L.E.D. and Resistors

 

Standard
fixed type

Its
Symbol

Resistors may be used to either change the voltages or the
currents in a circuit.

In this section we will see how we can use resistors to
protect L.E.D's. This is achieved by the resistor limiting the
amount of current that can flow through the L.E.D. By
preventing too much current entering the L.E.D. we avoid
damaging it.

We can simply say that a resistor 'resists' the battery's
attempts to push too much current around the circuit and
L.E.D.

 

L.E.D. - Resistor Circuit Diagram

Notice that the + side of the battery connects via the
resistor to the Anode (+ side) of the L.E.D..

Resistors come in many
different types and values
- We need to choose the
right one.

There are many different types of L.E.D. too as we have
seen and it is important to match them with the correct
value resistor.

  • If the resistor value is too big, too little current will flow in
    the circuit and the L.E.D. won't work.

  • If the resistor value is too small, too much current will
    flow, possibly damaging the L.E.D. permanently.

Resistors are measured in Ohms () - and this tells us its
resistance value.
A resistor can be smaller than1 ohm or
bigger than10,000,000 ohms.

Choosing the right resistor for an L.E.D.

 

Q25,

Open the L.E.D. Resistor link at the top of the screen.
An example Super Bright L.E.D. is shown. It needs the
correct protection resistor. (Information to help you
work out the required value resistor is provided).

Follow the instructions and write in the box below
the calculated value of resistor needed to protect the
"Super Bright L.E.D.". Please check your answer.

ohms

 

Identifying Resistors using Colour Codes

When you need to identify a resistor of a particular
value, you will be able to use the coloured
rings
or bands around its case to show you.

To help you understand how to do this; open
the"resistor codes" link at the top of the screen and
read the instructions carefully. Then answer the
following questions to check your understanding:-

Q26, The first and second coloured bands on a resistor are blue and red. So its resistance value
begins with the numbers:

             

Q27, The third coloured band of a resistor tells
us how many zeros to write after the first two
numbers. If it is brown for the resistor in the question
above, the total value of this resistor is:

             

Ohms

 

Q28, What would the colour coding be for a 56K
(56000) ohm resistor. It should be accurate to within
+/- 10%

To answer drag the correct colours on to the resistor
outline below and then check your work.

 

 

 

 

 

 

 

 

 

 

 

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