This is an emitter follower, or buffer amplifier, where the output is simply equal to the input minus a diode voltage drop (about 700 mV). The advantage of this circuit is that the transistor can provide current and power gain; the transistor draws a small current from the input. It provides a low output impedance to any circuit that uses the follower's output, which means the output will not sag under load. The capacitor and the 800 Ω resistors bias the transistor's base at 2.5 V, so that the average of the input is raised to this level. The base-emitter junction acts as a diode, so the emitter will be a diode drop below the base. The collector current will be 100 times the base current, so any current drawn by the load will be supplied by the power supply through the collector, rather than from the input through the base.
This page is a utility for simulating последователь эмиттера online with specified initial values.
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