Hisham Talib Qureshi
L1F16BSEE0121
POWER ELECTRONICS, ASSIGNMENT # 1
1. A diode takes less time to switch on, but a delay is observed once the diode the
switched off. This is because of the recombination of carriers across the PN-junction.
While the diode is forward biased, the current is flowing through the diode and carriers
are being flowed across the junction. Once the diode is switched off, the minority carriers
are pulled back into their original positions. So when the diode is switched from ON to
OFF, the direction of the forward current reverses momentarily. During this condition, the
respective minority carriers are readjusting themselves for the normalization of the
PN-junction, this takes some time. Because of this phenomenon, a delay is observed in
switching OFF. This can be observed in the graph below:
Forward current flows through the diode. The current decay decays for t3
duration and
the crosses zero. The current reaches maximum negative value after which the depletion
zone across the junction starts expanding gradually stopping the current flow and
reaching to zero.
