I've been trying to study BJT Voltage Divider Bias Circuits. In particular, as they relate to their active region, amplification, and operation in getting a crystal to oscillate. I've followed a video and saw that the node labelled 2.452 below is really 2.6024 in calcs I match. LT spice says its 2.4922. Why all the variation, I am using a beta of 200. I followed equations in the following video...
I believe they are correct. I wish to get at exact currents and voltages but cannot match to ltspice or even the sim below. I wish to look at things theoritical and ignore any time or heat dependent ramp up time.
The video I watched (and hopefully learned correctly from) would break the circuit below to a thevenin voltage source and resistance on the circuit that biases the 3904 transistor.
It arrives at currents and voltages by the following breakdown...
Where Re is R4
Vth = R2*8/(R1+R2)
Rth = R1 parallel R2
Vth - IbRth -Vbe -IeRe = 0
Vth - IbRth -Vbe -(B+1)IbRC = 0
Ib = ( Vth - Vbe ) / ( Rth + (B+1)Re )
Vcc - IcRc - Vce -IeRe = 0
Ib = BIb
Ie = (B+1)Ib
He made the approx that Ie is equal to Ic in one of the later lines.
In any case, I've got very comfortable with his explanation, but not been able to duplicate the results in LTSpice or below.
Even something simple like the voltage created from the voltage divider. I wish to know what get at currents and voltages and why there is no match to LTSPice (or below)? Thanks,Jeff