My usual focus is in digital electronics, and my BJT knowledge is fuzzy. I'm working on a design using the Intersil ICM7245 16-segment display driver. It recommends this circuit to drive the led segments with a higher drive current.
I'm having trouble figuring out exactly how this works, namely, so I can choose compatible BJTs for both the high and low sides, assuming my LEDs are Vf = 2v, If = 20mA.
2N2219 = NPN. 2N6034 = PNP Darlington
I duplicated it in Orcad/Pspice, and the results don't seem like it should work. I think I can just choose some BJTs that match, but I want to make sure before I get the PCBs ordered.
Edit: To clarify my question, I understand that each transistor has a gain (hFE) of ~100, hence 1mA->100mA, and 14mA->1.4A. I'm just not clear on how they made sure the bases would have those currents, and how much I can change the 14ohm resistor to keep my LEDs at ~20mA.