17-08-2012, 11:42 AM
A Simple Diode Model with Reverse Recovery
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INTRODUCTION
THE diode models widely used in circuit simulators such as SPICE are based on the original charge control model [l]
which includes the effects of charge storage during reverse recovery
operation but does not provide for reverse recovery of
the diode. Thus, these diode models always exhibit an instantaneous
or snappy recovery during commutation to the non-conducting
state.
Some of the appearance of a more gradual or softer recovery
can be obtained by adding extra parallel capacitance to the
diode. However, this practice gives the incorrect relation between
diode reverse current and voltage. Capacitive current is
non-dissipative, associated with energy storage in the capacitor.
Actual diode reverse recovery current is dissipative and is the
most important source of power dissipation for diodes used in
fast switching converters.
This paper extends the basic Charge-control diode model to
include reverse recovery. The model is derived from the semiconductor
charge transport equations and its performance is
demonstrated using the Saber simulator.
MODELD ERIVATIOANN D DESCRIPTION
A high voltage p-i-n structure operating in high level injection
is assumed as typical for most power diodes. The original
charge control diode model employs one charge storage node.
When the charge stored in that node becomes exhausted during
reverse conduction, the diode instantly switches to the reverse
blocking mode. In actual diodes, reverse recovery is caused by
diffusion of charge from the center of the i region; thus, one or
more additional charge storage nodes must be added to provide
for this diffusion current.
CONCLUSION
This new lumped charge diode model represents a significant
improvement to the basic diode model used in SPICE sirnulators
since 1972. Reverse recovery phenomena need no longer
be ignored in circuit simulations employing p-n and p-i-n
diodes. The lumped charge approach can also be extended to
the modeling of other high-voltage conductivity modulated devices
such as SCR’s, GTO’s, and IGBT’s.