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MMBT3904 – NPN Signal Transistor

The MMBT3904 is and SMD package NPN Transistor with VCE of 40V and a collector current of 200mA. It can be used as small signal switching transistor. It also has a low base voltage of 6V.


Pin Configuration

Pin Number

Pin Name




Current flows out through Emitter



Controls the biasing of the Transistor



Current flows in through Collector



  • NPN small signal Transistor
  • Continuous Collector Current (Ic) is 200mA
  • Collector to Emitter Voltage (VCE) is 40V
  • Emitter to Base Voltage (VEB) is 6V
  • Current Gain (hfe) is 100 to 300
  • Transition frequency: 300MHz
  • Available in SOT23 SMD package

Note: The complete technical information can be found at the datasheet given at the end of this page.


Through Hole Equivalent for MMBT3904



Other NPN Transistors:

BC549, BC636, BC639, 2N2222 TO-92, 2N2222 TO-18, 2N2369, 2N3055, 2N3906, 2SC5200


MMBT3904 Brief Description

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.



  • Driver Modules like Relay Driver, LED driver etc...
  • Amplifier modules like Audio amplifiers, signal Amplifier etc...
  • VCB and VBE is high hence can be used to control voltage loads up to 40V
  • Commonly used in TV and other home appliances



The BT3904 is an SMD Transistor and is available in SOT-23 Package. If you are looking for a through hole type then consider 2N3904. The dimension of the SOT-23 Package is shown below.

MMBT3904 Dimensions

Component Datasheet

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