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Home > Technology List > Introduction of NPN Signal Transistor-MMBT3904

Introduction of NPN Signal Transistor-MMBT3904

Published time: 2019-01-21

In order to prevent us from falling into the irritating description of the transistor, in the last issue, we specially selected RECOM Power's REC15E-Z, which tells about its characteristics and simple details. But the transistor is too important in the electronics industry, tens of thousands The electronic components are all related to him, so we can't ignore it. There are still a lot of things we need to know. In this issue, I chose NPN Signal Transistor-MMBT3904, and we will introduce some knowledge about it. Here I made a suggestion. After understanding MMBT3904, we can compare the electronic components introduced in the previous issues. I believe that you will get a different understanding.

Before reading, we need to understand:

What is an NPN transistor?

NPN is one of the two types of bipolar transistors, consisting of a layer of P-doped semiconductor (the "base") between two N-doped layers. A small current entering the base is amplified to produce a large collector and emitter current.

How do NPN transistors work?

The NPN transistor is designed to pass electrons from the emitter to the collector (so conventional current flows from collector to emitter). The emitter “emits” electrons into the base, which controls the number of electrons the emitter emits.  The transistor is kind of like an electron valve.

The overview of NPN Signal Transistor- MMBT3904

The MMBT3904 is a SMD package NPN Transistor with VCE of 40V and a collector current of 200mA. It can be used as small signal switching transistor.

MMBT3904 is a NPN Type Transistor,its Max Current-Collector (Ic) is 200mA,it has 300MHz Transition Frequency,It uses TO-236-3, SC-59, SOT-23-3 package.

DigiKey Supplier Device. Package is SOT-23-3.

Electronic Components Series associated with MMBT3904-BT3904

Description from a third party about BT3904.

BT3904 is a NPN transistor hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin. BT3904 has a maximum gain value of 300; this value determines the amplification capacity of the transistor. The maximum amount of current that could flow through the Collector pin is 200mA, hence we cannot connect loads that consume more than 200mA using this transistor. To bias a transistor we have to supply current to base pin, this current (IB) should be limited to 5mA.

When this transistor is fully biased then it can allow a maximum of 200mA to flow across the collector and emitter. This stage is called Saturation Region and the typical voltage allowed across the Collector-Emitter (V­CE) or Collector-Base (VCB) could be 40V and 60V respectively. When base current is removed the transistor becomes fully off, this stage is called as the Cut-off Region and the Base Emitter voltage could be around 600 mV.

The Features of MMBT3904

2.NPN small signal Transistor
3.Continuous Collector Current (Ic) is 200mA
4.Collector to Emitter Voltage (VCE) is 40V
5.Emitter to Base Voltage (VEB) is 6V
6.Current Gain (hfe) is 100 to 300

What is the application of MMBT3904 

1.Driver Modules like Relay Driver, LED driver etc...

2.Amplifier modules like Audio amplifiers, signal Amplifier etc...
3.VCB and VBE is high hence can be used to control voltage loads up to 40V

4.Commonly used in TV and other home appliances

The description of MMBT3904 Pinout

There is three pinouts on MMBT3904, which are Emitter, Base, and Collector. They correspond to different functions. For specific description about MMBT3904 Pinout, please refer to MMBT3904 datasheet.

You can free download MMBT3904 Pdf at the end of the article.We have helped you find the datasheet on the internet.


The Equivalent eletronics components for MMBT3904:2N3904

Other NPN Transistors:

BC549, BC636, BC639, 2N2222  2N2369, 2N3055, 2N3906, 2SC5200.




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