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Hey guys. I'm jumping into the world of electronics out of boredom and curiosity and am trying to wrap my mind around a few things. I'm on the topic of Transistors presently and have spend many hours learning about it's different modes of operation. I'm a bit confused about the Forward Active mode and was hoping someone could help me out. I think I understand the math as I will lay out. The problem is applying it to a real world example on my breadboard. For some reason the math doesn't add up to what I'm seeing. So here goes. Case in point:
A simple common emitter circuit consisting of the following measuring in at;
Power supply = 9.04V
Rb Resistor = 46.3kΩ
Rc Resistor = 462Ω
2N3904 Transistor with a β of 100 to 300 and Vbe = 0.628V
So first things first. Figuring out what mode the Transistor is operating at. For which it's my understanding that we solve the Forward Active model for DC and look at the resulting Vce to see where it lies;
Ib = Vcc  Vbe / Rb
= (9.04  0.628) / 46300
= 0.1816 mA
Ic = βIb
= 100(0.1816)
= 18.16mA
Vce = Vcc(Ic)(Rc)
= 9.04  (18.16mA)(462Ω)
= 0.65V > 0.2 ∴ Forward Active
With the Vce being greater than 0.2v (from Vce(sat) on the data sheet), The above should represent the circuit's behavior. So I slap this circuit together on my breadboard and start measuring using my multimeter.
I get a reading for Ib of 0.18mA which I expected. But then I measure Ic, I get 0.65mA.
Which doesn't seem right at all. I tested the BJT and swapped it out with a new one and I get the same reading. Tried using a different multimeter. (my Fluke 85 III was just calibrated last month) Same reading. Why am I only getting a gain of 3.6 when it should be at least 100?? I'm getting a voltage drop across Vce of 8.6V?? Am I doing something wrong. I laid the circuit out on a circuit simulator and it shows Ic at 18mA. So clearly the math is right. I get on the edge of understanding something and stuff like this happens. Can someone please help make me understand what I'm doing wrong and point me in the right direction.
Thanks!!
Ps. My first post with this community. Cheers!
A simple common emitter circuit consisting of the following measuring in at;
Power supply = 9.04V
Rb Resistor = 46.3kΩ
Rc Resistor = 462Ω
2N3904 Transistor with a β of 100 to 300 and Vbe = 0.628V
So first things first. Figuring out what mode the Transistor is operating at. For which it's my understanding that we solve the Forward Active model for DC and look at the resulting Vce to see where it lies;
Ib = Vcc  Vbe / Rb
= (9.04  0.628) / 46300
= 0.1816 mA
Ic = βIb
= 100(0.1816)
= 18.16mA
Vce = Vcc(Ic)(Rc)
= 9.04  (18.16mA)(462Ω)
= 0.65V > 0.2 ∴ Forward Active
With the Vce being greater than 0.2v (from Vce(sat) on the data sheet), The above should represent the circuit's behavior. So I slap this circuit together on my breadboard and start measuring using my multimeter.
I get a reading for Ib of 0.18mA which I expected. But then I measure Ic, I get 0.65mA.
Which doesn't seem right at all. I tested the BJT and swapped it out with a new one and I get the same reading. Tried using a different multimeter. (my Fluke 85 III was just calibrated last month) Same reading. Why am I only getting a gain of 3.6 when it should be at least 100?? I'm getting a voltage drop across Vce of 8.6V?? Am I doing something wrong. I laid the circuit out on a circuit simulator and it shows Ic at 18mA. So clearly the math is right. I get on the edge of understanding something and stuff like this happens. Can someone please help make me understand what I'm doing wrong and point me in the right direction.
Thanks!!
Ps. My first post with this community. Cheers!
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