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Darlington circuits

The Darlington system is a breakthrough invention discovered in the mid-twentieth century by Sidney Darlington, an American engineer working at Bell Laboratories (USA). The Darlington circuit, sometimes called 'Darlington transistors', was invented in 1953.

It is a phenomenon in the form of a system consisting of two interconnected transistors. However, this circuit is specific because the configuration of the components is a structure composed of two bipolar transistors connected in such a way that the current amplified by the first transistor is also amplified by the second transistor of the circuit. The emitter current of the first transistor becomes the base current of the second. Due to the fact that the collector currents add up in such a system, this type of transistor configuration provides the highest energy efficiency.

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Integrated circuit ULN2003A 7xDarlington - SMD

7-channel Darlington driver in SO-16 case.
Index: UCC-00189
Index: UCC-00189
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Regular price €0.21 Price €0.21

Integrated circuit ULN2803A 8xDarlington - THT

8-channel Darlington driver in THT case DIP18.
Index: UCC-02559
Index: UCC-02559
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Regular price €1.02 Price €1.02

Integrated circuit ULN2003AN 7xDarlington - THT - 5 pcs.

7-channel Darlington driver in DIP16 case. The set contains 5 pieces of ULN2003AN circuit.
Index: UCC-00188
Index: UCC-00188
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Regular price €1.28 Price €1.28

The Darlington circuit provides much greater current amplification than any other transistor used separately. Currently, such elements are often used in current and power systems, where high system gain is very important. The use of the Darlington system is common today. Robotics and programmable electronics enthusiasts also benefit from this discovery. Check out the ICs below that use the Darlington Effect!

Darlington circuits are a perfect way to boost amplification

One of the most important parameters for a bipolar transistor is its current gain. This parameter is extremely important because the greater the gain, the greater the current. Therefore, the current can be controlled by a given system depending on the gain. Hence, the use of a Darlington circuit is often recommended as a way to increase the transistor gain even by several orders of magnitude. Thanks to the use of two bipolar transistors connected to each other, a much greater gain is obtained, and thus much greater possibilities of a given system.

There are Darlington integrated pairs or even integrated circuits equipped with many parallel pairs of this kind. Such systems are often used to control high power loads with the help of systems with low current efficiency. The amplification effect will be very useful for GPIO pins of microcontrollers or single-board computers.

Darlington transistor – advantages and drawbacks

Darlington configuration has a lot of advantages. The main one is the possibility of getting very high current amplification, which we have presented above. With a relatively small base current, high emitter currents can be switched anyway. But the Darlington pair has much more to offer.

First of all, the system can provide very high input impedance (while keeping this configuration simple to build). The Darlington circuit can be assembled from two separate, discrete transistors, structures contained in a single housing or in an integrated circuit.

Of course, each solution has some drawbacks. In that case the main problem is doubling the base-emitter voltage. As standard, there are two connectors in the circuit between the base and emitter of the Darlington transistor. In the case of silicon transistors, this voltage is 0.65 V for one junction, so 1.3 V for a Darlington circuit. Another noticeable drawback of using Darlington configuration in some electronic designs is the large increase in saturation voltage. This phenomenon can cause problems when TTL logic circuits are controlled. Another disadvantage of the Darlington is the reduction of the work bandwidth. It is lower than the operating band of each of the components.

Darlington pairs – scheme and variety of use

From an external perspective, one Darlington pair behaves like a single transistor. It has one base, collector and one emitter. Usually Darlington configuration guarantees high current amplification in the system. Generally speaking, the relationship between the gain of the Darlington system βD with the gains of the constituent elements β1 and β2 should be: βD = β1 x β2 + β1 + β2. Thanks to this functionality, a really high gain can be obtained with the use of common, readily available semiconductor structures.

Darlington transistors are used to amplify the current, so practically in all electronic devices, in power amplifiers, power supplies, as well as in devices such as heater drivers or other power-loading devices. Most often, the transistor system consists of two discrete bipolar transistors connected within one common housing. This solution is perfect wherever a low base current is important. A great example will be microcontroller systems (certainly known to robotics enthusiasts). Often Darlington integrated circuits to control components with a higher current consumption.