Has anyone tried making a discrete bandgap voltage reference? I need a stable (with respect to temperature, etc.) adjustable voltage source, but precision voltage reference ICs are pretty expensive. The LM3046 is cheaper and contains 5 matched transistors on a single die. I was thinking something along the lines of a Brokaw cell, a representative schematic is attached. The only difficulty is most bandgap ICs rely on transistors with different emitter areas and therefore different emitter current densities to create a voltage differential - since the transistors in the LM3046 are identical the currents would have to be set externally instead of just using two identical resistors from the output as in the schematic. The equations for the various resistor and current values so the output voltage has a dV/dt of approximately 0 shouldn't be to hard to derive.

 

Have you consulted the "guru" ....

http://www.national.com/rap/Application/0,1570,24,00.html

 

Thanks for your reply - yep I've looked over that page, that's where I got the schematic from! There are many issues mentioned that I will not have much control over as this will be a discrete design and not laid out for manufacture as an IC. When I have a design that works OK I'll be sure to post it here!