Controlling of power MOSFET using humidity sensor

Abstract

In the dissertation work presented here, LMC555CM timers are used to generate the PWM signals on the basis of the humidity level present in the atmosphere. Here, we have designed a signal conditioning circuit for the triggering of semi-conductor devices such as BJT, MOSFET and IGBT etc. to control the power applied to the electrical load (5V PMDC motor). The circuit comprises of 555 dual timer, EX-OR gate (74LS86D), variable capacitor in the place of capacitive humidity sensor, 5v input supply and other basic electrical components. Signal conditioning circuit works on the principle that change in moisture level contributes to the change in dielectric constant of thin film Al2O3 based capacitive sensor used as sensing film between the two electrodes. PWM output of two dual timers is then compared by using EX-OR logic gate. The duty cycle of the logic gate output signal changes according to the change in capacitance of the capacitive sensor. For better switching performance 555 timers are used instead of other timers to get the PWM output at high frequency (near to 50 KHz). Totem-pole arrangement is used as a driver circuit for power MOSFET to reduce the switching losses at higher frequencies. These PWM signals are used as firing signals for the semi-conductor devices to control the speed of PMDC connected to the drain terminal of power MOSFET. The designed electronic circuit is simulated on NI-Multisim 12.0 software and implemented in real time on breadboard.