Dear all,
I am completely stuck on understanding a certain concept about AC current and transistors and am wondering if anyone could possibly help me.
I want to build an amplifier where I first amplify the AC voltage using a common-emitter circuit with an NPN transistor. I get this bit. I then want to amplify the AC current coming from this circuit using a emitter-follower circuit. Could someone please help me understand how AC current flows through a transistor.
I know that when analysing AC, all DC sources are grounded, and that the collector current is beta times the base current. When DC current flows, it goes from base to emitter and collector to emitter. If the DC source is grounded when analysing AC, does this mean that AC current can also flow from emitter to collector (Vcc is grounded)? I am confused about which direction AC flows through a transistor.
I also want to find my AC current flowing down the path of Vout (parallel to the load resistor). I want this because this is what I presume will then go on to being amplified in the emitter-follower circuit. Do I get this by finding the output impedance of the amplifier.
I am just generally confused about what the AC current on the right side of the transistor (emitter and collector) actually is (is it the DC current modulated or is it AC current passing through the transistor???), and which direction it travels.
I know there are easier ways to create amplifiers but I would like to know how to do it via transistors.
If anyone could help me on this issue I would be very grateful. I know how the amplifiers work as a concept as a whole but would like to be able to understand what is going on piece by piece.
Thanks
Tim
I am completely stuck on understanding a certain concept about AC current and transistors and am wondering if anyone could possibly help me.
I want to build an amplifier where I first amplify the AC voltage using a common-emitter circuit with an NPN transistor. I get this bit. I then want to amplify the AC current coming from this circuit using a emitter-follower circuit. Could someone please help me understand how AC current flows through a transistor.
I know that when analysing AC, all DC sources are grounded, and that the collector current is beta times the base current. When DC current flows, it goes from base to emitter and collector to emitter. If the DC source is grounded when analysing AC, does this mean that AC current can also flow from emitter to collector (Vcc is grounded)? I am confused about which direction AC flows through a transistor.
I also want to find my AC current flowing down the path of Vout (parallel to the load resistor). I want this because this is what I presume will then go on to being amplified in the emitter-follower circuit. Do I get this by finding the output impedance of the amplifier.
I am just generally confused about what the AC current on the right side of the transistor (emitter and collector) actually is (is it the DC current modulated or is it AC current passing through the transistor???), and which direction it travels.
I know there are easier ways to create amplifiers but I would like to know how to do it via transistors.
If anyone could help me on this issue I would be very grateful. I know how the amplifiers work as a concept as a whole but would like to be able to understand what is going on piece by piece.
Thanks
Tim