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Identical opamp circuits..but one with split supply, and other with single supply

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Flyback

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Hello,

The following two opamp circuits (schematic attached) are exactly the same except for the fact that one has a 5V single supply and the other has a +/-5V dual supply. They both have the same shape of input signal which is also shown attached.


LT1013 datasheet:
http://cds.linear.com/docs/en/datasheet/10134fe.pdf

If the circuit is made on a PCB, will the outputs be exactly the same for each of the circuits?
LTspice simulation also attached but it is not thought that it will be completely accurate
 

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dr pepper

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The first circuit might not work, depends on what the o/p voltage would be of the 2nd amp, the way you wired it the o/p cannot go below ground and its an inverting amp so may well try to.
 

ci139

Active Member
as you don't in particular bias your non-inverting inputs the both variants act as comparators - with yet "undefined" hysteresis -
. . . but due to a speculative assumption the "op amp" being more sensitive to inputs at near the supply median , then it is likely that the "+/-5V supply" variant is to respond faster (/?? be more noisy) . . . . . . . . . ((((from my personal "Spice" experience - linear voltage regulators (define the type of feedback for next) - everything above 30pF feedback may lead to "unexpected response of the circuit" at "yet not tested" conditions))))

- i passed a mistake (likely coz some of the forums admins censoring/cover up policies -- that wash out some other self-admiring egoistic members hands and the pointed out true image of . . . if they are afraid of themselves - the truth stays their worth enemy . . . whatever) so . .
. . both variants act as comparators - when their inverting inputs were referenced from fixed voltages right now they are inverting stages (while everything not underlined still applies)
 
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Flyback

Well-Known Member
Thansk, i believe the simulation is fairly accurate, so i dont think they're acting like comparators(?), and surely theres not a "problem " with outputs "trying" to go below ground(?).
Our worry is that the single supply opmap may suffer slow bandwidth when its output is near zero volts, and therefore, its output voltage woudl be more distorted and delayed compared to the split supply opamp.

Indeed, i believe opamps behave best when their inputs and outputs are inbetween the supplies, or at least 1.2v away from them....even though LT1013 is rated as being "rail to rail input and output", i still suspect the single supply version will be distorted in comparison with the split supply version? (not in the sim but on the bench)
 

MikeMl

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Directly from the LT1013 data sheet:

1013.png
 

MikeMl

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The LT1013 (and LM324, LM358) cannot drive the output pin all the way to ground, and that is where the single supply version falls short. With a resistor tied from output to ground, it gets better. If I sweep the dual-supply circuit to determine Vout vs Vin, I get a transfer function of Vout = 1.08-Vin. (Should that be 1.10-Vin?)

I model the Vout = 1.08-Vin function as a simple Behavioral Voltage source, B1 and use it as the ideal... I sweep the single supply version input from 0V to 1.00V, and plot the error V(2ndStage)-V(ideal), and you can see where the linearity goes bad as U2 cannot pull low enough.

The 1.08-Vin function can be implemented using only one single-supply opamp as shown on the right. I plot the error V(mikes)-V(ideal) to show that...

mikes.png
 

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MikeMl

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ps, I didn't model the AC behavior. You will have to shunt Mike's R7 with a capacitor to get back to low-pass filtering.
 
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