# LM723 PSU Design

I am designing a Power supply with the LM723 adjustable voltage regulator. I have gotten it working but I don't think that it is working right. I am
using the 7-37v positive voltage regulator circuit that is in the app notes. To power the circuit I am using a 24v (actual voltage is about 37v) 1.25amp wallwart. In the circuit, instead of using the two resistors (R1 & R2) to put the feeback voltage into the inverting input, I replaced it with a 2k pot. However with the 2k pot the circuit will not output the range of voltage that it should. When I adjust the pot to one side, I can go down to the refernce voltage (which is correct ~7.2v), but if I adjust it all the way to the other side I can only get up to ~10.6v from the output of the circuit. Is there a reason that I can only get this range of voltage out of circuit. The equation is, ref_voltage * (r1+r2)/r1 = output_voltage. Why is it then that I can only get up to 10.6v with a 2k pot?
If I replace the 2k pot with a 100k pot, I can go from the reference voltage all the way up to ~35.3v by adjusting the pot from on side to another. However, the output is not linear. When I adjust the pot to one side, the voltage goes up really fast, but if I adjust the pot to the other side the voltage doesn't go down as fast as it when up (on a graph it would be a curve). So I can easily dial in small voltages but when I get to higher voltages it increases to fast that it is hard to get a certain voltage, especially with a one turn pot.
Is this all normal operation of the LM723 or am I doing something wrong? Any help will be appreciated.
Thanks, Ryan Grandy
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What type of pot are you using ? logarithmic or linear?
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