Hi all A standard comparator f.x LM393, LM2903 etc commonly have a open-collector output. Does the group know about comparators with driver output, hence can pull up and down, and output like an ordinary opamp? How do I search for such ones? An ordinary opamp does not fit my need, as my application could balance itself WBR Sonnich
Comparator with driver output
Started by ●November 17, 2022
Reply by ●November 17, 20222022-11-17
On 11/17/2022 12:20 PM, sonnic...@gmail.com wrote:> Hi all > > A standard comparator f.x LM393, LM2903 etc commonly have a open-collector output. > Does the group know about comparators with driver output, hence can pull up and down, and output like an ordinary opamp? > > How do I search for such ones? > > An ordinary opamp does not fit my need, as my application could balance itself > > WBR > SonnichWithout knowing the output drive requirements, the TLV360x may be a place to start: https://www.ti.com/product/TLV3601
Reply by ●November 17, 20222022-11-17
On Thursday, November 17, 2022 at 12:20:08 PM UTC-8, sonnic...@gmail.com wrote:> Hi all > > A standard comparator f.x LM393, LM2903 etc commonly have a open-collector output. > Does the group know about comparators with driver output, hence can pull up and down, and output like an ordinary opamp? > > How do I search for such ones? > > An ordinary opamp does not fit my need, as my application could balance itselfYou can add hysteresis to most comparator circuits; something like a NE555 has builtin hysteresis and good pullup and pulldown capability.
Reply by ●November 17, 20222022-11-17
On Thu, 17 Nov 2022 12:20:03 -0800 (PST), "sonnic...@gmail.com" <sonnichjensen@gmail.com> wrote:>Hi all > >A standard comparator f.x LM393, LM2903 etc commonly have a open-collector output. >Does the group know about comparators with driver output, hence can pull up and down, and output like an ordinary opamp? > >How do I search for such ones?What input and output range do you need? What's the load? How fast do you need?> >An ordinary opamp does not fit my need, as my application could balance itselfI don't understand that. I use opamps as comparators now and then. Mouser and Digikey are good for searching for stuff like this, from multiple vendors.> >WBR >Sonnich
Reply by ●November 17, 20222022-11-17
On Thursday, November 17, 2022 at 3:20:08 PM UTC-5, sonnic...@gmail.com wrote:> Hi all > > A standard comparator f.x LM393, LM2903 etc commonly have a open-collector output. > Does the group know about comparators with driver output, hence can pull up and down, and output like an ordinary opamp? > > How do I search for such ones? > > An ordinary opamp does not fit my need, as my application could balance itselfThis is when I use the Digikey search. If you type in comparator it will take you to a search page with many parameters to adjust. You can select the output type and many other features. -- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209
Reply by ●November 17, 20222022-11-17
On Thursday, November 17, 2022 at 1:06:03 PM UTC-8, Ricky wrote:> On Thursday, November 17, 2022 at 3:20:08 PM UTC-5, sonnic...@gmail.com wrote: > > Hi all > > > > A standard comparator f.x LM393, LM2903 etc commonly have a open-collector output. > > Does the group know about comparators with driver output, hence can pull up and down, and output like an ordinary opamp? > > > > How do I search for such ones? > > > > An ordinary opamp does not fit my need, as my application could balance itself > This is when I use the Digikey search. If you type in comparator it will take you to a search page with many parameters to adjust. You can select the output type and many other features.Yeah, but... that's in-the-box searching, and it'll miss possibilities like using an op amp (or an unused section of a quad) or a discrete two-transistor circuit, or NE555, or TLV431, or power sequencer, all of which have comparator character. The "comparator" label isn't always the useful first-search-box criterion.
Reply by ●November 17, 20222022-11-17
On 18/11/22 07:20, sonnic...@gmail.com wrote:> Hi all > > A standard comparator f.x LM393, LM2903 etc commonly have a open-collector output. > Does the group know about comparators with driver output, hence can pull up and down, and output like an ordinary opamp?LTC8741 appears to have a symmetric output. Clifford Heath
Reply by ●November 17, 20222022-11-17
On Thursday, November 17, 2022 at 5:43:35 PM UTC-5, whit3rd wrote:> On Thursday, November 17, 2022 at 1:06:03 PM UTC-8, Ricky wrote: > > On Thursday, November 17, 2022 at 3:20:08 PM UTC-5, sonnic...@gmail.com wrote: > > > Hi all > > > > > > A standard comparator f.x LM393, LM2903 etc commonly have a open-collector output. > > > Does the group know about comparators with driver output, hence can pull up and down, and output like an ordinary opamp? > > > > > > How do I search for such ones? > > > > > > An ordinary opamp does not fit my need, as my application could balance itself > > This is when I use the Digikey search. If you type in comparator it will take you to a search page with many parameters to adjust. You can select the output type and many other features. > Yeah, but... that's in-the-box searching, and it'll miss possibilities like using an op amp (or > an unused section of a quad) or a discrete two-transistor circuit, or NE555, or TLV431, or power > sequencer, all of which have comparator character. The "comparator" label isn't always > the useful first-search-box criterion.Not sure what your point is. If you want a comparator, Digikey is a good way to search for one. If you want an alternative circuit, then search for that. What do the two have to do with one another? Interesting you mention transistor circuits. I needed to design a FF to remember power state when everything is shut down, including the MCU, which would only wake periodically. Because of the circuit, it worked better to power it from 12V, which could be as high as 15V, iirc. Digital logic was a bit too fast, making it subject to noise, etc and other concerns I don't recall at the moment (I think it had to do with undefined behavior with both set and reset asserted). So I opted for a transistor circuit, which included several more FETs for input and output drive, some in other than common source configurations. I checked it nine ways from Sunday, so I had confidence it would work fine. Since a handful of transistors would be easier to source than a couple of 4000 series CMOS, it wanted to use the transistors. Being a group project, some guy who never saw a Linear Tech device he didn't like (meaning it wasn't his money he was spending, why use something cheap when several things expensive would do?) kept criticizing it, not in engineering terms, but negging terms like kludge, etc. What he really meant, was, he didn't understand it. So how do you use two transistors to form a reasonable comparator? Is this something that only works in some special set of conditions? Some sort of positive feedback, perhaps? I can't think of any time when an opamp would be preferable to a comparator, unless the requirements were very lax and you simply wanted to reduce the BoM. -- Rick C. + Get 1,000 miles of free Supercharging + Tesla referral code - https://ts.la/richard11209
Reply by ●November 18, 20222022-11-18
On Thursday, November 17, 2022 at 4:56:17 PM UTC-8, Ricky wrote:> On Thursday, November 17, 2022 at 5:43:35 PM UTC-5, whit3rd wrote: > > On Thursday, November 17, 2022 at 1:06:03 PM UTC-8, Ricky wrote: > > > On Thursday, November 17, 2022 at 3:20:08 PM UTC-5, sonnic...@gmail.com wrote:> > > > An ordinary opamp does not fit my need, as my application could balance itself(I interpret this to mean he wants to exclude midrange parking of the output... which generally just requires some positive feedback, creating hysteresis)> > > This is when I use the Digikey search. If you type in comparator it will take you to a search page...> > Yeah, but... that's in-the-box searching, and it'll miss possibilities like using an op amp (or > > an unused section of a quad) or a discrete two-transistor circuit, or NE555, or TLV431, or power > > sequencer, all of which have comparator character. The "comparator" label isn't always > > the useful first-search-box criterion. > Not sure what your point is. If you want a comparator, Digikey is a good way to search for one. If you want an alternative circuit, then search for that. What do the two have to do with one another?The application could be comparison to midrange of power supply, and benefit from hysteresis, and require a high current output... so, an NE555 is a good off-the-shelf solution. Or it could just need a repeatable ON threshold, and a CMOS power monitor would do that. A two-transistor Schmitt trigger also has bistable output and an input threshold. True comparators with input common-mode insensitivity are not the only choices in reality, but are the only ones that will show up in a search.> So how do you use two transistors to form a reasonable comparator? Is this something that only works in some special set of conditions? Some sort of positive feedback, perhaps?I often use resistors to add positive feedback to a comparator, and of course the Schmitt trigger is a useful two-transistor circuit, might be preferable. Once you use positive feedback, an op amp is interchangeable with a comparator (no need for stability as with negative feedback, just gain).> I can't think of any time when an opamp would be preferable to a comparator, unless the requirements were very lax and you simply wanted to reduce the BoM.One time I used an op amp that way was an old design, LM301 (no compensation required) when I wanted a near-positive-rail input; the old comparators didn't match that requirement. On other occasions, I've simply had good stock of the op amps but not of comparators... I was mainly doing one-off jobs, didn't want to delay for a trip to/shipping from a supplier. Yeah, lax requirements is a major 'reason'.
Reply by ●November 18, 20222022-11-18
On 17/11/2022 20:20, sonnic...@gmail.com wrote:> Hi all > > A standard comparator f.x LM393, LM2903 etc commonly have a open-collector output. > Does the group know about comparators with driver output, hence can pull up and down, and output like an ordinary opamp? > > How do I search for such ones? > > An ordinary opamp does not fit my need, as my application could balance itself > > WBR > SonnichMicrochip has some nice little comparators with push-pull outputs: MCP6541 (low power) and MCP6561 (fast) piglet
