To bias a transistor we have to supply current to base pin, this current (IB) should be limited to 5mA. The maximum amount of current that could flow through the Collector pin is 100mA, hence we cannot connect loads that consume more than 100mA using this transistor. This is where a PNP transistor differs from a NPN transistor, a Logic state (blue colour) is used to toggle between Ground and Signal Voltage (Emitter-Base Voltage VBE) as shown belowīC557 has a gain value of 110 to 800, this value determines the amplification capacity of the transistor. BC557 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.
