How to choose a surface mount transistor
Release time:
2022-01-07
Selection of SMD transistors There are several main problems in the application of SMD transistors: The first is that in the past, through-hole assembled transistors were used to be used. How to find the corresponding chip transistors;
Selection of SMD transistors
There are several main problems in the application of SMD transistors:
The first is that in the past, through-hole assembled transistors were used to be used. How to find the corresponding chip transistors;
The second is that the transistor model found from the parameter circuit cannot be purchased on the market, how to replace it. This is often a big problem for designers, developers and maintenance personnel in application.
The reason for these two problems is that when the same tube core is made into devices with different packages, its model is different.
For example:
A low-power transistor with TO-92 package produced by Toshiba. Its model is 2SC1815, but when the same tube core is packaged in SOT-23. Its model becomes 2SC2712; and when SO-70 is packaged. The model becomes 2SC4732. According to this reality, when selecting or replacing, according to the basic parameter requirements of the transistor, the transistor with basically the same parameters and the package that meets the requirements should be found in the transistor manual.
Here we take the commonly used TO-92 packaged 9012 and 9013 as an example:
First find out the main parameters of 9012 and 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, Pcm is 625mW.
In the transistor manual, you can find SOT-23 packaged triodes. The models with similar parameters are shown in the table. In the table, Pcm is obviously smaller than 9012 or 9013. This is due to the small heat dissipation area of the sheet SOT-23. If Pcm is not required in actual use. You can test whether it meets the circuit requirements through experiments. If it meets the requirements 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 replacing, you must clearly understand the performance of the original tube (or the required tube) (general triode, switch triode, etc.), structure (such as Darlington tube, band-stop triode, combination triode) or special requirements (such as high reverse voltage, low noise, etc.) and some main parameters, and then find the same performance, function, structure and parameters from the manual (or company data manual) for testing or replacement. In addition, pay attention to the operating frequency (MF segment, HF segment, VHF segment or UHF segment, etc.). The selected f must meet the requirements of the operating frequency.
It must be pointed out here that there are thousands of various triode varieties. Here are just a few examples. It is important to collect information from major semiconductor device manufacturers. It not only has parameters and packaging, but also model codes, which provides great convenience for selection and replacement.
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