Opamp 741 Design Question

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Inforfang

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configuration lm358 741

Hi ...

I have a Saw-tooth 0-5 Volt Signal . I want to make output +5 Volt when Signal is higher than 3V and make output 0 Volt when input is lower than +3 volt .

I used Opamp 741 . I attach the schematic that i used . the output is Square Wave that is good but is between 1.5-4 Volt .



Why ? and How can i get 0-5 Volt Square Wave ?
I can fix the output by change the +Vcc to 6Volt and -Vcc to -1.4 Volt to have 0-5 Output But I don't Want to change my +Vcc and -Vcc pins and use 2 Power supply .

Should i change my opamp ? or My Design ? or Use Some IC Like LM311 to Compare Voltages ?

Regards .
 

op amp 741 design

It is because of the maximum output voltage swing for 741, Vcc-1.5V, or Vee+1.5V, because of the internal configuration. Another thing, 741 needs at least a ±5V supply, read datasheet before using.
**broken link removed**

You need a rail-to-rail opamp, like LM358 or better a comparator, opamps behave not so well at high frequency. For digital interfacing, a Schmitt trigger gate can be used, since the signal is in the TTL/CMOS range.
 

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    Inforfang

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op amp 741

I used LM358 and now i have 0-4 Volt P-P . near to TTL . My Frequency is very Low about 30Hz .

Thanks .
 

741 opamp comparator

Opamps are not design for such applications. Use a comparator instead. They don´t have the same compensation techniques as opamps, so they are faster.
 

uroddy said:
Opamps are not design for such applications. Use a comparator instead. They don´t have the same compensation techniques as opamps, so they are faster.
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That´s right. Your task is to compare an input signal (triangle or sawtooth) with a fixed voltage. Therefore: Use a comparator, which is designed especially for such a purpose.
 

Apart from special properties of some types, a comparator basically is an uncompensated OP with a higher slew rate. Thus I share Inforfang's viewpoint, that is well suited for a 30 Hz signal.
 

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