[SOLVED] How to compare multiple voltages （ II ）

[crutschow]

If you look at the simulation op amp output you will see that it goes to near the negative rail when it is not high. That may work in simulation, but it will likely zap the comparator input in real life.

As I previously said you need to use a "single supply" type op amp (such as the LT1079). The common-mode input voltage range and the output voltage range determine whether the op amp is a single-supply type device or not. A common single supply op amp is the LM324.

 

[BradtheRad]

well, why using the dual supply will cause this problem...?

My simulation shows that, dual supply is OK, and single supply doesn't work.

Attached is my signal supply circuit. it may need 5 mins to run the simulation.
....
update:

actually, I also find some opamps works in the signal supply, for example LT1079, I thinks it may depends on the opamp, although I don't know depends on which specification (offset bandwidth...)

I have been using an interactive simulator found at the falstad.com website.

The link below will open the website and bring in the specs to my schematic. It will run on your computer.

Click Allow to permit the connection. The second input has the potentiometer adjust. Slide the trackbar at the right to change it.

Right click on items you want to edit. A window will open.

The op amps can be edited. You determine single or bipolar supply operation, by typing in a minimum and maximum output voltage.

https://tinyurl.com/9rx26ch

If you hover over the op amps, you'll see each has a range of 0 to 5 V. However the outputs go slightly into the negative. I guess no simulator is perfect.

 

[crutschow]

I have been using an interactive simulator found at the falstad.com website.

.................................................

If you hover over the op amps, you'll see each has a range of 0 to 5 V. However the outputs go slightly into the negative. I guess no simulator is perfect.

True. But the falstad simulator is likely a simple simulation program with simplified models and thus is likely to have inaccuracies in its results. A Spice type simulator, such as LTspice, which is a complex and mature simulator program generally would give more accurate results.

 

[timedate]

Get it, many thanks.

If you look at the simulation op amp output you will see that it goes to near the negative rail when it is not high. That may work in simulation, but it will likely zap the comparator input in real life.

As I previously said you need to use a "single supply" type op amp (such as the LT1079). The common-mode input voltage range and the output voltage range determine whether the op amp is a single-supply type device or not. A common single supply op amp is the LM324.

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It is a cool simulator, thanks for introducing.

I have been using an interactive simulator found at the falstad.com website.

The link below will open the website and bring in the specs to my schematic. It will run on your computer.

Click Allow to permit the connection. The second input has the potentiometer adjust. Slide the trackbar at the right to change it.

Right click on items you want to edit. A window will open.

The op amps can be edited. You determine single or bipolar supply operation, by typing in a minimum and maximum output voltage.

https://tinyurl.com/9rx26ch

If you hover over the op amps, you'll see each has a range of 0 to 5 V. However the outputs go slightly into the negative. I guess no simulator is perfect.

 

[timedate]

True. But the falstad simulator is likely a simple simulation program with simplified models and thus is likely to have inaccuracies in its results. A Spice type simulator, such as LTspice, which is a complex and mature simulator program generally would give more accurate results.

the circuits works ! in real world~

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thanks you guys all

I have been using an interactive simulator found at the falstad.com website.

https://tinyurl.com/9rx26ch

If you hover over the op amps, you'll see each has a range of 0 to 5 V. However the outputs go slightly into the negative. I guess no simulator is perfect.