The over-temperature and cooling alarm circuit

Published:2011/7/6 2:40:00 Author:qqtang | Keyword: over-temperature, cooling alarm | From:SeekIC

Working principle The circuit is shown in figure 1. The diodes of VD1 and VD2 are both located in the constant temperature box, when the temperature is below the lower limit, the LEV of figured point a is higher than the threshold voltage U of the gate A input terminal, the output terminal of gate A is in a low LEV, which makes gate B output a high LEV, at the moment, the oscillator composed of gate C and gate D is starting to vibrating, the piezoelectric chip is making the alarm sound; when the temperature is over the upper limit, the LEV at point b is lower than the voltage U of the gate B threshold, which can also makes gate B output a high LEV, and the piezoelectric chip is making the alarm sound.



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