How to calculate dropping resistor?

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smeezekitty

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Say i have something that takes 9V @ 1ampere dc fed from a 12v regulated source.
What resistor / calculation to use to get the correct ohms in series to make the voltage within 9v +/- 1v.
 

(12V-9V) / 1A => 3Ω

Resistor's power rating:
Theoretical: P=RI² => 3W

In practice double this at least two times .. => ≥6W

IanP
 
You can try a dc-dc converter LM2575
**broken link removed**

Voltage dividing is ok if you are sure that the load is 9V 1A
will remain constant.

Best Regards,
Siong Boon
 

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