Monday, 26 May 2014

Make a 5volt 8-100mAmp transformerless electronic power supply or cell phon battery charger at home

How to make 5volt 8 to 100mAmp transformerless electronic power supply or cell phon battery charger simple compact, efficient and cheap at home.

Almost all of our electronic products or projects, we need a compact cheap power supply for converting mains AC voltage to a regulated DC voltage. For making a power supply designing of each and every component is essential. Here I’m going to discuss the designing of  regulated 5V Power Supply.

To make a transformerless electronic power supply or Capacitor Power Supplies, we use a Voltage Dropping non polar Capacitor in series with the main line. An ordinary capacitor can not be used in these applications because Mains Spikes may create holes in dielectric of ordinary capacitors and the capacitor will fail to work or even may explodes. This may destroy the device connected to such power supply. Thus we use X Rated Capacitor with required voltage is used for this project. X Rated Capacitors rated for 250v, 400v, 600v AC and higher voltage levels are also available. Reactance of the voltage dropping capacitor should be greater than the load resistance to keep constant current through the load otherwise the current may drop when connected to different loads.

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Here for X-rated capacitor the reactance can be calculated  by below formulae:
Reactance of Capacitor, X = 1/2ΠfC

Where f is the frequency of mains and C is the Capacitance. Thus a 0.22μF capacitor has reactance of 14.4KΩ on mains frequency (50Hz). The approximate value of maximum current can be find out by dividing mains voltage by reactance of the capacitor (assuming that load resistance is small).
I = V/X
I = 230 V / 14. 4 = 15.9 mA
Thus a 0.22μF capacitor can supply a maximum current about 15mA.

Circuit Diagram:

5v 8mA to 100mA transformerless electronic power supply circuit.

As shown in above circuit diagram 1A fuse may be used to avoid damages due to short circuit and a MOV (Metal Oxide Varistor) may be connected as shown above to just avoid the problems due to voltage transients. Here the resistor R1 is used to limit the high current that can occur during switching the power on.  Here capacitor C1 225K (2.2μF) is used as the Voltage Dropping Capacitor or x rated capacitor. A Bleeder resistor is connected parallel to it for discharging the charged capacitor when the supply is switched off and capacitor still holds the charge. Diodes D1 – D4 is wired as Bridge Rectifier and the capacitor C2 here is used to filter the ripples in  DC. Here zener diode is used to regulate the filtered DC not to exceed from 5 volts or we can also use an IC for Voltage Regulatoion if we want better results. Resistor R3 here is used to limit the current through the Zener Diode.
The following table shows the maximum current and open circuit voltage of some of the most commonly used capacitors to attain the standerd voltages and current levels:
104K48 mA
334K1022 mA
474K1225 mA
684K18V100 mA
105K24V40 mA

Advantages of transformerless electronic or capacitive power supply over other types of power supply circuits:

  • Significantly smaller in size and lesser in weight than transformer power supplies.
  • Lesser in Cost when compared to Transformer or Switcher based power supplies.
  • Capacitor Power Supply is more efficient than Resistive Transformer Less Power Supply.

Disadvantages of capacitive or transformerless electronic power supply circuits:

  • Higher Cost when compared to a Resistive Power Supply.
  • No isolation from AC mains which introduces many safety issues like surge current, residual charge in capacitors etc...

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