I've sussed out one of the purposes of that little capacitor in the feedback circuit. It's to block the feedback winding and resistor from the 0V connection so the high value start-up resistor can drive the power switching transistors base. Otherwise they would just shunt it's current almost completely.
I got this 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. I'm not going to go as far as saying that it's a safe device because it's track isolation isn't good enough and there are two other critical components that couple the low voltage side to the high voltage side. 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. The use of a proper opto-isolator for feedback is very impressive. Even if the voltage varies a bit under load it at least makes an effort to limit the upper threshold.
The case is clipped together, but is pretty solid and I wouldn't anticipate it coming apart accidentally even if it was put into a fairly tight socket.
In summary, it's very neat externally and internally, but I wouldn't trust it with USB items that had lots of exposed metal to touch or were too expensive to trust with a cheap power supply.
I got this 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. I'm not going to go as far as saying that it's a safe device because it's track isolation isn't good enough and there are two other critical components that couple the low voltage side to the high voltage side. 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. The use of a proper opto-isolator for feedback is very impressive. Even if the voltage varies a bit under load it at least makes an effort to limit the upper threshold.
The case is clipped together, but is pretty solid and I wouldn't anticipate it coming apart accidentally even if it was put into a fairly tight socket.
In summary, it's very neat externally and internally, but I wouldn't trust it with USB items that had lots of exposed metal to touch or were too expensive to trust with a cheap power supply.
Kindly do teardown for one transistor USB phone charger. How does USB phone charger that has only one transistor work?
I've been watching all your videos that are in n YouTube from the start to finish. You've come a long way since the beginning. Sometimes it is nice to see where things began.
Pls give circuit diagram separately. Thanks.
No earth connection, no safety circuit…is burning down your house, electrocuting yourself, or frying your mobile device worth saving $8 on the charger?
he is worth to watch ALL his Videos!
Are you listening AeV? They are way smarter than Bumble Fuck. They are going to render you useless.
why they don't put the transformer directly on the main voltage
And it even includes adapter. Adapter of mystery….
so nothing that a drop or two of hot glue can't fix
+bigclivedotcom I know this is a very old video, but do you know if you noticed the lack of earth connection? I see in the video that the earth pin existed on the mains side, but was never connected to anything visibly. This seems strange as far as designs go, to spend the money on the metal for the earth pin and not use it.
Thanks great show
mate, i love your videos!! I buy off eBay all the time and being a lay person, it's great to learn what exactly I have brought, and also learning how things work. even though I am in the USA.
And if you takin close to half amp out…you asking for trouble
Here in Perth (Western Australia) I was on an industrial site in the admin office when the power went. Site electrician quickly worked out it was an RCD trip. I helped isolate equipment from the circuit, we could not find the fault. About an hour later an office worker described getting a "tingle" as she was plugging her phone into an after market "Asian phone repair kiosk" charger. I grabbed my meter and measured between the USB shell and earth, expecting maybe a leakage voltage of 50vac or so… Nope 240Vac, what was worse was there was virtually 0R between Active and the USB shell !!! The device was reported to the office of energy who have taken it for analysis.
for some reason you keep mixing up japan and china….
I'd love to see a video of you reverse engineering the circuitry if a power supply like this. Whenever I try to do this myself i have no idea where to start, whereas your drawn schematics look like you've used a good methodological approach. I need this in my life!
Any idea if AULOLA branded chargers of this form-factor (colour shape etc too!) (not pretending to be Apple) are any good?
I'm curious though. In mainland europe we can plug an adapter in both ways, i.e. Live and neutral switched. Does that require a modification to the design, i.e. Are non uk adapters different?