Looking for a cheap, low voltage, low power, 'rail-to-rail' op-amp/comparator

[leppie]

Hi

This has probably been asked several times. Sorry if so

I need an op-amp that can work as low as 1.8V supply voltage (3.3V max) that would output at least 0.7 x V_supply.

I have no idea really how to determine the output voltage from the datasheets unless they say rail-to-rail (I am probably overlooking something  ) or state it like the LM358.

It needs to be a cheap and easy to get one (I really feel like ordering from RS, in South Africa, but will if I have to). Ideally in DIP for breadboarding.

Wont need to work at high speed, 100Hz-1kHz should be more than enough (I think...).

Any suggestions?

Thanks

leppie

[jmag999]

Microchip makes many parts that would fit your requirements.  For example: MCP6241.

[leppie]

Microchip makes many parts that would fit your requirements.  For example: MCP6241.

That looks a great fit, unfortunately only available from RS locally

[jmag999]

There are many many models you could pick from.  What manufacturers are available locally to you?

[leppie]

RS has pretty much everything, but as we have no local 'counter' any more, shipping is $10 and up

I did manage to find a local place selling MCP6547 which looks like it will do the job. Only $1.50 too 

They also have a MCP6002 in SOIC (need to look for those adapters I ordered years back...) for $0.50.

Thanks for the suggestions, it helped my pin point my search.

[LukeW]

MCP6001 is another possible candidate - very cheap, and rail to rail. But there are downsides of the limited 6v supply voltage and limited bandwidth.

[MrsR]

Try LM393 or LT1017/8
I've a project nearly finished using the LM393 but needed a LT type to test in LTSPICE IV.
I would have to double check the  LT models but it's on of the first row in comparators in LTSPICE IV.

HOPE THAT'S OF HELP
Rachael

[leppie]

Yeah, I have been testing on LTSpice and with a LM358 on breadboard.

It definitely seems I need a comparator and not an op-amp (but I might still need one for peak detection).

Found a nice app note from TI: Op Amp and Comparators – Don’t Confuse Them! http://nliebeaux.free.fr/ressources/aop_et_comp.pdf

[Zero999]

Yeah, I have been testing on LTSpice and with a LM358 on breadboard.

It definitely seems I need a comparator and not an op-amp (but I might still need one for peak detection).

Found a nice app note from TI: Op Amp and Comparators – Don’t Confuse Them! http://nliebeaux.free.fr/ressources/aop_et_comp.pdf

Yes, the general advice is not to do that, although there are application notes on datasheets, showing op-amps used as comparators and vice-versa. A classic example is the voltage controlled oscillator which requires both a Schmitt trigger (ideally a comparator) and an integrator (ideally an op-amp) so it's very tempting to use an op-amp or comparator IC to perform both functions.
Half of an LM358 op-amp used as a Schmitt trigger, thus acting as a comparator:
http://www.ti.com/lit/ds/symlink/lm158-n.pdf
A quarter of an LM339 comparator used as an integrator, thus acting as an op-amp:
http://www.ti.com/lit/ds/symlink/lm339-n.pdf

The best way to build this circuit is to use an op-amp and a comparator IC.