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sink and source current

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Junior Member level 2
Jun 23, 2015
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I have few questions
a. is sink current is associated with inputs alone or it is associated with output also.
b. similarly is source current associated with output alone or it is associated with inputs also.
c. sink and source are defined with respect to an ic or a circuit.
d. how to know the sink and source current of a circuit or an ic if I don't have datasheet.
please help

-sink and source current is applicable both to i/p and o/p.

--it is a characteristics of the circuit inside the ic.

--if no data sheet is available , you can measure it with appropriate instruments.


Sink and source current is more related to outputs i think. (But there may be inputs using that phrases)

Sink current is when an IC drives its output to the lower supply rail. A typical "sink only" output is an open collector output.

Source current is when an IC drives its output to the upper supply rail. Often used in cars to drive the lamps.

This is as well as for analog and for digital outputs.


Sink versus source is only a different (more graphical) way to describe current polarity.

Asking generally about "sink and source" current doesn't make much sense. The input or output current of device depends both on the external circuit and the internal function. A datasheet specification can have very different meanings, e.g. an input leakage or bias current, the maximum current that can be handled by an output under specific conditions.

Generally speaking, currents can be measured directley by an ammeter or indirectly by it's voltage drop across a known resistor.

i am understanding a little bit can I probably say something like this. if suppose a particular pin can sink some x current then if I give a current more than this, the transistor logic inside the ic gets damaged as the transistor has a limited current capability based on its manufacturing.

sink associated with inputs, the uc should have the capability to sink the current from the devices.
with low sink capability e the uc will get damage
Ex: switches or sensors like IR, PIR, Reed, magnet

source is associated with output
Ex: i. To drive a led, it needs current that should be passed from the uc, so the uc should have current source.
ii. To drive the dc motors, stepper motors, displays etc

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