LM135 temperature sensor and its application circuit

LM135 Temperature Sensor and Its Application

LM135/LM235/LM335 is a precision temperature sensor launched by National Semiconductor Corporation. It works similarly to a Zener diode. Its reverse breakdown voltage varies with temperature according to the law of +10mV/k. It can be used in precision temperature measurement equipment. It has three packaging forms suitable for various instrumentation requirements. Its main functional characteristics are as follows:

Calibrate directly on the absolute temperature scale with      an accuracy of 1°C.      Operating current 400uA-5mA.      Dynamic impedance 1Ω.      Easy to calibrate.      Wide operating temperature range 2001°C.      Low cost.     Figure 2 is the internal schematic diagram of LM135. V15 and V16 are temperature sensing elements. The physical structure of these two transistors has specific requirements. The emitter junction area of ​​V15 is 10 times that of V16. Their collector load resistances are exactly the same. If the currents flowing through these two resistors are different, the collector voltages of V15 and V16 are also different. They are amplified by the differential amplifier composed of V1-V8, and the internal resistance of V1 also changes. Then the current flowing through Rs will also change, and the voltage between V+ and V- will also change. The change in this voltage also changes with temperature.

The voltage difference ⊿V between LM135V+ and V- changes only in proportion to the ambient temperature, and a sensitivity output of 10mV/K is obtained.

The main electrical indicators of LM135V are as follows: