In this circuit there are several things required like the inductor and diode current, and the average power of the inductor, but what does really puzzle me is how can calculate the zener average power?
simulate this circuit – Schematic created using CircuitLab
I understand that the average power of any inductor is zero, but I don't know for the zener.
The inductor current is
$$i_{L}=\frac{1}{L}\int V_{CC}dt$$
and this would be the same current on the zener because when the transistor turns off the diode try to maintain the inductor current and breaks down.
The instantaneous power of the diode is \$I_{z}V_{z}\$ , but which is the average power?
Best Answer
I think you have to consider two situations. In discontinuous conduction mode the entire energy in the inductor (ideally) gets dissipated by the zener each off period.
The current in the inductor increases as i(t) = tV/L , so the energy at the end of the charge time \$t_{ON}\$on is
E= \$\frac{t_{ON}V^2}{2L}\$
In continuous conduction mode there is still some current flowing in the inductor at the end of the off period, so the current increases linearly from the initial current and the energy that goes into the zener is proportional to the differences of the squares of the initial and final currents. So in steady state there is some constant amount of energy stored in the inductor at the end of each off time.