This is very small audio
amplifier circuit which can be handled just with 1.5V DC battery. This
circuit just need very small power to work.
The maximum output current is I
P=V
P/R
L=62,5mA. If the transistor beta is B=150 then the maximum base current is about 400µA. This is quite much for an amplifier input so a preceding stage is very useful. IC designers normally would even build a 3 or 4 stage amplifier (and e.g. a 20 transistor bias circuit), but our PA should be as simple as possible. For maximum power gain in a direct coupled (best for low component count) amplifier the common emitter configuration is best suited, and a CB or CC stage is much worse. At low voltages a CC also has the disadvantage that the output voltage smaller than the input voltage by V
BE. If you want to drive a CE stage from a CC stage you need an input voltage of 2·V
BE»1,4V, which is nearly impossible form a single cell
supply. Two CE stages are much easier to connect, but this makes feedback more difficult because the total amplifier will be noninverting. A solution will be a differential pair which has nearly the same characteristics like a single CE stage but features an inverting and a noninerting input. A further advantage is that the inherent temparature compensation makes the biasing more stable.
more explanation, visit: http://www.weberconnect.de/nfpa2.htm
