Temperature To Pulse Width Converter Circuit Using LM3524

  
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The circuit is temperature to pulse width converter. The LM3524 to convert the output of an LM135 temperature transducer into a pulse width which can be measured by a digital system, such as a microprocessor controlled data acquisition system. In this circuit, the LM135`s temperature-dependent output (10 mV/ °K) is divided down and applied to A1`s
Temperature To Pulse Width Converter Circuit Using LM3524 - schematic

positive input. This moves A1`s output high, driving the input to the LM3524`s pulse width modulation circuitry. The LM3524 pulse-width output is clipped by the LM185 reference and integrated by the 1 MW-0. 1 µF combination. The DC level across the 0. 1 µF capacitor is fed back to A1`s negative input. This feedback path forces the LM3524`s output pulse width to vary in a highly linear fashion according to the potential at A1`s positive input. Here is a schematic drawing: The overall temperature to pulse width scale factor is adjusted with the gain trim  potentiometer. The 1000 pF capacitor provides stable loop compensation. A1, an LM358, allows voltages very close to ground to be sensed. This provides greater input range than the LM3524`s input amplifier, which has a common mode range of 1. 8 3. 4V. The oscillator output pulse at pin 3 may be used to reset counters or other digital circuitry because it occurs just before the output pulse width begins.



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