LM723 current limiting problem (PSU of SATT SAM 82 console) [solved]

[argintviu]

I have a few uA723 ICs that I'd like to use to make a bipolar +-15V power supply for a  voltage reference. As a basis for the design I used the schematic of SATT SAM 82 console PSU which uses 2 x 723 and PNP pass transistors (lower noise). The nice thing is that it also has a current limiting feature which other implementations lack.

Before making PCBs I simulated the circuit in LTSpice, but the current limiting feature doesn't seem to work. In the SAM 82 service manual, it says this:

Regulators are conventional 723 designs with modifications in the current limiting circuits. /../ Output voltage with a load of 200 mA shall be 15.0 - 15.8V. /../ The power supply is short circuit proof and current limiting occurs at approximately 330mA. The supply is capable of delivering 250 mA continuously at elevated temperature and with a 10 percent reduced mains voltage. /../ Noise and ripple is below 5 mV peak-to-peak.

In the simulation the limiting does nothing and the circuit pulls up to 2 amps from the supply (with both LM723 models that I found online). Now I don't want to try "live" because I fear that the 723 might get fried and they're pretty rare to come by these days (and also I have the TO-10 version which is hard to breadboard).

What am I missing here? I doubt the circuit is bad since it was in production. Maybe the simulation models are bad? I have attached the original schematic and the simulation files.

[Avelino Sampaio]

There is an error in the simulation circuit. The 15v output and C6 must be connected between R6 and R4.  All output current has to pass through R6, so that the LM723's current sensing transistor can act in protection.

[argintviu]

Thank you for the help, it works now. I should have followed the original schematic's layout to keep mistakes like this out. Truly embarrassing .