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Over-temperature alarm for LM45C temperature sensor

Overview

The circuit uses an LM45C, LM4041, LM358, two LEDs, an adjustable resistor, and an NPN transistor. It's very simple, and while there might be some issues, it's not a big deal; it works in my tests.
Remember to check the voltage before use. The adjustable resistor controls the voltage at the "-" terminal of the op-amp, and the "+" terminal connects to the LM45C. The LM45C outputs its own voltage; at 35 degrees Celsius, it outputs 0.35V. When the LM45C voltage is higher, the op-amp outputs a higher voltage, the transistor conducts, and the buzzer and LEDs light up.
The Type-C interface is for power, and the 2-pin connector is also for power; just choose one. I've tried it with a bunch of chargers without any problems.

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It is your responsibility to test the circuit yourself and determine its suitability for you. EEWorld will not be liable for direct, indirect, special, incidental, consequential or punitive damages arising from any cause or anything connected to any reference design used.

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Update:2026-03-26 15:25:17

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