Hello!
Just got me thinking... For some project I might need a precision DC voltage source controlled via a DAC. The problem is I need 4 quadrant operation - so opamp is the obvious solution. The voltage we are talking about might be say few +5V downto -50V, output current 1mA is more than enough, BW not critical, 1kHz very well sufficient.
The problem is, for +5-50V output I'd need an opamp designed for at least 60V supply operation. I know that some high voltage opamps do exist, but mostly expensive. I'd like to try to stick with jellybean parts for this, not afraid the component count will be a little higher. Only if that fails, I'll buy a high voltage opamp for this :-)
Do you have any suggestions, how to voltage boost the output of an opamp?
One of my first ideas was to ground the output of the opamp through a rather small impedance and then to use a pair of current mirrors in the opamp supply rails, to control the output voltage.
I have drawn my idea, please see below. Does it stand a chance to work? I think it just might, but I may well be mistaken.
Thank you for ideas as always!
Yansi
//EDIT: Just found
this voltage booster (the second image below). Almost exact schematic! Thats pleasing I have reinvented the wheel and it might work just fine. Also interesting to note the local feedback through R1 C1.
Still I do not get the purpose of matching/pairing the trannies in here. What will the assymetry cause? I can't figure out.