The 723 Voltage Regulator
The 723 Voltage Regulator
The 723 is ancient in the world of IC voltage regulators. It is a 14-pin IC that needs some outboard components to tell it what to do. By itself it isn’t that impressive with a current capacity of 150mA, but with the addition of an external series pass transistor it can control whatever current the transistor can handle. It is designed primarily to be used as a positive regulator, but it can also be made to function as a negative regulator. In addition, although it is rated to 37 volts, it can be used in a “floating” mode and regulate voltages above that limit. All in all, I’ve found it to be a very stable, precise, and versatile device.
The main IC: LM723 is specified at temperatures from -55°C to +125°C. This chip is a little harder to find, and is more expensive than the LM723C which is exactly the same (as far as I know) but for the temperature spec which is from 0°C to +70°C.
I’m including two other documents about the IC: “The Many Talented 723" by Glen Prescott was my introduction to using it. “My Experience With The 723” by Roger Furer is my own story of the different regulator circuits I’ve built with it and includes links to schematics and PC Board layouts.
Several companies manufacture the LM723, but the data sheets are pretty much the same.
Texas Instruments calls it the µA723: 
National Semiconductor calls it the LM723 and LM723C (reduced temperature version) 
On Semiconductor never heard of it, but ST Microelectronics makes the LM723 (with various suffixes) 
It is available as a 14-pin DIP from everyone. In a metal can: H10C from National, and as an SO-14 from STM and TI. There may be other packages available from other manufacturers, but I limited my search to these three. Note that only the DIP-14 package has the Vz pin--the output from the zener diode which is used for negative regulators. The metal can and the flat-pack do not have enough pins and so they skip this one.
Note: The LM723C is identical to the LM723 except that the LM723C has its performance guaranteed over a 0̊C to +70̊C temperature range, instead of −55̊C to +125̊C.
National Semiconductor part # :
LM723H, LM723H/883, or LM723CH : Metal Can Package (H), NS Package H10C
LM723J/883 : Ceramic Dual-In-Line Package (J), NS Package J14A
LM723CN : Molded Dual-In-Line Package (N), NS Package N14A
ST Microelectronics part # :
LM723N : DIP-14
LM723CN : DIP-14
LM723CD : SO-14
Texas Instruments part # :
µA723CN : Plastic DIP (N),
µA723CD : Small Outline (D)
NTE makes a substitute: NTE923
LM723CN, DIP-14, Jameco part# : 24467, price: 1+ 0.34
LM723H, TO-5, Jameco part# : 301719, price: 1+ 3.69
UA723CDE4 Jameco part# : 1129851, price: 50+ 0.319
UA723CNE4 Jameco part# : 1129914, price: 1000+ 0.295
LM723CN/NOPB Jameco part# : 840691, price: 10+ 0.482
KA723, DIP-14 Mouser part# : 512-KA723, price: 1+ .67
KA723DTF, SOP-14 Mouser part# : 512-KA723DTF, price: 1+ .67
LM723CD, SO-14 Mouser part# : 511-LM723CD, price: 1+ .38
LM723CN, DIP-14 Mouser part# : 511-LM723CN, price: 1+ .32
LM723N, DIP-14 Mouser part# : 511-LM723N, price: 1+ .64
Texas Instruments UA723CN, DIP-14 Mouser part# : 595-UA723CN, price: 1+ .53
LM723CH/NOPB, TO-5 Digikey part # : LM723CH-ND, price: 1+ 5.48
LM723H, TO-5 Digikey part # : LM723H-ND, price: 1+ 5.48
LM723CN/NOPB, DIP-14 Digikey part # : LM723CNNS-ND, price: 1+ 1.12
LM723N, DIP-14 Digikey part # : 497-4268-5-ND, price: 1+ 0.99
LM723CD, 14-SOIC Digikey part # : 497-1595-5-ND, price: 1+ 0.86
there are more, but you get the idea.