Edge detectors

In a square wave there is a rising edge/Positive edge and a falling edge/negative edge. The circuit which detects these edges( which are nothing but sudden rise in voltage or fall in voltage)and gives a pulse at output are called edge detectors. Edge detectors play an important role in digital electronics. These edge detectors come integrated with flip flops but if you want a edge detector as a individual circuit then yes ,"you are on the right page".

Edge detector are of two types:-

1) positive edge detector.

2) Negative edge detector.

1) Positive edge detector circuit.

This circuit gives a negative pulse when the input rises from low to high. Its made by using capacitor , transistor NPN and three resistors.

working of the circuit:- when the switched is pressed the capacitor starts to charge and during its being charged the current flowing in the circuit is towards the base of transistor which keeps the transistor "on" .Once the capacitor charges completely the transistor turns "off" .This gives us a -ve pulse at the output.

2)Negative edge detector circuit:-

This circuit gives a negative pulse when the input falls from high to low.Its made by using capacitor , transistor (BC547) NPN and three resistors.

working of the circuit:- In this circuit when we press the switch the capacitor discharges by 1/2vcc .During discharging the transistor is off as the direction of current is not towards the base of the transistor .The moment we release the switch it charges quickly to vcc turning the transistor on and giving a -ve pulse at output from collector. This action indicates that its detecting -ve edge.

practically explaining video