Precautions for the purchase of SMD transistors

There are several main problems in the application of SMD transistors:

1. In the past, I used to use through-hole assembly transistors, how to find the corresponding chip transistors;

2. The triode model found on the parameter circuit is not available in the market, and how to replace it. This is often a big problem for designers, developers and maintenance personnel in applications.

The reason for these two problems is that when the same die is made into different packaged devices, its models are different.

E.g:

　　 A low-power transistor produced by a company in TO-92 package. Its model is 2SC1815, but when the same die is used in SOT-23 package. Its model becomes 2SC2712; when using SO-70 package. The model number becomes 2SC4732 again. According to this reality, when selecting or replacing, the basic parameters of the transistor should be found in the transistor manual and the parameters are basically the same. And the package meets the requirements of the triode.

Here is an example of 9012 and 9013 that are commonly used in TO-92 packages:

First find out the main parameters of 9012, 9013:

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

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

Pcm is obviously less than 9012 or 9013. This is caused by the small heat dissipation area of the sheet-shaped SOT-23, and the Pcm requirement is not large in actual use. You can use experiments to see if the circuit requirements are met. If the requirements can be met through various tests (such as high and low temperature tests), it can be used in large quantities!

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

NPN 2SC2859 30 500 150

NPN 2SD596 25 700 200

PNP 2SB624 25 700 200

PNP 8C807 45 500 310

When substituting, it is necessary to understand clearly the performance, structure of the original pipe or have special requirements and some main parameters, and then from the specifications) find the same performance, function, structure and parameters similar to test or replace, in addition, it should be noted that working frequency. The selected f must meet the requirements of the operating frequency.