Is there any difference between comparator and op-amp?

[fred]

Does it make any difference if I buy the lm324
which has 4 op-amps, or the lm339 which has
4 comparators, these are the same thing in essense
aren't they, i.e. I can use op-amps as comparators,
and comparators as op-amp, it all depends on how
I wire them up, can anyone confirm this?

 

[Sir Charles W. Shults III]

"fred" <fred222@btinternet.com> wrote in message
news:2685a85f.0402020801.2001066f@posting.google.com...

Does it make any difference if I buy the lm324
which has 4 op-amps, or the lm339 which has
4 comparators, these are the same thing in essense
aren't they, i.e. I can use op-amps as comparators,
and comparators as op-amp, it all depends on how
I wire them up, can anyone confirm this?

Op amps and comparators are only "mostly" the same. Comparators are
usually op amps that are optimized for high slew rate (that means real fast
voltage swing) and also have a different output stage- one that is usually
an open collector transistor that requires a pullup or pulldown resistor to
function as you would expect.
In a pinch, you can use either as the other, but remember that you get
what you pay for.

Cheers!

Chip Shults

 

[John Popelish]

fred wrote:

Does it make any difference if I buy the lm324
which has 4 op-amps, or the lm339 which has
4 comparators, these are the same thing in essense
aren't they, i.e. I can use op-amps as comparators,
and comparators as op-amp, it all depends on how
I wire them up, can anyone confirm this?

There are several important differences between opamps and
comparators.
Opamps can pull up or down (source or sink current). Many
comparators, including the 339 sink current only. They rely on some
external means to pull the output positive when the output is off.

Comparators are usually designed to switch their outputs as fast and
hard as possible for the least input differential voltage. Opamps are
purposely slowed a bit, and their high frequency response rolled off,
to let them stabilize the output voltage at any point in its swing
whenever the inputs are brought to a match by negative feedback. If
you connect negative feedback around a comparator, it can be expected
to oscillate.

Opamps usually limit output current to some maximum value with an
active current measuring circuit, while comparators carry as much
current as the the output switch can carry. So the maximum current
the output will carry generally varies more with comparators than it
does with opamps, unit to unit.

Opamps are designed to produce an output voltage that is an arbitrary
function of input signals, based on the input and feedback networks.
Comparators are designed to tell you which input is more positive, as
quickly as possible.
--
John Popelish