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Ionising Smoke Detector

2017-12-21 04:18  
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Ionising Smoke Detector

Smoke particles entering an ionizing detection chamber generate signals of only a few pico-amperes. This signal must be buffered by a high input impedance Amplifier normally requiring an expensive low leakage J-FET. The leakage current through the high integrity silicon-oxide Gate of the Zetex BSS138 is negligible, hence the buffer circuit shown is ideal for this application. Two MOSFET’s have been used, coupled to produce a Schmitt-Trigger action. This eliminates unwanted current drain produced by many CMOS IC’s when their inputs are allowed to settle mid-supply. This circuit CAN also be used in Signal Conditioning circuits for battery operated CMOS Microcontrollers  Suitable for operation over the temperature range of -40°C to +75°C the circuit consumes only 0.65µA (excluding the sounder), thus giving a battery life limited only by internal battery leakage.

Ionising Smoke Detector application circuits

 

BSS138, BSS138 50V N-Channel Enhancement Mode MOSFET - ESD Protected, BSS138 Application circuits, BSS138 Circuit Diagrams