Transistor calculation problem

[patr0805]

Okay I have tried the following simulator:
http://transistor.20m.com/transistor2.html

Everything goes just fine until I want to find out how it calculated those numbers.
It tells me the formulas, but they dosn' t make sence because I don' t know where to start.
Vc=Vcc-(Ic*R1)
Ve=Vb-0.7
Vb=Vbb - (Ib*R3).
Ib=Ie-Ic
Ic=Ie*alpha (alpha=beta/(beta+1))
Ie=(Ve-Vee)/R2
Ve=Vb-0.7

Can you see my problem. I want to calculate Vc, but to do that I have to find Ic. The formula to Ic needs le and le needs Ve and Ve needs Vb and Vb needs Ib and then lb = le-lc and then I am back to lc that needs le that needs Ve... Its an endless cicle.

Please help. How do I calculate this?

My inputs are:
Vcc: 5V
Vbb: 12V
VEE: 0
Polarity: NPN
Beta: 100
R1: 10
R2: 1
R3: 3300

And I want to calculate Vc.

 

[(*steve*)]

It seems odd that Vbb is higher than Vcc, but let's pass on that at the moment.

Look at what base current will cause the 12 volts to be dropped across R3, the be junction, and the emitter resistor. (hint: rearrange the equations to get Ie in terms of Ib and beta)

 

[patr0805]

Answer

I am so confused. I tried to do what you said but can' t hit the right numbers. Okay can you please just tell me how to find 1 of those results, that would really help.

 

[patr0805]

answer

No wait now I see what you mean. Thanks alot

 

[(*steve*)]

Remember that the gain of a transistor varies significantly from part to part, and the Vbe is not a constant 0.7V, and the gain also varies with collector current.

Also remember to check your results for sanity. At the calculated base current, what is the emitter current and the collector current? Therefore, what is the voltage drop across the collector and emitter resistors? How much does that leave for Vce? (Is Vce negative or close to the saturation voltage?)

Those checks are definitely required because the voltage being applied to the base (via the resistor) is much greater than Vcc.