Darlington circuits

Layouts Darlingtona method to higher strengthen

One of the parameters characterizing the bipolar transistor is the current gain. This parameter is extremely important because the higher the gain, the greater the current, in which the system can operate at a given base current. The application of the system Darlingtona allows to increase the gain of the transistor even by several orders of magnitude, using two bipolar transistors. In commercially available fused pair Darlingtona or even the IP include several parallel pairs of this species. Such systems are often used for current amplification, for example, to control loads high power with small performance current, such as output GPIO microcontrollers or computers jednopłytkowych.

The principle of operation of a pair Darlingtona

Pair Darlingtona behaves from the outside as a separate transistor, which means that has one base, collector and emitter. As a rule, the system Darlingtona offers great amplification of current (approximately the product of the reinforcement of the two constituent transistors). In General, the relationship between the system gain ßD Darlingtona reinforcement constituent elements of β1 and β2 is: ßD = x β1 β2 + β1 + β2. Due to this, it really can be a big reinforcement with the use of simple, easily available semiconductor structures.

System Darlingtona - the advantages and Disadvantages of pairs of transistors

Layouts Darlingtona have a number of advantages, of which the main one is the possibility of obtaining a very high current amplificationequal to 1000 or more. Due to this small base current sufficient to switch the high current of the emitter/collector. Another advantage is to provide a very high input impedance, and ease of fabrication of this configuration. This system can be created from two separate, discrete transistors structures in a single package or chip. This kind of structure also has its drawbacks. One of them, approximately, a doubling of voltage base-emitter because the system has two connectors between the base and emitter of the transistor Darlingtona. In the case of silicon transistors, this voltage is 0.65 V for one connector, so that the 1.3 V for the system Darlingtona. Another disadvantage of pair Darlingtona increases the saturation voltage. This can cause problems when controlled by a logic circuit of TTL. The disadvantage darlingtonów also reducing range. It is lower than the range of each of the constituent elements.

Application Darlingtonów in electronics

The transistors in the system Darlingtona used where is important the strengthening of current, and therefore, power amplifiers, power supplies and control units, heaters or other high power loads. In this kind of applications often use two discrete bipolar transistors, compound in the system Darlingtona or a separate pair of transistors in this configuration in a single housing. This kind of elements are also used in places where the key is the low base current, for example, in systems mikrokontrolerowych, where it is often used combined system Darlingtona to control elements with high current consumption (e.g. a relay or lighting) through the digital pins of the processor.