I came across a constant current source calculator at Electronic Product website:enter link description here
For example, for a 13.5V input, 300mA output, it comes out the following parameters:
R1: 4.5 ohm R2: 45 ohm R3: 382 ohm
I put the circuti in LTSpice with above values, and set 2N2907 for Q1 and Q2, a Load resistor of 10Ohm then measured current at each node:
I1: 247 mA Iout: 245 mA IB-Q1: 1.6 mA I2: 27.5 mA I3: 29.1 mA IB-Q2: 119 uA
How can I calculate current through each component manually?