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how to work out a resistor value using ohms law

Calulate a resistor value uising Ohms Law

Submitted by Phil on Tue, 06/15/2010 - 16:50

I thought users would find this easy to understand

First of all we need to collect the following information:

  • The voltage of the supply
  • The forward voltage of the component eg L.E.Di<
  • The current the component uses

 

 

 

  • We can then apply Ohms law to calculate the value of resistori needed.

    • For calculating resistance we use the formula R= V ÷ I lets take the following as an example: Blue LED = 3.4V Forward voltage and 30mA maximum current, The supply voltage is 12V DC.

     

     

     

  • Step 1 We first need to work out the difference in the voltage between the source and the component this is 12V - 3.4V = 8.6V

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    Step 2 We convert the current rating from mA into A we simply divide by 1000.

     

    We now have R = 8.6 ÷ 0.03 Therefore R = 286 Ohms

     

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