Circuit voltage reduction

Gary Gauthier's picture

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Joined: Jul 05, 2019

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Circuit voltage reduction
July 5, 2019 - 11:38pm

I have a load powered by a 9 volt source. The circuit is a simple series circuit. The curcuit has a current of 180 Mille amps. If I were to power the load with a 12 volt source, what resistance would I have to put  in series to bring the voltage down to 9 volts. Thanks Gary

 

 

 

Ashutosh's picture

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Joined: Aug 27, 2018

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Resistor for voltage Reduction
July 7, 2019 - 12:22pm

Hi Gary,

Your understanting of resistor is bit wonrg here. I see that you have to convert a 12V power source to 9V to power your load which operates on 9V with a current consumption of 180 mA.

While it is okay to think of using a resitor to do the job. All you have to do is drop the excess 3V (12-9) across the ressistor and you are good to go. You can use this ohms law calculator https://circuitdigest.com/calculators/ohms-law-calculator to find the value of your required resistor. In this case enter voltage as 3V current as 180mA and click on calculae you will find resistance to be 16.6 Ohm with a 0.54 Watt power rating 

But speaking on engineering terms this is a very inaccurate way to regulate power, because you cannot find the exact value of resistor (16.6 ohms) and the voltage drop varies based on the current through the resistor. The practical way of doing it is by using a voltage regulator IC like the 7809 whcih will regulate 12V to 9V

Gary Gauthier's picture

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Resistor for voltage reduction
July 7, 2019 - 8:16pm

Thank you very much Ashutosh for the information, much appreciated Gary