I am having some difficulty in understanding this circuit.I was reading about the unity gain discrete transistor circuit.I tried to simulate the example circuit and see the result for different waves.
For a pure sine wave the circuit is acting as a unity gain buffer. But for a triangular wave, there is some kind of offset in the output. Could someone please explain why it is behaving differently in the triangular wave input?
Both the inputs are essentially AC input so I was expecting similar results on both the circuit.
Circuit

 

You have a 50 second time constant on the output, 100uF/500k. Therefore it will take about 500 seconds for the output DC level to settle to its final value. The sine wave starts at 0V while the triangle starts at +5V and that's why they give different results. If you run the simulation over 500 seconds then the triangle wave will settle to zero DC offset. To make it quicker, try changing the 500k to 2k (200mS time constant) and watching the result over 2 seconds.

 

If you start the sinewave at 5V (90° Phi) you will get the same result with both waveforms.

 

Awesome....thank you both for the quick reply....i started triangluar wave at 0 and the buffer same as it does with sine now.