TEMPERATURE_TO_PULSE_WIDTH

Published:2009/7/10 21:24:00 Author:May | From:SeekIC

Temperature-dependent current through thermistor TH1 develops voltage across R1 that is compared with fraction of increasing voltage across C1 by 741 opamp. When output of opamp goes negative, it triggers 555 IC connected as mono MVBR, to turn transistor on for about 100 μs and discharge C1. Circuit is based on similarity between resistan ce-tem peratu re curve of ther-mistor and inverse function of voltage across capacitor charging through resistor. For values shown, circuh gives 650-μs pulse width at 0℃, increasing 20 μs per degree with accuracy of ±1.2℃ up to 60℃. If IC output is used to gate clock oscillator, number of oscillator output pulses will be directly proportional to temperature.-T. P. Y. Sander, Temperature to PulseLength Converter, Wireless World, Jan. 1977, p 76.



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