Mobile Charger with Voltage Converter

The circuit allows a simple and safe charging of 1-10 Ni-Cd or Ni-MH cells from a 12V source. The voltage converter can be operated at 6V, in this case is the max. output voltage 12V (no load). The performance can be improved through the use of Schottky diodes (D2/D3). D4 (LED) can omitted if you dont want any indicator. An astable Mutivibrator generates the oscillation frequency. At the output (pin 3) connected the voltage doubler. At C5 is idling roughly double the input voltage. Thus, sufficient voltage difference exists to charge the connected batteries. Due to the high Switching frequency can be used relatively small capacitors. The charge current is indicated by a “real” load control (D4).

Mobile battery charger

List of components:

F 1 Fuse 0.5 A slow blow
D1 1N4007
D2, D3 or 1N4148 Schottky Diode
D4 LED red
R1 2.2 K 0.25 W
R2 10K .25 W
R3 27R 0.5 W
R4 47R 0.5 W
R5 68R 0.5 W
C1 47 uF 25V
C2 68 nF
C3 5nF
C4 10uF 40V
C5 47 uF 40V
C6 100n
IC 1 NE 555
Changes for 25 mA load current
R5 removes
R4 220R

The battery can be connected directly to the output. The charge current depends the components used about 50 ma (maximum output power). Depending on the number of cells can vary the desired load current through R4 be adjusted. The efficiency, depending on the load current between 70 and 85%.

Caution : The maximum input voltage is 18V, and at higher voltages will damage the IC. For sure the electrolytic capacitors with rated voltage types are used (no-load voltages!)The circuit is protected against reverse polarity of the supply voltage by D1 and F1.

Application : Portable radio batteries for charging up to 12V in the car, to obtain a second charge of battery as a voltage converter etc.

Power supply is an electronic device that supplies electric energy to an electrical load. The primary function of a power supply is to convert one form of electrical energy to another and, as a result, power supplies are sometimes referred to as electric power converters. Some power supplies are discrete, stand-alone devices, whereas others are built into larger devices along with their loads. Examples of the latter include power supplies found in desktop computers and consumer electronics devices.


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