How to make a wide range of voltage to be constand

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The discussion revolves around a project involving an LM35 temperature sensor that outputs a voltage proportional to temperature. The user needs to ensure that when the temperature is below 27˚C, a constant 5V is sent to a PLC input, despite the varying input voltage range of 5V to 50V. They have successfully implemented a comparator circuit but are confused about the feedback type, as they initially mentioned negative feedback instead of the required positive feedback for hysteresis. Suggestions include refining the comparator design and exploring other circuit components that can stabilize the output voltage. The user seeks practical advice on achieving a constant 5V output under the specified conditions.
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i am working on my project but i do not have much practical experience on connecting the circuit, hence asking for help here.

ok here's my problem.
i have a temperature sensor LM35 which its Vout = 10mV/˚C.
the output of the temperature sensor has to be connected to PLC input.
when the output is higher than 270mV (27˚C), the nothing will happen.
when the output is equal or lower than 270mV (27˚C), PLC input will receive 5V constant voltage.

i have done research with op-amp (comparator) with negative feedback and successfully make it into a positive voltage when the temperature is lower than 27˚C.
anyhow, the voltage is in a wide range from 5v to 50v, depends on the temperature difference.
i have also done research with voltage regulator but most of them do not receive such a wide range of input.

when the temperature is lower than 27˚C, how can i make it constantly 5V to the PLC input?
 
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idvdi said:
i am working on my project but i do not have much practical experience on connecting the circuit, hence asking for help here.

ok here's my problem.
i have a temperature sensor LM35 which its Vout = 10mV/˚C.
the output of the temperature sensor has to be connected to PLC input.
when the output is higher than 270mV (27˚C), the nothing will happen.
when the output is equal or lower than 270mV (27˚C), PLC input will receive 5V constant voltage.

i have done research with op-amp (comparator) with negative feedback and successfully make it into a positive voltage when the temperature is lower than 27˚C.
anyhow, the voltage is in a wide range from 5v to 50v, depends on the temperature difference.
i have also done research with voltage regulator but most of them do not receive such a wide range of input.

when the temperature is lower than 27˚C, how can i make it constantly 5V to the PLC input?

Welcome to the PF. It sounds like you are on the right track with the comparator circuit, but comparators use positive feedback, not negative feedback. The positive feedback is used to set the hysteresis of the comparator circuit.

http://en.wikipedia.org/wiki/Comparator

.
 

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