op amp

i've been trying to learn about op-amps, since i've never used them yet, i thought i might use one in a pic amp-meter. so far that i read, you need a negative voltage, so that it can "swing"
to zero. if and op-amp's data sheet say that it can "Output voltage can swing to ground", does
that mean that you would not need a negative supply? ST's chip# TS271 was a op-amp i was looking over. thanks

You don't need a negative supply. An opamp that can can "swing to ground" is a good one to use with the pic's A/D input, older opamps have voltage offset issues.

thank you, i've been reading alot this week. i might even try one of those new current/voltage monitor chips, but first i will give this op-amp a go. thanks again

Be aware that the TS271's output will not reach the positive rail. With no load, it will typically go to within about 1V. It gets worse is the current load increases. Also, the input common mode range appears to be from about 1V above the negative rail to about 2.6V below the positive rail. This is pretty poor.
Don't know if these specs are problems, but there are plenty of rail-to-rail input and output op amps available that I believe are reasonably priced.

^ Yeah, that could be better.

Joe - an LM6132 goes rail-to-rail with both the inputs and outputs, you might be happier with that.

Joe G said:

i've been trying to learn about op-amps, since i've never used them yet, i thought i might use one in a pic amp-meter. so far that i read, you need a negative voltage, so that it can "swing"
to zero. if and op-amp's data sheet say that it can "Output voltage can swing to ground", does
that mean that you would not need a negative supply? ST's chip# TS271 was a op-amp i was looking over. thanks

Click to expand...

Joe, here is an additional hint: Be aware that for single supply operation of the opamp you need a specific bias scheme to place the operating point somewhere in the middle of the quasi-linear output range (approx. half the supply voltage). If you can afford a dual supply - the design is simpler.

the meter would be for a computer psu hack. I thought that it may only go down to about a 1v min., i will ck out that LM6132. thanks all