Hello,I am trying to use AD8034 as a comparator,P12 is constant DC.
I put simple voltage divider to be in the minus of AD8034.
However when i connect the voltage divider to the minus of the AD8034 i get 1.6 instead of (12/30)*10=4V
Why the opamp ruins my voltage divider?
Thanks.

 

See page 6 of the data sheet.
https://www.analog.com/media/en/technical-documentation/data-sheets/AD8033_8034.pdf
ABSOLUTE MAXIMUM RATINGS: Differential Input voltage: 1.4V.
(It probably has back-to-back clamp diodes between the inputs)
If you use the device beyond its absolute maximum ratings, expect to destroy it,
The moral of the story is not to use an op-amp when you need a comparator.

 

Hello Ian, Comaprators have tendensy to need a pullup resistors because of open drain outputs.
could you reccomend me a comparator i could use and simulate whic does not have open drain output?
Thanks.

 

https://www.ti.com/amplifier-circuit/comparators/products.html
select "output type " = "push-pull"

 

Hello Ian, I have two DC inputs,
how do I calculate common voltage and differential voltage from these inputs?
Thanks.

 

I redrew the AD8034 circuit so I could understand it.

Comaprators have tendensy to need a pullup resistor because of open drain outputs.

There is no need for a pull up resistor on the output of the AD8034 because R6 pulls up.
I increased T4, R5 by 100x to limit the input current.

Why does M12 start out at 0V and go to -12V at 1mS? Not knowing what you want the AD8034 to do it is hard to know if there is a problem. Having M12=0V stops the part from working.

 

Differential voltage is easy: it's just the difference in voltage between the two inputs.

Common mode input voltage needs a bit more thought, and it's not usually shown the way it is in the AD datasheet.
If it applies to an op-amp, then it assumes that both inputs will be at the same voltage.
It is usually shown as a minimum and maximum voltage, and often the minimum is -0.3V and the maximum is Vdd+0.3V. Voltages are expressed with reference to the negative supply voltage, or they could be shown as Vss-0.3V.
In other words, the absolute maximum common mode voltage is likely to be from 0.3V below the negative supply to 0.3V above the positive: the voltages at which no current flows through the protection diodes.
Absolute maximum voltages are only concerned with voltages that may damage the device.

Then there are operational voltages. These are the voltages beyond which the device will cease to perform correctly, although it will not sustain any damage.
They are likely to be a smaller range than the absolute maximum ratings.
For a typical op-amp for audio use, the operational range may only extend from Vss+1.5V to Vdd-1.5V, in other words, it won't work if the inputs are closer to the supply voltage than 1.5V.
For an op-amp like a LM358, the operational range is from Vss-0.3 to Vdd-1.5V - it works right down to the negative supply, but NOT to the positive.

Comparators are slightly different, as "common mode" is a bit of a misnomer. It specifies the voltage, with respect to the amplifier's supply voltages at which it will work.

 

Hello Ian,I have tried to use TLV3231 push pull comparator,but as you can see I get 6V in a pules output.
I have 4V on the negative input and a GND on positive.
I am supposed to get M12 ouput (0 to -12) but as you can see Op1 is 6 to 0.
Where did i go wrong with this comparator?
Simulation files are attached.
Thanks.
https://www.ti.com/product/TLV3231-Q1

 

TLV3231 has a maximum supply voltage of 5.5V. What are you supplying it with? 24V?

 

Hello,I am trying to use AD8034 as a comparator,P12 is constant DC.

We are trying to help without any idea of what the circuit should do.
I don't understand why M12 changes voltage. Normally the (-) supply voltage is constant. Why dose M12 change voltage?