Samples of el-cheapo 7809Ts bought over EBay test 8.79 - 8.8v, within
4% tolerance stated on data sheets (5 chips tested). Is 4% much of an issue, and for what applications? Upgrading an old +/- 5 v bench supply I built years ago to output +/- 9 v for breadboarding op amp circuits. Simple matter of swapping out the old ICs for new and tidying up the
As Tim Wescott says, it probably isn't going to matter in your application.
The fact that the bunch of parts you bought all test out at 8.79V to 8.80V = probably just means that they came from the same batch.
Many years ago (1980s) I'd had to clean up the design of a National Semicon= ductor LM305-based voltage regulator, which ended up needing a select-on-te= st resistor to get the current limit to limit at the right current.
For the next couple of years, production would drop by every six months or = so to complain that value that they'd been selecting for the past six mont= hs didn't work any more. Purchasing was buying roughly six month's worth of= LM305s at a time (about 100, which got them the 100-up price) and each tra= nche would come from a single production batch, so when that tranche ran ou= t production would have to adapt to the new batch.
After a few years, all the board test technicians had been told the story, = and I didn't have to tell it any more.
Powering homemade effects pedals hooked up to homemade musical instruments. In the finest tradition of circuit-bending, imperfections aren't flaws, they're character.
V probably just means that they came from the same batch.
onductor LM305-based voltage regulator, which ended up needing a select-on-= test resistor to get the current limit to limit at the right current.
r so to complain that value that they'd been selecting for the past six =A0= months didn't work any more. Purchasing was buying roughly six month's wort= h of LM305s at a time (about 100, which got them the 100-up price) and each= tranche would come from a single production batch, so when that tranche ra= n out production would have to adapt to the new batch.
Nope. Op-amps are remarkably tolerant of different supplies. In fact, for a lot of uses they don't even have to be regulated (although supply variations do bleed into the output signal -- look for power supply rejection ratio (PSRR) in your data sheet to get an idea of how much).
The biggest impact that supplies have on the op-amp is the highest and lowest voltages that the op-amp can drive to. The second biggest (if you're doing a DC circuit) is that the bias voltage is generally specified when the inputs are riding at the point halfway between + and - supplies. The third biggest is the PSRR, unless you're mostly concerned with making a Really Quiet circuit, in which case it may be the biggest thing that you care about.
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Sure, but 'typical' parts are usually much better than the worst-case tolerance. Actually, I just a couple minutes ago asked for the 5V rail (78M05CDT) to be checked on a new board that a fellow is bringing up and it was 4.99V (0.2%). An error in the region of 4% is something I've never observed personally on that class of part, and if I ever saw it I would probably trash the lot. Field failures are too expensive in $ and reputation to risk.