Like for like they offer better performance than PNP transistors because electrons are the majority carriers and their mobility is higher than that of holes which are the majority carriers in PNP transistors. The NPN transistors are more widely used. It is important to choose the correct type otherwise all the circuit polarities will be wrong. There are two types of transistor: NPN transistors and PNP transistors. There are some useful SMD codebooks available that provide the data for these devices. However, identifying the manufacturers' type number of an SMD diode from the package code may not be easy at first sight. This can normally be accommodated on the small surface mount diode packages. As a result, a rather arbitrary coding system has developed, whereby the device package carries a simple two or three character identification code. However when using automated PCB assembly techniques and surface mount devices, it is found that many transistors are too small to carry the full number that might be used in a data sheet. The European Pro-Electron scheme is particularly good for this as it distinguishes between different types of transistor, for example a BC109 is a silicon audio frequency low power transistor, and a BFR90 is a low power RF transistor. There are three international schemes that are widely used: European Pro-Electron scheme US JEDEC (numbers start with 2N for transistors) and the Japanese system (numbers start with 2S).Īpart from just giving a standardised type number to the transistors, these schemes can provide information about the transistor performance. This enables the full data on its specifications to be checked on the manufacturers transistor datasheet to investigate its performance. The type number of the device is a unique identifier given to each type of transistor. In this case the specification parameters for all manufacturers should be closely checked to ensure they meet the requirements for the particular electronic circuit design. Often a second source and further sources may be required to give some level of insurance against a particular supplier or manufacturer ceasing their operation and the part becoming obsolete. For any critical parameters it is wise to use the actual figures from the manufacturer whose product is being used. It is also worth noting for electronic components that can be obtained from several manufacturers, that the specifications may vary slightly between manufacturers. Also electronic component distributors often have details of the specifications of components, or sometimes a link to the specification on the manufacturer's website. The specifications for transistors, like any other electronics component are normally available on the website of the manufacturer. The definitions of these parameters are outlined in the table below: There are a number of standard parameters with abbreviations that are used to define the performance of a transistor. Specific transistor part numbers are normally available as leaded versions and also for SMD transistors with the same electrical specifications, although aspects like the heat dissipation will differ because of the different package styles. Whilst most transistors made these days are SMD transistors because of the automated PCB assembly techniques used, there are still many leaded devices as well. With most PCB assembly now using surface mount technology to aid the automated electronics manufacturing of products and equipment, most transistors manufactured these days are SMD transistors. Not all the parameters are electrical - aspects such as the size of the package, and whether the device is a surface mount transistor, i.e. Therefore a variety of the parameters will need to be carefully matched. 2N3553 transistor in a TO39 metal canįor electronic circuit design, selecting the right transistor will need several of the transistor parameters to match the requirements for the circuit. Transistor manufacturers issue specification sheets for their transistors which are typically found on the Internet, although years ago engineers used to study data books to find out the information. Each of these transistor specifications define an aspect of the performance of the transistor. In order to define the parameters of a transistor there are many different specifications that are used. These have been designed to fulfil a variety of different applications in all areas of electronics. There is a huge number of bipolar transistors available both leaded and surface mount devices. Transistor basics Gain: Hfe, hfe & Beta Transistor specifications Transistor and diode numbering codes Choosing replacement transistors Transistor Specifications Explained There are many different transistor specifications defining aspects of a bipolar transistor's performance transistor to enable an informed choice of the right transistor for any circuit.
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