Hi all,

I had this also up on a spice topic but have it posted here again, pretty stumped about how the current flowing in R13 is calculated, I included a 5 ohm resistor to emulate the FET rds and the 4 resistors on the diodes have a parallel ressitance of 40Ohm - how is 2.46mA across R13 obtained?

 

I had this also up on a spice topic but have it posted here again, pretty stumped about how the current flowing in R13 is calculated, I included a 5 ohm resistor to emulate the FET rds and the 4 resistors on the diodes have a parallel ressitance of 40Ohm - how is 2.46mA across R13 obtained?

There are 5 resistors with diodes in series, not 4, and their parallel value is 40 kΩ, not 40 Ω. Their combined resistance is in parallel with the series pair of R15 and R16, yielding a total effective resistance of about 9.6 kΩ (ignoring the diode voltage drops).

Hence the 2.46 mA.

 

There are 5 resistors with diodes in series, not 4, and their parallel value is 40 kΩ, not 40 Ω. Their combined resistance is in parallel with the series pair of R15 and R16, yielding a total effective resistance of about 9.6 kΩ (ignoring the diode voltage drops).

Hence the 2.46 mA.

And it comes from "Ohm" and "Kirchhoff's" laws. The total consumption of the circuit is about "2.46mA", everything (every other resistor) is changing the current flow through "R13".

As for the calculations, they are in the upper post.