Description
Part
Note:
This simple circuit can give regulated 4.7 volts for charging a
mobile phone. USB outlet can give 5 volts DC at 100mA current which is
sufficient for the slow charging of mobile phones. Most of the Mobile
Phone batteries are rated 3.6 volts at 1000 to 1300 mAh. These battery
packs have 3 NiMh or Lithium cells having 1.2 volt rating. Usually the
battery pack requires 4.5 volts at 300-500 mA current for fast charging.
But low current charging is better to increase the efficiency of the
battery. The circuit described here provides 4.7 regulated voltage and
sufficient current for the slow charging of the mobile phone. Transistor
Q1 is used to give the regulated output. Any medium power NPN
transistor like CL100, BD139, TIP122 can be used. Zener diode D2
controls the output voltage and D1 protects the polarity of the output
supply. Front end of the circuit should be connected to a A type USB
plug.
Connect a red wire to pin1 and black wire to pin 4 of the plug for
easy polarity identification. Connect the output to a suitable charger
pin to connect it with the mobile phone. After assembling the circuit,
insert the USB plug into the socket and measure the output from the
circuit. If the output is OK and polarity is correct, connect it with
the mobile phone.
Circuit Diagram:Part
- Q1 = BD139
- D1 = 1N4001
- D2 = 4.7V - 1/2W
- R1 = 560R - 1/2W
- C1 = 16V - 100uF
If the polarity is incorrect, it will destroy the mobile battery. So take extreme care.
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