Looking for a cheap, low voltage, low power, 'rail-to-rail' op-amp/comparator - Page 1
Forum section: electronics / beginners

author: leppie
author_rank: Frequent Contributor
timestamp: July 23, 2014, 02:17:45 pm
content: HiThis has probably been asked several times. Sorry if soI 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?Thanksleppie

author: jmag999
author_rank: Contributor
timestamp: July 23, 2014, 02:27:58 pm
content: Microchip makes many parts that would fit your requirements. For example: MCP6241.

author: leppie
author_rank: Frequent Contributor
timestamp: July 23, 2014, 02:37:14 pm
content: Quote from: jmag999 on July 23, 2014, 02:27:58 pmThat looks a great fit, unfortunately only available from RS locally

author: jmag999
author_rank: Contributor
timestamp: July 23, 2014, 03:09:56 pm
content: There are many many models you could pick from. What manufacturers are available locally to you?

author: leppie
author_rank: Frequent Contributor
timestamp: July 24, 2014, 06:05:25 am
content: RS has pretty much everything, but as we have no local 'counter' any more, shipping is $10 and upI did manage to find a local place selling MCP6547 which looks like it will do the job. Only $1.50 tooThey 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.

author: LukeW
author_rank: Frequent Contributor
timestamp: July 24, 2014, 11:43:09 am
content: MCP6001 is another possible candidate - very cheap, and rail to rail. But there are downsides of the limited 6v supply voltage and limited bandwidth.

author: MrsR
author_rank: Regular Contributor
timestamp: July 24, 2014, 09:36:26 pm
content: Try LM393 or LT1017/8I'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 HELPRachael

author: leppie
author_rank: Frequent Contributor
timestamp: July 25, 2014, 10:14:53 am
content: 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

author: Zero999
author_rank: Super Contributor
timestamp: July 26, 2014, 02:49:13 pm
content: Quote from: leppie on July 25, 2014, 10:14:53 amYes, 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.pdfA quarter of an LM339 comparator used as an integrator, thus acting as an op-amp:http://www.ti.com/lit/ds/symlink/lm339-n.pdfThe best way to build this circuit is to use an op-amp and a comparator IC.