# opamp without negative supply

I connected the V- pin to ground and the V+ pin to +5V. I then connected in+ to ground and in- to +5V. I expected Vout to be a low value near ground (0V) but I'm getting about +1.7V. Is this normal?

• When running a +/- op-amp on a single supply voltage it is usual to bias the in+ to somewhere in-between ground and V+ (say at 50% with 2 matching resistors in a voltage divider). This provides a 'fake' ground signal. V+ becomes +½V and ground becomes -½V. – Majenko Jun 18 '11 at 13:56
• @Matt, thanks that does make sense. But I'm trying to build a voltage controlled current source and these limitations seem to mean that I'll need a ton of other components to hack it into a workable circuit. Time to order new parts methinks. – Steven Lu Jun 18 '11 at 14:15
• @Steven if you don't mind the delay you could get some free samples from National, Analog Devices, Maxim, etc... – Majenko Jun 18 '11 at 14:30
• @Matt - I think Steven first wants to know what to order (either as sample or purchase) :-) – stevenvh Jun 18 '11 at 14:37
• @stevenvh which is where your answer comes in. These comments are not just for the benefit of the OP but for others who come after. – Majenko Jun 18 '11 at 14:43

• @Steven - the LM324 is a classic, a bit like $\mu$A741. It works from 3V (good) but isn't rail-to-rail (bad). This overview says "Large output voltage swing 0V to V+ - 1.5V". In the datasheet look for "output voltage swing". – stevenvh Jun 18 '11 at 14:21