Hi,
On the silkscreen and in the old schematic a 220 Ohm resistor is used between the PIC and the TIP110. In the build instructions and the parts lister a 180 Ohm resistor is used.
Looking at the data-sheet for the TIP110 its max current draw is 50ma which should be fine for port B on the PIC, assuming we aren't driving anything else 'high' current.
So my question is do we even need the resistor at all?
With a 180 Ohm resistor and 50ma 9V would be dropped over the resistor, i.e. it's not possible even if the TIP was short circuited to deliver 50ma with a 180 Ohm resistor. Assuming the resistor had 4.5V across it, leaving 0.5V to switch the TIP, then the current would be 25ma. Assuming that were enough to switch the TIP, as 50ma is a maximum needed, we would only be getting a maximum of 1.4A dropping to 1A when hot through the TIP.
Is there something I'm missing?
Thanks in advance,
Pete
