download transistor as an amplifier for free

Let’s find collector and emitter resistors.Ĭontrary to the previous part, now we have to replace all DC voltage sources and capacitors with short-circuits (because we will choose capacitor values such that they pass the designed AC input frequency with little attenuation) to obtain the AC model of the amplifier. What I did here is to approximate the resistor values to the nearest 10% standard E12 resistance since these rounding does not change the operating conditions dramatically. (Note: for high speed applications, we need to think again) As a rule of thumb, we can choose R 1 current as 10 times the base current and R 2 current as 9 times. Now we can calculate the biasing resistors R 1 and R 2. 1, that is V BEQ base-emitter voltage at Q-point. Then we can choose the voltages of collector and emitter on quiescent.Īnother value we need, hidden in Fig. Looking at the curves, we can approximate the transistor’s gain parameter β for our desired operating-point of I CQ=5mA and V CEQ=10V.

With the assumptions above, we can end up with the load-line (a.k.a. 2 arbitrarily depending on the application, just like the following. Secondly, we can choose the collector-emitter voltage and quiescent collector-current looking at Fig. We need to replace all capacitors with open-circuit (because of the fact that capacitors do not allow DC elements) and eliminate the unnecessary parts to have the following.Įvery circuit needs a supply, so I don’t see any reason stopping us from choosing V CC=20V for this one. The Base-emitter voltage and output characteristics shown below are enough information to go.Ĭlass-A design requires the transistor to be in its active region even when no input signal is provided. Options were limited, so i picked 2SC4102, a small current transistor from ROHM. Let’s start with defining the desired input-output requirements and load conditions of the amplifier.įor a simple tutorial, I decided to pick a transistor that has good datasheet and good pre-installed model in LTspice.

It works with single supply and has DC-biasing stage as well as AC-coupling elements. While more detailed best-practice designs exist, the circuit above is the best for teaching purposes. Let’s see the circuit schematic for our amplifier.

Download transistor as an amplifier for free