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How to choose a patch transistor

Release date:2020-01-13

SMT transistor selection


There are several main problems in the application of SMT transistor:


One is the past use of through hole assembly transistor habit, how to find the corresponding chip transistor;


The other is to find out from the parameter circuit which transistor models are not available on the market and how to replace them. This is often a major problem for designers, developers, and maintainers in applications.


The reason for these two problems is that the models differ when you put the same type of kernel into a different device wrapper.


Such as:



Toshiba produces a small power triode in the to-92 package. However, when sot-23 is packaged in the same core, the model number is 2SC1815. Model number changed to 2SC2712; When the package is so-70. The model again becomes 2SC4732. According to this reality, transistors should be selected or replaced according to the basic parameters of the transistor, and the parameters found in the transistor manual are basically the same. And packaging to meet the requirements of the transistor.


Here is an example of 9012 and 9013 packages commonly used in to-92:


First, find the main parameters of 9012 and 9013:


9012 is PNP tube, Vceo is 30V, Ic is 500mA, Pcm is 625mW;


9013 is NPN tube, Vceo is 30V, Ic is 500mA, Pcm is 625mW.


You can find the sot-23 transistor in the transistor manual. A model with similar parameters is shown in the table. In the table, the Pcm- entry is significantly less than 9012 or 9013. This is because the cooling area of flake sot-23 is small, so the Pcm requirement is not large if it is actually used. Can pass the experiment, see whether to meet the circuit requirements, if through a variety of tests (such as high, low temperature test) can meet the requirements, can be used in large quantities!


Type Vceo (V) Ic (mA) Pcm (mW)


NPN sc2859 2 30500150

NPN 2 sd596 25, 700200

PNP sb624 2 25700200