A feedback circuit measures the output voltage and sends a signal to the controller IC, which adjusts the switching frequency to obtain the desired voltage. Note that this winding is heavy-gauge wire, since it is feeding the 1A output. Also take a look at Apple didn't revolutionize power supplies; new transistors did which examines the history of switching power supplies.
The isolation boundary between these areas is about 6mm in the Apple charger and can be seen in the above diagram. The Y capacitor is usually omitted from other designs.
In addition, the expansion header provides access to a second on-board serial port. Finally, this AC is converted into DC which is filtered to obtain smooth power free of interference, and this power is output through the USB jack. The Apple charger is higher quality and I estimate has about a dollar's worth of additional components inside.
The values of many of the resistors and capacitors are indicated through standard SMD three-digit markings two digits and then a power of ten, giving ohms or picofarads. The second transistor clamps voltage spikes, as will be explained below. The controller IC is visible above the transformer on the top of the primary board. Since this winding is on the primary side, it doesn't need to be triple insulated.
They didn't just improve the prongs slightly to make them more secure; clearly scheda madre con 4 slot ram was told to do whatever it takes to make sure there's absolutely no way the prongs could possibly come loose again under any circumstances.
In addition, we now offer a cable for the Baofeng UV-5R or similar: One interesting consequence of quasi-resonance is the switching frequency varies depending on the load with 70kHz as a typical value. Schematic I've put together an approximate schematic showing the charger circuit.
The chopped DC is fed into a flyback  transformer which converts it into low voltage AC. Also see comments on Hacker News. It is designed to stack on top of the Beaglebone Black.
The large components were removed in the diagrams, and are indicated in italics. It simply takes AC input anything between and volts and produce 5 watts of smooth 5 volt power, but the circuit to do this is surprisingly complex and innovative. Note the lack of components in the middle of the secondary board, forming an isolation boundary.
The innovative part of this circuit is that Q1 doesn't need special drive circuitry like other active clamp circuits; it is self-powered via the capacitors and diodes.
The Y capacitor was covered with black heat shrink tubing, there was tape around the side of the circuit, the fusible resistor was covered with black heat shrink tubing, and there was a black insulating cover over the USB connector.
Thus PC software that expects to see a serial port on the computer will interpret the TNC-X as being connected to such a port, even when the PC has no serial ports, or they are all used by other applications.
The solution is the high-voltage DC is dropped to a low level through startup power resistors to provide the initial power to the IC until the transformer starts up.
But in addition, super-cheap knockoff power supplies use variable frequency circuits almost identical to the Apple Beaglebone black power jack. Power is provided to the daughter board through the expansion header. Now, advanced controller ICs have gone back to variable frequency controls.
The picture above shows the flyback transformer yellow more clearly, above the USB jack. Transformer teardown The flyback transformer is the key component of the charger, the largest component, and probably the most expensive. This unusual and innovative circuit is patented by Flextronics.
The charger consists of two circuit boards, slightly under one inch square each.
The input AC first passes through a fusible resistor stripedwhich will break the circuit if there is a catastrophic overload. The DC is switched on and off by a transistor controlled by a power supply controller IC.
In addition, signals that would otherwise go to or from a host PC can be intercepted by the daughter board at the TTL level and processed. I could be misunderstanding this circuit, because it seems that Apple unnecessarily took up space and expensive components maybe 25 cents wow macro use trinket slot 1 implementing this feature in such a complex way.
This isn't enough to be officially high voltage but I'll call it high voltage for convenience.
The USB output also has specific resistances connected to the data pins to indicate to the iPhone how much current the charger can supply, through a proprietary Apple protocol. In additionthere is one packet connector that is used on a lot of radios for example: The DC voltage is approximately sqrt 2 times the AC voltage, since the diode charges the capacitor to the peak of the AC signal.