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This amplifier unlike the others I've built has no boot strap cirucuit it's all constant current sources but still a negative voltage feedbak design.
The constant current source (CCS) is another very basic part of almost all electronics It's operation allows a designer to achieve gain and a more stable operation over a larger voltage range then can be achieved with resistors. My example CCS will be a very common 2 transistor model used in many audio circuits as well as others. It contains a load transistor (q2) a tracking transistor (q1) and a few resistors. The purpose of a CCS's is a couple things, first it takes the place of resistors whose resistance is very much influenced by tempature, CCS's are also influenced by tempature but when compared to a standard resistor is insignifigant. CCS's also provide circiut gain over resistors, when you consider that resistor's work by resisting the flow of electrons and the main by product of this is heat then that heat is lost gain. This maybe more of an opinion then fact, but CCS's also assist the designer by removing power up and down concerns you have with current sinking resistors. This is done by the CCS's ability to provide working current much sooner and for a longer peroid of time after power is remove in the up down power cycle.
This CCS works by monitoring the load on q2 with q1 and adjusting the base current of q2 to maintain a constant current on q2's collector. Here is the operation: When the resistance increases or decreases on q2's collector there is also an increase or decrease in current flow on q2's emitter. Q2's emitter is connected to r2, a resistor, and as the current increases on the emmitter of q2 the voltage drop across r2 also increase (ohm's law) which increase's the voltage diiferance between the voltage source or rail and q2's emiiter. This resistor's voltage drop is applied to the base of q1 and q1's emmiter is tied to the same voltage source or rail mentioned earlier and when suffecient voltage is present between q1's base to emmiter junction it's forward biased and starts to conduct current. Q1's collector is split to ground through a resistor, r1, and the base of q2. When q1 begins to conduct current from the situation explained earlier it draws current away from q2's base bringing down the output current of of q2. So why doesn't the circuit just shut off you might ask. Remember that this whole process is depedent opun the current controlled voltage drop across r2 and as the current through q2 decrease the voltage drop across r2 also decrease's, decrease the amount of current that q1 removes from q2's base allowing q2 to conduct more current and this how it regulates or keeps the current constant.
Here are a few spice simulations showing the operation under varying load resistance 10, 1k, and 10k ohm loads.
notice how under these vary extreme load changes the current remains close, actually from 10 ohms to 10,000 ohms this circut maintais an 87% regulation factor, that's pretty good.
Also used on this amplifier is the current mirror.