IONIZATION_ALARM_USING_TRANSISTORS

Published:2009/7/5 22:21:00 Author:May | From:SeekIC

Use of continuous smoke alarm signal rather than beeping horn simplifies transistor circuits needed to trigger fire alarm and low-battery alarm. When high impedance of ionization chamber is lowered by smoke or gas, amplifier Q1-Q2-Q3 supplies 100-μA base current to Darlington Q4 for powering hom continuously as Iong as smoke content exceeds that set by threshold control R5. Low-battery circuit is tdpped at voltage range between 9.8 and 11.2 V, as determined by R13, to energize MVBR Q8-Q9 for driving horn 0.7 s, with 50-s OFF intervals.Battery is chosen to last at least t year while furnishing standby current of about 70μA.-A.Pshaenich, Solid State Gas/Smoke Detector Systems, Motorola, Phoenix, AZ, 1975, AN-735,p 8.



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