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BC177 Low Noise General Purpose PNP Transistor

The BC177 and BC177B are silicon planar epitaxial PNP transistors in the TO-18 metal case. They are suitable for use in driver stages, low noise input stages, and signal processing circuits of television receivers. This transistor comes with a VCE of -50V and a continuous collector current of -100mA. It can be used as a small signal switching transistor. It also has a low base voltage of -5V.


BC177 Pinout Configuration

Pin Number

Pin Name




Controls the biasing of the transistor



Electrons Emitted from Emitter Collected by the Collector



Electrons emitted from the emitter into the first PN junction 


Features & Specifications

  • Bi-Polar PNP Transistor
  • DC Current Gain (hFE) is 500 maximum
  • Continuous Collector current (IC) is -100mA with -200MA peak
  • Emitter Base Voltage (VBE) is -5V
  • Available in To-18 Metal Can Package
  • Collector Dissipation: 0.3 W
  • Transition Frequency: 200 MHz
  • Operating Junction Temperature Max (Tj): 175 °C
  • Noise Figure: 2-10 dB
  • Collector Capacitance 5pF


Note: Complete technical details of BC177 can be found in the BC177 datasheet given at the end of this page.


BC177 Equivalent Transistor

BC108, NTE159M, BC107, MMBT3904


Basic Working of a Transistor

The BC177 Transistor is a general-purpose PNP transistor, A PNP junction transistor is a sandwiched construction of P-type material with an N-type material in the middle. Depending upon the construction transistors are divided into two categories NPN transistor and PNP transistor, which are shown below.

Transistor Symbol


General Description of BC177 Transistor

The BC177 transistor is a very versatile transistor that can be used in many different applications. It is basically used when you want a simple switching device for low power loads, simultaneously it can be used in high-frequency RF applications, its gain-bandwidth product and its metal construction make it suitable for many different applications. The component is cheap and easy to work with so it is best suited when choosing a random switching device. BC177 can also be used as a basic power amplifier and its application includes amplifying low power signals.


When this transistor is in a biased condition, then it can allow a maximum current of -200mA across CE(Collector-Emitter) Junction, this state of the transistor is called the saturation state, and driving a load that consumes more current than 200mA may damage the device permanently. 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 no current flows through the C-E junction. The BC177 Transistor has a gain of 125 to 500 this value determines the amplification capacity of the transistor, the peak current that can be flown through this transistor is 200maA, which is combined with the gain value makes this transistor a perfect choice for RF applications.


How to use BC177 Transistor in a Circuit

Transistors are current-controlled devices so to turn them on a little current is needed. For the BC177 Transistor, this base current is less than 10mA, as BC177 is a PNP transistor that means it will be on when the base is connected to the ground, and it will be off when a positive voltage is applied to the base of the transistor.


The simulated circuit below shows how this transistor behaves when the base of the basic circuit is connected to the ground and when it's connected to 5V of the power supply.

 BC177 Transistor Circuit Diagram

When we turn on the transistor by connecting the base to the ground the transistor will remain on unless the voltage at the base of the transistor reaches more than the base turn-off voltage, for this transistor, it is somewhere in between 0.7 -0.9V. The base of the transistor cannot be left floating otherwise there could be false triggering, which may lead to issues in the circuit. To resolve the issue we need to add pullup resistors as shown in the example, a 10K resistor is used to pull up the base of the transistor to VCC.



  • Simple switching applications
  • Microphone preamplifiers
  • Lighting systems
  • Relay drivers
  • Audio Amplifiers
  • Signal Amplifiers


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.

BC177 Dimensions

Component Datasheet

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