually very good.

    Reply
  8. Tomi Engdahl says:

    Crappy PSU analysis
    https://www.youtube.com/watch?v=T88ej64aXUM
    Pulling apart a too-cheap-to-be-true PSU. Guess what… it was too cheap.

    Inside a reasonable quality Chinese PSU
    https://www.youtube.com/watch?v=1F3XlFI1JBo

    Reply
  9. Tomi Engdahl says:

    Wall plate death-dapter tests including fire and 1kV.
    https://www.youtube.com/watch?v=g0iFNKvkT6I

    Why settle for a wobbly death-daptor with flimsy electrical contacts and inadequate shuttering when you can have one permanently fixed into the fabric of your home. Better still, one with always-on electronics inside too. This product falls into the category of “Jack of all trades, but master of none.”

    Reply
  10. Tomi Engdahl says:

    There were many flaws in the Led floodlights

    European market surveillance authorities investigated the safety and compliance of LED bulbs with a joint control project. Indeed, 47% of the products were removed from the European market as non-compliant.

    Of the 82 LED floodlights tested, only two met the technical and administrative requirements of both legislation. As a result of the project, 47% of the tested LED spotlights were pulled out of the EU market. A total of 87 floodlights were tested for electrical safety requirements. 87 per cent of the tested products did not meet the requirements. Indeed, 71 percent of the products had flaws that could endanger the user’s safety.

    Tukes closely monitored the ten LED spotlights sold in Finland, of which five were withdrawn from the market

    Source: https://www.uusiteknologia.fi/2017/09/12/led-valonheittimista-loytyi-paljon-puutteita/

    Reply
  11. Tomi Engdahl says:

    Home> Power-management Design Center > Teardown
    Teardown: A better Chinese 12V adapter
    https://www.edn.com/design/power-management/4460247/Teardown–A-better-Chinese-12V-adapter

    Rather than admitting defeat after uncovering some horrid Chinese-made 12 V adapters, I only found my curiosity piqued. I decided to keep looking.

    Giving up on China-direct sources like AliExpress, I turned to Amazon. After browsing the reviews for many an AC adapter, it seemed pretty clear that the Amazon name wouldn’t guarantee a quality unit, but I still felt my chances were greater than with Ali.

    Some PSUs on the site are shipped from a third party, others by Amazon. I chose one of the latter, a couple of 12 V 6 A adapters, ostensibly made by a company called Selectec

    My initial Impressions were positive. The unit felt solid, and would supply up to 6.9 A before shutting down. At the rated 6 A, cable drop amounted to 0.75 V. Not great, but I’ve seen much worse.

    Letting it thermally stabilize with a 3 A load resulted in what I’d call acceptable temperature rise.
    I’d estimate a case hot-spot of maybe 50 °C, with most of the case being cooler. At a bit over 5 A however, I found the case became unacceptably hot

    The 6 A unit is admittedly in a small case for its rating (30×50×109 mm).

    But you came for a teardown. Let’s have a look.

    Notice the EMI filter? No, neither do I. Do you believe the FCC and CE certifications? No, neither do I.

    The AC connector is not IEC, but two-terminal “shaver” style. Yet there’s a ground connection on the PCB, which is connected to a couple of those blue ceramic HV caps, and…the negative DC output.

    A 12 V adapter that, while not a total horror, isn’t anything to get too excited about either.

    Reply
  12. Tomi Engdahl says:

    DANGEROUS Chinese USB charger (no isolation in the transformer!)
    https://www.youtube.com/watch?v=ehYYoU13i-I

    Reply
  13. Tomi Engdahl says:

    Really dodgy pink USB charger.
    https://www.youtube.com/watch?v=wqJnFhhPAis

    The cheap shitty pink USB charger from China song.
    https://www.youtube.com/watch?v=ioAq7PI1Uwg

    Reply
  14. Tomi Engdahl says:

    Really dodgy pink USB charger.
    https://www.youtube.com/watch?v=wqJnFhhPAis

    I was originally going to do a teardown on this, but the cramped circuitry and breathtakingly negligible safety tolerances ruled it out as a viable device from the start. I don’t think that having a PCB gap of 0.25mm or 0.01″ is really safe at all. Particularly when the gap between the two pads involved had a little line of flux impregnated with solder globs. Such a small clearance between the mains circuitry and the USB connector itself is just appalling. It really poses a shock risk for anyone touching a device with exposed “grounded” metal plugged into a charger like this.

    Reply
  15. Tomi Engdahl says:

    Are cheap chinese usb chargers getting better? (054)
    https://www.youtube.com/watch?v=hnQFO6jl4X4

    Today we’re taking a look at the construction, internals and performance of a cheap knock-off Samsung USB charger.

    Reply
  16. Tomi Engdahl says:

    Deadly USB Charger (Fake Apple) + Explosions
    https://www.youtube.com/watch?v=nMmySM2nar8

    A deadly dangerous USB charger (fake Apple iPhone charger) from China. Sold on Ebay for 90 cents including shipping. The PCB board has only 1mm distance between primary and secondary side. The EMI capacitor between primary and secondary side is only rated 1kV (should be Y1 class with a test voltage of 8kV). The transformer isolation is also questionable. The power supply has no fuse (just mains-bridge-electrolyte!). This poses serious risk of fire. When the power transistor shorts out (and it is likely to do so, because there’s no snubber network), the primary of the switching transistor gets essentially connected to mains with no fusing. This is likely to cause a meltdown of the transformer and get mains to the output.

    Reply
  17. Tomi Engdahl says:

    Teardown of an IKEA Koppla USB power supply
    https://www.youtube.com/watch?v=uRe9w5PKmsE

    I’ve always recommended using prominent brand USB chargers for safety. So I thought I’d take an IKEA one to bits and assess it for safety with regards to isolation and transformer construction.

    Reply
  18. Tomi Engdahl says:

    Horrific USB power supply fault. (Electrocution risk.)
    https://www.youtube.com/watch?v=3Hdn0MuCK_0

    Although I’ve come across some really dodgy power supplies with poor insulation between the mains and low voltage sides, this is the first one where the USB ports have carried full mains current. (via a rectifier)

    It’s a Swees QY08-05010 with this model and style carrying various other branding as well. Oddly it does appear to be relatively sensibly designed inside, but this one has a serious manufacturing fault that suggests others from the same run may also pose a risk of serious electric shock.

    Reply
  19. Tomi Engdahl says:

    12V 5A LED switching power supply – with schematic
    https://www.youtube.com/watch?v=Ej9ck8JoE2s

    Today I tested a 12V 5A 60W switching power supply that cost me only $3 including shipping from China. The listing says it’s for LED strips, CCTV and LCD monitors. The actual current capability is only 3.5A and some parts are underrated. The PCB board definitely seems repurposed. It looks bodged, but I have seen much worse SMPS designs :). This one has a proper fuse, EMI filters, very good isolation distance on the PCB and safe X2, Y1 capacitors. I managed to reverse engineer a full schematic of it.

    Reply
  20. Tomi Engdahl says:

    12V 2A LED Power Supply test – with schematic
    https://www.youtube.com/watch?v=bOR9SeYpkj0

    In this video I test a Chinese 12V “2A” switching power supply designed for LEDs, CCTV, routers, etc. It cost me only $ 1.80 including shipping. The actual current capability is about 0.5A and the safety is quite questionable. It’s a classic 2-transistor switching power supply with an optocoupler, but it’s quite underrated, has poor mains isolation and misses basic safety features like a fuse. It may be dangerous and it can only supply 1/4 of its rated current.

    Reply
  21. Tomi Engdahl says:

    Simple 12V 1A LED Power Supply – with schematic and transformer autopsy
    https://www.youtube.com/watch?v=2DyejSzCEW0

    Today I took a look at a very cheap Chinese 12V 1A adapter from Ebay. The listing says it is for LED strips, CCTV, routers, audio/video equipment, etc. This AC/DC adapter has 100-240V universal mains input and 12V 1A DC output.

    The isolation distance on the board is 1.5mm. I have seen more dangerous transformers, but also much safer ones.

    This switching power supply claims 1A current capability, but actually is capable of only 0.5A.

    I personally wouldn’t use it.

    Reply
  22. Tomi Engdahl says:

    DANGEROUS Chinese USB charger (no isolation in the transformer!)
    https://www.youtube.com/watch?v=ehYYoU13i-I

    Then I found that the transformer in it has no isolation between the windings! This USB charger from China (fake Apple iPhone charger) has a transformer with no insulation tape between the primary and secondary side. The output of it (and thus the entire phone including its metal casing) is isolated from mains just by a super thin layer of enamel (lacquer) on the magnet wire! This means a very high risk of an electric shock and death. This dangerous electrocution device comes in various colors including white, which looks just like a real Apple iPhone charger.

    Reply
  23. Tomi Engdahl says:

    Simple yet safe 5V switching power supply (with schematic and description)
    https://www.youtube.com/watch?v=7AfdD09q7KE

    reverse engineering the schematic of a very simple 5V switching power supply (probably a phone charger) and describing how does it work. It’s a super simple single transistor design, but it has a proper fusible resistor, EMI filter and a very good isolation, so it looks safe and compliant.

    Reply
  24. Tomi Engdahl says:

    Super Simple Power Supply & Transformer Autopsy
    https://www.youtube.com/watch?v=iAYDhtkozd8

    Another Chinese USB charger / power supply. Rated 5V 500mA. This one has probably the simplest possible schematic. Just a single transistor, no optocoupler, half wave rectifier, no interference filter at all. The isolation distance on the board is 2.5mm, this is above Chinese average, but still could be better. The transformer is dodgy, it has just 1 – 2 layers of sticky tape between windings.

    There’s no fuse, just a chinese “onboard fuse”. No inrush limiter. The output diode is 1N4148 rated 150mA, despite the supply is rated 500mA.

    Reply
  25. Tomi Engdahl says:

    Crappy chinese 24V ’360W’ power supply teardown (005)
    https://www.youtube.com/watch?v=rJ2SiBzijiw

    I compare a crappy chinese power supply to a high quality, previously torn down power supply. Enjoy!

    Reply
  26. Tomi Engdahl says:

    Repairing cheap power supplies!
    https://www.youtube.com/watch?v=gHBpDxf6eVA

    It’s easy to fix these simple power supplies with a keen eye and a few spares!

    Comment:

    Please, if you don’t have experience and formal training, DON’T MESS WITH MAINS VOLTAGE!
    I’m very much OK with someone soldering around on an Arduino board, RC model, or other low voltage/battery powered device. But a power supply is not something every average joe should take apart, “fix” and put back into service.

    Reply
  27. Tomi Engdahl says:

    Cheap $8 Ebay Power Supply vs $85 Cosel Power Supply Teardown
    https://www.youtube.com/watch?v=71NWT5vrbk8

    A teardown and comparison between a cheap $8 made-in-China power supply and a $85 Cosel power supply (50W, 24V).

    Why pay more for a name brand power supply? (037)
    https://www.youtube.com/watch?v=yJdRuTBE08M

    We’re having a good hard look at the differences between a no-name and a name brand power supply, specifically a Junke 240W and a Mean Well LRS-150-24 open frame power supply, differing about a factor of 2 in price.

    Reply
  28. Tomi Engdahl says:

    Comparing a genuine to a ‘replacement’ Lenovo adapter (036)
    https://www.youtube.com/watch?v=LXF1xlBB9Xg

    Reply
  29. Tomi Engdahl says:

    Cheap bench power supply tear-down (it’s bad!)
    https://www.youtube.com/watch?v=tL12onTZMzA

    Although I’ve been using this cheap MCH-K305D 30V, 5A 150W switching bench supply for quite a while, the current limiting has never worked so I figured I’d tear it down and take a look inside. It’s *awful* – but what do you expect for US$60 I guess?

    IMPORTANT: THIS DEVICE DOES NOT LIVE UP TO WESTERN ELECTRICAL SAFETY STANDARDS! PURCHASE AT YOUR OWN RISK. YOU MAY BE ENDANGERING YOUR LIFE AND THE LIVES OF OTHERS!

    Wanptek KPS305A – $65 30V/5A bench PSU review
    https://www.youtube.com/watch?v=M-3kJ59n67U

    Reply
  30. Tomi Engdahl says:

    R&D #12 Review: Yihua $50 power supply from Ebay
    https://www.youtube.com/watch?v=E0aRjuIOnso

    Test and adjustment of the Yihua power supply found from numerous sellers on Ebay.

    How To Repair a Power Supply- Bench / Lab Version
    https://www.youtube.com/watch?v=KRehfAg-ZBc

    How to repair a broken bench power supply (PSU)

    Reply
  31. Tomi Engdahl says:

    Test of bare eBay 12V 1A PSU module, including safety tests.
    https://www.youtube.com/watch?v=Pa-bPlZikfE

    There are a few of these little power supply modules on ebay, so I thought I’d get one and give it a thorough test. Voltage holds relatively well, with just a slight drop under overload conditions, and the module layout and filtering is actually very good.

    Comments:
    A cheap chines pwer supply that is actually safe? and the thing even performs well! we have a miricle on our hands somebody call the pope!

    Reply
  32. Tomi Engdahl says:

    Inside some dodgy Chinese USB power supplies from Greece
    https://www.youtube.com/watch?v=bNoGCdX1IdQ

    Reply
  33. Tomi Engdahl says:

    EEVblog #272 – Manson 9400 40A 3-15V Switchmode PSU Teardown
    https://www.youtube.com/watch?v=bX8IIjf15qY

    What’s inside the Manson SPS9400 40A 3V to 15V Switchmode Power Supply?
    Also known as the Jaycar Powertech MP3090 and BK Precision 1692

    http://www.eevblog.com/files/SPS9400_ServiceManual.pdf

    Reply
  34. Tomi Engdahl says:

    Simple 12V 1A LED Power Supply – with schematic and transformer autopsy
    https://www.youtube.com/watch?v=2DyejSzCEW0

    Today I took a look at a very cheap Chinese 12V 1A adapter from Ebay. The listing says it is for LED strips, CCTV, routers, audio/video equipment, etc. This AC/DC adapter has 100-240V universal mains input and 12V 1A DC output. I took a look at the board layout, reverse engineered the relatively simple schematic of it and made an autopsy of the transformer. This power supply is quite dodgy – there’s no fuse, no EMI filter, no inrush resistor, no snubber network and a very questionable capacitor between the primary and secondary side. The isolation distance on the board is 1.5mm. I have seen more dangerous transformers, but also much safer ones.

    Reply
  35. Tomi Engdahl says:

    12V 2A LED Power Supply test – with schematic
    https://www.youtube.com/watch?v=bOR9SeYpkj0

    In this video I test a Chinese 12V “2A” switching power supply designed for LEDs, CCTV, routers, etc. It cost me only $ 1.80 including shipping. The actual current capability is about 0.5A and the safety is quite questionable. It’s a classic 2-transistor switching power supply with an optocoupler, but it’s quite underrated, has poor mains isolation and misses basic safety features like a fuse.

    Reply

Leave a Comment

Your email address will not be published. Required fields are marked *

*

*