how can i find the equation of this circuit???

[mehdi999]

i have 2 transistor t1=t2=2N2222A , Ic=150 mA,Fhe=100 , E= 5 volt Vce=30 volt

is a two player Jeopardy Game style response circuit. First response locks out other.



how can i find the equation of this circuit???

 

[EN0]

It depends on what equation your looking for. What exactly do you want to calculate from "this" equation?

 

[mehdi999]

i want to calculate R1 R2 R3 end R4

 

[EN0]

You need to know your input, transistor parameters, and output in order to calculate anything. I would look into "Transistor Biasing" to start out with. I know that MIT has some good video lectures on the subject, except with MOSFETs. Ideally, you should be able to learn about MOSFETs and apply the fundamental concepts to BJTs.

 

[12345678901234567890]

First experiment or look up on a data sheet, the amount of current and the voltage drop across the output device.
That current will be (Io) and the voltage will be (Vo).

then use these equations to solve for R1 and R3.

R3 and R4 = (0.7 / Io)

R1 and R2 = [(E - Vo - 0.7) / Io]

Give that a try.

 

[mehdi999]

ok thank you

 

[mehdi999]

from what did you put 0.7

 

[12345678901234567890]

Assuming Vbe to be around 0.7v. for a silicon transistor.

 

[audioguru]

It looks like each transistor turns on a light bulb. The datasheet for the 2N2222 and most other transistors shows a low max saturation voltage loss when the base current is 1/10th the collector current which is the light bulb. You cannot calculate the value for R1 and R2 unless you know the resistance or current of each light bulb. Then R3 and R4 are a much higher value like 10k ohms.

 

[ti2cr]

Ok. From the initial values you gave I am not clear if they are given in the problem or if you just used the datasheet. The reason for this is that you mention E=5 [V], but also mention VCE=30 [V] from where does this additional voltage appear?

By taking a look at the circuit, if you find the values for one of them, the other should be exactly the same. Remember you already have Ic and Hfe, that should give you a start for finding Ib.

 

[audioguru]

hFE is used for a linear amplifier transistor that has plenty of collector to emitter voltage (10V) when it is turned on. But these transistors are not linear, they are used as a switch with a very low collector to emitter voltage when turned on. So hFE is not used but the spec in the datasheet about the saturation voltage is used instead where the base current is 1/10th the collector current.

The circuit operates from a 5V battery (E). The max allowed VCE voltage of a 2N2222 transistor is 30V which is not used here.