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S8550 Transistor

S8550 Pinout Configuration

Pin Number

Pin Name




Current Drains out through emitter, normally connected to ground



Controls the biasing of transistor, Used to turn ON or OFF the transistor



Current flows in through collector, normally connected to load



  • Low Voltage, High Current PNP Transistor
  • Continuous Collector current (IC) is 500mA
  • Collector-Emitter voltage (VCEO) is -25 V
  • Collector-Base voltage (VCB0) is -40V
  • Emitter Base Voltage (VBE0) is -5V
  • Current Gain (hFE), 85 to 300
  • Commonly used as Class B Push-pull transistors
  • Available in To-92 Package


Note: Complete Technical Details can be found at the S8550 transistor datasheet given at the end of this article.


Complementary NPN Transistor for S8550



S8550 Equivalent Transistor

BC527, KSA708, MPS750


Alternative PNP Transistors

BC557, 2N3906, A1015, 2SA1943, BD140


Brief Description on S8550 Transistor

S8550 is a PNP 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. It has a maximum gain value of 300; this value determines the amplification capacity of the transistor normally S8550. Since it is very high it is normally used for amplification purposes.

When this transistor is fully biased then it can allow a maximum of 700mA 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 20V and 30V respectively. When base current is removed the transistor becomes fully off, this stage is called as the Cut-off Region.


S8550 in Push-Pull Configuration

As mentioned in the features the S8550 transistor is commonly used in push pull configuration with Class B amplifier. So let us discuss how that is done.

A push pull amplifier, commonly known as Class B amplifier is type of multistage amplifier commonly used for audio amplification of loudspeakers. It is very simple to construct and requires two identical complimentary transistors operate. By complimentary it means that we need a NPN transistor and its equivalent PNP transistor. Like here the NPN transistor will be S8050 and its equivalent PNP transistor will be S8550. A simple circuit diagram of the Class B amplifier with the using the S8050 is shown below.

S8550 Transistor Sample Circuit Diagram



  • Audio Amplification Circuits
  • Class B Amplifiers
  • Push pull Transistors
  • Circuits where high gain is required
  • Low signal applications


2D model of the component

If you are designing a PCB or Perf board with this component then the following picture from the S8550 Datasheet will be useful to know its package type and dimensions.

S8550 Transistor Dimensions

Component Datasheet

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