This article will discuss the LM335 temperature sensor TO-92, including its basics, pinout, equivalents, schematics, internal operation, specifications, features, circuit working principles, applications, and comparisons.

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LM335 Temperature Sensor Basic

The LM335 temperature sensor in a TO-92 package is a small, easy-to-use analog sensor designed for accurate temperature measurement in electronic circuits. The TO-92 package is a compact, three-lead plastic casing commonly used for low-power sensors and transistors, making the LM335 suitable for breadboards, prototypes, and compact PCB designs.

The LM335 works by producing an output voltage directly proportional to absolute temperature in Kelvin, with a typical scale of 10 mV per Kelvin. For example, at room temperature (about 25 °C or 298 K), the sensor outputs approximately 2.98 V. Because of this linear behavior, converting the output voltage into temperature is simple using basic calculations or a microcontroller’s ADC.

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LM335 Temperature Sensor Pinout Details

Alternatives & Equivalent Model

• LM135

• LM135A

• LM235

• LM235A

• LM335A

LM335 Sensor Schematic Diagram

The LM335 basic temperature sensor schematic shows the simplest way to use the LM335. A resistor (R1) is connected between the supply voltage (V+) and the sensor to provide a small, stable bias current. The LM335 behaves like a temperature-dependent Zener diode, producing an output voltage that increases by about 10 mV per Kelvin. The output is taken directly from the junction between R1 and the sensor, making this circuit easy to use for basic temperature measurements.

The calibrated sensor schematic adds a 10 kΩ trim potentiometer connected to the adjustment pin of the LM335. This allows fine calibration of the output voltage so the sensor can be set accurately at a known reference temperature (such as 25 °C). Calibration improves measurement accuracy by compensating for small device tolerances, while the output still maintains the same 10 mV/K linear relationship.

Functional Block Diagram

The functional block diagram of the LM335 shows how internal transistor networks work together to sense temperature accurately. At the core of the circuit is a temperature-dependent semiconductor junction that generates a voltage proportional to absolute temperature (Kelvin). This behavior is based on predictable changes in transistor characteristics as temperature varies.

Several transistor stages act as current sources, amplifiers, and stabilizers, ensuring that the sensor operates with a constant bias current and maintains a linear output. The matched transistor pairs help cancel errors caused by supply voltage changes, which improves accuracy and stability. Capacitors inside the circuit assist with noise reduction and stable operation.

The right side of the diagram includes the adjustment network, which allows fine trimming of the output voltage during calibration. This ensures the LM335 produces the correct 10 mV/K output, making it reliable for precise temperature measurement in analog and microcontroller-based systems.

LM335 Technical Specifications

LM335 Temperature Sensor Features

Directly calibrated to the Kelvin temperature scale

The LM335 outputs a voltage that is directly proportional to absolute temperature in Kelvin. This makes temperature calculations straightforward and avoids complex conversions inside analog or digital systems.

1 °C initial accuracy available

The sensor offers good factory accuracy, especially in higher-grade versions. With proper calibration, it can provide reliable and repeatable temperature measurements for precision applications.

Operates from 400 µA to 5 mA

The LM335 works over a wide bias current range, allowing flexible circuit design while maintaining stable and predictable performance.

Less than 1 Ω dynamic impedance

Low dynamic impedance improves output stability and reduces sensitivity to noise, making the sensor suitable for accurate analog signal processing.

Easily calibrated

An adjustment pin allows fine trimming of the output voltage at a known reference temperature, improving overall accuracy.

Wide operating temperature range

The LM335 supports a broad temperature span, making it suitable for both low- and high-temperature environments.

Low cost

Its simple design and wide availability make the LM335 an economical choice for educational, industrial, and DIY temperature-sensing projects.

Linear output voltage characteristic

The LM335 provides a highly linear voltage output over its operating range. This linearity simplifies signal processing and improves accuracy when converting voltage readings to temperature values.

Good long-term stability

The sensor maintains consistent performance over time with minimal drift. This makes it reliable for continuous monitoring and long-term temperature measurements.

Low self-heating

Due to its low operating current, the LM335 generates very little internal heat. This helps prevent measurement errors caused by the sensor heating itself.

Simple interface with microcontrollers

The analog output can be directly connected to an ADC pin of microcontrollers such as Arduino or PIC, reducing the need for additional signal-conditioning circuits.

Insensitive to supply voltage variations

Internal circuitry helps minimize the effect of supply voltage changes, allowing stable temperature readings even when the power source is not perfectly regulated.

Available in multiple accuracy grades

The LM335 family includes different accuracy options, allowing designers to choose a version that best matches their precision and cost requirements.

Compact TO-92 package

The small TO-92 package makes the LM335 easy to mount on PCBs and breadboards, ideal for compact designs and prototyping.