LM35: Wrong reading at room temperature

Priyanka Jantre62

Part Number: LM35

Hi,

We are using LM35 Temperature sensor on our boards but the sensor is attached to one of the sides of Heat Sink and not on the center. In some cases the LM 35 measures 220 - 250 mV at room temperature. However in most of the cases the reading is 356 or 321 mV at room temperature. Do you have any recommendation for using the part with Heat sink. Our heat sink is shared with 3 other parts and the pins of LM35 are soldered on board without touching any portion of Heat sink would it make any difference.

Please let us know.

Thanks,

Priyanka

over 7 years ago

0 Ren Schackmann over 7 years ago

TI__Mastermind 41155 points

Hi Priyanka,

Which package are you using? I would recommend the TO-220 package for use with a heatsink.

Ren

0 Jose Arteaga4 over 7 years ago

TI__Expert 5695 points

Our support team will contact you shortly

0 Priyanka Jantre62 over 7 years ago in reply to Ren Schackmann

Prodigy 90 points

Hi Ren,

We are using TO_220_VERT package.

Thanks,
Priyanka

0 Kelvin Le THS over 7 years ago in reply to Priyanka Jantre62

TI__Expert 6895 points

Priyanka,

I would recommend using thermal grease to improve thermal conductivity between your sensor and heat sink. With the thermal grease, a small change in contact pressure can have significant change in temperature readout. The temperature gradient can be very large, you will have to keep that in mind when doing physical layout.

-Kelvin

0 Priyanka Jantre62 over 7 years ago in reply to Kelvin Le THS

Prodigy 90 points

Thank you Kelvin. We are already using Thermal Grease, however in our case LM35 surface is connected to aluminium part of Copper heatsink. Please see attached picture we have a high voltage MOSFET, covered by copper heat sink, has aluminium holder to screw the heatsink and LM35 connected to surface of AL plate at the edge.

This may not be good mounting technique, but it would be interesting to know how much effect it will have on the thermistor reading.

Thanks,

Priyanka

0 Kelvin Le THS over 7 years ago in reply to Priyanka Jantre62

TI__Expert 6895 points

Priyanka,

I don't see your attachment...

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LM35: Wrong reading at room temperature