schmitt trigger comparator

I built up a schmitt trigger circuit (attached). I placed an o-scope on the output pin (#3) and saw that my high transitions are clipped whereas my low transitions are not clipped (see 2nd attachment).

My resistor values suggest that a negative transition occurs when a voltage of 4.921V or greater is at +Vin (pin #2).

My resistor values suggests that a positive transition occurs when a voltage of 2.98V or less is at +Vin (pin #2).

Since Im using a sine wave input going into pin 2 (via a function generator) why am I not seeing a clipped sine for both positive and negative transitions?

Please help.......

hi
i think u use here open collector comparatore bcz use R 3k between output pin and vcc.

i do simple simullation for ur circuit with lm339 its work ok but positive transition
occur at 3.9v .

function generatore here is sin wave 50hz swing from 0....to 5v i add a d.c components to shift sin wave.
if u apply sin wave swing from positive to negative ur circuit will not work
just chek that

nashwan said:

hi
i think u use here open collector comparatore bcz use R 3k between output pin and vcc.

i do simple simullation for ur circuit with lm339 its work ok but positive transition
occur at 3.9v .

function generatore here is sin wave 50hz swing from 0....to 5v i add a d.c components to shift sin wave.
if u apply sin wave swing from positive to negative ur circuit will not work
just chek that

Click to expand...

3K is just a pullup resistor........

I didn't calculate the threshold voltage myself. I used an online voltage threshold calculator. Its telling me triggering voltage occurs at 4.9V and 2.9V.....

http://hyperphysics.phy-astr.gsu.edu/HBASE/electronic/schmitt.html

my sine wave from the function generator was 1KHz swing from 0.....to 5V with no dc component. I will add dc offset and see if that changes anything......But why will it not work with positive and negative swing sine wave?

Added after 50 minutes:

nashwan said:

hi
i think u use here open collector comparatore bcz use R 3k between output pin and vcc.

i do simple simullation for ur circuit with lm339 its work ok but positive transition
occur at 3.9v .

function generatore here is sin wave 50hz swing from 0....to 5v i add a d.c components to shift sin wave.
if u apply sin wave swing from positive to negative ur circuit will not work
just chek that

Click to expand...

-2.5V DC Offset provides what I believe to be the correct ouptut I would expect to see from a schmitt trigger comparator. But why does -2.5V seem to work but 1.5V and/or 1.8V dc offset doesn't provide a clipped sine wave output?

Please help.....

hi
the circuit in that link
http://hyperphysics.phy-astr.gsu.edu/HBASE/electronic/schmitt.html

use dual power supply and output of that comparatore is push-pull
with this circuit u can apply ac signal swing from positive to negative

but ur circuit seems like single power supply with open collector output.
check that pls

if u work with single power supply and ur input signal swing from 0..to vdd
u can use digital ics as CD4093,CD40106,CD4584 as schmitt trig

why am I not seeing a clipped sine for both positive and negative transitions

Click to expand...

Yes, that's a plausible question.
Actually a square wave could be expected with a correct working comparator.

I think, your comparator is not working correctly, because you the input voltage, also the threshold at the +ve input is exceeding
the common mode voltage of Vcc - 1.5 V. You may want to correct the problem by changing the resistor ratio, e.g. 2k ínstead of 110k.

Input voltages below zero aren't a problem as long you limit the comparator input current. A series resistor of e.g. 1 k would do.

As another comment, changing the oscilloscope input coupling to DC would considerably improve the informational value of
the waveforms. It's a bit annoying to see this fine instrument used improperly.

nashwan said:

hi
i think u use here open collector comparatore bcz use R 3k between output pin and vcc.

i do simple simullation for ur circuit with lm339 its work ok but positive transition
occur at 3.9v .

function generatore here is sin wave 50hz swing from 0....to 5v i add a d.c components to shift sin wave.
if u apply sin wave swing from positive to negative ur circuit will not work
just chek that

Click to expand...

what software are you using for this simulation. Is it free?

hi robis
i use circuit maker its not free but there is CircuitMaker Student Edition is a free download
**broken link removed**

and see that
**broken link removed**

and
www.tina.com