EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: leppie on July 23, 2014, 02:17:45 pm
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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 :palm:) 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
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Microchip makes many parts that would fit your requirements. For example: MCP6241.
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Microchip makes many parts that would fit your requirements. For example: MCP6241.
That looks a great fit, unfortunately only available from RS locally :(
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There are many many models you could pick from. What manufacturers are available locally to you?
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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.
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MCP6001 is another possible candidate - very cheap, and rail to rail. But there are downsides of the limited 6v supply voltage and limited bandwidth.
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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 :-+
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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 (http://nliebeaux.free.fr/ressources/aop_et_comp.pdf)
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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 (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 (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 (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.