- #1

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Rb=40 ohms

RL=100 ohms

Vcc=15V

I need help in figuring this problem out, I understand if anyone here doesn't want to give me the answer but I would appreciate if someone would give me a formula in which I could solve the problem myself.

- Thread starter Alexa431
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- #1

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Rb=40 ohms

RL=100 ohms

Vcc=15V

I need help in figuring this problem out, I understand if anyone here doesn't want to give me the answer but I would appreciate if someone would give me a formula in which I could solve the problem myself.

- #2

- 827

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Perhaps Rb=40kohms?

- #3

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Yeah Its 40 ohms I checked again to make sure.

- #4

gneill

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Determining the gain theoretically will involve modelling the transistor to some extent.

- #5

berkeman

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- 8,890

EDIT -- Dang it! Beaten out by gneill again!

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- #7

gneill

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- #8

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The capacitor was 0.1uF, the B was 100

- #9

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- #10

gneill

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Well, with only the β you can start by finding the approximate DC operating point. You'll have to assume a typical value for the base-emitter voltage. Since the base current is going to be pretty substantial for this circuit (I'd guess on the order of a couple of milliamps thanks to the collector current pulling down the voltage at the collector and limiting the voltage at the "top" of RThe capacitor was 0.1uF, the B was 100

- #11

gneill

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Unless you can find this circuit already analyzed somewhere you won't find a "standard formula". There are many different configurations for transistors, each requiring their own analysis and producing different formulas. The approach here would be to replace the transistor with a simple equivalent model and then apply circuit analysis to the resulting circuit.

- #12

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The 'standard way' to analyze a circuit like this is the following:

Rb=40 ohms

RL=100 ohms

Vcc=15V

1. assume infinite beta so base current = 0

2. therefore, the input current is Vin/Zc = current thru the feedback resistor Rb. Zc = 1/ωC.

3. this gives you Vc = collector voltage.

4. sum currents to zero at the collector. This gives you Ic = collector current.

You can use this approach for either ac or dc analysis.

Problem is, your resistor values are way too low to make this approach work in the lab. Who came up with 40 and 100 ohms? What is the range of ω? What is Vcc? I predict a puff of smoke for this circuit ...

- #13

- 827

- 220

Yes - there is something like a "standard formula"; better:

You have to solve a system of

* Base current Ib=

*

The two unknowns are the collector voltage Vc and the current Ic.

However, as mentioned already - this is a pure academical exercise without much practical relevance.

- #14

- 827

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However, because the voltage Vce is in the order of 1V only, the input signal must not exceed a value of app. 10mV.

This applies for a very large coupling capacitor (100uF) and a frequency which is sufficiently high (some kHz).

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