Mobile phone charger circuit works - Power Circuit - Circuit Diagram - Huaqiang Electronic Network

Industrial Router Crystal 3.2*2.5mm 3225 26M (26.000MHZ) 12PF 10PPM 20PPM 30PPM

MOS Power IC Full Range

Photocoupler

In today's market, there are countless mobile phone chargers available, and the number of universal chargers continues to grow. However, the quality of these chargers is often lacking, and they frequently encounter issues. It's unfortunate to discard them without proper repair. Hence, I want to share how to analyze the principles behind mobile phone chargers, hoping it will provide assistance in fixing them. When analyzing a power supply, we typically begin with the input. The 220V AC input enters one side through a 4007 half-wave rectifier, while the other side goes through a 10-ohm resistor before being filtered by a 10uF capacitor. This 10-ohm resistor serves as a protective measure. If an overcurrent occurs due to a fault further along the circuit, the resistor will blow to prevent a more severe issue. On the right side, the 4007, a 4700pF capacitor, and an 82KΩ resistor form a high-voltage snubber circuit. When the switch tube 13003 turns off, it absorbs the induced voltage on the coil, preventing high voltage from damaging the switch tube 13003. The 13003 is the switch tube (officially known as MJE13003), with a voltage tolerance of 400V, a maximum collector current of 1.5A, and a maximum collector power dissipation of 14W, used to control the connection and disconnection of the primary winding and the power supply. When the primary winding repeatedly turns on and off, a varying magnetic field forms in the switching transformer, inducing a voltage in the secondary winding. Since the same-name end of the windings isn't indicated in the diagram, we cannot determine if it's a forward or flyback design. However, based on the structure of this circuit, it can be inferred that this power supply is likely flyback. The 510KΩ resistor on the left acts as a startup resistor, providing the base current for initiating the switch. The 10Ω resistor below the 13003 is the current-sampling resistor. The current is sampled and converted into a voltage (value = 10*I). This voltage is applied to the base of transistor C945 via diode 4148. When the sampling voltage exceeds 1.4V, i.e., when the switch tube current exceeds 0.14A, transistor C945 turns on, lowering the base voltage of switch tube 13003, reducing its collector current, and limiting the current of the switch to prevent overheating or damage (this is essentially a constant current structure, capping the maximum current of the switch tube at around 140mA). The induced voltage from the sampling winding (located at the bottom-left of the transformer) is rectified by diode 4148 and filtered by a 22uF capacitor to create a sampling voltage. For ease of analysis, let’s consider the emitter of transistor C945 as ground. The sampling voltage then becomes negative (around -4V), and the higher the output voltage, the more negative the sampling voltage. After passing through the 6.2V Zener diode, the sampling voltage is applied to the base of switch transistor 13003. As mentioned earlier, the more negative the sampling voltage, the higher the output voltage. Once the sampling voltage reaches a certain negative level, the 6.2V Zener diode breaks down, lowering the base potential of switch 13003, which interrupts or delays the conduction of the switch, controlling the energy input into the transformer and regulating the rise of the output voltage. The 1KΩ resistor and the 2700pF capacitor in series form a positive feedback branch, taking the induced voltage from the sampling winding and applying it to the base of the switch transistor to sustain oscillation. The secondary winding on the right is straightforward; it’s rectified by diode RF93 and filtered by a 220uF capacitor to produce a 6V output. Unfortunately, no specific data could be found for diode RF93. It’s likely a fast-recovery diode, such as a Schottky diode like 1N5816 or 1N5817. Given the high operating frequency of the switch-mode power supply, a diode with a suitable operating frequency is necessary. Additionally, the transformer must also be a high-frequency switching transformer, typically using a high-resistivity ferrite core to minimize eddy currents.