comparator as a pulse generator

[xmat]

Hello,

I cannot seem to make it work..

I have a voltage comparator (LM301),

I insert to (both) its inputs varying voltages,

and I am assuming that every time (and for as long as) the + input has a greater voltage than -input,

the comparator should trigger a pulse (of variable duration in accordance to differential input) that goes from 0 volts to "supply voltage" volts (9V in my case, I am using a dual voltage supply made with batteries).

The input(s) is filtered-low-frequency-audio content.

So, assuming the input (audio, i.e 100Hz) has an envelope duration of 20ms, the pulse's duration should be (in theory-works also in workbench) about 4ms.

But instead of having a pulse at LM301 output, I have a very low signal there (maybe less than millivolts) that looks more like a triangle waveform and less like a pulse.

Can u tell what is wrong..??

I am suspecting that differential input is very low, could that be the case..??

Many thanks in advance,

xmat.

 

[Styx]

for starters the LM301 is an opamp and not a comparator, that is not to say an OPAMP cannot be used as a comparator, except a comparator has a higher open-loop gain and their slew rate is alot higher

https://www.electro-tech-online.com/custompdfs/2005/01/LM301.pdf

 

[xmat]

for starters the LM301 is an opamp and not a comparator, that is not to say an OPAMP cannot be used as a comparator, except a comparator has a higher open-loop gain and their slew rate is alot higher

https://www.electro-tech-online.com/custompdfs/2005/01/LM301-1.pdf

sorry, I meant LM311....not that good in coordinating what I think to what I type..that type of hour..

Hope someone could help.

 

[FRIED]

LM311 needs pullup on the output to +V

 

[Styx]

yup that was going to be my next point IF it was the comparator I was thinking - in fact most of them

open-collector ouput

easy mistake to do. take a 3.3k resistor from the output to +5V

 

[xmat]

thanks fro the help, still problems..

Hello, many thanx for the help, I must admit I should have used a pull-up resistor.Good point.

But I think I have encountered another problem...soo silly..I used a 9V supply voltage...and I think LM311 max Sup/Volt is 5 Volts, right??

So, are there any suggestions about a 9V supply voltage comparator?

If u have anyone in mind, does it still need to have a pull up resistor?

Many thanx in advance,

xmat.

PS:In case u know, what r the key elements of a comparator for such a use??(as a pulse generator of differential input voltages caused by audio -low- frequency content)..I mean, high slew rate, hysterisis, high open loop gain and anything else??

 

[Sebi]

LM311 can operate from 5V up to 30V, so don't worry about 9V.For open collector always need a pull-up resistor. This is a big advantage, when You need a TTL output, just pull-up to 5V and the comparator supply can be e.g.20V.