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How to design a phone charger as Cheap as 1000 Naira Only


  As an engineer, dealing with electronic stuffs is just like the interaction between body and blood, hence making it compulsory for engineers in practice to know a gratifying knowledge about it. I know many readers will take it for granted, but its importance make me think of talking about it, as anybody who have chance to go through it will learn something even if he is not able to practice.

  Any direct current (DC) charger is doing nothing but converting alternating current (AC) from a specific value to a required value in DC form through four processes (stages) transformation, rectification, filtration and regulation.

TRANSFORMATION
  Is a stage in which the specified AC source is transformed to a required Ac for rectification E.g 240v(AC) to 12v(AC)/9v(AC)/6v(AC) and so on.
To achieved this transformation we have different approaches like by using step up/ step down / resistor or Zener diode.

RECTIFICATION 
  Is a stage in which the AC voltage is converted to pulsating DC voltage using diode which allow the passage of current in only one direction.

FILTRATION
  In this process the converted pulsating DC voltage is filtered meaning the amount of ripple presence during conversion is removed or reduced using capacitor.

REGULATION 
  Is a stage used to regulate the amount of converted DC voltage to a required fixed value of voltage and current even if the input AC source is fluctuating (varying) E.g phone charger ~5v, computer charger ~19v and DC Fan ~31v.
With the brief explanation let go straight to the point and have the idea on how to design and implement your own phone charger that cost less than #1000.

DESIGN 
  Designing of phone charger having 5v DC output and 0.5A with 2% ripple factor


PROCEDURE 
  Firstly For the transformation stage we have different type of approach but here i am going to use the simplest one which is using a step down transformer of rating 240/9v AC as shown in figure 1.1 below and for rectification stage it's advisable to always use full bridge rectification method which is to use four diode. 

Rectification Calculations
PIV (peak inverse voltage)= Vrms × √2
Where Vrms = 9 v
PIV = 9 × √2 = 12.728 v
So IN4001 50v 1A diode is ok

Filter calculation
Here we calculate the value of filter capacitor to be used using our charger specification
C = 1 ÷ 4√3×f×ripple factor×Rl 

Where :
Rl is the load resistor and f is the frequency
Rl = Vl ÷ Il = 5 ÷0.5 = 10Ω
C= 1 ÷ 4√3×50×0.02×10
= 14433.75micro farad
So we can use 10000 micro farad standard capacitor
Note that the bigger the value of the capacitor the lower the ripple present during filtration.

Regulation stage
For the regulation also there is different approach but just go simple one that is IC7805 regulator as shown below:



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