1 Presented by: Adamou MOUSSA ISSAKA January, 9 th 2023 Description of the LM35 Temperature Sensor

2  What is the LM35 Outline of the presentation  Operating principle of the LM35  Description of the electronic components inside the LM35 Sensor

Voltage output-Temperature of LM35 The LM35 is an inexpensive precision centigrade temperature sensor manufactured by Texas Instruments. Specifications of LM35 Sensor Supply voltage4V – 30V Operating current60µA Temperature difference-55°C à + 155°C Accuracy±0,5°C à +25°C ±1°C de -55°C à +150°C Output scale factor10 mV/°C Output voltage at 25°C250 mV Output scale factor = 10 mV/°C Temperature (°C) = V OUT / 10 LM35 Sensor What is the LM35

Operating principle of LM35 (1/3)  This causes a voltage across the resistor R1 that is proportional to the absolute temperature (PTAT) Internal circuit of LM35 The LM35 is an integrated circuit sensor that can be used to measure temperature with an electrical output proportional to the temperature (in °C).  There are two transistors in the center of the drawing.  One has ten times the emitter area of the other.  This means it has one tenth of the current density, since the same current is going through both transistors.

 The amplifier at the right converts absolute temperature (measured in Kelvin) into either Fahrenheit or Celsius, depending on the part (LM34 or LM35). Internal circuit of LM35  The amplifier at the top ensures that the voltage at the base of the left transistor (Q1) is proportional to absolute temperature (PTAT) by comparing the output of the two transistors. Operating principle of LM35 (2/3)  The little circle with the "i" in it is a constant current source circuit.

Operating principle of LM35 (3/3) Internal circuit of LM35 From the internal circuit of the LM35 Sensor, one can see that it’s composed with basic electronic components such as:  Resistors  Transistors  Diode  Operational Amplifier  Constant current source circuit  Ground

Description of the electronic components inside the LM35 Sensor (1/4)  Resistor: is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses.  Resistor Composition: most common, modern resistors are made out of either a carbon, metal, or metal-oxide film. In these resistors, a thin film of conductive (though still resistive) material is wrapped in a helix around and covered by an insulating material.  Resistor

Description of the electronic components inside the LM35 Sensor (1/4)  The transistor is an electronic component that is used in most electronic circuits (logic circuits, amplifiers, voltage stabilizers, signal modulation, etc.) in both low and high voltage.  A transistor is a semiconductor device with three active electrodes, which allows to control a current or a voltage on the output electrode (the collector for a bipolar transistor and the drain for a field effect transistor) thanks to an input electrode (the base for a bipolar transistor and the gate for a field effect transistor).  With the circuit connected to the "collector" and "emitter" terminals, the transistor is insulating without voltage on the “Base” terminal, and conducting with voltage on the “Base” terminal.  In other words, it is an electronically controlled switch, without any mechanical part.  Transistor

 Mainly, they are of two types – PNP and NPN transistors  These transistors are typically fabricated by means of five basic techniques as follows: Diffused Technique Point contact Technique Fused or Alloy Technique Rate-Grown or Grown Technique Epitaxial Technique Description of the electronic components inside the LM35 Sensor (1/4)

 Diode  The diode is a basic component of electronics. It is a non-linear and polarized (or non-symmetric) dipole.  The direction of connection of a diode determines the operation of the electronic circuit in which it is placed.  Without precision, this word designates a dipole which allows the electric current to pass only in one direction.  This dipole is called a rectifier diode when it is used to make rectifiers that allow the transformation of alternating current into direct current.  A diode is created by joining an electron-deficient substrate, i.e. rich in holes (P-type semiconductor) to a substrate rich in free electrons (N-type semiconductor or metal).  Most diodes are made by joining two semiconductors: one doped "P" the other doped "N".

 An operational amplifier (often op amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.  In this configuration, an op amp produces an output potential (relative to circuit ground) that is typically 100,000 times larger than the potential difference between its input terminals.  The operational amplifier traces its origin and name to analog computers, where they were used to perform mathematical operations in linear, non-linear, and frequency-dependent circuits.  The popularity of the op amp as a building block in analog circuits is due to its versatility. By using negative feedback, the characteristics of an op-amp circuit, its gain, input and output impedance, bandwidth etc. are determined by external components and have little dependence on temperature coefficients or engineering tolerance in the op amp itself. Description of the electronic components inside the LM35 Sensor (1/4)  Op Amp

 An op amp consists of multiple transistors packaged in an integrated circuit chip. It senses the fluctuating voltage difference between two inputs, uses power from an external supply to amplify that difference, and uses negative feedback to ensure that the output is an accurate replica of the input. Description of the electronic components inside the LM35 Sensor (1/4)

 Constant Current Source Circuit Description of the electronic components inside the LM35 Sensor (1/4)  It is a power source that maintains a constant current to a load despite changes and variances in the load resistance.  Another way of putting it is that a constant current source supplies a steady output current regardless of load resistance.  In this way, a constant current source is precious for supplying steady current regardless of any variations in resistance, even a significant variance in resistance. In circuits with regular current requirements, this is useful. Constant Current Source Circuit Diagram