PI op-amps supply voltage

[1843]

Hi All,

Why in most PIs +5V and -5V rails are used for their op-amps?

For say if we drive PI's op-amps with +4V and -4V, what effect have?

Thanks in advance.

[TheWizard]

Hi All,
Why in most PIs +5V and -5V rails are used for their op-amps?
For say if we drive PI's op-amps with +4V and -4V, what effect have?
Thanks in advance.

+5 for TTL or MCU or ADC....
If you use 3.3v MCU or ADC, you can use +3.3v / -3.3v op-amp....

[diggerbarns]

4v v 5v

+- 5volt regs are cheap and easy to get so why bother

[1843]

Ok!
So the lower voltage is better... but is difficult to obtain.

Best regards

[digger barns]

why better

what advantage by going 1 volt less. Most P I, start with a 12 volt battery and then get +- 5v some way. I cant say that I can see any point in going to +- 4v. I you are looking to save the planet by saving energy may be better to look for low current regulators. Having said that must admit to have been surprised when I see Technetics T2 uses just two AA batteries or does it use four AA. Still good going though. Old Technetics ST used about eight C cells.
Do believe some minelab manage on four AA.

[1843]

The input of ADC is 0-2.56V in my circuit, so op-amps shuld be run by +-3.5 to 4V.

[Carl-NC]

It doesn't matter what supply you run the opamps on. Just a matter of convenience etc. I'm currently designing a PI detector with 2.5v rails.

- Carl

[1843]

It doesn't matter what supply you run the opamps on. Just a matter of convenience etc. I'm currently designing a PI detector with 2.5v rails.

- Carl

Hi Carl,

Ok, I saw the Tiny PI from www.pulsdetektor.de that uses +-8V to run their opamps on. I doubted about its performance ...

Regards

[Elie]

Back in the old days, before op amps were powered by the same voltages as logic ICs, they were powered by much higher voltages, often +/- 15v, and sometimes even higher voltages.

[Max]

Hi Carl,

Ok, I saw the Tiny PI from www.pulsdetektor.de that uses +-8V to run their opamps on. I doubted about its performance ...

Regards

Hi,
there is no direct relationship between supply voltage of op. amps and performaces.

What you need is enough voltage to right supply them. Older ones, as Elie said, used e.g. +15/-15 to work right. Today op. amp. use also +2,5/-2,5 or even less.

Then another factor is how much you have to stay away from saturation... having much gap between rails gives you more flexibility with gains settings.
But you have to consider the bigger swing (so chose right SR for them).

There are also rail-to-rail op amps that are good when low supply is involved: an example are TLC2262 used in BANDIDOII, they can operate till rail voltages (so with an extended range respect to others).

Kind regards,
Max

[1843]

Can I use low pass filter to reduce the rails voltage? ( Doesn't make bad effect?)
By choosing 220R resistors and 470uF caps, I could obtain +-3V for driving opamps.

Another question is about low-pass filters:
I see in various circuits, various low-pass filters! What difference is there between them? please explain.

Thanks in advance,
1843

[gef12]

New Project ?

Hmmmm
So Carl is there is a new PI on the project drawing board ???
Can you confirm or deni this .... any further info or you keeping quiet for a while ??
Keep the sunny side up n the greasy side down

cheers
gef

[Carl-NC]

Hmmmm
So Carl is there is a new PI on the project drawing board ???
Can you confirm or deni this .... any further info or you keeping quiet for a while ??
Keep the sunny side up n the greasy side down

cheers
gef

I cannot deny that I am designing a new PI detector. However, this is a commercial design, so I will not be able to divulge the schematics. I can say, that the whole thing will run on less than 5mA of current.

- Carl

[Elie]

I cannot deny that I am designing a new PI detector. However, this is a commercial design, so I will not be able to divulge the schematics. I can say, that the whole thing will run on less than 5mA of current.

- Carl

Who is going to produce it?
Are you going to quit your day job?

[Carl-NC]

Who is going to produce it?
Are you going to quit your day job?

Can't say right now. Day job is still secure.