Well, I'm clearly not understanding something here.
I tried the TIP120 transistor (a Darlington) using 0 to 5 Volts instead of 0 to 12 Volts. The highest output I got was 3.7 Volts. Then I tried using a MOSFET and the highest output was less, about 3.0 Volts. I can't figure out why I cannot get the full 5 Volts.
What am I missing?
UPDATE: This situation is about what Jackrae said in post #2.
jackrae:
This will limit output signal to around 4.3 volts
But I do not understand why the voltage is limited. I tried using 12 Volts as the supply (rather than 5 Volts) and got about the same results.