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Diffrential amp design

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ali_asadzadeh:
Thanks Zero999 :-+, so the BJT  would allow for a 5V output swing?

Zero999:

--- Quote from: ali_asadzadeh on January 31, 2020, 11:52:34 am ---Thanks Zero999 :-+, so the BJT  would allow for a 5V output swing?

--- End quote ---
It won't allow the output to completely reach 5V, but it'll get within a couple of hundred mV or so. Obviously it won't be able to swing to -5V. Oh and don't bother simulating this trick. It invariably doesn't work with most SPICE op-amp models because they don't accurately replicate the behaviour of the output stage.

That raises another point: what's the input voltage range of the ADC? Presumably it can't go below zero, yet both the circuit you posted at the start of the thread and mine will output negative voltages.

ali_asadzadeh:
The ADC input range is 0-3.3V

Zero999:

--- Quote from: ali_asadzadeh on February 01, 2020, 06:02:05 am ---The ADC input range is 0-3.3V

--- End quote ---
Ok then the PNP pull-up isn't needed, but what happens when the op-amp's output drops below zero?

ali_asadzadeh:
There is a Reverse Biased Diode parallel to the ADC input

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