Multiple LM35 temperature sensors with summing amplifier?

Question

I have two big heatsinks with four power MOSFETs on each of them, I want to control the temperature of each heatsinks so that doesn't exceed 80℃ using two LM35 temperature sensors:

schematic

^{simulate this circuit – Schematic created using CircuitLab}

There's no MCU involved and using another op amp I'll pulldown the MOSFETs gates when the limit is reached, the error up to 1-2℃ is acceptable.

Is this a good way to combine two sensors readings using analog circuitry or is there a better approach?

What power supplies are you using? Why use two LM35s per heatsink? One should do (per heatsink). How will you use the 2nd op-amp (crucial given your previous question)? — Andy aka, Sep 03 '21 at 07:05
I think you gonna need a resistor to the GND at the R1/R2 node. — Marko Buršič, Sep 03 '21 at 07:05
@Andyaka One sensor per heatsink. just using a comparator and another MOSFET. — ElectronSurf, Sep 03 '21 at 07:12

Marko Buršič · Accepted Answer · 2021-09-03T08:02:59.830

2

schematic

^{simulate this circuit – Schematic created using CircuitLab}

Let we have two voltage sources connected together trough resistors, as your idea. We then place a voltmeter which shows the average voltage of both sources (2+1)/2=1.5. But there is a difference between voltage source and LM35. The V1 would sink the current, while LM35 can't sink the current.

SOLUTION:

schematic

^{simulate this circuit}

edited Sep 03 '21 at 08:02

answered Sep 03 '21 at 07:19

Marko Buršič

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So what's the solution? – ElectronSurf Sep 03 '21 at 07:20
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Hey, sorry I didn't see the update to your answer. – ElectronSurf Sep 04 '21 at 20:01

Multiple LM35 temperature sensors with summing amplifier?

1 Answers1