Ive been reading some of the LT application notes on Jim William's Analog Circuit Design book, and there's something I don't quite understand. I'm attaching a scan of the circuit in question.
The LT1070 has its ground pin at -12V, and Q1 is forcing a current of around 1mA through the 1.24k resistor, this produces a 1.24V drop through that resistor, which corresponds to the 1.24V reference inside the FB pin (the error amplifier).
Ok I understand that, what I don't understand is why use the transistor in the first place? Why not just use a simple resistive voltage divider? whats the advantage of using Q1 rather than a simple resistive voltage divider?