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LM35: Supply Voltage

Arick Goetz
Prodigy 20 points
Part Number: LM35

I have tried a circuit with a LM35DZ supplied with 24 volts, but the temperature does not seem to be working right. I can heat up the sensor and get very minimal change in the Vout pin. Tried a 10 volt power supply and getting the same results.   Do i just have a bad sensor, or is the supply voltage too high and damaged it. I seen on the data sheet Max Voltage is 30vdc, but in one of the pictures it shows 4 - 20vdc

  • 0
    TI__Mastermind 35895 points

    Hi Arick,

    The LM35 has an Absolute Max Rating of 35V and a Recommended operating max of 30V. The sensitivity is 10mV/C. Are you able to easily resolve millivolts in your measurement?

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 20 points

    I have tested the analog input is working correctly on the controller. I am reading the same voltage as the controller is displaying with a volt meter. But heating up the sensor doesn't change the voltage.

    I just seen on the data sheet that the max voltage was updated January 2016. Is it possible that I have sensors from before this revision change? 

    Changes from Revision F (January 2016) to Revision G Page

    • Equation 1, changed From: 10 mV/°F To: 10mv/°C ............................................................................................................ 13

    • Power Supply Recommendations, changed From: "4-V to 5.5-V power supply" To: "4-V to 30-V power supply: .............. 19

  • 0 in reply to Arick Goetz
    TI__Mastermind 35895 points

    Arick,

    I think the datasheet was wrong. The LM35 was released by National Semiconductor in 1983, and, as far as I can tell, has always had a 35V max. When TI acquired National Semiconductor in 2011, the documents were (eventually) translated to TI formatting. The mistake probably happened in translation. 

    thanks,

    ren