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How come I can't get any voltage out of this op amp ? (I have to use that one, can't change it)

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THe green signal is the input, the blue one is the output.

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3 Answers 3

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This device does not pull its output high. You must connect a resistor to a positive voltage to the output pin if you want it go high. This is considered a “feature” for comparators.

Some other devices do have an output that goes high without a resistor.

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The answer is in the datasheet (emphasis added):

Output Transistor The LT1011 output transistor is truly floating in the sense that no current flows into or out of either the collector or emitter when the transistor is in the “off” state. The equivalent circuit is shown in Figure 5.

To get an output that goes from near ground to some other (positive) voltage (assuming emitter is grounded) you need a pullup resistor. This allows a comparator with (say) +/- 15V supplies to be used with 3.3V or 5V logic.

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For example, here is a pair used as a "window comparator" with 3.3V output. The output is only high when the input is within the range of +5 to -5V.

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The opamp is a comparator, If you want a sine wave output, you need to use an op amp.

If you did have an op amp, you need negative feedback (though the negative terminal)

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