![]() Since the increasing of base current is not possible due to the supply source, the only way to increase the load current capability is to increase the gain of the transistor. We know that the load current in the transistor is the product of input current and gain of the transistor. But in some applications, the input base current from source may not sufficient to drive the load. In the above example, we have seen driving of a load (Lamp) using single transistor. This is the current amplification in the transistor. When the resistance is too small, sufficient amount of current will flow through the base which results a very large current flow through the lamp so the lamp becomes brighter. If the resistance value of the variable resistor is more, the base current is reduced so the transistor becomes OFF. ![]() Here, in this circuit the base current is the only factor that decides the current flow through the collector and emitter so that the light will glow from dim to very bright by varying the resistance of the variable resistor. The above relation tells that the current available to drive the load is 100 times that of the input current of the transistor.Ĭonsider the below figure where NPN transistor is used to switch the lamp with variable resistor connected between the source and the base terminal. Load current = Current gain (β) × base current Transistor gain or Current gain (β) = load or collector current/ input or base current The current gain or beta of a transistor is the ratio of collector current to base current. Darlington TransistorīACK TO TOP Why We Use Darlington Transistor?Īs we know that to drive the transistor into the conduction mode a small base current is required, when the base is connected as input, emitter as common and collector as the output.īut, when we consider the load at the collector terminal, this small base current may not enough to drive the transistor into conduction. Let us look in brief about this transistor with applications. Many opto-isolator circuits are made with Darlington transistors to have high current capacity at the output stage. These transistors are found in different types of applications such as power regulators, motor controllers, audio amplifiers, etc. In today’s market, wide variety of Darlington transistors are available that are varied by polarity, collector current, power dissipation, package type, maximum CE voltage and so on. Darlington configuration was invented by Sidney Darlington in the year of 1953. Example of Darlington Transistor CircuitĪ Darlington transistor or simply Darlington pair is mainly used to offer a very high current gain even with low base current.Darlington Transistor or Darlington Pair.
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