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creating '0' or '1' logics.

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allegro

New Member
I'm looking for a low cost, low consumption device that will perform this:

circuit-jpg.26673

VDD = 3.3V.
VSS = GND (0V).
Input = Analog input.

OUT =
VDD if Input is equal to or higher than 3V.
0V if Input is lower than 3V.

Thank you.
 

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ericgibbs

Well-Known Member
Most Helpful Member
LM311, LM393, LM339.
These are comperators, 1, 2 and 4 parts in one housing

hi,
Problem with some comparators they dont work correctly when the threshold voltage is close to the Vsupply.. that is Vs-1.5V approx.:)
 

colin55

Well-Known Member
How accurately do you want the detection?

Use a set of resistors on the front-end of an NPN transistor.
 

crutschow

Well-Known Member
Most Helpful Member
hi,
Problem with some comparators they dont work correctly when the threshold voltage is close to the Vsupply.. that is Vs-1.5V approx.:)
Use a two-resistor attenuator on each input (four resistors total) to reduce the voltage below the common-mode voltage range of the comparator.
 

ccurtis

Well-Known Member
Maxim has a wide variety of the type of device attached. Adjust resistor voltage divider so that 3 Volts at Vin results in 1.235 Volts at the IN+ of the device.

The MAX921 is a similar device that doesn't need a pull-up resistor, and appears to be more widely available.

The devices consume a mere few microamps and cost around $1.50 in unit quantities.

Maxim is very generous with free samples. Just go to their website and click on "free sample" .
 

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ericgibbs

Well-Known Member
Most Helpful Member
Then make a voltage divider at the inputs for comparing, than you don't have that problem!

Geeee... I never would have thought of that.!:p

Why are you telling me.? Im not the OP.:)

I was trying make the OP aware he cant just input 3V into a comparator powered by 3.3V and expect it to work.
 
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ericgibbs

Well-Known Member
Most Helpful Member
Yust helping everybody, nothing else !

hi,
No problem, just teasing.:)

This threshold point about comparators comes up so often, where the OP is trying to set the max threshold too within [+V -1.5] and he gets an inversion effect.

Regards
 
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