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BC547 N-Channel General Purpose Transistor SMD

The BC547 is an SMD SOT23-3 package NPN Transistor with VCE of 45V and a collector current of 100mA. It can be used as a small signal switching transistor. It also has a low base voltage of 6V. BC547 is an NPN transistor so when no power is applied to the base, the collector and emitter will be left open (Reverse biased). When a positive voltage is applied to the base pin, the transistor will turn on. The max gain of this transistor is 800, which determines the amplification factor of the device. The maximum base current is limited to 5mA and the collector-emitter current for this device is 100mA, more than this value could damage the device.


When this transistor is in biased condition, it can allow a maximum current of 100mA across CE(Collector Emitter) Junction, this state of the transistor is called the saturation state, and driving a load that consumes more current than 100mA may damage the device in this condition. As you already may know, a transistor is a current controlled device so when base current is removed the transistor becomes fully off, in this stage the transistor is working in its Cut-off Region and the Base Emitter voltage could be around 660 mV.


BC547 SMD Pinout Configuration

Pin Number

Pin Name




Controls the biasing of the transistor



Electrons emitted from the emitter into the first PN junction 



Electrons Emitted from Emitter Collected by the Collector


Basic Overview and Features

  • Bi-Polar NPN Transistor
  • DC Current Gain (hFE) is 800 maximum
  • Continuous Collector current (IC) is 100mA
  • Emitter Base Voltage (VBE) is 6V
  • Base Current (IB) is 5mA maximum
  • Available in SOT23-3 Package
  • Maximum Collector-Base Voltage |Vcb|: 45 V
  • Collector Dissipation: 0.3 W
  • Transition Frequency:100 MHz
  • Operating Junction Temperature Max (Tj): 175 °C
  • Noise Figure: 2-10 dB
  • Operating and Storage Junction Temperature Range -65 to +175 °C
  • Collector Capacitance 5pF


Note: Complete technical details can be found in the BC547 SMD datasheet given at the end of this page.


BC547 Equivalent

MMBT3904, MMBT2222A, KST42, BC845, BC847


Basic Working of a Transistor

The BC547 Transistor is a general-purpose N-P-N transistor. A junction transistor is a sandwiched construction between two layers of N-type material or P-type material. Depending upon the construction transistors are divided into two categories NPN transistor and PNP transistor, which are shown below. Transistors are made up of silicon or germanium, depending upon the application it is chosen.

Transistor Symbol


How to use BC547 Transistor

Transistors are current-controlled devices, means they can be turned on or off by supplying the required base current (for the BC547 transistor it is 5mA). BC547 is an NPN transistor that means it will be left open when no current is applied to its base, but when we apply a base voltage, the transistor will turn on. The simulated circuit below shows how this transistor behaves when a base current is applied to the base and when no current is provided to the base.

BC547 Transistor Circuit Diagram

When we turn on the transistor by supplying a required current to the base of the transistor, it will remain on unless the voltage at the base of the transistor reaches zero. The base of the transistor cannot be left floating otherwise there could be false triggering to the transistor which may lead to issues in the circuit. To resolve the issue, we need to add pulldown resistors for the above example a 10K resistor is used to pull down the base of the transistor.



  • LED dimmers or flashers
  • Switching Applications
  • Preamplifier for Power Amplifier
  • High frequency switching
  • Driver Modules like Relay Driver, LED driver etc..


2D Model and Dimensions

If you are designing a PCB or Perf board with this component then the following picture from the Datasheet will be useful to know its package type and dimensions.

BC547 Dimensions

Component Datasheet

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