mdfrahim1 said:
Thanks a lot Shane.
Just for my info. While considering circuits and calculating currents shall i replace IC's by a short circuit or a open circuit ?
What is the internal resistance of an LED ?
What
i think your taking on to much infomation about to many things at once?
why do you need to know the internal resistance of an LED for?
ill give you quick example how a LED works
A LED has a maximum mA it can draw before it will burn out, if you were to put that LED connected to say, a car battery, it would burn out straight away or even explode in your face because the LED will try and draw more current than it can handle, so you need to connect a resistor suited to that LED, the best way for you to work out all that info is to mabye go to your local electronics shop and buy there parts catalogue, it will have all the info you need, eg: if you wanted to buy a LED and test to see how current and voltage and resistors work together
inside the catalogue you pick a LED you want to use , and it might say
red
30mA max
1.8V
so that is telling you that its red and you need to supply 30mA at 1.8Volts
so now you need to find a resistor that will supply your LED with 30mA
so you get the power supply you will be using eg: 12V and you minus the voltage drop across your LED and thats 1.8Volts
now you have 10.2V so to find the correct resistor you simply divide the mA it will use which is 30mA by the 10.2Volts, and your resistor will be 340ohms resistor(340R) the the equation goes like this
12V - 1.8 = 10.2V then 10.2V / 0.030mA = 340R
so i hope that this example helps you understand a little more about how current & volts work.