SUKKUR INSTITUTE OF BUSINESS ADMINISTRATION
SUKKUR
Example sheet #1:
DC-DC Converter CCM
Example 1:
Analyze and design a Buck-Boost converter in continuous conduction mode (CCM):
A buck-boost converter is illustrated in Fig: 1(a), and practical implementation using
transistor and diode is shown in Fig: 1(b).
Fig: 1(a)
Fig: 1(b)
(a)
Derive the expressions for the dc components of each capacitor voltage and
inductor current, as a function of the duty cycle D, the input voltage Vg and
the load resistance R.
ANS: V= -DVg/(1-D), IL= DVg/R(1-D)2
(b) Derive the expression for the inductor peak current ripple and the capacitor
peak voltage ripple.
ANS: i = VgDTs/2L, v = VgD2Ts/2RC(1-D)
Example 2:
Given the following values for the boost converter
Input voltage
Vg = 12V
Output voltage
V = -5V
Switching frequency fs = 200 kHz
Load resistance
R = 2.5Ω
(a) Calculate the values of D and I.
ANS: D=0.294, IL=2.831
(b) Choose the value of L that will make the peak inductor current ripple i equal
to fifteen percent of the average inductor current I.
ANS: L=20.75 μH
(c) Choose C such that peak output voltage ripple v is 25 mV. ANS: C=58.82μF
(d) Calculate & sketch the MOSFET current and voltage waveforms, including
ripples.
ANS: IQ= 3.255A, VQ =17.025v
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