EE462L, Power Electronics, DC-DC Boost Converter Version ... - ECS

EE462L, Power Electronics, DC-DC Boost Converter
Version Oct. 3, 2011
Current Ratings in Continuous Conduction
Conservative current ratings for the inductor in continuous conduction correspond to the
situation where
Δ Imax = 2I in , (11)
which, as explained in the Buck Converter experiment, yields
1 2
2
⎛ ⎞
=
2 +
2 1
I Lrms, max Iin
( 2Iin
) = Iin
⎜1
+ ⎟ , (12)
12
⎝ 3 ⎠
so that
2
I Lrms , max = I in . (13)
3
Conservative current ratings for the MOSFET and diode are when D is large, so that (13) applies
for them also.
To determine the rms current through C, consider the capacitor current in Figure 8, and the
worst-case scenario in Figure 9.
2 I
−
in I out
0
Iin − I out
DT
(1–D)T
Figure 9. Maximum Ripple Current Case for Capacitor Current
When the switch is closed, the capacitor current is − Iout
. When the switch is open, the
capacitor current is iL
− Iout
. If the “switch closed” interval lasted for the entire T, the squared
2
rms value would be I out . If the “switch open” interval lasted for the entire T, the rms value
would be, for the maximum ripple case, 2 1
( I in − Iout
) + ( 2Iin
) 2 . The time-weighted average
12
of the two gives the squared rms current
−
I out
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