Since it is a combination of two circuits it can also allows high current to pass through it (upto 1.2A) which makes it ideal for high current applications. Normal transistor have a current gain for around 100-300 but our Darlington transistor has a gain of 20000 hence it can be easily used in amplifier applications. The 2N5306 transistor is very much similar to the commonly used NPN transistors, but it is way more powerful than those since it is a Darlington transistor. Where to use 2N5306 Darlington Transistor? This is exactly where a Darlington transistor comes in. But in some application, the base current will be limited and cannot be increase during which we have to increase the transistor gain. So for loads consuming high power it becomes mandatory to increase the base current. Load current=i/p current X transistor gain As we know a transistor is turned on by providing an input current to the base pin (current controlled device) and when it turns on it allows the load current to flow through it which can be given by the formulae It decides how much times the load current can be amplified based on the input current to the bias pin. The current gain is an important property for a Darlington transistor. What is Current Gain? Why is it important? For example the transistor here has a current gain of 20000 and a collector continuous current of 1.2A because of its Darlington properties. One very important function of a transistor is its very high current gain. Yes the transistor you see above is actually a combination of two transistors provided in a single package to make it easy to use in our circuits. Out of which one transistor will be an NPN transistor and the other will be a PNP transistor. The Darlington Transistors are made up of two transistors combined togather. Collector-Emitter voltage (VCE) is 25 V.Continuous Collector current (IC) is 1.2A.High DC Current Gain (hFE), typically 20,000 when IC=100mA.As you can see, when the collector current increases, h FE decreases.Current Drains out through emitter, normally connected to groundĬontrols the biasing of transistor, Used to turn ON or OFF the transistorĬurrent flows in through collector, normally connected to load The graph above shows h FE on the y-axis and collector current on the x-axis for a general-purpose transistor. Students often find it difficult to visualise the relationship between h FE and collector current. The h FE parameter is not a constant though, because a transistor may have many ratings for different collector currents Ic. Hence, the current flowing through the collector is proportional to the base current multiplied by gain, as shown by the formula below. How large this current flow is depends upon a gain factor known as "h FE", also sometimes called the DC current gain, and beta. Remember that a bipolar transistor is a current amplifier, because a small amount of current "Ib" through the base controls a larger amount of current "Ic" flowing through its collector. For hard saturation, engineers usually choose a value of 10. Value for transistor switching purposes we always choose the minimum rating as the worst case because we want the transistor to conduct in the saturation region. The parameter "h FE" represents the DC gain,Īnd this is the parameter to consider. Small case "h fe" represents the small-signal current gain or AC gain,Īnd we do not use this parameter when using the transistor as a switch. In transistor literature, there are two different types of gain parameters with the same three letters. There are two calculators in this multi-page section of the article, and the first one is for when the load resistance is known, whilst the second, is for when the load current is known. A proper value of base resistance is therefore required for conduction in this region, and this value is different for different input switching voltages. In these types of switching applications, we require the transistor to behave as a switch and conduct fully in For hard saturation, engineers usually use a DC current gain h FEĪn NPN transistor requires a positive voltage at the base junction to switch ONĪnd control a load (RL) such as a low-voltage relay with a known resistance value. This resistor determines the amount of saturation current I b(sat) flowing into the base junction, and that controls the amount of saturation current I c(sat) flowing through the collectorĪnd emitter junctions. Engineers often have to consider the required value of the base resistor that controls the amount of current entering the base junction of a bipolar junction transistor (BJT) to cause it to conduct in the saturation region.
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