LM723 negative regulator

[Rendon]

I have configured the LM723 as a negative regulator as per figure 18 in the data sheet EXACTLY as shown and have checked it many times, but it doesn't work no matter what. I have measured the voltages at the inv. and N.I pins; there is a significant voltage difference. The output at the transistor is between 9 and 10 volts, no matter what I set my feedback ratio to. The reference divider ratio is fixed at 50% (i.e R3 = R4). This is freaking me out. Why the hell does it not work?

Any help or insight will be appreciated.

 

[FvM]

Not explicitely said in the datasheet, but the basic negative regulator circuit isn't able to regulate voltages below 9.5 V, which is the minimum LM723 input voltage.

 

[Rendon]

Thanks. That is the insight I was looking for. I'm a little annoyed that I didn't pick it up myself, but that definitely puts things in perspective. Many thanks