# common collector amplifier

#### xylon89del

Joined Dec 28, 2011
17
Hi,

I have read the text books regarding common collector amplifier. But, stil very confused.

Anyone can provide a step-by-step guidelines to design a good common collector amplifier?

#### xylon89del

Joined Dec 28, 2011
17
Hello,

The common-collector amplifier

http://en.wikipedia.org/wiki/Common_collector_amplifier

Bertus
I need the steps on how to determine the biasing network depends on the requirement, such as need to set the output resistance, then find the Icq, then determine the emitter resistor, then find the R1 and R2.

This is what I have read from a book, but I am still quite confused with the method. In my calculation, I always get negative resistance.

#### PaulEE

Joined Dec 23, 2011
474
I need the steps on how to determine the biasing network depends on the requirement, such as need to set the output resistance, then find the Icq, then determine the emitter resistor, then find the R1 and R2.

This is what I have read from a book, but I am still quite confused with the method. In my calculation, I always get negative resistance.
Choose 1/2Vcc output voltage and output current, calculate output resistor based on voltage and current, use beta of transistor to approximate base current, solve voltage divider equation to get correct base voltage (and equivalent thevenin network that yields current) along with solving the bottom resistor-BEjunction-emitter resistor loop equation to simultaneously get R1 and R2.

Rout is dynamic and depends upon the instantaneous output voltage/current through the transistor (and hence the resistor). Calculations are usually done midpoint on the load line of the transistor's characteristic curves and values are derived that way.

There are many websites that explain this process better than I just did and in much more detail

Aside from all that, remember always that transistors are ACTIVE devices and resistors are PASSIVE. The transistor's behavior governs how the circuit acts through calculations.