> > > > Was the failed IC marked '723' or some house number? > > > > -tony > > Hi Tony As I recall, it was marked LAS723-2.5Luckily, before I simply > replaced it, I checked the > feedbackresistor values. They didn't make sense for 7V.My guess is that it > made using the 723 > for 5V supplies morepractical, although it could be wired up.The data sheet > seems to indicate
The error amplifier of the 723 has both inputs brought out, the reference is not connected to it [1]. So for 5V (or voltages under the reference voltage) you can link the sense wire directly to the +ve input of the error amplifier and a divided down refence to the -ve input. The only practcal advantage of the lower reference is that you can run the chip with a lower supply voltage I guess [1] It is not at all uncommon in systems with multiple 723s to use the reference of only one of them, feeding the error amplifiers of all the ICs. All PSU outputs should then track together. Or in some cases to ignore the reference altogether and, for example tie one input of the error amplifier to ground and the other to a potential divider between the output of that section (configured as a -ve regulator) and a positive supply rail. This then gives you supplies balanced about the ground rail. HP98x0 machines are one place this turns up, there are many others. > a better tolerance.The 2.5V references are usually bandgap and are > tightertolerance. As I recall, > in the supply I was working on, it was a low current 12V line.Dwight Possibly, although for most applications this would not be important. -tony