output voltage of single supply comparator

[manishanand14]

Hello Guys!

I know that output of dual supply comparator like 741 swings between +Vcc-1 & -Vee+1.

Please tell me what happens with the output of single supply comparator like LM293, when given Vcc=5V ?

What will be the high and low value of the output?

I tried with Vcc=5V and getting values 4V[high] & 2.6V[low] for LM293.

Is there any way to make low as zero volt?

 

[goldsmith]

I know that output of dual supply comparator like 741

Hi manishanand14

Before trying to answer your question , a notice : 741 is not a comparator ! it is an op amp which can be used as either linear device or comparator . when you name 741 as a comparator it is wrong ! comparators are different .

Please tell me what happens with the output of single supply comparator like LM293, when given Vcc=5V ?

What will be the high and low value of the output?

Is there any way to make low as zero volt?

Let me change format of your question ! for example if you have an LM339 which is a single supply comparator , your out put can be between zero and VCC ( approximately ) . if it isn't , then you can be sure that your circuit has some problems ! because a usual comparator should work as what i've explained . unless you use an opamp for comparison then it is possible to have some faults like that but it can be optimized as well !
Best Wishes
Goldsmith

 

[IanP]

Hello Guys!

I know that output of dual supply comparator like 741 swings between +Vcc-1 & -Vee+1.

Please tell me what happens with the output of single supply comparator like LM293, when given Vcc=5V ?

What will be the high and low value of the output?

I tried with Vcc=5V and getting values 4V[high] & 2.6V[low] for LM293.

Is there any way to make low as zero volt?

The output of the LM293 is OC (open-collector - see attached picture), without a pull-up load (resistor) you won’t measure anything. With the output transistor OFF (H) and a pull-up in place, the output voltage should be 5V.
When the output transistor is ON (L) it will sink up to 16mA to 0V.
The saturation voltage (according to the DataSheet) is below 0.4V.
:wink:
IanP

 

[manishanand14]

Thanks

Please tell me whether I can make a Schmitt trigger with LM358 without pull-up resistor.In the diagram from the datasheet,it is given so.
Is it an open collector output?


Also please tell me the design formula for given UTP & LTP for LM393.

 

[D.A.(Tony)Stewart]

As long as you are aware of variations of Voh with load resistance, temperature, no pullup is needed. But with pullup the output can go to supply rail but then this affects output impedance and Hysteresis calculations

 

[manishanand14]

Please tell me whether LM358 output is open collector or not?

 

[D.A.(Tony)Stewart]

not but you can overcome the 50uA current sink when lower PNP would be off. But not very efficient tho, so my solution of a pull up is not as good as the other choices.

Keep in mind the subtle effects of Vol, Voh. with < 1K load vs > 10K load. Precision, temp. stable levels are hard to achieve with this part without total understanding of behaviours.

See page 4

 

[manishanand14]

Thanks

Can you give me the design formula if I want to design a Schmitt Trigger using LM393 with given LTP & UTP with diagram.

Since it has an open collector output, shall I prefer it?

 

[manishanand14]

Someone please reply.

 

[goldsmith]

Can you give me the design formula if I want to design a Schmitt Trigger using LM393 with given LTP & UTP with diagram.

Since it has an open collector output, shall I prefer it?

Someone please reply.

Hi manishanand14

A general rule : If you have a component which has been named comparator you should know comparators are open collector . and you have to tie them to the supply rail via a resistor .
For op amps : op amps are internally biased and when you are about to use an op amp for a comparison mode you won't need to use any pull up or pull down resistor .
ok ?
About the formula , you could have a bit search in google . didn't you try about it ?
Take a look here please :
https://www.google.com/url?sa=t&rct...VLVwTb2GBf_aDcPXsySfhaQ&bvm=bv.46340616,d.bGE
https://www.indiabix.com/electronics-circuits/schmitt-trigger-with-op-amps/
https://en.wikipedia.org/wiki/Schmitt_trigger

Best Wishes + Good Luck
Goldsmith

 

[manishanand14]

A general rule : If you have a co9mponent which has been named comparator you should know comparators are open collector . and you have to tie them to the supply rail via a resistor .
For op amps : op amps are internally biased and when you are about to use an op amp for a comparison mode you won't need to use any pull up or pull down resistor .

Thanks for this part.

 

[BradtheRad]

A comparator can be used to make a schmitt trigger.



The simulated op amp has a diode after the output, in order to mimic a comparator.
A comparator can only sink current. It cannot source current.

The pullup resistor is necessary.

 

[manishanand14]

Thanks everyone!

What about TLV3701:


NANOPOWER PUSH-PULL OUTPUT COMPARATORS

Does it have an open collector output too, because as per above discussions it should have . It is not very clear from the datasheet.

 

[BradtheRad]

Push-pull output suggests it can provide a path to either supply rail.

So maybe it is not like the traditional comparator, nor like the op amp.

Over the years there has been a divergence of varieties. It's up to us to find out what are the similarities and differences.

 

[keith1200rs]

Thanks everyone!

What about TLV3701:
View attachment 93769

NANOPOWER PUSH-PULL OUTPUT COMPARATORS

Does it have an open collector output too, because as per above discussions it should have . It is not very clear from the datasheet.

The "absolute maximum ratings" is not the place to find the answer. While the "push-pull output" tells you it is not open drain/collector, you can confirm that by looking at the input/output characteristics in the data sheet.

Quite a few comparators are made in two versions - one open collector/drain, the other push-pull so you can choose what you need.

Keith