GPIO / resistors - electronics beginner question - Raspberry Pi Forums

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hi everyone!

have set 5v pc fan hooked pi powered 5v gpio pin on , has ground going through npn transmitter.

base of transmitter connected 3.3v pin on pi , put 10k resistor between them. when put 3.3v pin "on" mode - transmitter lets current flow 5v pin fan.


question is: resistor affect fan in case? aren't parts of same circuit (they 'meet' @ pi's ground)?

appreciate this!

the resistor necessary limit current through diode. 10k resistor current flowing limited 3v3 - 0.7v (the diodes forward voltage) = 2,6v / 10.000 = 0.26ma.
transistor as switch has current amplification (that different , lower hfe) of between 50 , 200, transistor conduct 50 300 times 0.26ma, or 13ma 52ma, bit low feed fan.

gpio pin can deliver 15ma, lower 10k resistor more base current can flow.


raspberrypi



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