Audio amplifier 60 w with 2n3055

The circuit it's based on 2n3055 transistor. This is how the circuit works: The PNP input stage is configured as a common emitter amplifier with lots of current feedback through the emitter resistor that is tied to the output bus. It also regulates the DC operating point of the output bus. With feedback as such, it has essentially unity AC and DC gain. The top left capacitor and resistor are noise decoupling for the bias source for the input transistor to keep it from amplifying the power supply noise and ripple. A signal is picked off the collector resistor to drive the base of the lower BD286. It is the high voltage gain element and requires a frequency compensation cap (C2) to prevent oscillation. C1 and the resistor above it also provide frequency comp by reducing the AC feed back to the input stage. The BC107 is the bias regulator that develops approx 3 junction drops (1.95V) to properly drive the complementary transistors (top BC286 and the BC287). If the bases of these two transistors were tied together, it would be a zero bias class B, but the bias regulator develops just enough voltage to put the complementary transistors just on the edge of conduction. The complementary transistors are both connected in the common collector configuration (emitter followers) so they have essentially unity voltage gain. Coupled to the BC286 is the 2N3055 in a Darlington configuration. The lower 2N3055 is connected to the BC287 in a composite connection that essentially turns the BC287 into a high current gain PNP transistor. The 100-200uf capacitor is a “bootstrap” capacitor that couples the output bus to the 1-3K pullup resistor. In this way, the anode of the capacitor actually transcends the bus voltage when the output bus goes positive so that the BC286 has lots of base drive and can easily turn on fully. The 1500uf coupling cap keeps the DC portion of the output bus voltage off the speaker. Since the speaker is a reactive load (especially at high audio frequencies), the reactance is reduced via the 100nf, 10Ω resistor –helps prevent oscillation. I Took the circuit from that site: http://www.electroschematics.com/269/audio-power-amplifier-60w-with-2n3055/ The description is copied from Jim Keith's comment

published 8 years ago