Do you know the working principle of cell phone charger circuit?
2022-12-08 Views：35
For the cell phone power adapter seen everywhere on the market, the universal charger continues to increase, but the quality is not very high, there are often problems, throwing a pity, BON cell phone charger manufacturers to teach you a few tricks to analyze the analysis of the principle of cell phone power adapter, I hope to bring you some help in repair.
Analysis of a power supply, often starting from the input. 220V AC input, one end through a 4007 half-wave rectifier, the other end after a 10-ohm resistor, filtered by a 10uF capacitor. This 10-ohm resistor is used to do protection, if the back of a fault, etc., resulting in overcurrent, then this resistor will be burned out, thus avoiding causing a larger fault.
The right 4007, 4700pF capacitor, 82KΩ resistor, constituting a high-voltage absorption circuit, when the switch 13003 off, responsible for absorbing the induced voltage on the coil, thus preventing the high voltage added to the switch 13003 and lead to breakdown. 13003 for the switch (the full name should be MJE13003), withstand voltage 400V, the maximum collector current, the maximum Collector power consumption of 14W, used to control the primary winding and power supply between the on and off.
When the primary winding keeps on and off, it will form a changing magnetic field in the switching transformer, which will generate an induced voltage in the secondary winding. The left end of 510KΩ for the start-up resistor, to provide the switching tube to start with the base current. 13003 below the 10Ω resistor for the current sampling resistor, the current is sampled into a voltage (its value is 10 * I), this voltage after the diode 4148, added to the base of the triode C945.
When the sampling voltage is approximately greater than 1.4V, that is, the switching tube current is greater than when the transistor C945 conducts, thereby pulling down the base voltage of the switching tube 13003, thus reducing the collector current, which limits the current of the switch to prevent excessive current and burn (in fact, this is a constant current structure, the maximum current limit of the switching tube at about 140mA). The induction voltage of the winding at the bottom left of the transformer (sampling winding) is rectified by rectifier diode 4148 and filtered by a 22uF capacitor to form the sampling voltage.
For the convenience of analysis, we take the emitter end of the triode C945 for the ground. Then the sampling voltage is negative (-4V or so), and the higher the output voltage, the more negative the sampling voltage. Sampling voltage after 6.2V regulator diode, added to the base of the switch tube 13003. As mentioned earlier, when the higher the output voltage, then the more negative the sampling voltage, when the negative to a certain extent, the 6.2V regulator diode is broken, thus pulling down the base potential of the switch 13003, which will cause the switch to disconnect or delay the switch conduction, thus controlling the energy input to the transformer, which also controls the rise of the output voltage, to achieve the function of regulating the output.
The 1KΩ resistor below is connected in series with a 2700pF capacitor, which is a positive feedback branch, taking the induced voltage from the sampling winding and adding it to the base of the switching tube to maintain oscillation. The secondary winding on the right is not much to say, rectified by diode RF93, 220uF capacitor filtered output voltage of 6V. Did not find the diode RF93 information, it is estimated that a fast recovery tube, such as Schottky diodes, etc., because of the high operating frequency of switching power supplies, so the need to work frequency diodes.
Here you can use the common 1N5816, 1N5817 and other Schottky diodes instead. Also because of the high frequency, the transformer must also use a high frequency switching transformer, the core is generally a high frequency ferrite core with high resistivity to reduce eddy currents.
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