Electronics > Beginners
Voltage drop across resistor
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medical-nerd:
Hiya

Aaaarghhh....

I'm probably having a face palm moment but am having a blank at the moment.

I know how to calculate basic voltage drops using ohm's law by calculating current flow first. But what do I do if current is a known fixed value?

If I have a module that uses e.g  275mA at a supply of 5V, if there is a resistance of 10ohm after the voltage regulator, what is the voltage drop across the resistor?

Cheers
capt bullshot:
U = I * R

multiply the current by the resistors value
mikerj:

--- Quote from: medical-nerd on June 21, 2018, 12:50:10 pm ---If I have a module that uses e.g  275mA at a supply of 5V, if there is a resistance of 10ohm after the voltage regulator, what is the voltage drop across the resistor?

--- End quote ---

At 275mA a 10 ohm resistor will drop 0.275*10=2.75volts.  The problem here is that with the resistor in circuit your load is now only seeing 5-2.75=2.25v, so is unlikely to be taking 275mA any more (unless it's a constant current sink).  Current sensing resistors usually have low values to minimise voltage drop, which may then require amplification to get a useful signal.
Audioguru:

--- Quote from: medical-nerd on June 21, 2018, 12:50:10 pm ---if there is a resistance of 10ohm after the voltage regulator
--- End quote ---

Is the 10 ohms resistor in series with the 275mA module? Then the module is not getting 5V and probably is not drawing 275mA anymore.
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