Author Topic: logic for adding two diodes in LM35 question  (Read 421 times)

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Offline john23Topic starter

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logic for adding two diodes in LM35 question
« on: December 09, 2025, 09:23:30 am »
Hello , I need to use LM35 in order to check for temperature and if needed to shut down current supply.
I have found a spice model for the LM35 but the  it has only one port of out.
How can I make a 3 port device like in the datasheet?
Also in the datasheet they use 2 diodes as in the photo ,why are they needed?(as shown in the photo)
Thanks.
https://www.ti.com/lit/ds/symlink/lm35.pdf?ts=1765256004717&ref_url=https%253A%252F%252Fwww.google.com%252F

* LM35 Model
.subckt LM35 Out
I1 0 N001 1
R0 N001 0 1 tc1=0.01
I2 0 N002 1
R1 N002 0 1 tc1=0.01 TEMP=0
G1 0 Out N001 N002 10
R2 Out 0 0.1
.ends
 

Online ledtester

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Re: logic for adding two diodes in LM35 question
« Reply #1 on: December 09, 2025, 09:39:17 am »
According to:

https://electronics.stackexchange.com/a/421014/

Quote
The whole point about this circuit is that the 18 kohm resistor is tied to a negative voltage relative to Vout- and this ensures that the LM35 can produce a signal that reflects negative temperatures. Without the bias resistor to a negative supply rail (relative to Vout-), the LM35 only works from +1 or 2 degC
...

For a 3-terminal model, I found this posting:

https://www.electro-tech-online.com/threads/spice-model-for-lm34-lm35.113289/

I've included the attachments from that post below.



« Last Edit: December 09, 2025, 09:48:08 am by ledtester »
 
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