Electronics > Beginners
How to calculate total amps required for various voltages?
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shai:
Say I have 12V for power, but I have a PCB with loads that use 3v, 5v and 12v. How do I figure out the total amps all the loads consume? Do I do 3V x amps = watts and then add up all the watts and divide by 12v to figure out the total amps? Is watts used as a common denominator? Thanks!
Rerouter:
in this case it would be (3V x amps) / efficiency = input watts, then input watts / 12 = input amps.

your probably using switchmode regulators, but they are not 100% efficient so they will pull a bit extra than just the load watts would say.
Ian.M:
If there are any linear regulators, their input current is their output current + their quiescent current (usually negligible).  The difference between their input and output powers (calculated from V*I) is thrown away as heat.
shai:
Hi, thank you for the help, but I am confused what you mean by efficiency? I'm using a linear regulator, specifically the LM1117. Can you please post an example calculation on how I can figure out how much 12V amps I need to feed the PCB if I have a 12V 2A component and a 3V 0.5A component?
sleemanj:
Since you are only using linear regulators, just sum all three (load) currents.  Input current = output current for a linear regulator, ignoring quiescent.

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