Hi, I have looked at CA3140 data sheets and seen that the output can reach close to the positive rail on a split rail supply, and (allegedly) right down to the negative rail.
This isn't as clear as it should be. First, on a single rail supply, the offset cannot be trimmed to get a true zero output, you MUST have some negative. At least, this is true on the two I just tested. Second, all the specs I've seen assume a symmetrical split supply, or a low single rail supply.
As I want as much positive overhead as I can get (to measure thirty watts at 1W/V from a thermopile sensor), my idea is to use a split rail supply whose total is 34 volts, with just a few hundred mV (possibly derived by Schottky diode drop) for negative, leaving me a full 30 volts on the positive side. I want a gain of about 11, so the input values are within bounds for the full output, and I should now get the full through-zero adjustment for input offset to appear corretly on the output.
Will this work without frying the IC? And can anyone suggest some common, low price and good performing IC's that can do this? Given this concept it doesn't have to be capable of a single rail supply with to-zero output, it just has to accept a VERY asymmetrical split rail. :) I'm hoping the LF411 or LF412 (with external offset trim) can do this.