These modules consist of two transistors and available in a single casing.It provides very large input impedance or transformation of impedance so it can change input impedance from high to low or low to high.It generates a very large current gain than the one transistor.These are some advantages of Darlington pair transistor.Due to that circuity gets shorted and load current flows due to that buzzer or bell operate.With the increment of water level sensor gets active and provides base current to Darlington pair which is required.Therefore, the circuit is open and no current flows.If the level is not high that will close the sensor Darlington is in off condition.As Darlington pair gives large collector current so it will operate bell connected with as output to the circuitry.This circuitry is for water level indicator and Darlington pair operates as a switch.The given figure shows a circuit for the alarm which will function through the Darlington pair.The configuration for PNP pair is almost the same as the NPN transistor.Now we discuss Darlington pair which is constructed with the PNP transistor.When a switch is unclosed both transistors are in a cutoff of mode of operation and a current flowing through the load is 0.Due to that light-emitting diode emits light of high intensity irrespective of variation in base resistance.Due to that voltage pair become active and current passes through the load.When the switch is closed then certain value of voltage larger than the 1.4 volts is given to the pair.The one hundred ohm resistance in a circuit is used to provide protection to the pair.The switch at the base can be substituted with a touching sensor so after touching led operates.The given diagram shows the running of LED with the Darlington pair.This configuration of a transistor is normally used in switching and amplifier circuits.Β=(β 1β 2) Darlington Transistor Applications After neglecting individual gain we have resultant equation.Base current for second transistor will be given as.The current at the collector will be some of two currents.Same this current gain for next transistor will be.As the 2 transistors are working in this pair so for voltage at the base should be greater than 1.4 volts.Normally to on the transistor, the base input voltage should be larger than 0.7 volts.So this large gain provides a large current for load. This gain is very large than a gain of a single transistor.So-net current gain of Darlington pair will be ten thousand as it is a product of two transistors. The value of β for a standard transistor is one hundred.Let’s assume that gain current of first transistor is β1 and gain of the second transistor is (β2) so the net gain of this pair will be a product of these to gain β1. ![]()
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