Hello!
I'm trying to teach myself some basic electronics and this is giving me several brain damage because of the little knowledge I have.
In most of the circuits involving an IC driving a LED, a resistor is usually used between the IC's output and the LED: The explanation given is that the resistor is needed to protect both the IC and the LED from becoming a nice puff of magic smoke. I can believe that this is true, but I really want to understand it.
After some research, I understand why a LED should not be connected directly to a power source: When the LED is operating it has a very small resistance so the current gets very high and it burns the LED.
The problem comes when an IC is added to the circuit, and I'll talk precisely about a PIC because its what concerns me.
Most PIC schematics I've seen don't use a resistor to power it making it seem that the PIC don't suffer the same fate as the LED when directly connected to a power source. This lead me to deduce that the PIC is offering some resistance. Immediately I went to this PIC's data sheet and found an "Unit Resistor Value" of 2k.
So, If the PIC is working as a 2k resistor, why do I need to use resistors at its outputs?
Thanks in advance, and sorry for my poor English.