Articles & Blogs > Simply Put - 2N3904 NPN Transistor

Simply Put - 2N3904 NPN Transistor

作者：John LeDuc

投稿人：DigiKey

2017-06-15

The 2N3904 is an extremely popular NPN transistor that is used as a simple electronic switch or amplifier that can handle 200 mA (absolute maximum) and frequencies as high as 100 MHz when used as an amplifier.

Image of pin out of a standard TO-92 package ON Semiconductor 2N3904

Figure 1: An illustration of the pin out of a standard TO-92 package for DigiKey part number 2N3904FS-ND: E = Emitter, B = Base, C = Collector.

Figure 2 shows a circuit example which turns on the collector emitter junction by energizing the base or biasing the transistor to turn it on by bringing 5 volts to the base via a slide switch. This example lights an LED which is considered to be the load in this case. The proper use of resistors to prevent over current draw is required when biasing the base. I used leaded parts in a bread board to test my example circuit. Most engineers will use surface-mount components (much smaller size then a TO-92 package) when it comes to using transistors in a new product design going to market. Here is a link that shows various package sizes for 3904 transistors.

Image of Scheme-it 2N3904 circuit example

Figure 2: 2N3904 circuit example - drawn in Scheme-it®.

Since the 2N3904 is an NPN transistor, that means the base needs positive biasing (appropriate voltage levels and resistance) to turn on the collector emitter junction for proper current flow. Use of a load resistor (R1 above) is also important so there is not too much current being driven through the LED and transistor. For the complete specifications on the 2N3904FS-ND, see the On Semiconductor datasheet associated with this part.

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关于此作者

John LeDuc

John LeDuc 是 DigiKey 的数字业务项目经理，1984 年参加工作，现在负责帮助 DigiKey 客户解决技术问题以及产品目录中产品的审核和添加。他专长对 National Semiconductor 的 INS8073 微型基本演示板提供支持。John 现在通过收集和提出独特的想法来提高我们工程客户的数字体验，以优化我们的网站。他拥有电子技术副学士学位，是一名“午夜工程师”，业余时间喜欢摆弄电子产品，用 3D 打印机创作独特的设计。