Ordinary radios are generally powered by dry batteries. They need to consume a large amount of dry batteries, which will increase the cost of users. In addition, the batteries contain heavy metals such as mercury, which seriously pollute the environment. Does not meet the modern "low carbon life" approach.
In response to this situation, we have made a small improvement on the mobile phone charger, so that the mobile phone charger can not only charge the mobile phone battery, but also power the radio to achieve the purpose of "one machine and two uses".
The mobile phone charger is powered by 220V AC, after transformer transformer or switching power supply. Output low voltage to charge the phone battery.
Generally, the design output of the mobile phone charger is 5V, the voltage is high, and the radio cannot be directly powered. It is necessary to add a small voltage step-down board to reasonably improve the output of the mobile phone charger. The improvement method is as follows. The following figure shows the voltage drop. Improved circuit for the platen. The forward voltage drop of a diode is between 0.6V and 0.7V. This feature can be fully utilized. Three diodes are connected in series with the positive terminal at the input of the small converter board to make the output voltage meet the requirements of the radio.
The voltage drop of the three diodes is 1.8V to 2.1V; 5V-2.1V = 2.9V; 5V to 1.8V = 3.2V.
The output voltage of the voltage step-down board is about 2.9V~3.2V, which meets the requirements of the radio supply voltage.
The design of the mobile phone charger only considers charging the battery, and the output ripple voltage is large: such as the old Nokia (NOKIA) mobile phone charger is basically a transformer type charger, there is no filter capacitor inside the charger, the output ripple voltage Very large, if you do not add a filter capacitor, the sound quality of the radio will be greatly reduced:
In order to control the cost, the capacitance value of the output of the switching power supply charger is also small, and the ripple voltage is also large, and the filter capacitor must be added on the buck board. Considering that the power supply has a great influence on the sound quality of the radio, generally the low-frequency filter capacitor selects an electrolytic capacitor of 220μF to l000μF, and it is preferable to select an electrolytic capacitor of Rubycon of Japan. The ESR is small, the filtering performance is good, and the sound quality of the radio is greatly improved. A 0.1 μF ceramic capacitor is connected in parallel at both ends of the large capacitor to filter out high-frequency clutter caused by the mains and reduce the power supply to the radio. The switching power supply type charger is preferably connected with a 0.1μμF ceramic capacitor in parallel with the input end of the buck board to filter out noise interference generated by the switching power supply itself. 
Things to note when making a voltage step-down board:
1. The input end of the voltage step-down board needs to add a power carrier matched with the mobile phone charger, and the output end directly leads out a wire with a power plug, which is matched with the external power supply of the radio.
2. It is important to note that the polarity of the buck plate cannot be mistaken, preventing polarity reversal and burning the radio. First test with a multimeter before testing. If there is no multimeter, you can also test with LED lkΩ resistor in series (as shown on the right), confirm the positive and negative terminals of the charger output plug and the positive and negative poles of the voltage step-down output plug.
3. If the mobile phone charger is a charger (no output lead and output plug), and the internal space of the charger is large, put the circuit in Figure 1 into the charger without affecting the original function of the charger (note this) The circuit is remote from the 220V primary high voltage section to prevent secondary introduction of dangerous high voltages. A section of the battery with a power plug can be used to draw power from the battery's electrodes.
4. Portable audio-visual equipment such as MP3/MP4/small CD player with 3V power supply can also be powered by this method in places with 220V power supply (only low-power portable audio-visual equipment) to reduce the consumption of dry batteries.
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