Transistor switch

In this circuit we have used Q1 Transistor as switch , U1 opamp as comparator , U2 AND gate . Case Normal Operation = In normal operation, we feed the 3.3v coming from Microcontroller to the AND gate which produces High voltage at the base of transistor only if the both the inputs are High. Then transistor will goes into Saturation Region and current starts to flow from load to the Transistor CE. Few volts are dropped across the Resistor R6, Which is less than the ref voltage (500mV) . So comparator will produce High Outptut. which we feed to the AND gate. Case Short Circuit = If we short the 12v supply to the collector of transistor Q1 by pressing the switch. The High current will flow through the transistor Collector to Emitter so high voltage will drop across the Resistor R6 than the Ref Voltage 500mV. Then Opamp , which acts as comparator will produce approximately 0v at the output, which we feed to the input of AND Gate which produces Low Voltage to the base of transistor , so transistor gets turned off and will acts as insulator between Collector and Emitter.