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, where mobile phone chargers are ubiquitous, there is an ever-increasing demand for universal chargers. However, the quality of these chargers is often lacking, leading to frequent issues. It's unfortunate to discard them without attempting repairs. Therefore, I want to share with you how to analyze the principles behind mobile phone chargers, hoping to provide some assistance in repairing them. When analyzing a power supply, it’s usually best to start with the input stage. The 220V AC input enters the system, with one end going through a 4007 half-wave rectifier while the other end passes through a 10-ohm resistor before being filtered by a 10uF capacitor. This 10-ohm resistor serves as a protective measure; in case of an overcurrent fault downstream, it will blow up to prevent any larger faults from occurring. On the right side, the 4007, along with a 4700pF capacitor and an 82KΩ resistor, forms a high-voltage snubber circuit. This circuit absorbs the induced voltage on the coil when the switch tube 13003 turns off, protecting the switch tube from high voltages that could cause breakdowns. The 13003 is the switch tube (officially known as MJE13003), with a withstand voltage of 400V, a collector maximum current of 1.5A, and a maximum collector power dissipation of 14W. Its role is to control the on/off state of the primary winding and the power supply. When the primary winding is repeatedly switched on and off, it generates a varying magnetic field in the switching transformer, inducing a voltage in the secondary winding. Since the same-named ends of the windings are not marked in the diagram, it’s unclear whether it’s a forward or flyback configuration. However, based on the circuit structure, it seems likely that this power supply uses a flyback design. The 510KΩ resistor on the left acts as a startup resistor, providing the necessary base current to start the switch. Below the 13003, the 10Ω resistor functions as a current-sampling resistor. The sampled current is converted into a voltage (equal to 10 times the current value). This voltage is then applied to the base of transistor C945 via a 4148 diode. When the sampling voltage exceeds 1.4V—that is, when the switch tube current surpasses 0.14A—the transistor C945 turns on, reducing the base voltage of the 13003 switch tube, thereby decreasing the collector current. This mechanism limits the current flowing through the switch, preventing it from becoming too large and burning out (essentially forming a constant current structure, capping the maximum current of the switch tube at around 140mA). The induced voltage from the winding (sampling winding) at the bottom-left of the transformer is rectified by a 4148 diode and filtered by a 22uF capacitor to create a sampling voltage. For simplicity, let’s assume the emitter of the transistor C945 is grounded. In this case, the sampling voltage becomes negative (approximately -4V), and the higher the output voltage, the more negative the sampling voltage becomes. Once the sampling voltage passes through a 6.2V Zener diode, it is applied to the base of the switching transistor 13003. As mentioned earlier, the more negative the sampling voltage, the higher the output voltage. When it reaches a certain negative threshold, the 6.2V Zener diode breaks down, lowering the base potential of the switch 13003, causing the switch tube to disconnect or delaying its conduction. This controls the energy input into the transformer, regulating the rise of the output voltage and achieving a regulated output. The lower 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 switching transistor to sustain oscillation. The secondary winding on the right is relatively straightforward. It is rectified by a diode RF93 and filtered by a 220uF capacitor to output 6V. Unfortunately, no specific data was found for the diode RF93. It is likely a fast recovery diode, such as a Schottky diode like 1N5816 or 1N5817. Given the higher operating frequency of the switching power supply, a diode with a suitable operating frequency is required. Due to the high frequency, the transformer must also use a high-frequency switching transformer. The core is typically made of a high-frequency ferrite material with high resistivity to minimize eddy currents.