![]() (These wires were cut during disassembly.) The secondary board converts the low voltage from the transformer to DC, filters it, and then feeds it out through the USB connector (the silver rectangle in the lower left). (The second transistor clamps voltage spikes, as will be explained below.) The chopped DC goes to the flyback transformer (yellow, barely visible behind the transistors), which has low voltage output wires going to the secondary board below. Next, the high voltage DC is chopped at high frequency by a MOSFET switching transistor, which is the large three-pinned component in the upper left. The input AC is converted to high-voltage DC, which is smoothed by the two large electrolytic capacitors (black with white text and stripe) and the inductor (green). The input AC first passes through a fusible resistor (striped), which will break the circuit if there is a catastrophic overload. ![]() The top board is the primary, which has the high voltage circuitry, and the bottom board, the secondary, has the low voltage output circuitry. The charger consists of two circuit boards, slightly under one inch square each. The side view above shows some of the larger components. 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. 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 chopped DC is fed into a flyback transformer which converts it into low voltage AC. The DC is switched on and off by a transistor controlled by a power supply controller IC. ![]() In more detail, the AC line power is first converted to high voltage DC by a diode bridge. Because of their design, switching power supplies are generally compact and efficient and generate little waste heat compared to simpler linear power supplies. ![]() The iPhone power adapter is a switching power supply, where the input power is switched on and off about 70,000 times a second in order to get the exact output voltage required. It simply takes AC input (anything between 100 and 240 volts) and produce 5 watts of smooth 5 volt power, but the circuit to do this is surprisingly complex and innovative. This article is now available in Vietnamese Bộ sạc iPhone của Apple.ĭisassembling Apple's diminutive inch-cube iPhone charger reveals a technologically advanced flyback switching power supply that goes beyond the typical charger. ![]()
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