The LM35 temperature sensor is a widely used precision analog device designed to provide accurate and linear temperature measurements directly in degrees Celsius. This article will discuss the LM35 temperature sensor in detail, including its pinout, specifications, features, functional block diagram, application circuits, and more.

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LM35 Temperature Sensor Overview

The LM35 temperature sensor is a precision integrated-circuit device designed to measure temperature accurately and efficiently. Its output voltage changes linearly with temperature in degrees Celsius, which makes temperature readings simple and direct. Since the sensor is factory-calibrated, it does not require additional calibration or complex signal processing, reducing design effort in electronic systems.

One of the key advantages of the LM35 is its low output impedance and minimal self-heating, allowing it to deliver stable and reliable readings even during continuous operation. It operates with single or dual power supplies and supports a wide temperature range, making it suitable for both industrial and consumer applications. The sensor is available in multiple package options, which helps designers integrate it easily into different circuit layouts.

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LM35 Temperature Sensor CAD Models

LM35 Temperature Sensor Pinout Details

Alternatives & Equivalent Model

LM35 Functional Block Diagram

The LM35 block diagram shows how temperature is converted into a precise voltage output inside the sensor. At the core of the circuit is a temperature-sensing element based on transistor junction behavior, which generates a voltage that changes predictably with temperature. This internal reference produces a small temperature-dependent signal that forms the basis of the measurement.

This signal is first processed by an internal amplifier stage that stabilizes and conditions it. The diagram shows how the sensor uses matched transistors and resistors to create a voltage that increases linearly as temperature rises. This design helps ensure good accuracy and consistency across the operating range.

Finally, the conditioned signal is fed into an output amplifier that scales it to a usable level. This stage produces the familiar LM35 output of 10 mV per degree Celsius at the VOUT pin. The output stage also provides low output impedance, making the sensor easy to connect directly to microcontrollers, ADCs, or measurement circuits without additional signal conditioning.

LM35 Temperature Sensor Specifications

LM35 Temperature Sensor Features

Calibrated Directly in Celsius (Centigrade)

The LM35 provides an output voltage that directly corresponds to temperature in degrees Celsius, removing the need for unit conversion from Kelvin or Fahrenheit.

Linear 10 mV/°C Scale Factor

The output increases by 10 millivolts for every 1°C rise in temperature, making temperature calculations simple and predictable.

0.5°C Ensured Accuracy at 25°C

The sensor delivers reliable readings around room temperature, which is important for indoor, laboratory, and electronic monitoring applications.

Rated for Full −55°C to +150°C Temperature Range

The LM35 can operate across a wide temperature range, allowing it to be used in both low-temperature and high-temperature environments.

Suitable for Remote Applications

Its low output impedance and stable signal allow accurate temperature measurement even when the sensor is located far from the readout or control circuit.

Low Cost Due to Wafer-Level Trimming

Factory calibration during manufacturing eliminates the need for external trimming components, reducing overall system cost.

Operates from 4 V to 30 V Supply

The wide operating voltage range makes the LM35 compatible with many power sources, including batteries and regulated power supplies.

Less Than 60 µA Current Drain

Very low power consumption helps minimize energy usage and makes the sensor suitable for low-power and battery-operated systems.

Low Self-Heating (0.08°C in Still Air)

Minimal internal heat generation ensures that the sensor does not significantly affect its own temperature readings.

Low Non-Linearity (±0.25°C Typical)

The sensor maintains a highly linear response over its operating range, which improves measurement accuracy.

Low-Impedance Output (0.1 Ω for 1 mA Load)

A low output impedance allows the LM35 to drive ADC inputs and signal lines directly without additional buffering circuits.

LM35 Typical Application Circuits

The basic centigrade temperature sensor circuit shows the LM35 connected using a single positive power supply. In this configuration, the sensor directly outputs an analog voltage that increases linearly with temperature at a rate of 10 mV per degree Celsius. Since the output starts at 0 mV near 0°C, this setup is well suited for temperature measurements above freezing. Its simple wiring makes it ideal for general-purpose monitoring, microcontroller projects, and applications that only require positive temperature readings.

The full-range centigrade temperature sensor circuit demonstrates how the LM35 can measure temperatures below 0°C by using both positive and negative supply voltages. The added resistor connected to the negative supply allows the output to shift, enabling accurate sensing across the full temperature range. This configuration is useful in environments where temperatures may drop below freezing and more complete temperature coverage is required.