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How to find resistances values in a voltage divider?

Angy15

Nov 18, 2015
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Nov 18, 2015
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I want to know the formula as to how to find Resistance values when voltages are known.If you refer the attached file voltages are Known how to calculate Resistance values .Thnx u .
 

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Arouse1973

Adam
Dec 18, 2013
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Dec 18, 2013
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You first have to choose a value of current you are happy with. These voltages can be produced with either very high or very low current. Let's say you are ok with 20 mA total current draw. Being a series circuit the same current will pass through each resistor.

So you need to work out the total resistance value which is going to give you 20 mA. This is 500 Ohms (10 Volts / 0.02 Amps = 500). So now you know each resistor will be some fraction of 500 Ohms.

All resistors apart from the bottom one has 2 Volts across it but the bottom one has 4 Volts across it. So you know the bottom resistor is going to be twice the value of the other ones. Work out the first 3 values (which will be the same) as 2 Volts / 0.02 Amps = 100 Ohms. So because you have 3 of these they are going to take 300 of the 500 Ohms leaving you with 200 Ohms.

This is the expected value as it is double the others because of twice the voltage drop. So your values from top to bottom will be 100, 100, 100, 200. Giving you the voltages you require.

Adam
 
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