Mobile phone charger repair. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Mobile telephony
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The article talks about a typical malfunction of mobile phone chargers. A diagram of one of these blocks, compiled according to a "live" model, is given, recommendations are given for changing the output parameters and using the repaired block in amateur radio practice.
Nowadays, mobile phone chargers are even more common than phones themselves. The radio markets have a large number of used devices (power supplies) at low prices. Among them, there are quite a lot of substandard ones. Just they are of particular interest to radio amateurs because of their purely symbolic value. The output voltage of the unit, as a rule, differs significantly from that indicated on the nameplate, and its stabilization is almost completely absent.
An analysis of several blocks from various manufacturers showed that they are similar, like twins, not only constructively, but also circuitry. It turned out to be a similar error.
A diagram of one of the options for a mobile phone charger is shown in Fig. 1. It is compiled according to a "live" model, so the designation of the positions of the elements is conditional.
(click to enlarge)
When the unit was connected to the network, the LED was lit, which means that the power supply was started and, in principle, worked. The output voltage without load was 5,5 V, and with a load (13,5 V incandescent bulb) it dropped to 3,5 V. A slight “crackle” of the transformer was heard in both cases.
The assumption that breakdowns are observed in the transformer or there is a short circuit of the turns in the winding has not been confirmed. There was also no loss of capacitance in electrolytic capacitors.
The culprit was the zener diode, conditionally indicated in the diagram of Fig. 1 by the number 7. It had a leak and “floating” parameters.
The free space in the power supply housing made it possible to use a chain of several series-connected domestic zener diodes instead. At the same time, it was easy to obtain other, except for the passport, values of the output voltage (see table).
This will probably be of interest to radio amateurs, since they will always find use for such a powerful and small-sized power supply. The location of the elements on the board is shown in Fig.2.
See other articles Section Mobile telephony.
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