BC847 NPN SMD Transistor

BC847 is an NPN transistor so when no power is applied to the base, the collector and emitter will be left open (Reverse biased) and 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 is 100mA for this device, more than that could damage the device. It comes with VCE OF 40V and can be used as a small signal switching transistor. It also has a low base voltage of 6V.

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 the 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.

This transistor is the SMD equivalent for the popular BC547/BC847 transistor, which is commonly used in many general-purpose applications like switching circuits to control low current loads like pumps, solenoids, LEDs, etc. The transistor also has an equivalent PNP transistor called BC557/BC957, both combined can be used to form push-pull circuits or Class B amplifier Designs.

BC847 Pinout Configuration

Basic Overview and Features

• Bi-Polar NPN Transistor
• DC Current Gain (hFE) is 600 maximum
• Continuous Collector current (IC) is 100mA
• Emitter Base Voltage (VBE) is 6V
• Base Current(IB) is 5mA maximum
• Available in SOT23-3 Package

Note: Complete Technical Details can be found in the BC847 Datasheet given at the end of this page.

BC847 Equivalent Transistor

MMBT3904, MMBT2222A, KST42, BC845, BC547

Basic Working of a Transistor

The BC847 transistor is a general-purpose N-P-N transistor. NPN transistors are formed when a p-type semiconductor material (either Silicon or Germanium) is fused between two n-type semiconductor materials. 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.

How to use BC847 Transistor

Transistors are current-controlled devices, means they can be turned on or off by supplying the required base current (for the BC847 transistor it is 5mA). BC847 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.

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 this issue we need to add pulldown resistors for example in the above case, a 10K resistor is used to pull down the base of the transistor.

Applications

• 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.