Hey Everyone,
Firstly, let me introduce you to my simple yet seemingly extensive goal; to take any BJT transistor out there and bias it in order to make it a Class-A amplifier. In the future, I plan to move from one amp to the next, thus I am now designing Class-A amps and next it will be Class-AB. Then I will use MOSFETs and such, but first things first. In addition, I will use this particular thread whenever the need of asking questions is evident to me and also to look back on for review. My first design was a practical approach on how to get the BC547B in its linear region. Many of my Class-A amps are designated for audio amplifier operation. I encourage all comments, questions, and suggestions for the benefit of everyone; so please post when you would like to. I'm sure many would feel apprehensive at the length of this thread, but I beg that the knowledgeable come and read it anyway; posting with comments and suggestions.
Attempt #1:
Thanks,
Austin
Firstly, let me introduce you to my simple yet seemingly extensive goal; to take any BJT transistor out there and bias it in order to make it a Class-A amplifier. In the future, I plan to move from one amp to the next, thus I am now designing Class-A amps and next it will be Class-AB. Then I will use MOSFETs and such, but first things first. In addition, I will use this particular thread whenever the need of asking questions is evident to me and also to look back on for review. My first design was a practical approach on how to get the BC547B in its linear region. Many of my Class-A amps are designated for audio amplifier operation. I encourage all comments, questions, and suggestions for the benefit of everyone; so please post when you would like to. I'm sure many would feel apprehensive at the length of this thread, but I beg that the knowledgeable come and read it anyway; posting with comments and suggestions.
Attempt #1:
- Upon looking at the BC547 transistors specifications (http://www.fairchildsemi.com/ds/BC%2FBC547.pdf) I looked at the hFE (DC Current Gain) under "Electrical Characteristics". Under the "Test Condition" column, it advises the following conditions: Vce=5V, and Ic=2mA.
- That being said, I now looked at the saturation conditions of the transistor and noted that the base current should be 1/20th of the collector current (the provide examples in both the Vce(sat) and Vbe(sat), both of which say that Ib should equal 1/20th of the Ic).
- I then set forth the conditions I can now provide-Vce=5V, Ic=2mA, and Ib=0.1mA.
- Next, I remembered the equation Vc=Vcc/2 which means that Vc=6V (see schematic in attachment for details). Therefore, I can now choose the collector resistor (Rc). 6V/2mA = 3k
- The voltage divider can now be determined: R1=6k and R2=1k. Since I want the emitter voltage to be 1V (according to Vce. Vce=Vc-Ve-or so I think), the base voltage should be 1.7V which the voltage divider ensures.
- Now I need to calculate the emitter resistor (Re). Based upon the equation Ie=Ic+Ib, I arrived to the conclusion that Ie should equal 2.1mA. Therefore, 1V/2.1mA = 476Ω.
Thanks,
Austin
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