BC556, BC557 and BC558 PNP Amplifier Transistors are not only popular today but very ancient, it is used as a General Purpose device and a popular LED control in small products.This Silicon device along with some others replaced Germanium Devices in Preamplifiers and Portable Transistor Radios and Portable Tape Recorders. A Complement is the BC547B NPN General Purpose Transistor. Now for Specs 45V, 100mA, 200 beta approx.
I will explain in a way most can comprehend. Do not use this for circuits working around 30-40 Volts. Use it for circuits upto 24 volts on the safer side. (45 V max rating)
Do not subject the base emmiter (diode path ) to any kind of reverse bias. That includes kickback from coils of relays or solenoids. This will damage the device, protect with a diode if needed.
Do not work it hot, it is not a metal device, use it for small signal. Reed Relay driving is possible, Single LED drive is also ok. Microphone Amplifiers, Bass, Treble and Presence controls. LED Flashers, Graphic Equalizers are things you could make with this, using Filter Circuits.
Continuous current rating is 100mA, this is fine if transistor is saturated or fully on, when voltage across device is very less and current is 100mA. Power Dissipation is tolerable. If Transistor is just partially ON or Switching fast, The Power Dissipation can peak and eventually damage the device. The device can manage to survive say 500 mW or a little more, but remember that the battery is draining fast.
A 200 Beta is pretty good, it depends on temperature, voltage and other factors. 100uA base drive can can turn on a LED at 20mA in the collector path. You can drive a LED from Opamp or Logic IC using this device, just add a 22k in series to the base.
Design products that are safe, last long and use very little power. That is pretty Green.
BC557 PNP Transistor General Purpose - bc556b-d.pdf
- delabs Notes from 1988 offline notes to 1999 online notes. enhanced 2019