Cheap USB charger teardown

Here is teardown of another cheap USB charger bought some time ago for around two euros from some chinese online shop. Brand “Designed by Able” Model 1300.


Circuit board

Closeup of circuit board

One finding is that rectifier is replaced with diode, meaning that this half-wave rectifies mains power.

Other findings:

- The switcher circuit is based on two transistors (SW 13003 and UTC S8030) and optiosolator feedback

- There does not seem to be any fuse (or fusible resistor or other protection component) anywhere, the mains power is directly rectified with 1N4007 diode to main capactor

- The insulation distances between promary and secondary on the circuit board are quite small: shortest distance around 3 mm from solder to solder and slightly over 2 mm track-to-track

I don’t don’t thinks this is safe or good quality power supply. It might not be immediately dangerous, but the safely level is very low -I quess that this might not get though all the electrical safety regulations if gets tested by regulators.

If you need USB power supply, get something safer.


  1. Tomi Engdahl says:

    On the right side of the circuit board (when looking the copped side) there seems to be some very thin traces that look a little bit that they could be designed as fuse in circuit board. Maybe there was idea that this would be fuse, and maybe would have worked as such if original bridge rectifier would have been put to circuit board. But the board is no built so that the mains power does not go through this “circuit board fuse”.

    Can thin sections of copper traces be used as fuses?

    Is it safe to use thin sections of copper traces as one-shot fuses when cost is important, but when it is also vital to protect the rest of the circuitry? Should the solder mask be removed at that location?

    It’s certainly been done.

    It’s a bit more of a crapshoot than a traditional fuse, like a printed spark gap, but can be done. The trace should not be exposed. An exposed trace will be subject to contamination, possibly conductive contamination, which changes the amount of conductor you designed for a certain current. Admittedly a minor concern, but I don’t see any pros for exposing the trace.

    This paper explores and provides calculations for determining trace size for a printed fuse with a variety of copper weights.

    A salient point from the paper, in case it isn’t always available is the approximation for the time in seconds (t) before a trace reaches melting temperature given current passing through it (I) and its cross sectional area in mils squared (A):

    t=0.0346×((A^2) / I)

    Note that this is the approximate time to melt the copper given a 20°C ambient temperature. It might fail long before or a short time after this value.

  2. Tomi Engdahl says:


    IMHO pcb trace can be used as a fuse, if the requirements are not very precise. In other words, diffrence between operating current and fault current are very wide, and the purpose is primarly to prevent fire than protect some other components. For instance it mightbe good enough in a car environment, where the battery for sure delivers plenty of current in case of a short circuit, and while the load to be protected is something simple with quite predictable failure modes (short to chassis or similar).

    One big trouble is that the PCB is seriously damaged when the fuse blows.

    I would in most cases recommend a pcb solderable chip fuse, or other well specified “real” fuse.

  3. Tomi Engdahl says:

    99% of fake Apple chargers fail a basic safety test, new study says

    It should go without saying, but if you buy a spare charger for an Apple device, you should absolutely make sure it’s from a known, reputable company.

    Your latest reminder of this comes from the Chartered Trading Standards Institute, a UK consumer protection organization that teamed up with Illinois-based safety testers UL to examine 400 “counterfeit Apple chargers” from various suppliers.

    According to the study, all but three of the 400 counterfeit chargers failed a “basic” safety test, in which high voltages were applied to the chargers to see if they had enough isolation to protect against electric shocks.

    The study comes just a few weeks after Apple reportedly conducted its own study on third-party power accessories, and found that roughly 90% of Apple chargers and cables sold through Amazon were unsafe.

    Whatever the case, fake chargers are still more common than they should be today.

    Getting chargers and cables directly from Apple is the easiest thing to do. Especially on the cable side, if you don’t want to pay the premium Apple often slaps on, look for accessories with Apple’s MFi (Made for iPhone/iPad/iPod) certification on its packaging.


  4. Tomi Engdahl says:

    Similar looking USB charger also analyzed here:

    USB Power Supply/charger Test

  5. Tomi Engdahl says:

    Do not use these: The authorities in Finland tested UBS chargers – half revealed dangerous

    Randomly selected 10 of the device, only one passed the test Tukes clean slate.

    Finnish Safety and Chemicals Agency (Tukes) says in a statement of tested 10 online shops sold charger and have found significant shortcomings.

    sale five-charger banned altogether. Shortcomings related to the insulation of the equipment and caused an electric shock hazard.

    Four charger got the note labels or inadequate instructions for use. Only one charger got a clean bill of health.


  6. Tomi Engdahl says:

    Inside some dodgy Chinese USB power supplies from Greece.

    VERY shady USB chargers which he bought from a Chinese outlet in Greece.

    The flat one has one of the scariest transformers yet with no extra insulation between the secondary and sense windings. It also had a rather odd output capability of around just 20mA before the voltage plummeted.

  7. Tomi Engdahl says:

    Cheap $8 Ebay Power Supply vs $85 Cosel Power Supply Teardown

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

  8. Tomi Engdahl says:

    A dozen USB chargers in the lab: Apple is very good, but not quite the best

    So what charger should you spend your hard-earned money on? First, make sure the charger will work with your phone – for instance, newer iPhones only work with certain chargers. Second, don’t buy a counterfeit charger; the price is great, but it’s not worth risking your expensive device or your safety. Beyond that, it’s your decision on how much quality is worth versus price, and I hope the data here helps you make a decision

  9. Tomi Engdahl says:

    Deadly USB Charger (Fake Apple) + Explosions

    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.

  10. Tomi Engdahl says:

    Inside some dodgy Chinese USB power supplies from Greece.

    The flat one has one of the scariest transformers yet with no extra insulation between the secondary and sense windings. It also had a rather odd output capability of around just 20mA before the voltage plummeted.

  11. Tomi Engdahl says:

    Autopsy of an exploded USB power supply. (With skidmark)

    Thanks to Gerard for sending in this 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.

    It’s a shame, because the transformer is the only bit that really lets it down. The circuitry looks like a textbook switchmode based around a dedicated chip.

    The reason for the failure is not clear, but a short has occurred that has made a track on the output of the rectifier blow like a fuse and cause a more serious short by virtue of the metal laden plasma.
    The glass fuse has blown in half s they are not really suited to breaking high current faults.

  12. Tomi Engdahl says:

    Teardown of a cheap UK style USB power supply.

    little USB PSU from Banggood for a measly $2 purely to examine its circuitry and internal electrical isolation. I thought it was going to be a bit more crowded inside than it is, but was very surprised to see that it uses a single sided board with standard through-hole components, but still manages to provide a tolerable level of electrical separation on the PCB.

    The transformer itself could potentially just have a layer of tape between the primary and secondary windings, and the capacitor used between the primary and secondary could also pose a shock hazard if it failed.
    But aside from these potential weak points the unit is quite intriguingly simple. It doesn’t use any non-standard components other than the custom would transformer and that includes common TO92 NPN transistors.

  13. Tomi Engdahl says:

    Inside a well built charger:

    Samsung USB Charger Failure and Repair

    In this video I’m examining and repairing my faulty USB phone charger (5V 1A switching power supply). It failed after 2 years of seldom use. I’ve drawn a partial schematic in the video. Full reverse engineered schematic of this charger is here:

  14. Tomi Engdahl says:

    Test of the Yihua 502D USB bench power supply. (With fix!)

  15. Tomi Engdahl says:

    Dangerous Chinese Travel Extension with USB Charger – teardown

    The charger can’t continuously supply the claimed 4.8A current and the mains isolation is questionable. Risk of electric shock and fire.

  16. Tomi Engdahl says:

    Kun tilaat laturin EU:n ulkopuolelta – omalla vastuulla


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