Bc558 Pnp Transistor

BC558 is a PNP transistor hence the collector and emitter will be closed (Forward biased) when the base pin is held at ground and will be opened (Reverse biased) when a signal is provided to base pin. This is where a PNP transistor differs from a NPN transistor.

BC558 has a gain value of 110 to 800; this value determines the amplification capacity of the transistor. The peak current that could flow through the Collector pin is 200mA, this combined with the high gain value makes it an ideal choice for audio amplification applications.

When this transistor is fully biased then it can allow continues current of 100mA to flow across the collector and emitter. This stage is called Saturation Region and the typical voltage allowed across the Collector-Emitter (V­CE) or Base-Emitter (VBE) could be 200 and 900 mV 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 660 mV.

Features:
Bi-Polar PNP Amplifier Transistor
DC Current Gain (hFE) is 800 maximum
Continuous Collector current (IC) is 100mA
Peak Collector current (Ic) is 200mA
Emitter Base Voltage (VBE) is 5V
Base Current(IB) is 200mA peak
Available in To-92 Package
BC558 as switch
When a transistor is used as a switch it is operated in the Saturation and Cut-Off Region as explained above. As discussed a transistor will act as an Open switch during Forward Bias and as a closed switch during Reverse Bias, this biasing can be achieved by supplying the required amount of current to the base pin. A resistor is always added in series with base pin to limit the base current. The value of this resistor (RB) can be calculated using below formulae.