The Junction Rectifier — Question 9

Question 9

Stored charge gives a finite reverse-recovery interval

After commutation, a diode reverse-current pulse is approximated as a triangle of peak magnitude $I_R=2.00\,\mathrm A$ and total base width $t_{rr}=100\,\mathrm{ns}$. The blocking voltage during charge removal is approximated by $V_R=50.0\,\mathrm V$.

1. Find recovered charge and estimated switching energy $E_{rr}\simeq V_RQ_{rr}$.

2. At switching frequency 100 kHz, estimate average recovery loss and its change if the recovery interval is halved at fixed peak current.

Question 9 - Solution

Stored charge gives a finite reverse-recovery interval

(a) Method and calculation

$$\boxed{Q_{rr}=\int|I_R(t)|dt=\tfrac12I_Rt_{rr}=100\,\mathrm{nC}}.$$$$\boxed{E_{rr}\simeq V_RQ_{rr}=5.00\,\mu\mathrm J}.$$

(b) Interpretation and further calculation

$$\boxed{P_{rr}\simeq f_sE_{rr}=.500\,\mathrm W}.$$$$t_{rr}\to t_{rr}/2\Rightarrow\boxed{Q_{rr},E_{rr},P_{rr}\to\tfrac12\text{ their initial values}}.$$

Physical check

The triangular pulse and constant-voltage energy estimate are supplied approximations. Real current-voltage overlap determines the switching loss.