need help with Comparator hysteresis

R

rjvh

New Member

• Jan 24, 2008

• #1

what do i wrong???

i can't get anny hysteresis in the switching of this comparator

i did try this set up with a comparator from a LM 723 in an other design and that works fine

but what's going on if i use the lm 324

the plan is to put a variable resistor in the R hysteresis to have a set switching point with a range

thanks in advance
Robert-Jan

 

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ronsimpson

Well-Known Member

Most Helpful Member

• Jan 24, 2008

• #2

You need a resistor from what you are measuring to the + input of the amp.

 

audioguru

Well-Known Member

Most Helpful Member

• Jan 24, 2008

• #3

Yes, you need an input resistor so the input source doesn't short the hysteresis.

Also, the lousy old LM324 opamp is one of the slowest. Its max full output frequency is only 1kHz or 2kHz. At higher frequencies its output level reduces because its output becomes a slowly ramping triangle-wave.

 

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R

rjvh

New Member

• Jan 24, 2008

• #4

thanks guys it's working
for about the LM 324 i use it only as comparator for swiching by a sensor signal that has a sample rate of 7.5 KHz to 1.5 KHz

and the aplication doesn't have to react that fast

thanks
Robert-Jan

 

audioguru

Well-Known Member

Most Helpful Member

• Jan 24, 2008

• #5

An LM358 is a dual opamp like the quad opamps in an LM324. The LM358 is in an 8-pins package.

 

R

rjvh

New Member

• Jan 24, 2008

• #6

i know but i need more than one switch levels from one sensor and i need to invert the analog signal also to drive a VSD so to do that i need at least 2 comparators and 1 opamp (not critical in specs) the 1 left over leave unused

Robert-Jan