Window comparator as perfect rectifyer? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 26, 2019, 06:01:14 pm
content: Imagine some standard run of the mill rectifier circuit with maybe 1V ripple, connect it to a zero droop window comparetor and last connect it to an opamp.Let the opamp get power from the standard rectifier.Would the opamp not try to keep it's output exactly as the comparetor's linear signal?

author: Benta
author_rank: Super Contributor
timestamp: May 26, 2019, 06:30:54 pm
content: I'm not certain you really mean "window comparator".Make a sketch of what you want, please.

author: wraper
author_rank: Unknown
timestamp: May 26, 2019, 06:41:44 pm
content: Go google about synchronous rectification if meaning high efficiency power rectification or precision rectifier if you need a signal itself.https://en.wikipedia.org/wiki/Active_rectificationhttps://en.wikipedia.org/wiki/Precision_rectifierAs of what you described is weird. And comparator has only 2 states on it's output, what linear signal?

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 26, 2019, 07:59:16 pm
content: Quote from: Benta on May 26, 2019, 06:30:54 pmWhat i mean is a circuit that detects highest positive voltage that the rectyfier is delivering, I do not know how to draw it but I'll try to explain again:-)if you have that "max volt detector" and put the result into an opamp, the opamp will try it's best to deliver that as output.My thought was that the end result will be an opamp that keep fighting to maintain the same max value.Quote from: wraper on May 26, 2019, 06:41:44 pmGreat links, it looks like what I am thinking of!Am I wronh in thinking that this circuit:https://upload.wikimedia.org/wikipedia/commons/c/ca/Op-Amp_Precision_Rectifier_%28Improved%29.svgonly is a half-bridge rectifier?And combined with the comparator, it gets to be a full bridge rectifier?Hmm does it not loose a lot power in that configuration?

author: wraper
author_rank: Unknown
timestamp: May 26, 2019, 08:05:04 pm
content: Peak detector is not a comparator. Also it does not help at rectifying in any way.

author: wraper
author_rank: Unknown
timestamp: May 26, 2019, 08:13:11 pm
content: Quote from: FriedMule on May 26, 2019, 07:59:16 pmComparator again... Add another diode and opamp and you will have full wave rectifier.

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 26, 2019, 08:35:47 pm
content: Thanks a lot!I have only seen something that is called window comparator, where it detects if peak voltage is above or below trigger voltage and have that voltage storedSo my thought was to let the "window" be configured so that it only triggers with max voltage i.e. 5V and send these 5V to the opamp.But your drawing is fare better, thanks.

author: wraper
author_rank: Unknown
timestamp: May 26, 2019, 08:40:28 pm
content: Quote from: FriedMule on May 26, 2019, 08:35:47 pmWindow comparator basically is just two regular comparators set to different voltage + AND logic. It does not store anything and it does not have anything to do with peak voltage. Usual comparator only detects if signal is above/below set level. Window comparator detects if it is within certain range or not. One comparator is set to maximum level, another to minimum level.https://en.wikipedia.org/wiki/Window_detectorQuoteStrange logic. So you idea "works" (it doesn't) only if input voltage is already is known. Why then bother rectifying anything at all?

author: Benta
author_rank: Super Contributor
timestamp: May 26, 2019, 08:49:17 pm
content: A Window Comparator is an array of comparators coupled to combinatorial logic.As an example:Analog input voltage 0...5 V0...<1 V: output 1 active1...<2 V: output 2 active2...<3 V: output 3 active3...<4 V: output 4 active4...5 V: output 5 activeRelating that to a rectifier is difficult at best...

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 26, 2019, 09:28:56 pm
content: I am glad for your help, can't find the video where the window comparator was presented in the wrong way.As I am a noob, I tend to believe in the videos I find, but thanks to you, I'd learn that nothing all is true:-)

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 27, 2019, 01:53:04 pm
content: I was trying to play with the circuit, just to learn but the online simulator is confusing me big time:http://tinyurl.com/y4jcz6861VAC in 15VDC out

author: Audioguru
author_rank: Super Contributor
timestamp: May 27, 2019, 02:04:47 pm
content: Your opamps have no part number and no power supply voltage so they will not work.The second opamp has positive feedback so if there is a tiny positive input to it then its output will go as high as it can and stay like that (even if the input signal stops) until the power supply is turned off.I guess the supply is +15V and the opamp is "rail to rail" allowing its output to go as high as +15V.

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 27, 2019, 02:27:35 pm
content: Quote from: Audioguru on May 27, 2019, 02:04:47 pmOh thanks a lot, it makes sense, no the AC is 1V.But I'll change the errors:-)

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 27, 2019, 06:02:17 pm
content: Quote from: wraper on May 26, 2019, 08:13:11 pmI have redrawen my circuit (read stolen a solution)You show two examples and here is a third:http://tinyurl.com/y3yhr8ktBut how do I know what to choose, what is the difference?