I have two questions:1. Can somebody please explain to me how transformer coupling is so good for maximum power transfer? Please be thorough. Is it because of the primary ac resistance and bjt output impedance being equal? I mean this should work because the power on the primary coil is the same as the power on the secondary coil so the power delivered to the primary coil which is the maximum power in this case, would ideally be delivered to the secondary coil, right? 2. And how can transformers be used to increase the overall voltage gain of a two stage common emitter based amplifier, something like
1) Its basically impedance matching: the relatively high output impedance of the first stage can be matched to the much lower Hie input impedance of the second stage. Also any attenuation caused by the shunt resistance of the bias resistors working against the output impedance of the first stage (as shown in the R-C C coupled figure for question 2) can be eliminated by applying the bias network voltage at the low side of the transformer secondary, with that point bypassed with a capacitor to provide a good ac ground 2) Replace the 4K collector resistor with the transformer primary winding, eliminate the capacitor C3, connect the high side of the secondary directly to the base of Q2, connect the junction of R1 R2 to the low side of the secondary and add a capacitor from that point to ground to provide adequate low impedance at the lowest frequency of interest. Transformer coupling is efficient, but bandwidth is limited by the transformer, and the overall gain will vary with individual transistors. Both of these warts can be improved by applying negative feedback from the output back to the input stage.
Transformer Coupled Amplifier
