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| Opa2350 negative half of voltage |
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| Midgard:
I am using opa2350 as a current sensor in inverter as that combination: and when output voltage is >20 VAC i have problem with sensing current in negative sinusoidal: Positive half looks quite okay. I try it with diffrent shunt resistor value, but the problem stay always for negative voltage. Why my opamp have trouble with negative half? |
| StillTrying:
You'd see more with the scope on DC coupled. I think the input phases of the op amps are the wrong way around, they'd be better with the +ve input going to the top of the 0.04Rs to give a +ve going output with increasing 0.04R current. |
| SiliconWizard:
--- Quote from: StillTrying on August 28, 2019, 03:35:58 pm ---I think the input phases of the op amps are the wrong way around, they'd be better with the +ve input going to the top of the 0.04Rs to give a +ve going output with increasing 0.04R current. --- End quote --- Agreed. |
| Midgard:
Thank you for answers. I switched 20k resistors with 1k and the output is a lot better. --- Quote from: StillTrying on August 28, 2019, 03:35:58 pm ---You'd see more with the scope on DC coupled. --- End quote --- When I turn on DC coupling my signal is moving out of range of oscilloscope. |
| StillTrying:
"I switched 20k resistors with 1k and the output is a lot better." You reduced the gain from -20 to -1 ? We were suggesting changing the gain to +21 by swapping the 1k inputs on the 0.04Rs so that the op amp outputs rise towards 3V with more current rather than 0V. You need to know the maximum current to be measured through the 0.04Rs to set the op amp gain to give about 0-3V output, or whichever voltage range you need from the op amp output. "When I turn on DC coupling my signal is moving out of range of oscilloscope." You can move the channel's 0V position to the bottom of the screen as the outputs from the op amps are all only positive(0-3V). |
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