single op-amp window comparator

[Lee]

the usual circuit design of a window comparator uses two
op-amps...does anyone know about a single op-amp window comparator
circuit...tnx in advance

 

[Pooh Bear]

the usual circuit design of a window comparator uses two
op-amps...does anyone know about a single op-amp window comparator
circuit...tnx in advance

Yup, you can do it with a couple of extra diodes. It's not as accurate (
and needs to oversome the Vf of the diodes ) but may suffice. Don't
have a schematic handy though.


Graham

 

[Ban]

the usual circuit design of a window comparator uses two
op-amps...does anyone know about a single op-amp window comparator
circuit...tnx in advance

with a rectifier in front of the comparator you could do that, but you loose
the ability to randomly choose the thresholds.

 

[Ken Smith]

with a rectifier in front of the comparator you could do that, but you loose
the ability to randomly choose the thresholds.

Not really. You loose a lot of accuracy because of the diode drops but
for moderatly large values of random, you can get any values you want like
this:

If you make this circuit and its top to bottom flipped version, the Vx
voltages are determined by R1 and R2 or Vin depending on Vin.

!
/
\ R1
/
\
!
Vin -!<--+
V
---
+-------- Vx
!
/
\ R2
/
\
!


Further resistor dividers on the Vx and Vx' signals can give you whatever
dead band you want. As a result, you can set the deadband and the center
point.

 

[[email protected]]

Not really. You loose a lot of accuracy because of the diode drops but
for moderatly large values of random, you can get any values you want like
this:

If you make this circuit and its top to bottom flipped version, the Vx
voltages are determined by R1 and R2 or Vin depending on Vin.

!
/
\ R1
/
\
!
Vin -!<--+
V
---
+-------- Vx
!
/
\ R2
/
\
!


Further resistor dividers on the Vx and Vx' signals can give you whatever
dead band you want. As a result, you can set the deadband and the center
point.

The inputs to the opamp go where?
Vx is?


NT

 

[Ken Smith]

Ken Smith wrote: [....]

!
/
\ R1
/ !
\ \
! /
Vin -!<--+ \
V /
--- !
+------/\/\/\---+------ One op-amp input
!
/
\ R2
/
\
!

The inputs to the opamp go where?
Vx is?

The top to bottom mirror image goes to the other op-amp input.

 

[Jamie]

the usual circuit design of a window comparator uses two
op-amps...does anyone know about a single op-amp window comparator
circuit...tnx in advance

a simple hack version comes to mind.

using an OP-AMp from a +&- rail supply to get a
0 volt output into a mini bridge rectifier to convert
the signal to always + or - what ever.

by setting setting one input of the Op-amp to a voltage
and using the other to monitor the external source voltage,
one can then adjust the gain using a loop back into the -
input and adjust the + input for the comparator center point.
the idea is to produce no voltage or low voltage at the
output as the reference voltage starts to get near the set
voltage..
basicly we are looking at a simple OP-amp circuit that you
can set the + input using a dual rail supply.

the output can drive some schmitt
trigger or mechanical relay etc..

like i said, just a hack in thinking of course.

 

[Rene Tschaggelar]

the usual circuit design of a window comparator uses two
op-amps...does anyone know about a single op-amp window comparator
circuit...tnx in advance

Lee,
you should ask for a single resistor solution.


Rene

 

[Ken Smith]

Lee,
you should ask for a single resistor solution.

Thats easy:


T \----------------------
---O
!
---------------------------
Vin ------/\/\/\----VMiddle


When the voltage is far enough from Vmiddle to be either voltage, it heats
up the thermstat and it closes.