Is the LEFT circuit of darlington pair, equivallent to the RIGHT transistor circuit?
Is my asumption true?
I replaced the two transistors in darlington pair with one; having beta equal to the product of betas of the two transistors, and the voltage from of 1.4 (0.7+0.7) across Base and Emitter.
Then I am calculating the Ib and hence the Ic.
In practical experiments, I found that my calculations are not very exact, but close enough.
For example, for the circuit to the right I found:
* Ib = 63 nano Amprear
* Ie = 4.5 mA
In measurements, I am finding the Ie about 5.5 mA.
For most applications your approximations are OK. However the collector current of the T2 does not flow through the 50 Ohm resistor, so your approximation could show T2 saturating , when it is not.
Frank