- #1
tangodirt
- 54
- 1
All electron flow nuances aside, let's look at simple circuit analysis. Hopefully you guys can clarify something for me. Say we have to drive an LED. We have a +5V source, a 3.4V forward voltage, and a 150 Ohm current limiting resistor:
+5V --> Resistor --> LED --> GND
Okay, so let's add an NPN transistor in here to turn the LED on and off (ignore the base for now). We have two possible configurations:
+5V --> NPN Trans. --> Resistor --> LED --> GND
or
+5V --> Resistor --> LED --> NPN Trans. --> GND
Of course, the first one would have the transistor in a "source" mode while the second one would have it in a "sink" mode.
Which one is better for driving the LED, or does it not matter?
+5V --> Resistor --> LED --> GND
Okay, so let's add an NPN transistor in here to turn the LED on and off (ignore the base for now). We have two possible configurations:
+5V --> NPN Trans. --> Resistor --> LED --> GND
or
+5V --> Resistor --> LED --> NPN Trans. --> GND
Of course, the first one would have the transistor in a "source" mode while the second one would have it in a "sink" mode.
Which one is better for driving the LED, or does it not matter?